// <auto-generated/>
/*
The MIT License (MIT)

Copyright (c) 2016-2020 Maksim Volkau

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included AddOrUpdateServiceFactory
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/

// ReSharper disable CoVariantArrayConversion

/*
// Lists the target platforms that are Not supported by FEC - simplifies the direct referencing of Expression.cs file
*/
#if !PCL && !NET35 && !NET40 && !NET403 && !NETSTANDARD1_0 && !NETSTANDARD1_1 && !NETSTANDARD1_2 && !NETCOREAPP1_0 && !NETCOREAPP1_1
#define SUPPORTS_FAST_EXPRESSION_COMPILER
#endif

#if !SUPPORTS_FAST_EXPRESSION_COMPILER
namespace FastExpressionCompiler.LightExpression
{
    using System;
    using System.Linq.Expressions;

    /// <summary>Polyfill for absence of FastExpressionCompiler: https://github.com/dadhi/FastExpressionCompiler </summary>
    public static class ExpressionCompiler
    {
        internal static object TryCompileBoundToFirstClosureParam(Type delegateType,
            Expression bodyExpr, ParameterExpression[] paramExprs, Type[] closurePlusParamTypes, Type returnType) => null;

        internal static Func<T1, R> CompileFast<T1, R>(this Expression<Func<T1, R>> lambdaExpr) => lambdaExpr.Compile();

        internal class ArrayClosure {}
    }
}
#else
// ReSharper disable CoVariantArrayConversion
namespace FastExpressionCompiler.LightExpression
{
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Linq.Expressions;
    using System.Reflection;
    using System.Reflection.Emit;
    using System.Threading;

    /// <summary>Compiles expression to delegate ~20 times faster than Expression.Compile.
    /// Partial to extend with your things when used as source file.</summary>
    // ReSharper disable once PartialTypeWithSinglePart
    public static partial class ExpressionCompiler
    {
#region Expression.CompileFast overloads for Delegate, Func, and Action

        /// <summary>Compiles lambda expression to TDelegate type. Use ifFastFailedReturnNull parameter to Not fallback to Expression.Compile, useful for testing.</summary>
        public static TDelegate CompileFast<TDelegate>(this LambdaExpression lambdaExpr,
            bool ifFastFailedReturnNull = false) where TDelegate : class =>
            (TDelegate)(TryCompileBoundToFirstClosureParam(typeof(TDelegate) == typeof(Delegate) ? lambdaExpr.Type : typeof(TDelegate), 
                    lambdaExpr.Body, lambdaExpr.Parameters, GetClosureTypeToParamTypes(lambdaExpr.Parameters), lambdaExpr.ReturnType)
            ?? (ifFastFailedReturnNull ? null : lambdaExpr.CompileSys()));

        /// Compiles a static method to the passed IL Generator.
        /// Could be used as alternative for `CompileToMethod` like this <code><![CDATA[funcExpr.CompileFastToIL(methodBuilder.GetILGenerator())]]></code>.
        /// Check `IssueTests.Issue179_Add_something_like_LambdaExpression_CompileToMethod.cs` for example.
        public static bool CompileFastToIL(this LambdaExpression lambdaExpr, ILGenerator il, bool ifFastFailedReturnNull = false)
        {
            var closureInfo = new ClosureInfo(ClosureStatus.ShouldBeStaticMethod);

            var parentFlags = lambdaExpr.ReturnType == typeof(void) ? ParentFlags.IgnoreResult : ParentFlags.Empty;
            if (!EmittingVisitor.TryEmit(lambdaExpr.Body, lambdaExpr.Parameters, il, ref closureInfo, parentFlags))
                return false;

            il.Emit(OpCodes.Ret);
            return true;
        }

        /// <summary>Compiles lambda expression to delegate. Use ifFastFailedReturnNull parameter to Not fallback to Expression.Compile, useful for testing.</summary>
        public static Delegate CompileFast(this LambdaExpression lambdaExpr, bool ifFastFailedReturnNull = false) =>
            (Delegate)TryCompileBoundToFirstClosureParam(lambdaExpr.Type, lambdaExpr.Body, lambdaExpr.Parameters,
                GetClosureTypeToParamTypes(lambdaExpr.Parameters), lambdaExpr.ReturnType)
            ?? (ifFastFailedReturnNull ? null : lambdaExpr.CompileSys());

        /// <summary>Unifies Compile for System.Linq.Expressions and FEC.LightExpression</summary>
        public static TDelegate CompileSys<TDelegate>(this Expression<TDelegate> lambdaExpr) where TDelegate : class =>
            lambdaExpr
            .ToLambdaExpression()
            .Compile();

        /// <summary>Unifies Compile for System.Linq.Expressions and FEC.LightExpression</summary>
        public static Delegate CompileSys(this LambdaExpression lambdaExpr) =>
            lambdaExpr
            .ToLambdaExpression()
            .Compile();

        /// <summary>Compiles lambda expression to TDelegate type. Use ifFastFailedReturnNull parameter to Not fallback to Expression.Compile, useful for testing.</summary>
        public static TDelegate CompileFast<TDelegate>(this Expression<TDelegate> lambdaExpr,
            bool ifFastFailedReturnNull = false)
            where TDelegate : class => ((LambdaExpression)lambdaExpr).CompileFast<TDelegate>(ifFastFailedReturnNull);

        /// <summary>Compiles lambda expression to delegate. Use ifFastFailedReturnNull parameter to Not fallback to Expression.Compile, useful for testing.</summary>
        public static Func<R> CompileFast<R>(this Expression<Func<R>> lambdaExpr,
            bool ifFastFailedReturnNull = false) =>
            (Func<R>)TryCompileBoundToFirstClosureParam(typeof(Func<R>), 
                lambdaExpr.Body, lambdaExpr.Parameters, _closureAsASingleParamType, typeof(R))
            ?? (ifFastFailedReturnNull ? null : lambdaExpr.CompileSys());

        /// <summary>Compiles lambda expression to delegate. Use ifFastFailedReturnNull parameter to Not fallback to Expression.Compile, useful for testing.</summary>
        public static Func<T1, R> CompileFast<T1, R>(this Expression<Func<T1, R>> lambdaExpr,
            bool ifFastFailedReturnNull = false) =>
            (Func<T1, R>)TryCompileBoundToFirstClosureParam(typeof(Func<T1, R>), 
                lambdaExpr.Body, lambdaExpr.Parameters, new[] { typeof(ArrayClosure), typeof(T1) }, typeof(R))
            ?? (ifFastFailedReturnNull ? null : lambdaExpr.CompileSys());

        /// <summary>Compiles lambda expression to TDelegate type. Use ifFastFailedReturnNull parameter to Not fallback to Expression.Compile, useful for testing.</summary>
        public static Func<T1, T2, R> CompileFast<T1, T2, R>(this Expression<Func<T1, T2, R>> lambdaExpr,
            bool ifFastFailedReturnNull = false) =>
            (Func<T1, T2, R>)TryCompileBoundToFirstClosureParam(typeof(Func<T1, T2, R>), 
                lambdaExpr.Body, lambdaExpr.Parameters, new[] { typeof(ArrayClosure), typeof(T1), typeof(T2) },
                typeof(R))
            ?? (ifFastFailedReturnNull ? null : lambdaExpr.CompileSys());

        /// <summary>Compiles lambda expression to delegate. Use ifFastFailedReturnNull parameter to Not fallback to Expression.Compile, useful for testing.</summary>
        public static Func<T1, T2, T3, R> CompileFast<T1, T2, T3, R>(
            this Expression<Func<T1, T2, T3, R>> lambdaExpr, bool ifFastFailedReturnNull = false) =>
            (Func<T1, T2, T3, R>)TryCompileBoundToFirstClosureParam(typeof(Func<T1, T2, T3, R>), 
                lambdaExpr.Body, lambdaExpr.Parameters, new[] { typeof(ArrayClosure), typeof(T1), typeof(T2), typeof(T3) }, typeof(R))
            ?? (ifFastFailedReturnNull ? null : lambdaExpr.CompileSys());

        /// <summary>Compiles lambda expression to TDelegate type. Use ifFastFailedReturnNull parameter to Not fallback to Expression.Compile, useful for testing.</summary>
        public static Func<T1, T2, T3, T4, R> CompileFast<T1, T2, T3, T4, R>(
            this Expression<Func<T1, T2, T3, T4, R>> lambdaExpr, bool ifFastFailedReturnNull = false) =>
            (Func<T1, T2, T3, T4, R>)TryCompileBoundToFirstClosureParam(typeof(Func<T1, T2, T3, T4, R>), 
                lambdaExpr.Body, lambdaExpr.Parameters,
                new[] { typeof(ArrayClosure), typeof(T1), typeof(T2), typeof(T3), typeof(T4) }, typeof(R))
            ?? (ifFastFailedReturnNull ? null : lambdaExpr.CompileSys());

        /// <summary>Compiles lambda expression to delegate. Use ifFastFailedReturnNull parameter to Not fallback to Expression.Compile, useful for testing.</summary>
        public static Func<T1, T2, T3, T4, T5, R> CompileFast<T1, T2, T3, T4, T5, R>(
            this Expression<Func<T1, T2, T3, T4, T5, R>> lambdaExpr, bool ifFastFailedReturnNull = false) =>
            (Func<T1, T2, T3, T4, T5, R>)TryCompileBoundToFirstClosureParam(typeof(Func<T1, T2, T3, T4, T5, R>), 
                lambdaExpr.Body, lambdaExpr.Parameters,
                new[] { typeof(ArrayClosure), typeof(T1), typeof(T2), typeof(T3), typeof(T4), typeof(T5) }, typeof(R))
            ?? (ifFastFailedReturnNull ? null : lambdaExpr.CompileSys());

        /// <summary>Compiles lambda expression to delegate. Use ifFastFailedReturnNull parameter to Not fallback to Expression.Compile, useful for testing.</summary>
        public static Func<T1, T2, T3, T4, T5, T6, R> CompileFast<T1, T2, T3, T4, T5, T6, R>(
            this Expression<Func<T1, T2, T3, T4, T5, T6, R>> lambdaExpr, bool ifFastFailedReturnNull = false) =>
            (Func<T1, T2, T3, T4, T5, T6, R>)TryCompileBoundToFirstClosureParam(typeof(Func<T1, T2, T3, T4, T5, T6, R>), 
                lambdaExpr.Body, lambdaExpr.Parameters,
                new[] { typeof(ArrayClosure), typeof(T1), typeof(T2), typeof(T3), typeof(T4), typeof(T5), typeof(T6) }, typeof(R))
            ?? (ifFastFailedReturnNull ? null : lambdaExpr.CompileSys());

        /// <summary>Compiles lambda expression to delegate. Use ifFastFailedReturnNull parameter to Not fallback to Expression.Compile, useful for testing.</summary>
        public static Action CompileFast(this Expression<Action> lambdaExpr, bool ifFastFailedReturnNull = false) =>
            (Action)TryCompileBoundToFirstClosureParam(typeof(Action), 
                lambdaExpr.Body, lambdaExpr.Parameters, _closureAsASingleParamType, typeof(void))
            ?? (ifFastFailedReturnNull ? null : lambdaExpr.CompileSys());

        /// <summary>Compiles lambda expression to delegate. Use ifFastFailedReturnNull parameter to Not fallback to Expression.Compile, useful for testing.</summary>
        public static Action<T1> CompileFast<T1>(this Expression<Action<T1>> lambdaExpr,
            bool ifFastFailedReturnNull = false) =>
            (Action<T1>)TryCompileBoundToFirstClosureParam(typeof(Action<T1>), 
                lambdaExpr.Body, lambdaExpr.Parameters, new[] { typeof(ArrayClosure), typeof(T1) }, typeof(void))
            ?? (ifFastFailedReturnNull ? null : lambdaExpr.CompileSys());

        /// <summary>Compiles lambda expression to delegate. Use ifFastFailedReturnNull parameter to Not fallback to Expression.Compile, useful for testing.</summary>
        public static Action<T1, T2> CompileFast<T1, T2>(this Expression<Action<T1, T2>> lambdaExpr,
            bool ifFastFailedReturnNull = false) =>
            (Action<T1, T2>)TryCompileBoundToFirstClosureParam(typeof(Action<T1, T2>), 
                lambdaExpr.Body, lambdaExpr.Parameters, new[] { typeof(ArrayClosure), typeof(T1), typeof(T2) },
                typeof(void))
            ?? (ifFastFailedReturnNull ? null : lambdaExpr.CompileSys());

        /// <summary>Compiles lambda expression to delegate. Use ifFastFailedReturnNull parameter to Not fallback to Expression.Compile, useful for testing.</summary>
        public static Action<T1, T2, T3> CompileFast<T1, T2, T3>(this Expression<Action<T1, T2, T3>> lambdaExpr,
            bool ifFastFailedReturnNull = false) =>
            (Action<T1, T2, T3>)TryCompileBoundToFirstClosureParam(typeof(Action<T1, T2, T3>), 
                lambdaExpr.Body, lambdaExpr.Parameters,
                new[] { typeof(ArrayClosure), typeof(T1), typeof(T2), typeof(T3) }, typeof(void))
            ?? (ifFastFailedReturnNull ? null : lambdaExpr.CompileSys());

        /// <summary>Compiles lambda expression to delegate. Use ifFastFailedReturnNull parameter to Not fallback to Expression.Compile, useful for testing.</summary>
        public static Action<T1, T2, T3, T4> CompileFast<T1, T2, T3, T4>(
            this Expression<Action<T1, T2, T3, T4>> lambdaExpr, bool ifFastFailedReturnNull = false) =>
            (Action<T1, T2, T3, T4>)TryCompileBoundToFirstClosureParam(typeof(Action<T1, T2, T3, T4>), 
                lambdaExpr.Body, lambdaExpr.Parameters,
                new[] { typeof(ArrayClosure), typeof(T1), typeof(T2), typeof(T3), typeof(T4) }, typeof(void))
            ?? (ifFastFailedReturnNull ? null : lambdaExpr.CompileSys());

        /// <summary>Compiles lambda expression to delegate. Use ifFastFailedReturnNull parameter to Not fallback to Expression.Compile, useful for testing.</summary>
        public static Action<T1, T2, T3, T4, T5> CompileFast<T1, T2, T3, T4, T5>(
            this Expression<Action<T1, T2, T3, T4, T5>> lambdaExpr, bool ifFastFailedReturnNull = false) =>
            (Action<T1, T2, T3, T4, T5>)TryCompileBoundToFirstClosureParam(typeof(Action<T1, T2, T3, T4, T5>), 
                lambdaExpr.Body, lambdaExpr.Parameters,
                new[] { typeof(ArrayClosure), typeof(T1), typeof(T2), typeof(T3), typeof(T4), typeof(T5) }, typeof(void))
            ?? (ifFastFailedReturnNull ? null : lambdaExpr.CompileSys());

        /// <summary>Compiles lambda expression to delegate. Use ifFastFailedReturnNull parameter to Not fallback to Expression.Compile, useful for testing.</summary>
        public static Action<T1, T2, T3, T4, T5, T6> CompileFast<T1, T2, T3, T4, T5, T6>(
            this Expression<Action<T1, T2, T3, T4, T5, T6>> lambdaExpr, bool ifFastFailedReturnNull = false) =>
            (Action<T1, T2, T3, T4, T5, T6>)TryCompileBoundToFirstClosureParam(typeof(Action<T1, T2, T3, T4, T5, T6>), 
                lambdaExpr.Body, lambdaExpr.Parameters,
                new[] { typeof(ArrayClosure), typeof(T1), typeof(T2), typeof(T3), typeof(T4), typeof(T5), typeof(T6) }, typeof(void))
            ?? (ifFastFailedReturnNull ? null : lambdaExpr.CompileSys());

#endregion

        /// <summary>Tries to compile lambda expression to <typeparamref name="TDelegate"/></summary>
        public static TDelegate TryCompile<TDelegate>(this LambdaExpression lambdaExpr) where TDelegate : class =>
            (TDelegate)TryCompileBoundToFirstClosureParam(typeof(TDelegate) == typeof(Delegate) ? lambdaExpr.Type : typeof(TDelegate), 
                lambdaExpr.Body, lambdaExpr.Parameters, GetClosureTypeToParamTypes(lambdaExpr.Parameters), lambdaExpr.ReturnType);

        /// <summary>Tries to compile lambda expression to <typeparamref name="TDelegate"/> 
        /// with the provided closure object and constant expressions (or lack there of) -
        /// Constant expression should be the in order of Fields in closure object!
        /// Note 1: Use it on your own risk - FEC won't verify the expression is compile-able with passed closure, it is up to you!
        /// Note 2: The expression with NESTED LAMBDA IS NOT SUPPORTED!
        /// Note 3: `Label` and `GoTo` are not supported in this case, because they need first round to collect out-of-order labels</summary>
        public static TDelegate TryCompileWithPreCreatedClosure<TDelegate>(this LambdaExpression lambdaExpr,
            params ConstantExpression[] closureConstantsExprs)
            where TDelegate : class
        {
            var constValues = new object[closureConstantsExprs.Length];
            for (var i = 0; i < constValues.Length; i++)
                constValues[i] = closureConstantsExprs[i].Value;

            var closureInfo = new ClosureInfo(ClosureStatus.UserProvided | ClosureStatus.HasClosure, constValues);

            var closurePlusParamTypes = GetClosureTypeToParamTypes(lambdaExpr.Parameters);
            var method = new DynamicMethod(string.Empty, lambdaExpr.ReturnType, closurePlusParamTypes,
                typeof(ExpressionCompiler), skipVisibility: true);

            var il = method.GetILGenerator();

            EmittingVisitor.EmitLoadConstantsAndNestedLambdasIntoVars(il, ref closureInfo);

            var parentFlags = lambdaExpr.ReturnType == typeof(void) ? ParentFlags.IgnoreResult : ParentFlags.Empty;
            if (!EmittingVisitor.TryEmit(lambdaExpr.Body, lambdaExpr.Parameters, il, ref closureInfo, parentFlags))
                return null;
            il.Emit(OpCodes.Ret);

            var delegateType = typeof(TDelegate) != typeof(Delegate) ? typeof(TDelegate) : lambdaExpr.Type;
            var @delegate = (TDelegate)(object)method.CreateDelegate(delegateType, new ArrayClosure(constValues));
            ReturnClosureTypeToParamTypesToPool(closurePlusParamTypes);
            return @delegate;
        }

        /// <summary>Tries to compile expression to "static" delegate, skipping the step of collecting the closure object.</summary>
        public static TDelegate TryCompileWithoutClosure<TDelegate>(this LambdaExpression lambdaExpr)
            where TDelegate : class
        {
            var closureInfo = new ClosureInfo(ClosureStatus.UserProvided);
            var closurePlusParamTypes = GetClosureTypeToParamTypes(lambdaExpr.Parameters);

            var method = new DynamicMethod(string.Empty, lambdaExpr.ReturnType, closurePlusParamTypes,
                typeof(ArrayClosure), skipVisibility: true);

            var il = method.GetILGenerator();
            var parentFlags = lambdaExpr.ReturnType == typeof(void) ? ParentFlags.IgnoreResult : ParentFlags.Empty;
            if (!EmittingVisitor.TryEmit(lambdaExpr.Body, lambdaExpr.Parameters, il, ref closureInfo, parentFlags))
                return null;
            il.Emit(OpCodes.Ret);

            var delegateType = typeof(TDelegate) != typeof(Delegate) ? typeof(TDelegate) : lambdaExpr.Type;
            var @delegate = (TDelegate)(object)method.CreateDelegate(delegateType, EmptyArrayClosure);
            ReturnClosureTypeToParamTypesToPool(closurePlusParamTypes);
            return @delegate;
        }

#region Obsolete

        /// Obsolete
        [Obsolete("Not used - candidate for removal")]
        public static TDelegate TryCompile<TDelegate>(
            Expression bodyExpr, IReadOnlyList<ParameterExpression> paramExprs, Type[] paramTypes, Type returnType)
            where TDelegate : class =>
            (TDelegate)TryCompile(typeof(TDelegate), bodyExpr, paramExprs, paramTypes, returnType);

        /// Obsolete
        [Obsolete("Not used - candidate for removal")]
        public static object TryCompile(Type delegateType,
            Expression bodyExpr, IReadOnlyList<ParameterExpression> paramExprs, Type[] paramTypes, Type returnType) =>
            TryCompileBoundToFirstClosureParam(
                delegateType != typeof(Delegate) ? delegateType : Tools.GetFuncOrActionType(paramTypes, returnType), 
                bodyExpr, paramExprs, GetClosureTypeToParamTypes(paramExprs), returnType);

#endregion

        internal static object TryCompileBoundToFirstClosureParam(Type delegateType,
            Expression bodyExpr, IReadOnlyList<ParameterExpression> paramExprs, Type[] closurePlusParamTypes, Type returnType)
        {
            var closureInfo = new ClosureInfo(ClosureStatus.ToBeCollected);
            if (!TryCollectBoundConstants(ref closureInfo, bodyExpr, paramExprs, false, ref closureInfo))
                return null;

            var nestedLambdas = closureInfo.NestedLambdas;
            if (nestedLambdas.Length != 0)
                for (var i = 0; i < nestedLambdas.Length; ++i)
                    if (!TryCompileNestedLambda(ref closureInfo, i))
                        return null;

            var closure = (closureInfo.Status & ClosureStatus.HasClosure) == 0
                ? EmptyArrayClosure
                : new ArrayClosure(closureInfo.GetArrayOfConstantsAndNestedLambdas());

            var method = new DynamicMethod(string.Empty,
                returnType, closurePlusParamTypes, typeof(ArrayClosure), true);

            var il = method.GetILGenerator();

            if (closure.ConstantsAndNestedLambdas != null)
                EmittingVisitor.EmitLoadConstantsAndNestedLambdasIntoVars(il, ref closureInfo);

            var parentFlags = returnType == typeof(void) ? ParentFlags.IgnoreResult : ParentFlags.Empty;
            if (!EmittingVisitor.TryEmit(bodyExpr, paramExprs, il, ref closureInfo, parentFlags))
                return null;

            il.Emit(OpCodes.Ret);

            var @delegate = method.CreateDelegate(delegateType, closure);
            ReturnClosureTypeToParamTypesToPool(closurePlusParamTypes);
            return @delegate;
        }

        private static Type[] PrependClosureTypeToParamTypes(IReadOnlyList<ParameterExpression> paramExprs)
        {
            var count = paramExprs.Count;
            var closureAndParamTypes = new Type[count + 1];
            closureAndParamTypes[0] = typeof(ArrayClosure);
            for (var i = 0; i < count; i++)
            {
                var parameterExpr = paramExprs[i];
                closureAndParamTypes[i + 1] = parameterExpr.IsByRef ? parameterExpr.Type.MakeByRefType() : parameterExpr.Type;
            }
            return closureAndParamTypes;
        }

        private static readonly Type[] _closureAsASingleParamType = { typeof(ArrayClosure) };
        private static readonly Type[][] _closureTypePlusParamTypesPool = new Type[8][];

        private static Type[] GetClosureTypeToParamTypes(IReadOnlyList<ParameterExpression> paramExprs)
        {
            var paramCount = paramExprs.Count;
            if (paramCount == 0)
                return _closureAsASingleParamType;

            if (paramCount < 8)
            {
                var closureAndParamTypes = Interlocked.Exchange(ref _closureTypePlusParamTypesPool[paramCount], null);
                if (closureAndParamTypes != null)
                {
                    for (var i = 0; i < paramExprs.Count; i++)
                    {
                        var parameterExpr = paramExprs[i];
                        closureAndParamTypes[i + 1] = parameterExpr.IsByRef ? parameterExpr.Type.MakeByRefType() : parameterExpr.Type;
                    }
                    return closureAndParamTypes;
                }
            }

            return PrependClosureTypeToParamTypes(paramExprs);
        }

        private static void ReturnClosureTypeToParamTypesToPool(Type[] closurePlusParamTypes)
        {
            var paramCount = closurePlusParamTypes.Length - 1;
            if (paramCount != 0 && paramCount < 8)
                Interlocked.Exchange(ref _closureTypePlusParamTypesPool[paramCount], closurePlusParamTypes);
        }

        private struct BlockInfo
        {
            public object VarExprs;     // ParameterExpression  | IReadOnlyList<ParameterExpression>
            public int[]  VarIndexes;
        }

        [Flags]
        private enum ClosureStatus
        {
            ToBeCollected        = 1,
            UserProvided         = 1 << 1,
            HasClosure           = 1 << 2,
            ShouldBeStaticMethod = 1 << 3
        }

        /// Track the info required to build a closure object + some context information not directly related to closure.
        private struct ClosureInfo
        {
            public bool LastEmitIsAddress;

            /// Helpers to know if a Return GotoExpression's Label should be emitted.
            /// First set bit is ContainsReturnGoto, the rest is ReturnLabelIndex
            private int[] _tryCatchFinallyInfos; 
            public int CurrentTryCatchFinallyIndex;

            /// Tracks the stack of blocks where are we in emit phase
            private LiveCountArray<BlockInfo> _blockStack;

            /// Dictionary for the used Labels in IL
            private KeyValuePair<LabelTarget, Label?>[] _labels;

            public ClosureStatus Status;

            /// Constant expressions to find an index (by reference) of constant expression from compiled expression.
            public LiveCountArray<object> Constants;

            /// Parameters not passed through lambda parameter list But used inside lambda body.
            /// The top expression should Not contain not passed parameters. 
            public ParameterExpression[] NonPassedParameters;

            /// All nested lambdas recursively nested in expression
            public NestedLambdaInfo[] NestedLambdas;

            /// Constant usage count and variable index
            public LiveCountArray<int> ConstantUsage;

            /// Populates info directly with provided closure object and constants.
            public ClosureInfo(ClosureStatus status, object[] constValues = null)
            {
                Status = status;

                Constants = new LiveCountArray<object>(constValues ?? Tools.Empty<object>());
                ConstantUsage = new LiveCountArray<int>(constValues == null ? Tools.Empty<int>() : new int[constValues.Length]);

                NonPassedParameters = Tools.Empty<ParameterExpression>();
                NestedLambdas = Tools.Empty<NestedLambdaInfo>();

                LastEmitIsAddress = false;
                CurrentTryCatchFinallyIndex = -1;
                _tryCatchFinallyInfos = null;
                _labels = null;
                _blockStack = new LiveCountArray<BlockInfo>(Tools.Empty<BlockInfo>());
            }

            public void AddConstant(object value)
            {
                Status |= ClosureStatus.HasClosure;

                var constItems = Constants.Items;
                var constIndex = Constants.Count - 1;
                while (constIndex != -1 && !ReferenceEquals(constItems[constIndex], value))
                    --constIndex;
                if (constIndex == -1)
                {
                    Constants.PushSlot(value);
                    ConstantUsage.PushSlot(1);
                }
                else
                {
                    ++ConstantUsage.Items[constIndex];
                }
            }

            public void AddNonPassedParam(ParameterExpression expr)
            {
                Status |= ClosureStatus.HasClosure;

                if (NonPassedParameters.Length == 0)
                {
                    NonPassedParameters = new[] { expr };
                    return;
                }

                var count = NonPassedParameters.Length;
                for (var i = 0; i < count; ++i)
                    if (ReferenceEquals(NonPassedParameters[i], expr))
                        return;

                if (NonPassedParameters.Length == 1)
                    NonPassedParameters = new[] { NonPassedParameters[0], expr };
                else if (NonPassedParameters.Length == 2)
                    NonPassedParameters = new[] { NonPassedParameters[0], NonPassedParameters[1], expr };
                else
                {
                    var newItems = new ParameterExpression[count + 1];
                    Array.Copy(NonPassedParameters, 0, newItems, 0, count);
                    newItems[count] = expr;
                    NonPassedParameters = newItems;
                }
            }

            public void AddNestedLambda(NestedLambdaInfo nestedLambdaInfo)
            {
                Status |= ClosureStatus.HasClosure;

                var nestedLambdas = NestedLambdas;
                var count = nestedLambdas.Length;
                if (count == 0)
                    NestedLambdas = new[] { nestedLambdaInfo };
                else if (count == 1)
                    NestedLambdas = new[] { nestedLambdas[0], nestedLambdaInfo };
                else if (count == 2)
                    NestedLambdas = new[] { nestedLambdas[0], nestedLambdas[1], nestedLambdaInfo };
                else
                {
                    var newNestedLambdas = new NestedLambdaInfo[count + 1];
                    Array.Copy(nestedLambdas, 0, newNestedLambdas, 0, count);
                    newNestedLambdas[count] = nestedLambdaInfo;
                    NestedLambdas = newNestedLambdas;
                }
            }

            public void AddLabel(LabelTarget labelTarget)
            {
                if (labelTarget != null &&
                    GetLabelIndex(labelTarget) == -1)
                    _labels = _labels.WithLast(new KeyValuePair<LabelTarget, Label?>(labelTarget, null));
            }

            public Label GetOrCreateLabel(LabelTarget labelTarget, ILGenerator il) =>
                GetOrCreateLabel(GetLabelIndex(labelTarget), il);

            public Label GetOrCreateLabel(int index, ILGenerator il)
            {
                var labelPair = _labels[index];
                var label = labelPair.Value;
                if (!label.HasValue)
                    _labels[index] = new KeyValuePair<LabelTarget, Label?>(labelPair.Key, label = il.DefineLabel());
                return label.Value;
            }

            public int GetLabelIndex(LabelTarget labelTarget)
            {
                if (_labels != null)
                    for (var i = 0; i < _labels.Length; ++i)
                        if (_labels[i].Key == labelTarget)
                            return i;
                return -1;
            }

            public void AddTryCatchFinallyInfo()
            {
                ++CurrentTryCatchFinallyIndex;
                var infos = _tryCatchFinallyInfos;
                if (infos == null)
                    _tryCatchFinallyInfos = new int[1];
                else if (infos.Length == 1)
                    _tryCatchFinallyInfos = new[] { infos[0], 0 };
                else if (infos.Length == 2)
                    _tryCatchFinallyInfos = new[] { infos[0], infos[1], 0 };
                else
                {
                    var sourceLength = infos.Length;
                    var newInfos = new int[sourceLength + 1];
                    Array.Copy(infos, newInfos, sourceLength);
                    _tryCatchFinallyInfos = newInfos;
                }
            }

            public void MarkAsContainsReturnGotoExpression()
            {
                if (CurrentTryCatchFinallyIndex != -1)
                    _tryCatchFinallyInfos[CurrentTryCatchFinallyIndex] |= 1;
            }

            public void MarkReturnLabelIndex(int index)
            {
                if (CurrentTryCatchFinallyIndex != -1)
                    _tryCatchFinallyInfos[CurrentTryCatchFinallyIndex] |= index << 1;
            }

            public bool TryCatchFinallyContainsReturnGotoExpression() =>
                _tryCatchFinallyInfos != null && (_tryCatchFinallyInfos[++CurrentTryCatchFinallyIndex] & 1) != 0;

            public object[] GetArrayOfConstantsAndNestedLambdas()
            {
                var constCount = Constants.Count;
                var nestedLambdas = NestedLambdas;
                if (constCount == 0)
                {
                    if (nestedLambdas.Length == 0)
                        return null;

                    var nestedLambdaItems = new object[nestedLambdas.Length];
                    for (var i = 0; i < nestedLambdas.Length; i++)
                    {
                        var nestedLambda = nestedLambdas[i];
                        if (nestedLambda.ClosureInfo.NonPassedParameters.Length == 0)
                            nestedLambdaItems[i] = nestedLambda.Lambda;
                        else
                            nestedLambdaItems[i] = new NestedLambdaWithConstantsAndNestedLambdas(
                                nestedLambda.Lambda, nestedLambda.ClosureInfo.GetArrayOfConstantsAndNestedLambdas());
                    }

                    return nestedLambdaItems;
                }

                var constItems = Constants.Items;
                if (nestedLambdas.Length == 0)
                    return constItems;

                var itemCount = constCount + nestedLambdas.Length;

                var closureItems = constItems;
                if (itemCount > constItems.Length)
                {
                    closureItems = new object[itemCount];
                    for (var i = 0; i < constCount; ++i)
                        closureItems[i] = constItems[i];
                }

                for (var i = 0; i < nestedLambdas.Length; i++)
                {
                    var nestedLambda = nestedLambdas[i];
                    if (nestedLambda.ClosureInfo.NonPassedParameters.Length == 0)
                        closureItems[constCount + i] = nestedLambda.Lambda;
                    else
                        closureItems[constCount + i] = new NestedLambdaWithConstantsAndNestedLambdas(
                            nestedLambda.Lambda, nestedLambda.ClosureInfo.GetArrayOfConstantsAndNestedLambdas());
                }

                return closureItems;
            }

            /// LocalVar maybe a `null` in collecting phase when we only need to decide if ParameterExpression is an actual parameter or variable
            public void PushBlockWithVars(ParameterExpression blockVarExpr)
            {
                ref var block    = ref _blockStack.PushSlot();
                block.VarExprs   = blockVarExpr;
            }

            public void PushBlockWithVars(ParameterExpression blockVarExpr, int varIndex)
            {
                ref var block = ref _blockStack.PushSlot();
                block.VarExprs = blockVarExpr;
                block.VarIndexes = new[] { varIndex };
            }

            /// LocalVars maybe a `null` in collecting phase when we only need to decide if ParameterExpression is an actual parameter or variable
            public void PushBlockWithVars(IReadOnlyList<ParameterExpression> blockVarExprs, int[] localVarIndexes = null)
            {
                ref var block    = ref _blockStack.PushSlot();
                block.VarExprs   = blockVarExprs;
                block.VarIndexes = localVarIndexes;
            }

            public void PushBlockAndConstructLocalVars(IReadOnlyList<ParameterExpression> blockVarExprs, ILGenerator il)
            {
                var localVars = new int[blockVarExprs.Count];
                for (var i = 0; i < localVars.Length; i++)
                    localVars[i] = il.GetNextLocalVarIndex(blockVarExprs[i].Type);

                PushBlockWithVars(blockVarExprs, localVars);
            }

            public void PopBlock() => _blockStack.Pop();

            public bool IsLocalVar(object varParamExpr)
            {
                for (var i = _blockStack.Count - 1; i > -1; --i)
                {
                    var varExprObj = _blockStack.Items[i].VarExprs;
                    if (ReferenceEquals(varExprObj, varParamExpr))
                        return true;

                    if (varExprObj is IReadOnlyList<ParameterExpression> varExprs)
                        for (var j = 0; j < varExprs.Count; j++)
                            if (ReferenceEquals(varExprs[j], varParamExpr))
                                return true;
                }

                return false;
            }

            public int GetDefinedLocalVarOrDefault(ParameterExpression varParamExpr)
            {
                for (var i = _blockStack.Count - 1; i > -1; --i)
                {
                    ref var block = ref _blockStack.Items[i];
                    var varExprObj = block.VarExprs;

                    if (ReferenceEquals(varExprObj, varParamExpr))
                        return block.VarIndexes[0];

                    if (varExprObj is IReadOnlyList<ParameterExpression> varExprs)
                        for (var j = 0; j < varExprs.Count; j++)
                            if (ReferenceEquals(varExprs[j], varParamExpr))
                                return block.VarIndexes[j];
                }
                return -1;
            }

            public bool IsTryReturnLabel(int index)
            {
                var tryCatchFinallyInfos = _tryCatchFinallyInfos;
                if (tryCatchFinallyInfos != null)
                    for (var i = 0; i < tryCatchFinallyInfos.Length; ++i)
                        if (tryCatchFinallyInfos[i] >> 1 == index)
                            return true;
                return false;
            }
        }

#pragma warning disable CS1591 // Missing XML comment for publicly visible type or member

        public static readonly ArrayClosure EmptyArrayClosure = new ArrayClosure(null);

        public static FieldInfo ArrayClosureArrayField =
            typeof(ArrayClosure).GetTypeInfo().GetDeclaredField(nameof(ArrayClosure.ConstantsAndNestedLambdas));

        public static FieldInfo ArrayClosureWithNonPassedParamsField =
            typeof(ArrayClosureWithNonPassedParams).GetTypeInfo().GetDeclaredField(nameof(ArrayClosureWithNonPassedParams.NonPassedParams));

        public static ConstructorInfo ArrayClosureWithNonPassedParamsConstructor =
            typeof(ArrayClosureWithNonPassedParams).GetTypeInfo().DeclaredConstructors.GetFirst();

        public class ArrayClosure
        {
            public readonly object[] ConstantsAndNestedLambdas;
            public ArrayClosure(object[] constantsAndNestedLambdas) => ConstantsAndNestedLambdas = constantsAndNestedLambdas;
        }

        public sealed class ArrayClosureWithNonPassedParams : ArrayClosure
        {
            public readonly object[] NonPassedParams;

            public ArrayClosureWithNonPassedParams(object[] constantsAndNestedLambdas, object[] nonPassedParams) : base(constantsAndNestedLambdas) =>
                NonPassedParams = nonPassedParams;
        }

        public sealed class NestedLambdaWithConstantsAndNestedLambdas
        {
            public static FieldInfo NestedLambdaField =
                typeof(NestedLambdaWithConstantsAndNestedLambdas).GetTypeInfo().GetDeclaredField(nameof(NestedLambda));

            public static FieldInfo ConstantsAndNestedLambdasField =
                typeof(NestedLambdaWithConstantsAndNestedLambdas).GetTypeInfo().GetDeclaredField(nameof(ConstantsAndNestedLambdas));

            public readonly object NestedLambda;
            public readonly object ConstantsAndNestedLambdas;
            public NestedLambdaWithConstantsAndNestedLambdas(object nestedLambda, object constantsAndNestedLambdas)
            {
                NestedLambda = nestedLambda;
                ConstantsAndNestedLambdas = constantsAndNestedLambdas;
            }
        }

        private sealed class NestedLambdaInfo
        {
            public readonly LambdaExpression LambdaExpression;
            public ClosureInfo ClosureInfo;
            public object Lambda;
            public int UsageCountOrVarIndex;

            public NestedLambdaInfo(LambdaExpression lambdaExpression)
            {
                LambdaExpression = lambdaExpression;
                ClosureInfo = new ClosureInfo(ClosureStatus.ToBeCollected);
                Lambda = null;
            }
        }

        internal static class CurryClosureFuncs
        {
            public static readonly MethodInfo[] Methods =
                typeof(CurryClosureFuncs).GetTypeInfo().DeclaredMethods.AsArray();

            public static Func<R> Curry<C, R>(Func<C, R> f, C c) =>
                () => f(c);

            public static Func<T1, R> Curry<C, T1, R>(Func<C, T1, R> f, C c) =>
                t1 => f(c, t1);

            public static Func<T1, T2, R> Curry<C, T1, T2, R>(Func<C, T1, T2, R> f, C c) =>
                (t1, t2) => f(c, t1, t2);

            public static Func<T1, T2, T3, R> Curry<C, T1, T2, T3, R>(Func<C, T1, T2, T3, R> f, C c) =>
                (t1, t2, t3) => f(c, t1, t2, t3);

            public static Func<T1, T2, T3, T4, R> Curry<C, T1, T2, T3, T4, R>(Func<C, T1, T2, T3, T4, R> f, C c) =>
                (t1, t2, t3, t4) => f(c, t1, t2, t3, t4);

            public static Func<T1, T2, T3, T4, T5, R> Curry<C, T1, T2, T3, T4, T5, R>(Func<C, T1, T2, T3, T4, T5, R> f,
                C c) => (t1, t2, t3, t4, t5) => f(c, t1, t2, t3, t4, t5);

            public static Func<T1, T2, T3, T4, T5, T6, R>
                Curry<C, T1, T2, T3, T4, T5, T6, R>(Func<C, T1, T2, T3, T4, T5, T6, R> f, C c) =>
                (t1, t2, t3, t4, t5, t6) => f(c, t1, t2, t3, t4, t5, t6);
        }

        internal static class CurryClosureActions
        {
            public static readonly MethodInfo[] Methods =
                typeof(CurryClosureActions).GetTypeInfo().DeclaredMethods.AsArray();

            public static Action Curry<C>(Action<C> a, C c) =>
                () => a(c);

            public static Action<T1> Curry<C, T1>(Action<C, T1> f, C c) =>
                t1 => f(c, t1);

            public static Action<T1, T2> Curry<C, T1, T2>(Action<C, T1, T2> f, C c) =>
                (t1, t2) => f(c, t1, t2);

            public static Action<T1, T2, T3> Curry<C, T1, T2, T3>(Action<C, T1, T2, T3> f, C c) =>
                (t1, t2, t3) => f(c, t1, t2, t3);

            public static Action<T1, T2, T3, T4> Curry<C, T1, T2, T3, T4>(Action<C, T1, T2, T3, T4> f, C c) =>
                (t1, t2, t3, t4) => f(c, t1, t2, t3, t4);

            public static Action<T1, T2, T3, T4, T5> Curry<C, T1, T2, T3, T4, T5>(Action<C, T1, T2, T3, T4, T5> f,
                C c) => (t1, t2, t3, t4, t5) => f(c, t1, t2, t3, t4, t5);

            public static Action<T1, T2, T3, T4, T5, T6>
                Curry<C, T1, T2, T3, T4, T5, T6>(Action<C, T1, T2, T3, T4, T5, T6> f, C c) =>
                (t1, t2, t3, t4, t5, t6) => f(c, t1, t2, t3, t4, t5, t6);
        }

#region Collect Bound Constants

        /// Helps to identify constants as the one to be put into the Closure
        public static bool IsClosureBoundConstant(object value, TypeInfo type) =>
            value is Delegate || 
            !type.IsPrimitive && !type.IsEnum && value is string == false && value is Type == false && value is decimal == false;

        // @paramExprs is required for nested lambda compilation
        private static bool TryCollectBoundConstants(ref ClosureInfo closure, Expression expr,
            IReadOnlyList<ParameterExpression> paramExprs, bool isNestedLambda, ref ClosureInfo rootClosure)
        {
            while (true)
            {
                if (expr == null)
                    return false;

                switch (expr.NodeType)
                {
                    case ExpressionType.Constant:
                        var constantExpr = (ConstantExpression)expr;
                        var value = constantExpr.Value;
                        if (value != null && IsClosureBoundConstant(value, value.GetType().GetTypeInfo()))
                            closure.AddConstant(value);
                        return true;

                    case ExpressionType.Quote:
                        //var operand = ((UnaryExpression)expr).Operand;
                        //if (operand != null && IsClosureBoundConstant(operand, expr.Type.GetTypeInfo()))
                        //    closure.AddConstant(operand);
                        return false;

                    case ExpressionType.Parameter:
                        // if parameter is used BUT is not in passed parameters and not in local variables,
                        // it means parameter is provided by outer lambda and should be put in closure for current lambda
                        var p = paramExprs.Count - 1;
                        while (p != -1 && !ReferenceEquals(paramExprs[p], expr)) --p;
                        if (p == -1 && !closure.IsLocalVar(expr))
                        {
                            if (!isNestedLambda)
                                return false;
                            closure.AddNonPassedParam((ParameterExpression)expr);
                        }
                        return true;

                    case ExpressionType.Call:
                        var callExpr = (MethodCallExpression)expr;
                        var callObjectExpr = callExpr.Object;

                        var fewCallArgCount = callExpr.FewArgumentCount;
                        if (fewCallArgCount == 0)
                        {
                            if (callObjectExpr != null)
                            {
                                expr = callObjectExpr;
                                continue;
                            }

                            return true;
                        }

                        if (fewCallArgCount > 0)
                        {
                            if (callObjectExpr != null && 
                                !TryCollectBoundConstants(ref closure, callObjectExpr, paramExprs, isNestedLambda, ref rootClosure))
                                return false;

                            if (fewCallArgCount == 1)
                            {
                                expr = ((OneArgumentMethodCallExpression)callExpr).Argument;
                                continue;
                            }
                            
                            if (fewCallArgCount == 2)
                            {
                                var twoArgsExpr = (TwoArgumentsMethodCallExpression)callExpr;
                                if (!TryCollectBoundConstants(ref closure, twoArgsExpr.Argument0, paramExprs, isNestedLambda, ref rootClosure))
                                    return false;
                                expr = twoArgsExpr.Argument1;
                                continue;
                            }

                            if (fewCallArgCount == 3)
                            {
                                var threeArgsExpr = (ThreeArgumentsMethodCallExpression)callExpr;
                                if (!TryCollectBoundConstants(ref closure, threeArgsExpr.Argument0, paramExprs, isNestedLambda, ref rootClosure) ||
                                    !TryCollectBoundConstants(ref closure, threeArgsExpr.Argument1, paramExprs, isNestedLambda, ref rootClosure))
                                    return false;
                                expr = threeArgsExpr.Argument2;
                                continue;
                            }

                            if (fewCallArgCount == 4)
                            {
                                var fourArgsExpr = (FourArgumentsMethodCallExpression)callExpr;
                                if (!TryCollectBoundConstants(ref closure, fourArgsExpr.Argument0, paramExprs, isNestedLambda, ref rootClosure) ||
                                    !TryCollectBoundConstants(ref closure, fourArgsExpr.Argument1, paramExprs, isNestedLambda, ref rootClosure) ||
                                    !TryCollectBoundConstants(ref closure, fourArgsExpr.Argument2, paramExprs, isNestedLambda, ref rootClosure))
                                    return false;
                                expr = fourArgsExpr.Argument3;
                                continue;
                            }

                            var fiveArgsExpr = (FiveArgumentsMethodCallExpression)callExpr;
                            if (!TryCollectBoundConstants(ref closure, fiveArgsExpr.Argument0, paramExprs, isNestedLambda, ref rootClosure) ||
                                !TryCollectBoundConstants(ref closure, fiveArgsExpr.Argument1, paramExprs, isNestedLambda, ref rootClosure) ||
                                !TryCollectBoundConstants(ref closure, fiveArgsExpr.Argument2, paramExprs, isNestedLambda, ref rootClosure) ||
                                !TryCollectBoundConstants(ref closure, fiveArgsExpr.Argument3, paramExprs, isNestedLambda, ref rootClosure))
                                return false;
                            expr = fiveArgsExpr.Argument4;
                            continue;
                        }

						var methodArgs = callExpr.Arguments;
                        var methodArgCount = methodArgs.Count;
                        if (methodArgCount == 0)
                        {
                            if (callObjectExpr != null)
                            {
                                expr = callObjectExpr;
                                continue;
                            }

                            return true;
                        }

                        if (callObjectExpr != null && 
                            !TryCollectBoundConstants(ref closure, callExpr.Object, paramExprs, isNestedLambda, ref rootClosure)) 
                            return false;

                        for (var i = 0; i < methodArgCount - 1; i++)
                            if (!TryCollectBoundConstants(ref closure, methodArgs[i], paramExprs, isNestedLambda, ref rootClosure))
                                return false;

                        expr = methodArgs[methodArgCount - 1];
                        continue;

                    case ExpressionType.MemberAccess:
                        var memberExpr = ((MemberExpression)expr).Expression;
                        if (memberExpr == null)
                            return true;
                        expr = memberExpr;
                        continue;

                    case ExpressionType.New:
                        var newExpr = (NewExpression)expr;

                        var fewArgCount = newExpr.FewArgumentCount;
                        if (fewArgCount == 0)
                            return true;

                        if (fewArgCount > 0)
                        {
                            if (fewArgCount == 1)
                            {
                                expr = ((OneArgumentNewExpression)newExpr).Argument;
                                continue;
                            }

                            if (fewArgCount == 2)
                            {
                                var twoArgsExpr = (TwoArgumentsNewExpression)newExpr;
                                if (!TryCollectBoundConstants(ref closure, twoArgsExpr.Argument0, paramExprs, isNestedLambda, ref rootClosure))
                                    return false;
                                expr = twoArgsExpr.Argument1;
                                continue;
                            }

                            if (fewArgCount == 3)
                            {
                                var threeArgsExpr = (ThreeArgumentsNewExpression)newExpr;
                                if (!TryCollectBoundConstants(ref closure, threeArgsExpr.Argument0, paramExprs, isNestedLambda, ref rootClosure) ||
                                    !TryCollectBoundConstants(ref closure, threeArgsExpr.Argument1, paramExprs, isNestedLambda, ref rootClosure))
                                    return false;
                                expr = threeArgsExpr.Argument2;
                                continue;
                            }

                            if (fewArgCount == 4)
                            {
                                var fourArgsExpr = (FourArgumentsNewExpression)newExpr;
                                if (!TryCollectBoundConstants(ref closure, fourArgsExpr.Argument0, paramExprs, isNestedLambda, ref rootClosure) ||
                                    !TryCollectBoundConstants(ref closure, fourArgsExpr.Argument1, paramExprs, isNestedLambda, ref rootClosure) ||
                                    !TryCollectBoundConstants(ref closure, fourArgsExpr.Argument2, paramExprs, isNestedLambda, ref rootClosure))
                                    return false;
                                expr = fourArgsExpr.Argument3;
                                continue;
                            }

                            if (fewArgCount == 4)
                            {
                                var fourArgsExpr = (FourArgumentsNewExpression)newExpr;
                                if (!TryCollectBoundConstants(ref closure, fourArgsExpr.Argument0, paramExprs, isNestedLambda, ref rootClosure) ||
                                    !TryCollectBoundConstants(ref closure, fourArgsExpr.Argument1, paramExprs, isNestedLambda, ref rootClosure) ||
                                    !TryCollectBoundConstants(ref closure, fourArgsExpr.Argument2, paramExprs, isNestedLambda, ref rootClosure))
                                    return false;
                                expr = fourArgsExpr.Argument3;
                                continue;
                            }

                            var fiveArgsExpr = (FiveArgumentsNewExpression)newExpr;
                            if (!TryCollectBoundConstants(ref closure, fiveArgsExpr.Argument0, paramExprs, isNestedLambda, ref rootClosure) ||
                                !TryCollectBoundConstants(ref closure, fiveArgsExpr.Argument1, paramExprs, isNestedLambda, ref rootClosure) ||
                                !TryCollectBoundConstants(ref closure, fiveArgsExpr.Argument2, paramExprs, isNestedLambda, ref rootClosure) ||
                                !TryCollectBoundConstants(ref closure, fiveArgsExpr.Argument3, paramExprs, isNestedLambda, ref rootClosure))
                                return false;
                            expr = fiveArgsExpr.Argument4;
                            continue;
                        }

                        var ctorArgs = ((NewExpression)expr).Arguments;
                        var ctorLastArgIndex = ctorArgs.Count - 1;
                        if (ctorLastArgIndex == -1)
                            return true;

                        for (var i = 0; i < ctorLastArgIndex; i++)
                            if (!TryCollectBoundConstants(ref closure, ctorArgs[i], paramExprs, isNestedLambda, ref rootClosure))
                                return false;
                        expr = ctorArgs[ctorLastArgIndex];
                        continue;

                    case ExpressionType.NewArrayBounds:
                    case ExpressionType.NewArrayInit:
                        var elemExprs = ((NewArrayExpression)expr).Expressions;
                        var elemExprsCount = elemExprs.Count;
                        if (elemExprsCount == 0)
                            return true;

                        for (var i = 0; i < elemExprsCount - 1; i++)
                            if (!TryCollectBoundConstants(ref closure, elemExprs[i], paramExprs, isNestedLambda, ref rootClosure))
                                return false;

                        expr = elemExprs[elemExprsCount - 1];
                        continue;

                    case ExpressionType.MemberInit:
                        return TryCollectMemberInitExprConstants(
                            ref closure, (MemberInitExpression)expr, paramExprs, isNestedLambda, ref rootClosure);

                    case ExpressionType.Lambda:
                        var nestedLambdaExpr = (LambdaExpression)expr;

                        // Look for the already collected lambdas and if we have the same lambda, start from the root
                        var nestedLambdas = rootClosure.NestedLambdas;
                        if (nestedLambdas.Length != 0)
                        {
                            var foundLambdaInfo = FindAlreadyCollectedNestedLambdaInfo(nestedLambdas, nestedLambdaExpr, out var foundInLambdas);
                            if (foundLambdaInfo != null)
                            {
                                // if the lambda is not found on the same level, then add it
                                if (foundInLambdas == closure.NestedLambdas)
                                {
                                    ++foundLambdaInfo.UsageCountOrVarIndex;
                                }
                                else
                                {
                                    closure.AddNestedLambda(foundLambdaInfo);
                                    var foundLambdaNonPassedParams = foundLambdaInfo.ClosureInfo.NonPassedParameters;
                                    if (foundLambdaNonPassedParams.Length != 0)
                                        PropagateNonPassedParamsToOuterLambda(ref closure, paramExprs, nestedLambdaExpr.Parameters, foundLambdaNonPassedParams);
                                }

                                return true;
                            }
                        }

                        var nestedLambdaInfo = new NestedLambdaInfo(nestedLambdaExpr);
                        if (!TryCollectBoundConstants(ref nestedLambdaInfo.ClosureInfo,
                            nestedLambdaExpr.Body, nestedLambdaExpr.Parameters, true, ref rootClosure))
                            return false;

                        closure.AddNestedLambda(nestedLambdaInfo);
                        var nestedNonPassedParams = nestedLambdaInfo.ClosureInfo.NonPassedParameters;
                        if (nestedNonPassedParams.Length != 0)
                            PropagateNonPassedParamsToOuterLambda(ref closure, paramExprs, nestedLambdaExpr.Parameters, nestedNonPassedParams);

                        return true;

                    case ExpressionType.Invoke:
                        var invokeExpr = (InvocationExpression)expr;
                        var invokeArgs = invokeExpr.Arguments;
                        var invokeArgsCount = invokeArgs.Count;
                        if (invokeArgsCount == 0)
                        {
                            // optimization #138: we inline the invoked lambda body (only for lambdas without arguments)
                            // therefore we skipping collecting the lambda and invocation arguments and got directly to lambda body.
                            // This approach is repeated in `TryEmitInvoke`
                            expr = (invokeExpr.Expression as LambdaExpression)?.Body ?? invokeExpr.Expression;
                            continue;
                        }
                        else if (!TryCollectBoundConstants(ref closure, invokeExpr.Expression, paramExprs, isNestedLambda, ref rootClosure))
                            return false;

                        for (var i = 0; i < invokeArgs.Count - 1; i++)
                            if (!TryCollectBoundConstants(ref closure, invokeArgs[i], paramExprs, isNestedLambda, ref rootClosure))
                                return false;

                        expr = invokeArgs[invokeArgsCount - 1];
                        continue;

                    case ExpressionType.Conditional:
                        var condExpr = (ConditionalExpression)expr;
                        if (!TryCollectBoundConstants(ref closure, condExpr.Test,    paramExprs, isNestedLambda, ref rootClosure) ||
                            !TryCollectBoundConstants(ref closure, condExpr.IfFalse, paramExprs, isNestedLambda, ref rootClosure))
                            return false;
                        expr = condExpr.IfTrue;
                        continue;

                    case ExpressionType.Block:

                        if (expr is OneVariableTwoExpressionBlockExpression simpleBlock)
                        {
                            closure.PushBlockWithVars(simpleBlock.Variable);
                            if (!TryCollectBoundConstants(ref closure, simpleBlock.Expression1, paramExprs, isNestedLambda, ref rootClosure) ||
                                !TryCollectBoundConstants(ref closure, simpleBlock.Expression2, paramExprs, isNestedLambda, ref rootClosure))
                                return false;
                            closure.PopBlock();
                            return true;
                        }

                        var blockExpr = (BlockExpression)expr;
                        var blockVarExprs = blockExpr.Variables;
                        var blockExprs = blockExpr.Expressions;

                        if (blockVarExprs.Count == 0)
                        {
                            for (var i = 0; i < blockExprs.Count - 1; i++)
                                if (!TryCollectBoundConstants(ref closure, blockExprs[i], paramExprs, isNestedLambda, ref rootClosure))
                                    return false;
                            expr = blockExprs[blockExprs.Count - 1];
                            continue;
                        }
                        else
                        {
                            if (blockVarExprs.Count == 1)
                                closure.PushBlockWithVars(blockVarExprs[0]);
                            else
                                closure.PushBlockWithVars(blockVarExprs);

                            for (var i = 0; i < blockExprs.Count; i++)
                                if (!TryCollectBoundConstants(ref closure, blockExprs[i], paramExprs, isNestedLambda, ref rootClosure))
                                    return false;
                            closure.PopBlock();
                        }

                        return true;

                    case ExpressionType.Loop:
                        var loopExpr = (LoopExpression)expr;
                        closure.AddLabel(loopExpr.BreakLabel);
                        closure.AddLabel(loopExpr.ContinueLabel);
                        expr = loopExpr.Body;
                        continue;

                    case ExpressionType.Index:
                        var indexExpr = (IndexExpression)expr;
                        var indexArgs = indexExpr.Arguments;
                        for (var i = 0; i < indexArgs.Count; i++)
                            if (!TryCollectBoundConstants(ref closure, indexArgs[i], paramExprs, isNestedLambda, ref rootClosure))
                                return false;
                        if (indexExpr.Object == null)
                            return true;
                        expr = indexExpr.Object;
                        continue;

                    case ExpressionType.Try:
                        return TryCollectTryExprConstants(ref closure, (TryExpression)expr, paramExprs, isNestedLambda, ref rootClosure);

                    case ExpressionType.Label:
                        var labelExpr = (LabelExpression)expr;
                        var defaultValueExpr = labelExpr.DefaultValue;
                        closure.AddLabel(labelExpr.Target);
                        if (defaultValueExpr == null)
                            return true;
                        expr = defaultValueExpr;
                        continue;

                    case ExpressionType.Goto:
                        var gotoExpr = (GotoExpression)expr;
                        if (gotoExpr.Kind == GotoExpressionKind.Return)
                            closure.MarkAsContainsReturnGotoExpression();

                        if (gotoExpr.Value == null)
                            return true;

                        expr = gotoExpr.Value;
                        continue;

                    case ExpressionType.Switch:
                        var switchExpr = ((SwitchExpression)expr);
                        if (!TryCollectBoundConstants(ref closure, switchExpr.SwitchValue, paramExprs, isNestedLambda, ref rootClosure) ||
                            switchExpr.DefaultBody != null && 
                            !TryCollectBoundConstants(ref closure, switchExpr.DefaultBody, paramExprs, isNestedLambda, ref rootClosure))
                            return false;
                        var switchCases = switchExpr.Cases;
                        for (var i = 0; i < switchCases.Count - 1; i++)
                            if (!TryCollectBoundConstants(ref closure, switchCases[i].Body, paramExprs, isNestedLambda, ref rootClosure))
                                return false;
                        expr = switchCases[switchCases.Count - 1].Body;
                        continue;

                    case ExpressionType.Extension:
                        expr = expr.Reduce();
                        continue;

                    case ExpressionType.Default:
                        return true;

                    default:
                        if (expr is UnaryExpression unaryExpr)
                        {
                            expr = unaryExpr.Operand;
                            continue;
                        }

                        if (expr is BinaryExpression binaryExpr)
                        {
                            if (!TryCollectBoundConstants(ref closure, binaryExpr.Left, paramExprs, isNestedLambda, ref rootClosure))
                                return false;
                            expr = binaryExpr.Right;
                            continue;
                        }

                        if (expr is TypeBinaryExpression typeBinaryExpr)
                        {
                            expr = typeBinaryExpr.Expression;
                            continue;
                        }

                        return false;
                }
            }
        }

        private static void PropagateNonPassedParamsToOuterLambda(
            ref ClosureInfo closure, IReadOnlyList<ParameterExpression> paramExprs, 
            IReadOnlyList<ParameterExpression> nestedLambdaParamExprs, ParameterExpression[] nestedNonPassedParams)
        {
            // If nested non passed parameter is not matched with any outer passed parameter, 
            // then ensure it goes to outer non passed parameter.
            // But check that having a non-passed parameter in root expression is invalid.
            for (var i = 0; i < nestedNonPassedParams.Length; i++)
            {
                var nestedNonPassedParam = nestedNonPassedParams[i];

                var isInNestedLambda = false;
                if (nestedLambdaParamExprs.Count != 0)
                    for (var p = 0; !isInNestedLambda && p < nestedLambdaParamExprs.Count; ++p)
                        isInNestedLambda = ReferenceEquals(nestedLambdaParamExprs[p], nestedNonPassedParam);

                var isInOuterLambda = false;
                if (paramExprs.Count != 0)
                    for (var p = 0; !isInOuterLambda && p < paramExprs.Count; ++p)
                        isInOuterLambda = ReferenceEquals(paramExprs[p], nestedNonPassedParam);

                if (!isInNestedLambda && !isInOuterLambda)
                    closure.AddNonPassedParam(nestedNonPassedParam);
            }
        }

        private static NestedLambdaInfo FindAlreadyCollectedNestedLambdaInfo(
            NestedLambdaInfo[] nestedLambdas, LambdaExpression nestedLambdaExpr, out NestedLambdaInfo[] foundInLambdas)
        {
            for (var i = 0; i < nestedLambdas.Length; i++)
            {
                var lambdaInfo = nestedLambdas[i];
                if (ReferenceEquals(lambdaInfo.LambdaExpression, nestedLambdaExpr))
                {
                    foundInLambdas = nestedLambdas;
                    return lambdaInfo;
                }

                var deeperNestedLambdas = lambdaInfo.ClosureInfo.NestedLambdas;
                if (deeperNestedLambdas.Length != 0)
                {
                    var deeperLambdaInfo = FindAlreadyCollectedNestedLambdaInfo(deeperNestedLambdas, nestedLambdaExpr, out foundInLambdas);
                    if (deeperLambdaInfo != null)
                        return deeperLambdaInfo;
                }
            }

            foundInLambdas = null;
            return null;
        }

        private static bool TryCompileNestedLambda(ref ClosureInfo outerClosureInfo, int nestedLambdaIndex)
        {
            // 1. Try to compile nested lambda in place
            // 2. Check that parameters used in compiled lambda are passed or closed by outer lambda
            // 3. Add the compiled lambda to closure of outer lambda for later invocation
            var nestedLambdaInfo = outerClosureInfo.NestedLambdas[nestedLambdaIndex];
            if (nestedLambdaInfo.Lambda != null)
                return true;

            var nestedLambdaExpr = nestedLambdaInfo.LambdaExpression;
            ref var nestedLambdaClosureInfo = ref nestedLambdaInfo.ClosureInfo;

            var nestedLambdaParamExprs = nestedLambdaExpr.Parameters;
            var nestedLambdaNestedLambdas = nestedLambdaClosureInfo.NestedLambdas;
            if (nestedLambdaNestedLambdas.Length != 0)
                for (var i = 0; i < nestedLambdaNestedLambdas.Length; ++i)
                    if (!TryCompileNestedLambda(ref nestedLambdaClosureInfo, i))
                        return false;

            ArrayClosure nestedLambdaClosure = null;
            if (nestedLambdaClosureInfo.NonPassedParameters.Length == 0)
            {
                if ((nestedLambdaClosureInfo.Status & ClosureStatus.HasClosure) == 0)
                    nestedLambdaClosure = EmptyArrayClosure;
                else
                    nestedLambdaClosure = new ArrayClosure(nestedLambdaClosureInfo.GetArrayOfConstantsAndNestedLambdas());
            }

            var nestedReturnType = nestedLambdaExpr.ReturnType;
            var closurePlusParamTypes = GetClosureTypeToParamTypes(nestedLambdaParamExprs);

            var method = new DynamicMethod(string.Empty, 
                nestedReturnType, closurePlusParamTypes, typeof(ArrayClosure), true);

            var il = method.GetILGenerator();

            if ((nestedLambdaClosureInfo.Status & ClosureStatus.HasClosure) != 0)
                EmittingVisitor.EmitLoadConstantsAndNestedLambdasIntoVars(il, ref nestedLambdaClosureInfo);

            var parentFlags = nestedReturnType == typeof(void) ? ParentFlags.IgnoreResult : ParentFlags.Empty;
            if (!EmittingVisitor.TryEmit(nestedLambdaExpr.Body, nestedLambdaParamExprs, il, ref nestedLambdaClosureInfo, parentFlags))
                return false;
            il.Emit(OpCodes.Ret);

            if (nestedLambdaClosure != null)
            {
                nestedLambdaInfo.Lambda = method.CreateDelegate(nestedLambdaExpr.Type, nestedLambdaClosure);
            }
            else
            {
                // Otherwise create a static or an open delegate to pass closure later with `TryEmitNestedLambda`,
                // constructing the new closure with non-passed arguments and the rest of items
                nestedLambdaInfo.Lambda = method.CreateDelegate(
                    Tools.GetFuncOrActionType(closurePlusParamTypes, nestedReturnType),
                    null);
            }

            ReturnClosureTypeToParamTypesToPool(closurePlusParamTypes);
            return true;
        }

        private static bool TryCollectMemberInitExprConstants(ref ClosureInfo closure, MemberInitExpression expr,
            IReadOnlyList<ParameterExpression> paramExprs, bool isNestedLambda, ref ClosureInfo rootClosure)
        {
            var newExpr = expr.NewExpression
                          ?? expr.Expression
                ;
            if (!TryCollectBoundConstants(ref closure, newExpr, paramExprs, isNestedLambda, ref rootClosure))
                return false;

            var memberBindings = expr.Bindings;
            for (var i = 0; i < memberBindings.Count; ++i)
            {
                var memberBinding = memberBindings[i];
                if (memberBinding.BindingType == MemberBindingType.Assignment &&
                    !TryCollectBoundConstants(
                        ref closure, ((MemberAssignment)memberBinding).Expression, paramExprs, isNestedLambda, ref rootClosure))
                    return false;
            }

            return true;
        }

        private static bool TryCollectTryExprConstants(ref ClosureInfo closure, TryExpression tryExpr,
            IReadOnlyList<ParameterExpression> paramExprs, bool isNestedLambda, ref ClosureInfo rootClosure)
        {
            closure.AddTryCatchFinallyInfo();

            if (!TryCollectBoundConstants(ref closure, tryExpr.Body, paramExprs, isNestedLambda, ref rootClosure))
                return false;

            var catchBlocks = tryExpr.Handlers;
            for (var i = 0; i < catchBlocks.Count; i++)
            {
                var catchBlock = catchBlocks[i];
                var catchExVar = catchBlock.Variable;
                if (catchExVar != null)
                {
                    closure.PushBlockWithVars(catchExVar);
                    if (!TryCollectBoundConstants(ref closure, catchExVar, paramExprs, isNestedLambda, ref rootClosure))
                        return false;
                }

                if (catchBlock.Filter != null && 
                    !TryCollectBoundConstants(ref closure, catchBlock.Filter, paramExprs, isNestedLambda, ref rootClosure))
                    return false;

                if (!TryCollectBoundConstants(ref closure, catchBlock.Body, paramExprs, isNestedLambda, ref rootClosure))
                    return false;

                if (catchExVar != null)
                    closure.PopBlock();
            }

            if (tryExpr.Finally != null && 
                !TryCollectBoundConstants(ref closure, tryExpr.Finally, paramExprs, isNestedLambda, ref rootClosure))
                return false;

            --closure.CurrentTryCatchFinallyIndex;
            return true;
        }

#endregion

        // The minimal context-aware flags set by parent
        [Flags]
        internal enum ParentFlags
        {
            Empty = 0,
            IgnoreResult = 1 << 1,
            Call = 1 << 2,
            MemberAccess = 1 << 3, // Any Parent Expression is a MemberExpression
            Arithmetic = 1 << 4,
            Coalesce = 1 << 5,
            InstanceAccess = 1 << 6,
            DupMemberOwner = 1 << 7,
            TryCatch = 1 << 8,
            InstanceCall = Call | InstanceAccess
        }

        internal static bool IgnoresResult(this ParentFlags parent) => (parent & ParentFlags.IgnoreResult) != 0;

        /// <summary>Supports emitting of selected expressions, e.g. lambdaExpr are not supported yet.
        /// When emitter find not supported expression it will return false from <see cref="TryEmit"/>, so I could fallback
        /// to normal and slow Expression.Compile.</summary>
        private static class EmittingVisitor
        {
#if NETSTANDARD1_1 || NETSTANDARD1_2 || NETSTANDARD1_3 || NETSTANDARD1_4 || NETSTANDARD1_5 || NETSTANDARD1_6
            private static readonly MethodInfo _getTypeFromHandleMethod =
                typeof(Type).GetTypeInfo().GetDeclaredMethod("GetTypeFromHandle");

            private static readonly MethodInfo _objectEqualsMethod = GetObjectEquals();
            private static MethodInfo GetObjectEquals()
            {
                var ms = typeof(object).GetTypeInfo().GetDeclaredMethods("Equals");
                foreach (var m in ms)
                    if (m.GetParameters().Length == 2)
                        return m;
                throw new InvalidOperationException("object.Equals is not found");
            }
#else
            private static readonly MethodInfo _getTypeFromHandleMethod =
                ((Func<RuntimeTypeHandle, Type>)Type.GetTypeFromHandle).Method;

            private static readonly MethodInfo _objectEqualsMethod =
                ((Func<object, object, bool>)object.Equals).Method;
#endif

            public static bool TryEmit(Expression expr, IReadOnlyList<ParameterExpression> paramExprs,
                ILGenerator il, ref ClosureInfo closure, ParentFlags parent, int byRefIndex = -1)
            {
                while (true)
                {
                    closure.LastEmitIsAddress = false;

                    switch (expr.NodeType)
                    {
                        case ExpressionType.Parameter:
                            return (parent & ParentFlags.IgnoreResult) != 0 ||
                                   TryEmitParameter((ParameterExpression)expr, paramExprs, il, ref closure, parent, byRefIndex);

                        case ExpressionType.TypeAs:
                        case ExpressionType.IsTrue:
                        case ExpressionType.IsFalse:
                        case ExpressionType.Increment:
                        case ExpressionType.Decrement:
                        case ExpressionType.Negate:
                        case ExpressionType.NegateChecked:
                        case ExpressionType.OnesComplement:
                        case ExpressionType.UnaryPlus:
                        case ExpressionType.Unbox:
                            return TryEmitSimpleUnaryExpression((UnaryExpression)expr, paramExprs, il, ref closure, parent);

                        case ExpressionType.Quote:
                            //return TryEmitNotNullConstant(true, expr.Type, ((UnaryExpression)expr).Operand, il, ref closure);
                            return false;

                        case ExpressionType.TypeIs:
                            return TryEmitTypeIs((TypeBinaryExpression)expr, paramExprs, il, ref closure, parent);

                        case ExpressionType.Not:
                            return TryEmitNot((UnaryExpression)expr, paramExprs, il, ref closure, parent);

                        case ExpressionType.Convert:
                        case ExpressionType.ConvertChecked:
                            return TryEmitConvert((UnaryExpression)expr, paramExprs, il, ref closure, parent);

                        case ExpressionType.ArrayIndex:
                            var arrIndexExpr = (BinaryExpression)expr;
                            return TryEmit(arrIndexExpr.Left, paramExprs, il, ref closure, parent) &&
                                   TryEmit(arrIndexExpr.Right, paramExprs, il, ref closure, parent) &&
                                   TryEmitArrayIndex(expr.Type, il);

                        case ExpressionType.ArrayLength:
                            var arrLengthExpr = (UnaryExpression)expr;
                            return TryEmitArrayLength(arrLengthExpr, paramExprs, il, ref closure, parent);

                        case ExpressionType.Constant:
                            var constExpr = (ConstantExpression)expr;
                            if ((parent & ParentFlags.IgnoreResult) != 0)
                                return true;

                            if (constExpr.Value == null)
                            {
                                il.Emit(OpCodes.Ldnull);
                                return true;
                            }

                            return TryEmitNotNullConstant(true, constExpr.Type, constExpr.Value, il, ref closure);

                        case ExpressionType.Call:
                            return TryEmitMethodCall(expr, paramExprs, il, ref closure, parent);

                        case ExpressionType.MemberAccess:
                            return TryEmitMemberAccess((MemberExpression)expr, paramExprs, il, ref closure, parent);

                        case ExpressionType.New:
                            return TryEmitNew(expr, paramExprs, il, ref closure, parent);

                        case ExpressionType.NewArrayBounds:
                        case ExpressionType.NewArrayInit:
                            return EmitNewArray((NewArrayExpression)expr, paramExprs, il, ref closure, parent);

                        case ExpressionType.MemberInit:
                            return EmitMemberInit((MemberInitExpression)expr, paramExprs, il, ref closure, parent);

                        case ExpressionType.Lambda:
                            return TryEmitNestedLambda((LambdaExpression)expr, paramExprs, il, ref closure);

                        case ExpressionType.Invoke:
                            // optimization #138: we inline the invoked lambda body (only for lambdas without arguments) 
                            if (((InvocationExpression)expr).Expression is LambdaExpression lambdaExpr && lambdaExpr.Parameters.Count == 0)
                            {
                                expr = lambdaExpr.Body;
                                continue;
                            }

                            return TryEmitInvoke((InvocationExpression)expr, paramExprs, il, ref closure, parent);

                        case ExpressionType.GreaterThan:
                        case ExpressionType.GreaterThanOrEqual:
                        case ExpressionType.LessThan:
                        case ExpressionType.LessThanOrEqual:
                        case ExpressionType.Equal:
                        case ExpressionType.NotEqual:
                            var binaryExpr = (BinaryExpression)expr;
                            return TryEmitComparison(binaryExpr.Left, binaryExpr.Right, binaryExpr.NodeType,
                                paramExprs, il, ref closure, parent);

                        case ExpressionType.Add:
                        case ExpressionType.AddChecked:
                        case ExpressionType.Subtract:
                        case ExpressionType.SubtractChecked:
                        case ExpressionType.Multiply:
                        case ExpressionType.MultiplyChecked:
                        case ExpressionType.Divide:
                        case ExpressionType.Modulo:
                        case ExpressionType.Power:
                        case ExpressionType.And:
                        case ExpressionType.Or:
                        case ExpressionType.ExclusiveOr:
                        case ExpressionType.LeftShift:
                        case ExpressionType.RightShift:
                            var arithmeticExpr = (BinaryExpression)expr;
                            return TryEmitArithmetic(arithmeticExpr, expr.NodeType, paramExprs, il, ref closure, parent);

                        case ExpressionType.AndAlso:
                        case ExpressionType.OrElse:
                            return TryEmitLogicalOperator((BinaryExpression)expr, paramExprs, il, ref closure, parent);

                        case ExpressionType.Coalesce:
                            return TryEmitCoalesceOperator((BinaryExpression)expr, paramExprs, il, ref closure, parent);

                        case ExpressionType.Conditional:
                            return TryEmitConditional((ConditionalExpression)expr, paramExprs, il, ref closure, parent);

                        case ExpressionType.PostIncrementAssign:
                        case ExpressionType.PreIncrementAssign:
                        case ExpressionType.PostDecrementAssign:
                        case ExpressionType.PreDecrementAssign:
                            return TryEmitIncDecAssign((UnaryExpression)expr, paramExprs, il, ref closure, parent);

                        case ExpressionType.AddAssign: 
                        case ExpressionType.AddAssignChecked:
                        case ExpressionType.SubtractAssign:
                        case ExpressionType.SubtractAssignChecked:
                        case ExpressionType.MultiplyAssign:
                        case ExpressionType.MultiplyAssignChecked:
                        case ExpressionType.DivideAssign:
                        case ExpressionType.ModuloAssign:
                        case ExpressionType.PowerAssign:
                        case ExpressionType.AndAssign:
                        case ExpressionType.OrAssign:
                        case ExpressionType.ExclusiveOrAssign:
                        case ExpressionType.LeftShiftAssign:
                        case ExpressionType.RightShiftAssign:
                        case ExpressionType.Assign:
                            return TryEmitAssign((BinaryExpression)expr, paramExprs, il, ref closure, parent);

                        case ExpressionType.Block:
                            if (expr is OneVariableTwoExpressionBlockExpression simpleBlockExpr)
                            {
                                closure.PushBlockWithVars(simpleBlockExpr.Variable, il.GetNextLocalVarIndex(simpleBlockExpr.Variable.Type));
                                if (!TryEmit(simpleBlockExpr.Expression1, paramExprs, il, ref closure, parent | ParentFlags.IgnoreResult) ||
                                    !TryEmit(simpleBlockExpr.Expression2, paramExprs, il, ref closure, parent))
                                    return false;
                                closure.PopBlock();
                                return true;
                            }

                            var blockExpr = (BlockExpression)expr;
                            var blockVarExprs = blockExpr.Variables;
                            var blockVarCount = blockVarExprs.Count;
                            if (blockVarCount == 1)
                                closure.PushBlockWithVars(blockVarExprs[0], il.GetNextLocalVarIndex(blockVarExprs[0].Type));
                            else if (blockVarCount > 1)
                                closure.PushBlockAndConstructLocalVars(blockVarExprs, il);

                            var statementExprs = blockExpr.Expressions; // Trim the expressions after the Throw - #196
                            var statementCount = statementExprs.Count;
                            expr = statementExprs[statementCount - 1]; // The last (result) statement in block will provide the result

                            // Try to trim the statements up to the Throw (if any)
                            if (statementCount > 1)
                            {
                                var throwIndex = statementCount - 1;
                                while (throwIndex != -1 && statementExprs[throwIndex].NodeType != ExpressionType.Throw)
                                    --throwIndex;

                                // If we have a Throw and it is not the last one
                                if (throwIndex != -1 && throwIndex != statementCount - 1)
                                {
                                    // Change the Throw return type to match the one for the Block, and adjust the statement count
                                    expr = Expression.Throw(((UnaryExpression)statementExprs[throwIndex]).Operand, blockExpr.Type);
                                    statementCount = throwIndex + 1;
                                }
                            }

                            // handle the all statements in block excluding the last one
                            if (statementCount > 1)
                                for (var i = 0; i < statementCount - 1; i++)
                                    if (!TryEmit(statementExprs[i], paramExprs, il, ref closure, parent | ParentFlags.IgnoreResult))
                                        return false;

                            if (blockVarCount == 0)
                                continue; // OMG, no recursion, continue with last expression

                            if (!TryEmit(expr, paramExprs, il, ref closure, parent))
                                return false;

                            closure.PopBlock();
                            return true;

                        case ExpressionType.Loop:
                            return TryEmitLoop((LoopExpression)expr, paramExprs, il, ref closure, parent);

                        case ExpressionType.Try:
                            return TryEmitTryCatchFinallyBlock((TryExpression)expr, paramExprs, il, ref closure,
                                parent | ParentFlags.TryCatch);

                        case ExpressionType.Throw:
                            {
                                if (!TryEmit(((UnaryExpression)expr).Operand, paramExprs, il, ref closure, parent & ~ParentFlags.IgnoreResult))
                                    return false;
                                il.Emit(OpCodes.Throw);
                                return true;
                            }

                        case ExpressionType.Default:
                            if (expr.Type != typeof(void) && (parent & ParentFlags.IgnoreResult) == 0)
                               EmitDefault(expr.Type, il);
                            return true;

                        case ExpressionType.Index:
                            return TryEmitIndex((IndexExpression)expr, paramExprs, il, ref closure, parent);

                        case ExpressionType.Goto:
                            return TryEmitGoto((GotoExpression)expr, paramExprs, il, ref closure, parent);

                        case ExpressionType.Label:
                            return TryEmitLabel((LabelExpression)expr, paramExprs, il, ref closure, parent);

                        case ExpressionType.Switch:
                            return TryEmitSwitch((SwitchExpression)expr, paramExprs, il, ref closure, parent);

                        case ExpressionType.Extension:
                            expr = expr.Reduce();
                            continue;

                        default:
                            return false;
                    }
                }
            }

            private static bool TryEmitNew(Expression expr, IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure,
                ParentFlags parent)
            {
                var newExpr = (NewExpression)expr;

                var argCount = newExpr.FewArgumentCount;
                if (argCount > 0)
                {
                    var args = newExpr.Constructor.GetParameters();
                    if (argCount == 1)
                    {
                        var argExpr = ((OneArgumentNewExpression)newExpr).Argument;
                        if (!TryEmit(argExpr, paramExprs, il, ref closure, parent, args[0].ParameterType.IsByRef ? 0 : -1))
                            return false;
                    }
                    else if (argCount == 2)
                    {
                        var twoArgsExpr = (TwoArgumentsNewExpression)newExpr;
                        if (!TryEmit(twoArgsExpr.Argument0, paramExprs, il, ref closure, parent, args[0].ParameterType.IsByRef ? 0 : -1) ||
                            !TryEmit(twoArgsExpr.Argument1, paramExprs, il, ref closure, parent, args[1].ParameterType.IsByRef ? 1 : -1))
                            return false;
                    }
                    else if (argCount == 3)
                    {
                        var threeArgsExpr = (ThreeArgumentsNewExpression)newExpr;
                        if (!TryEmit(threeArgsExpr.Argument0, paramExprs, il, ref closure, parent, args[0].ParameterType.IsByRef ? 0 : -1) ||
                            !TryEmit(threeArgsExpr.Argument1, paramExprs, il, ref closure, parent, args[1].ParameterType.IsByRef ? 1 : -1) ||
                            !TryEmit(threeArgsExpr.Argument2, paramExprs, il, ref closure, parent, args[2].ParameterType.IsByRef ? 2 : -1))
                            return false;
                    }
                    else if (argCount == 4)
                    {
                        var fourArgsExpr = (FourArgumentsNewExpression)newExpr;
                        if (!TryEmit(fourArgsExpr.Argument0, paramExprs, il, ref closure, parent, args[0].ParameterType.IsByRef ? 0 : -1) ||
                            !TryEmit(fourArgsExpr.Argument1, paramExprs, il, ref closure, parent, args[1].ParameterType.IsByRef ? 1 : -1) ||
                            !TryEmit(fourArgsExpr.Argument2, paramExprs, il, ref closure, parent, args[2].ParameterType.IsByRef ? 2 : -1) ||
                            !TryEmit(fourArgsExpr.Argument3, paramExprs, il, ref closure, parent, args[3].ParameterType.IsByRef ? 3 : -1))
                            return false;
                    }
                    else if (argCount == 5)
                    {
                        var fourArgsExpr = (FiveArgumentsNewExpression)newExpr;
                        if (!TryEmit(fourArgsExpr.Argument0, paramExprs, il, ref closure, parent, args[0].ParameterType.IsByRef ? 0 : -1) ||
                            !TryEmit(fourArgsExpr.Argument1, paramExprs, il, ref closure, parent, args[1].ParameterType.IsByRef ? 1 : -1) ||
                            !TryEmit(fourArgsExpr.Argument2, paramExprs, il, ref closure, parent, args[2].ParameterType.IsByRef ? 2 : -1) ||
                            !TryEmit(fourArgsExpr.Argument3, paramExprs, il, ref closure, parent, args[3].ParameterType.IsByRef ? 3 : -1) ||
                            !TryEmit(fourArgsExpr.Argument4, paramExprs, il, ref closure, parent, args[4].ParameterType.IsByRef ? 4 : -1))
                            return false;
                    }

                    // ReSharper disable once ConditionIsAlwaysTrueOrFalse
                    if (newExpr.Constructor != null)
                        il.Emit(OpCodes.Newobj, newExpr.Constructor);
                    else if (newExpr.Type.IsValueType())
                        EmitLoadLocalVariable(il, InitValueTypeVariable(il, newExpr.Type));
                    else
                        return false;
                    return true;
                }

                var argExprs = newExpr.Arguments;
                if (argExprs.Count != 0)
                {
                    var args = newExpr.Constructor.GetParameters();
                    for (var i = 0; i < args.Length; ++i)
                        if (!TryEmit(argExprs[i], paramExprs, il, ref closure, parent, args[i].ParameterType.IsByRef ? i : -1))
                            return false;
                }

                // ReSharper disable once ConditionIsAlwaysTrueOrFalse
                if (newExpr.Constructor != null)
                    il.Emit(OpCodes.Newobj, newExpr.Constructor);
                else if (newExpr.Type.IsValueType())
                    EmitLoadLocalVariable(il, InitValueTypeVariable(il, newExpr.Type));
                else
                    return false;
                return true;
            }

            private static bool TryEmitArrayLength(UnaryExpression arrLengthExpr,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure,
                ParentFlags parent)
            {
                if (!TryEmit(arrLengthExpr.Operand, paramExprs, il, ref closure, parent))
                    return false;

                if ((parent & ParentFlags.IgnoreResult) == 0)
                {
                    il.Emit(OpCodes.Ldlen);
                    il.Emit(OpCodes.Conv_I4);
                }

                return true;
            }

            private static bool TryEmitLoop(LoopExpression loopExpr, 
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure, ParentFlags parent)
            {
                // Mark the start of the loop body:
                var loopBodyLabel = il.DefineLabel();
                il.MarkLabel(loopBodyLabel);

                if (loopExpr.ContinueLabel != null)
                    il.MarkLabel(closure.GetOrCreateLabel(loopExpr.ContinueLabel, il));

                if (!TryEmit(loopExpr.Body, paramExprs, il, ref closure, parent))
                    return false;

                // If loop hasn't exited, jump back to start of its body:
                il.Emit(OpCodes.Br, loopBodyLabel);

                if (loopExpr.BreakLabel != null)
                    il.MarkLabel(closure.GetOrCreateLabel(loopExpr.BreakLabel, il));

                return true;
            }

            private static bool TryEmitIndex(IndexExpression indexExpr, 
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure, ParentFlags parent)
            {
                if (indexExpr.Object != null &&
                    !TryEmit(indexExpr.Object, paramExprs, il, ref closure, parent))
                    return false;

                var indexArgExprs = indexExpr.Arguments;
                for (var i = 0; i < indexArgExprs.Count; i++)
                    if (!TryEmit(indexArgExprs[i], paramExprs, il, ref closure, parent,
                        indexArgExprs[i].Type.IsByRef ? i : -1))
                        return false;

                var indexerProp = indexExpr.Indexer;
                if (indexerProp != null)
                    return EmitMethodCall(il, indexerProp.DeclaringType.FindPropertyGetMethod(indexerProp.Name));

                if (indexExpr.Arguments.Count == 1) // one dimensional array
                    return TryEmitArrayIndex(indexExpr.Type, il);

                // multi dimensional array
                return EmitMethodCall(il, indexExpr.Object?.Type.FindMethod("Get"));
            }

            private static bool TryEmitLabel(LabelExpression expr,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure, ParentFlags parent)
            {
                var index = closure.GetLabelIndex(expr.Target);
                if (index == -1)
                    return false; // should be found in first collecting constants round

                if (closure.IsTryReturnLabel(index))
                    return true; // label will be emitted by TryEmitTryCatchFinallyBlock

                // define a new label or use the label provided by the preceding GoTo expression
                var label = closure.GetOrCreateLabel(index, il);

                il.MarkLabel(label);

                return expr.DefaultValue == null || TryEmit(expr.DefaultValue, paramExprs, il, ref closure, parent);
            }

            private static bool TryEmitGoto(GotoExpression expr,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure, ParentFlags parent)
            {
                var index = closure.GetLabelIndex(expr.Target);
                if (index == -1)
                {
                    if ((closure.Status & ClosureStatus.ToBeCollected) == 0)
                        return false; // if no collection cycle then the labels may be not collected
                    throw new InvalidOperationException("Cannot jump, no labels found");
                }

                if (expr.Value != null &&
                    !TryEmit(expr.Value, paramExprs, il, ref closure, parent & ~ParentFlags.IgnoreResult))
                    return false;

                switch (expr.Kind)
                {
                    case GotoExpressionKind.Break:
                    case GotoExpressionKind.Continue:
                        // use label defined by Label expression or define its own to use by subsequent Label
                        il.Emit(OpCodes.Br, closure.GetOrCreateLabel(index, il));
                        return true;

                    case GotoExpressionKind.Goto:
                        if (expr.Value != null)
                            goto case GotoExpressionKind.Return;

                        // use label defined by Label expression or define its own to use by subsequent Label
                        il.Emit(OpCodes.Br, closure.GetOrCreateLabel(index, il));
                        return true;

                    case GotoExpressionKind.Return:

                        // check that we are inside the Try-Catch-Finally block
                        if ((parent & ParentFlags.TryCatch) != 0)
                        {
                            // Can't emit a Return inside a Try/Catch, so leave it to TryEmitTryCatchFinallyBlock
                            // to emit the Leave instruction, return label and return result
                            closure.MarkReturnLabelIndex(index);
                        }
                        else
                        {
                            // use label defined by Label expression or define its own to use by subsequent Label
                            il.Emit(OpCodes.Ret, closure.GetOrCreateLabel(index, il));
                        }

                        return true;

                    default:
                        return false;
                }
            }

            private static bool TryEmitCoalesceOperator(BinaryExpression exprObj,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure, ParentFlags parent)
            {
                var labelFalse = il.DefineLabel();
                var labelDone = il.DefineLabel();

                var left = exprObj.Left;
                var right = exprObj.Right;

                if (!TryEmit(left, paramExprs, il, ref closure, parent | ParentFlags.Coalesce))
                    return false;

                var leftType = left.Type;
                if (leftType.IsValueType()) // Nullable -> It's the only ValueType comparable to null
                {
                    var varIndex = EmitStoreLocalVariableAndLoadItsAddress(il, leftType);
                    il.Emit(OpCodes.Call, leftType.FindNullableHasValueGetterMethod());

                    il.Emit(OpCodes.Brfalse, labelFalse);
                    EmitLoadLocalVariableAddress(il, varIndex);
                    il.Emit(OpCodes.Call, leftType.FindNullableGetValueOrDefaultMethod());

                    il.Emit(OpCodes.Br, labelDone);
                    il.MarkLabel(labelFalse);
                    if (!TryEmit(right, paramExprs, il, ref closure, parent | ParentFlags.Coalesce))
                        return false;

                    il.MarkLabel(labelDone);
                    return true;
                }

                il.Emit(OpCodes.Dup); // duplicate left, if it's not null, after the branch this value will be on the top of the stack
                il.Emit(OpCodes.Ldnull);
                il.Emit(OpCodes.Ceq);
                il.Emit(OpCodes.Brfalse, labelFalse);

                il.Emit(OpCodes.Pop); // left is null, pop its value from the stack

                if (!TryEmit(right, paramExprs, il, ref closure, parent | ParentFlags.Coalesce))
                    return false;

                if (right.Type != exprObj.Type)
                {
                    if (right.Type.IsValueType())
                        il.Emit(OpCodes.Box, right.Type);
                }

                if (left.Type == exprObj.Type)
                    il.MarkLabel(labelFalse);
                else
                {
                    il.Emit(OpCodes.Br, labelDone);
                    il.MarkLabel(labelFalse);
                    il.Emit(OpCodes.Castclass, exprObj.Type);
                    il.MarkLabel(labelDone);
                }

                return true;
            }

            private static void EmitDefault(Type type, ILGenerator il)
            {
                if (!type.GetTypeInfo().IsValueType)
                {
                    il.Emit(OpCodes.Ldnull);
                }
                else if (
                    type == typeof(bool) ||
                    type == typeof(byte) ||
                    type == typeof(char) ||
                    type == typeof(sbyte) ||
                    type == typeof(int) ||
                    type == typeof(uint) ||
                    type == typeof(short) ||
                    type == typeof(ushort))
                {
                    il.Emit(OpCodes.Ldc_I4_0);
                }
                else if (
                    type == typeof(long) ||
                    type == typeof(ulong))
                {
                    il.Emit(OpCodes.Ldc_I4_0);
                    il.Emit(OpCodes.Conv_I8);
                }
                else if (type == typeof(float))
                    il.Emit(OpCodes.Ldc_R4, default(float));
                else if (type == typeof(double))
                    il.Emit(OpCodes.Ldc_R8, default(double));
                else
                    EmitLoadLocalVariable(il, InitValueTypeVariable(il, type));
            }

            private static bool TryEmitTryCatchFinallyBlock(TryExpression tryExpr,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure, ParentFlags parent)
            {
                var containsReturnGotoExpression = closure.TryCatchFinallyContainsReturnGotoExpression();
                il.BeginExceptionBlock();

                if (!TryEmit(tryExpr.Body, paramExprs, il, ref closure, parent))
                    return false;

                var exprType = tryExpr.Type;
                var returnsResult = exprType != typeof(void) && (containsReturnGotoExpression || !parent.IgnoresResult());
                var resultVarIndex = -1;

                if (returnsResult)
                    EmitStoreLocalVariable(il, resultVarIndex = il.GetNextLocalVarIndex(exprType));

                var catchBlocks = tryExpr.Handlers;
                for (var i = 0; i < catchBlocks.Count; i++)
                {
                    var catchBlock = catchBlocks[i];
                    if (catchBlock.Filter != null)
                        return false; // todo: Add support for filters in catch expression

                    il.BeginCatchBlock(catchBlock.Test);

                    // at the beginning of catch the Exception value is on the stack,
                    // we will store into local variable.
                    var exVarExpr = catchBlock.Variable;
                    if (exVarExpr != null)
                    {
                        var exVarIndex = il.GetNextLocalVarIndex(exVarExpr.Type);
                        closure.PushBlockWithVars(exVarExpr, exVarIndex);
                        EmitStoreLocalVariable(il, exVarIndex);
                    }

                    if (!TryEmit(catchBlock.Body, paramExprs, il, ref closure, parent))
                        return false;

                    if (exVarExpr != null)
                        closure.PopBlock();

                    if (returnsResult)
                        EmitStoreLocalVariable(il, resultVarIndex);
                }

                var finallyExpr = tryExpr.Finally;
                if (finallyExpr != null)
                {
                    il.BeginFinallyBlock();
                    if (!TryEmit(finallyExpr, paramExprs, il, ref closure, parent))
                        return false;
                }

                il.EndExceptionBlock();

                if (returnsResult)
                    EmitLoadLocalVariable(il, resultVarIndex);

                --closure.CurrentTryCatchFinallyIndex;
                return true;
            }

            private static bool TryEmitParameter(ParameterExpression paramExpr,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure,
                ParentFlags parent, int byRefIndex = -1)
            {
                // if parameter is passed through, then just load it on stack
                var paramType = paramExpr.Type;

                var paramIndex = paramExprs.Count - 1;
                while (paramIndex != -1 && !ReferenceEquals(paramExprs[paramIndex], paramExpr))
                    --paramIndex;
                if (paramIndex != -1)
                {
                    if ((closure.Status & ClosureStatus.ShouldBeStaticMethod) == 0)
                        ++paramIndex; // shift parameter index by one, because the first one will be closure

                    closure.LastEmitIsAddress = !paramExpr.IsByRef && paramType.IsValueType() &&
                        ((parent & ParentFlags.InstanceCall) == ParentFlags.InstanceCall || 
                         (parent & ParentFlags.MemberAccess) != 0);

                    if (closure.LastEmitIsAddress)
                        il.Emit(OpCodes.Ldarga_S, (byte)paramIndex);
                    else
                    {
                        if (paramIndex == 0)
                            il.Emit(OpCodes.Ldarg_0);
                        else if (paramIndex == 1)
                            il.Emit(OpCodes.Ldarg_1);
                        else if (paramIndex == 2)
                            il.Emit(OpCodes.Ldarg_2);
                        else if (paramIndex == 3)
                            il.Emit(OpCodes.Ldarg_3);
                        else
                            il.Emit(OpCodes.Ldarg_S, (byte)paramIndex);
                    }

                    if (paramExpr.IsByRef)
                    {
                        if ((parent & ParentFlags.MemberAccess) != 0 && paramType.IsClass() ||
                            (parent & ParentFlags.Coalesce) != 0)
                            il.Emit(OpCodes.Ldind_Ref);
                        else if ((parent & ParentFlags.Arithmetic) != 0)
                            EmitDereference(il, paramType);
                    }

                    return true;
                }

                // If parameter isn't passed, then it is passed into some outer lambda or it is a local variable,
                // so it should be loaded from closure or from the locals. Then the closure is null will be an invalid state.
                // Parameter may represent a variable, so first look if this is the case
                var varIndex = closure.GetDefinedLocalVarOrDefault(paramExpr);
                if (varIndex != -1)
                {
                    if (byRefIndex != -1 ||
                        paramType.IsValueType() && (parent & (ParentFlags.MemberAccess | ParentFlags.InstanceAccess)) != 0)
                        EmitLoadLocalVariableAddress(il, varIndex);
                    else
                        EmitLoadLocalVariable(il, varIndex);
                    return true;
                }

                if (paramExpr.IsByRef)
                {
                    EmitLoadLocalVariableAddress(il, byRefIndex);
                    return true;
                }

                // the only possibility that we are here is because we are in the nested lambda,
                // and it uses the parameter or variable from the outer lambda
                var nonPassedParams = closure.NonPassedParameters;
                var nonPassedParamIndex = nonPassedParams.Length - 1;
                while (nonPassedParamIndex != -1 && !ReferenceEquals(nonPassedParams[nonPassedParamIndex], paramExpr))
                    --nonPassedParamIndex;
                if (nonPassedParamIndex == -1)
                    return false; // what??? no chance

                // Load non-passed argument from Closure - closure object is always a first argument
                il.Emit(OpCodes.Ldarg_0);
                il.Emit(OpCodes.Ldfld, ArrayClosureWithNonPassedParamsField);
                EmitLoadConstantInt(il, nonPassedParamIndex);
                il.Emit(OpCodes.Ldelem_Ref);

                // source type is object, NonPassedParams is object array
                if (paramType.IsValueType())
                    il.Emit(OpCodes.Unbox_Any, paramType);

                return true;
            }

            private static void EmitDereference(ILGenerator il, Type type)
            {
                if (type == typeof(Int32))
                    il.Emit(OpCodes.Ldind_I4);
                else if (type == typeof(Int64))
                    il.Emit(OpCodes.Ldind_I8);
                else if (type == typeof(Int16))
                    il.Emit(OpCodes.Ldind_I2);
                else if (type == typeof(SByte))
                    il.Emit(OpCodes.Ldind_I1);
                else if (type == typeof(Single))
                    il.Emit(OpCodes.Ldind_R4);
                else if (type == typeof(Double))
                    il.Emit(OpCodes.Ldind_R8);
                else if (type == typeof(IntPtr))
                    il.Emit(OpCodes.Ldind_I);
                else if (type == typeof(UIntPtr))
                    il.Emit(OpCodes.Ldind_I);
                else if (type == typeof(Byte))
                    il.Emit(OpCodes.Ldind_U1);
                else if (type == typeof(UInt16))
                    il.Emit(OpCodes.Ldind_U2);
                else if (type == typeof(UInt32))
                    il.Emit(OpCodes.Ldind_U4);
                else
                    il.Emit(OpCodes.Ldobj, type);
                //todo: UInt64 as there is no OpCodes? Ldind_Ref?
            }

            private static bool TryEmitSimpleUnaryExpression(UnaryExpression expr,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure,
                ParentFlags parent)
            {
                var exprType = expr.Type;

                // todo: support decimal here
                if (exprType == typeof(decimal))
                    return false;

                if (!TryEmit(expr.Operand, paramExprs, il, ref closure, parent))
                    return false;

                if ((parent & ParentFlags.IgnoreResult) != 0)
                    il.Emit(OpCodes.Pop);
                else
                {
                    if (expr.NodeType == ExpressionType.TypeAs)
                    {
                        il.Emit(OpCodes.Isinst, exprType);
                    }
                    else if (expr.NodeType == ExpressionType.IsFalse)
                    {
                        var falseLabel    = il.DefineLabel();
                        var continueLabel = il.DefineLabel();
                        il.Emit(OpCodes.Brfalse, falseLabel);
                        il.Emit(OpCodes.Ldc_I4_0);
                        il.Emit(OpCodes.Br, continueLabel);
                        il.MarkLabel(falseLabel);
                        il.Emit(OpCodes.Ldc_I4_1);
                        il.MarkLabel(continueLabel);
                    }
                    else if (expr.NodeType == ExpressionType.Increment)
                    {
                        if (!TryEmitNumberOne(il, exprType))
                            return false;
                        il.Emit(OpCodes.Add);
                    }
                    else if (expr.NodeType == ExpressionType.Decrement)
                    {
                        if (!TryEmitNumberOne(il, exprType))
                            return false;
                        il.Emit(OpCodes.Sub);
                    }
                    else if (expr.NodeType == ExpressionType.Negate || expr.NodeType == ExpressionType.NegateChecked)
                    {
                        il.Emit(OpCodes.Neg);
                    }
                    else if (expr.NodeType == ExpressionType.OnesComplement)
                    {
                        il.Emit(OpCodes.Not);
                    }
                    else if (expr.NodeType == ExpressionType.Unbox)
                    {
                        il.Emit(OpCodes.Unbox_Any, exprType);
                    }
                    else if (expr.NodeType == ExpressionType.IsTrue)
                    { }
                    else if (expr.NodeType == ExpressionType.UnaryPlus)
                    { }
                }
                return true;
            }

            private static bool TryEmitTypeIs(TypeBinaryExpression expr,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure,
                ParentFlags parent)
            {
                if (!TryEmit(expr.Expression, paramExprs, il, ref closure, parent))
                    return false;

                if ((parent & ParentFlags.IgnoreResult) != 0)
                    il.Emit(OpCodes.Pop);
                else
                {
                    il.Emit(OpCodes.Isinst, expr.TypeOperand);
                    il.Emit(OpCodes.Ldnull);
                    il.Emit(OpCodes.Cgt_Un);
                }

                return true;
            }

            private static bool TryEmitNot(UnaryExpression expr,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure,
                ParentFlags parent)
            {
                if (!TryEmit(expr.Operand, paramExprs, il, ref closure, parent))
                    return false;
                if ((parent & ParentFlags.IgnoreResult) > 0)
                    il.Emit(OpCodes.Pop);
                else
                {
                    if (expr.Type == typeof(bool))
                    {
                        il.Emit(OpCodes.Ldc_I4_0);
                        il.Emit(OpCodes.Ceq);
                    }
                    else
                    {
                        il.Emit(OpCodes.Not);
                    }
                }
                return true;
            }

            private static bool TryEmitConvert(UnaryExpression expr,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure, ParentFlags parent)
            {
                var opExpr = expr.Operand;
                var method = expr.Method;
                if (method != null && method.Name != "op_Implicit" && method.Name != "op_Explicit")
                {
                    if (!TryEmit(opExpr, paramExprs, il, ref closure, parent & ~ParentFlags.IgnoreResult | ParentFlags.InstanceCall, 0))
                        return false;

                    il.Emit(method.IsVirtual ? OpCodes.Callvirt : OpCodes.Call, method);
                    if ((parent & ParentFlags.IgnoreResult) != 0 && method.ReturnType != typeof(void))
                        il.Emit(OpCodes.Pop);
                    return true;
                }

                var sourceType = opExpr.Type;
                var sourceTypeIsNullable = sourceType.IsNullable();
                var underlyingNullableSourceType = Nullable.GetUnderlyingType(sourceType);
                var targetType = expr.Type;

                if (sourceTypeIsNullable && targetType == underlyingNullableSourceType)
                {
                    if (!TryEmit(opExpr, paramExprs, il, ref closure, parent & ~ParentFlags.IgnoreResult | ParentFlags.InstanceAccess))
                        return false;

                    if (!closure.LastEmitIsAddress) 
                        EmitStoreLocalVariableAndLoadItsAddress(il, sourceType);

                    il.Emit(OpCodes.Call, sourceType.FindValueGetterMethod());

                    if ((parent & ParentFlags.IgnoreResult) != 0)
                        il.Emit(OpCodes.Pop);
                    return true;
                }

                if (!TryEmit(opExpr, paramExprs, il, ref closure, parent & ~ParentFlags.IgnoreResult & ~ParentFlags.InstanceAccess))
                    return false;

                var targetTypeIsNullable = targetType.IsNullable();
                var underlyingNullableTargetType = Nullable.GetUnderlyingType(targetType);
                if (targetTypeIsNullable && sourceType == underlyingNullableTargetType)
                {
                    il.Emit(OpCodes.Newobj, targetType.GetTypeInfo().DeclaredConstructors.GetFirst());
                    return true;
                }

                if (sourceType == targetType || targetType == typeof(object))
                {
                    if (targetType == typeof(object) && sourceType.IsValueType())
                        il.Emit(OpCodes.Box, sourceType);
                    if (IgnoresResult(parent))
                        il.Emit(OpCodes.Pop);
                    return true;
                }

                // check implicit / explicit conversion operators on source and target types
                // for non-primitives and for non-primitive nullable - #73
                if (!sourceTypeIsNullable && !sourceType.IsPrimitive())
                {
                    var actualTargetType = targetTypeIsNullable ? underlyingNullableTargetType : targetType;
                    var convertOpMethod = method ?? sourceType.FindConvertOperator(sourceType, actualTargetType);
                    if (convertOpMethod != null)
                    {
                        il.Emit(OpCodes.Call, convertOpMethod);

                        if (targetTypeIsNullable)
                            il.Emit(OpCodes.Newobj, targetType.GetTypeInfo().DeclaredConstructors.GetFirst());

                        if ((parent & ParentFlags.IgnoreResult) != 0)
                            il.Emit(OpCodes.Pop);

                        return true;
                    }
                }
                else if (!targetTypeIsNullable)
                {
                    var actualSourceType = sourceTypeIsNullable ? underlyingNullableSourceType : sourceType;

                    var convertOpMethod = method ?? actualSourceType.FindConvertOperator(actualSourceType, targetType);
                    if (convertOpMethod != null)
                    {
                        if (sourceTypeIsNullable)
                        {
                            EmitStoreLocalVariableAndLoadItsAddress(il, sourceType);
                            il.Emit(OpCodes.Call, sourceType.FindValueGetterMethod());
                        }

                        il.Emit(OpCodes.Call, convertOpMethod);
                        if ((parent & ParentFlags.IgnoreResult) != 0)
                            il.Emit(OpCodes.Pop);

                        return true;
                    }
                }

                if (!targetTypeIsNullable && !targetType.IsPrimitive())
                {
                    var actualSourceType = sourceTypeIsNullable ? underlyingNullableSourceType : sourceType;

                    // ReSharper disable once ConstantNullCoalescingCondition
                    var convertOpMethod = method ?? targetType.FindConvertOperator(actualSourceType, targetType);
                    if (convertOpMethod != null)
                    {
                        if (sourceTypeIsNullable)
                        {
                            EmitStoreLocalVariableAndLoadItsAddress(il, sourceType);
                            il.Emit(OpCodes.Call, sourceType.FindValueGetterMethod());
                        }

                        il.Emit(OpCodes.Call, convertOpMethod);
                        if ((parent & ParentFlags.IgnoreResult) != 0)
                            il.Emit(OpCodes.Pop);

                        return true;
                    }
                }
                else if (!sourceTypeIsNullable)
                {
                    var actualTargetType = targetTypeIsNullable ? underlyingNullableTargetType : targetType;
                    var convertOpMethod = method ?? actualTargetType.FindConvertOperator(sourceType, actualTargetType);
                    if (convertOpMethod != null)
                    {
                        il.Emit(OpCodes.Call, convertOpMethod);

                        if (targetTypeIsNullable)
                            il.Emit(OpCodes.Newobj, targetType.GetTypeInfo().DeclaredConstructors.GetFirst());

                        if ((parent & ParentFlags.IgnoreResult) != 0)
                            il.Emit(OpCodes.Pop);

                        return true;
                    }
                }

                if (sourceType == typeof(object) && targetType.IsValueType())
                {
                    il.Emit(OpCodes.Unbox_Any, targetType);
                }
                else if (targetTypeIsNullable)
                {
                    // Conversion to Nullable: `new Nullable<T>(T val);`
                    if (!sourceTypeIsNullable)
                    {
                        if (!TryEmitValueConvert(underlyingNullableTargetType, il, isChecked: false))
                            return false;

                        il.Emit(OpCodes.Newobj, targetType.GetTypeInfo().DeclaredConstructors.GetFirst());
                    }
                    else
                    {
                        var sourceVarIndex = EmitStoreLocalVariableAndLoadItsAddress(il, sourceType);
                        il.Emit(OpCodes.Call, sourceType.FindNullableHasValueGetterMethod());

                        var labelSourceHasValue = il.DefineLabel();
                        il.Emit(OpCodes.Brtrue_S, labelSourceHasValue); // jump where source has a value

                        // otherwise, emit and load a `new Nullable<TTarget>()` struct (that's why a Init instead of New)
                        EmitLoadLocalVariable(il, InitValueTypeVariable(il, targetType));

                        // jump to completion
                        var labelDone = il.DefineLabel();
                        il.Emit(OpCodes.Br_S, labelDone);

                        // if source nullable has a value:
                        il.MarkLabel(labelSourceHasValue);
                        EmitLoadLocalVariableAddress(il, sourceVarIndex);
                        il.Emit(OpCodes.Call, sourceType.FindNullableGetValueOrDefaultMethod());

                        if (!TryEmitValueConvert(underlyingNullableTargetType, il,
                            expr.NodeType == ExpressionType.ConvertChecked))
                        {
                            var convertOpMethod = method ?? underlyingNullableTargetType.FindConvertOperator(underlyingNullableSourceType, underlyingNullableTargetType);
                            if (convertOpMethod == null)
                                return false; // nor conversion nor conversion operator is found
                            il.Emit(OpCodes.Call, convertOpMethod);
                        }

                        il.Emit(OpCodes.Newobj, targetType.GetTypeInfo().DeclaredConstructors.GetFirst());
                        il.MarkLabel(labelDone);
                    }
                }
                else
                {
                    if (targetType.GetTypeInfo().IsEnum)
                        targetType = Enum.GetUnderlyingType(targetType);

                    // fixes #159
                    if (sourceTypeIsNullable)
                    {
                        EmitStoreLocalVariableAndLoadItsAddress(il, sourceType);
                        il.Emit(OpCodes.Call, sourceType.FindValueGetterMethod());
                    }

                    // cast as the last resort and let's it fail if unlucky
                    if (!TryEmitValueConvert(targetType, il, expr.NodeType == ExpressionType.ConvertChecked))
                        il.Emit(OpCodes.Castclass, targetType);
                }

                if ((parent & ParentFlags.IgnoreResult) != 0)
                    il.Emit(OpCodes.Pop);

                return true;
            }

            private static bool TryEmitValueConvert(Type targetType, ILGenerator il, bool isChecked)
            {
                if (targetType == typeof(int))
                    il.Emit(isChecked ? OpCodes.Conv_Ovf_I4 : OpCodes.Conv_I4);
                else if (targetType == typeof(float))
                    il.Emit(OpCodes.Conv_R4);
                else if (targetType == typeof(uint))
                    il.Emit(isChecked ? OpCodes.Conv_Ovf_U4 : OpCodes.Conv_U4);
                else if (targetType == typeof(sbyte))
                    il.Emit(isChecked ? OpCodes.Conv_Ovf_I1 : OpCodes.Conv_I1);
                else if (targetType == typeof(byte))
                    il.Emit(isChecked ? OpCodes.Conv_Ovf_U1 : OpCodes.Conv_U1);
                else if (targetType == typeof(short))
                    il.Emit(isChecked ? OpCodes.Conv_Ovf_I2 : OpCodes.Conv_I2);
                else if (targetType == typeof(ushort) || targetType == typeof(char))
                    il.Emit(isChecked ? OpCodes.Conv_Ovf_U2 : OpCodes.Conv_U2);
                else if (targetType == typeof(long))
                    il.Emit(isChecked ? OpCodes.Conv_Ovf_I8 : OpCodes.Conv_I8);
                else if (targetType == typeof(ulong))
                    il.Emit(isChecked ? OpCodes.Conv_Ovf_U8 : OpCodes.Conv_U8);
                else if (targetType == typeof(double))
                    il.Emit(OpCodes.Conv_R8);
                else
                    return false;
                return true;
            }

            private static bool TryEmitNotNullConstant(
                bool considerClosure, Type exprType, object constantValue, ILGenerator il, ref ClosureInfo closure)
            {
                var constValueType = constantValue.GetType();
                if (considerClosure && IsClosureBoundConstant(constantValue, constValueType.GetTypeInfo()))
                {
                    var constItems = closure.Constants.Items;
                    var constIndex = closure.Constants.Count - 1;
                    while (constIndex != -1 && !ReferenceEquals(constItems[constIndex], constantValue))
                        --constIndex;
                    if (constIndex == -1)
                        return false;

                    var varIndex = closure.ConstantUsage.Items[constIndex] - 1;
                    if (varIndex > 0)
                        EmitLoadLocalVariable(il, varIndex);
                    else
                    {
                        il.Emit(OpCodes.Ldloc_0); // load constants array from variable
                        EmitLoadConstantInt(il, constIndex);
                        il.Emit(OpCodes.Ldelem_Ref);
                        if (exprType.IsValueType())
                            il.Emit(OpCodes.Unbox_Any, exprType);
                    }
                }
                else
                {
                    if (constantValue is string s)
                    {
                        il.Emit(OpCodes.Ldstr, s);
                        return true;
                    }

                    if (constantValue is Type t)
                    {
                        il.Emit(OpCodes.Ldtoken, t);
                        il.Emit(OpCodes.Call, _getTypeFromHandleMethod);
                        return true;
                    }

                    // get raw enum type to light
                    if (constValueType.GetTypeInfo().IsEnum)
                        constValueType = Enum.GetUnderlyingType(constValueType);

                    if (!TryEmitNumberConstant(il, constantValue, constValueType))
                        return false;
                }

                var underlyingNullableType = Nullable.GetUnderlyingType(exprType);
                if (underlyingNullableType != null)
                    il.Emit(OpCodes.Newobj, exprType.GetTypeInfo().DeclaredConstructors.GetFirst());

                // boxing the value type, otherwise we can get a strange result when 0 is treated as Null.
                else if (exprType == typeof(object) && constValueType.IsValueType())
                    il.Emit(OpCodes.Box, constantValue.GetType()); // using normal type for Enum instead of underlying type

                return true;
            }

            // todo: can we do something about boxing?
            private static bool TryEmitNumberConstant(ILGenerator il, object constantValue, Type constValueType)
            {
                if (constValueType == typeof(int))
                {
                    EmitLoadConstantInt(il, (int)constantValue);
                }
                else if (constValueType == typeof(char))
                {
                    EmitLoadConstantInt(il, (char)constantValue);
                }
                else if (constValueType == typeof(short))
                {
                    EmitLoadConstantInt(il, (short)constantValue);
                }
                else if (constValueType == typeof(byte))
                {
                    EmitLoadConstantInt(il, (byte)constantValue);
                }
                else if (constValueType == typeof(ushort))
                {
                    EmitLoadConstantInt(il, (ushort)constantValue);
                }
                else if (constValueType == typeof(sbyte))
                {
                    EmitLoadConstantInt(il, (sbyte)constantValue);
                }
                else if (constValueType == typeof(uint))
                {
                    unchecked
                    {
                        EmitLoadConstantInt(il, (int)(uint)constantValue);
                    }
                }
                else if (constValueType == typeof(long))
                {
                    il.Emit(OpCodes.Ldc_I8, (long)constantValue);
                }
                else if (constValueType == typeof(ulong))
                {
                    unchecked
                    {
                        il.Emit(OpCodes.Ldc_I8, (long)(ulong)constantValue);
                    }
                }
                else if (constValueType == typeof(float))
                {
                    il.Emit(OpCodes.Ldc_R4, (float)constantValue);
                }
                else if (constValueType == typeof(double))
                {
                    il.Emit(OpCodes.Ldc_R8, (double)constantValue);
                }
                else if (constValueType == typeof(bool))
                {
                    il.Emit((bool)constantValue ? OpCodes.Ldc_I4_1 : OpCodes.Ldc_I4_0);
                }
                else if (constValueType == typeof(IntPtr))
                {
                    il.Emit(OpCodes.Ldc_I8, ((IntPtr)constantValue).ToInt64());
                }
                else if (constValueType == typeof(UIntPtr))
                {
                    unchecked
                    {
                        il.Emit(OpCodes.Ldc_I8, (long)((UIntPtr)constantValue).ToUInt64());
                    }
                }
                else if (constValueType == typeof(decimal))
                {
                    EmitDecimalConstant((decimal)constantValue, il);
                }
                else
                {
                    return false;
                }

                return true;
            }

            internal static bool TryEmitNumberOne(ILGenerator il, Type type)
            {
                if (type == typeof(int) || type == typeof(char) || type == typeof(short) ||
                    type == typeof(byte) || type == typeof(ushort) || type == typeof(sbyte) ||
                    type == typeof(uint))
                {
                    il.Emit(OpCodes.Ldc_I4_1);
                }
                else if (type == typeof(long) || type == typeof(ulong) ||
                         type == typeof(IntPtr) || type == typeof(UIntPtr))
                {
                    il.Emit(OpCodes.Ldc_I8, (long)1);
                }
                else if (type == typeof(float))
                {
                    il.Emit(OpCodes.Ldc_R4, 1f);
                }
                else if (type == typeof(double))
                {
                    il.Emit(OpCodes.Ldc_R8, 1d);
                }
                else
                {
                    return false;
                }

                return true;
            }

            internal static void EmitLoadConstantsAndNestedLambdasIntoVars(ILGenerator il, ref ClosureInfo closure)
            {
                // Load constants array field from Closure and store it into the variable
                il.Emit(OpCodes.Ldarg_0);
                il.Emit(OpCodes.Ldfld, ArrayClosureArrayField);
                EmitStoreLocalVariable(il, il.GetNextLocalVarIndex(typeof(object[])));

                var constItems = closure.Constants.Items;
                var constCount = closure.Constants.Count;
                var constUsage = closure.ConstantUsage.Items;

                int varIndex;
                for (var i = 0; i < constCount; i++)
                {
                    if (constUsage[i] > 1)
                    {
                        il.Emit(OpCodes.Ldloc_0);// load array field variable on a stack
                        EmitLoadConstantInt(il, i);
                        il.Emit(OpCodes.Ldelem_Ref);

                        var varType = constItems[i].GetType();
                        if (varType.IsValueType())
                            il.Emit(OpCodes.Unbox_Any, varType);

                        varIndex = il.GetNextLocalVarIndex(varType);
                        constUsage[i] = varIndex + 1; // to distinguish from the default 1
                        EmitStoreLocalVariable(il, varIndex);
                    }
                }

                var nestedLambdas = closure.NestedLambdas;
                for (var i = 0; i < nestedLambdas.Length; i++)
                {
                    var nestedLambda = nestedLambdas[i];
                    if (nestedLambda.UsageCountOrVarIndex > 1)
                    {
                        il.Emit(OpCodes.Ldloc_0);// load array field variable on a stack
                        EmitLoadConstantInt(il, constCount + i);
                        il.Emit(OpCodes.Ldelem_Ref);
                        varIndex = il.GetNextLocalVarIndex(nestedLambda.Lambda.GetType());
                        nestedLambda.UsageCountOrVarIndex = varIndex + 1;
                        EmitStoreLocalVariable(il, varIndex);
                    }
                }
            }

            private static void EmitDecimalConstant(decimal value, ILGenerator il)
            {
                //check if decimal has decimal places, if not use shorter IL code (constructor from int or long)
                if (value % 1 == 0)
                {
                    if (value >= int.MinValue && value <= int.MaxValue)
                    {
                        EmitLoadConstantInt(il, decimal.ToInt32(value));
                        il.Emit(OpCodes.Newobj, typeof(decimal).FindSingleParamConstructor(typeof(int)));
                        return;
                    }

                    if (value >= long.MinValue && value <= long.MaxValue)
                    {
                        il.Emit(OpCodes.Ldc_I8, decimal.ToInt64(value));
                        il.Emit(OpCodes.Newobj, typeof(decimal).FindSingleParamConstructor(typeof(long)));
                        return;
                    }
                }

                if (value == decimal.MinValue)
                {
                    il.Emit(OpCodes.Ldsfld, typeof(decimal).GetTypeInfo().GetDeclaredField(nameof(decimal.MinValue)));
                    return;
                }

                if (value == decimal.MaxValue)
                {
                    il.Emit(OpCodes.Ldsfld, typeof(decimal).GetTypeInfo().GetDeclaredField(nameof(decimal.MaxValue)));
                    return;
                }

                var parts = decimal.GetBits(value);
                var sign = (parts[3] & 0x80000000) != 0;
                var scale = (byte)((parts[3] >> 16) & 0x7F);

                EmitLoadConstantInt(il, parts[0]);
                EmitLoadConstantInt(il, parts[1]);
                EmitLoadConstantInt(il, parts[2]);

                il.Emit(sign ? OpCodes.Ldc_I4_1 : OpCodes.Ldc_I4_0);
                EmitLoadConstantInt(il, scale);

                il.Emit(OpCodes.Conv_U1);

                il.Emit(OpCodes.Newobj, _decimalCtor.Value);
            }

            private static readonly Lazy<ConstructorInfo> _decimalCtor = new Lazy<ConstructorInfo>(() =>
            {
                foreach (var ctor in typeof(decimal).GetTypeInfo().DeclaredConstructors)
                    if (ctor.GetParameters().Length == 5)
                        return ctor;
                return null;
            });

            private static int InitValueTypeVariable(ILGenerator il, Type exprType)
            {
                var locVarIndex = il.GetNextLocalVarIndex(exprType);
                EmitLoadLocalVariableAddress(il, locVarIndex);
                il.Emit(OpCodes.Initobj, exprType);
                return locVarIndex;
            }

            private static bool EmitNewArray(NewArrayExpression expr,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure, ParentFlags parent)
            {
                var arrayType = expr.Type;
                var elems = expr.Expressions;
                var elemType = arrayType.GetElementType();
                if (elemType == null)
                    return false;

                var rank = arrayType.GetArrayRank();
                if (rank == 1) // one dimensional
                {
                    EmitLoadConstantInt(il, elems.Count);
                }
                else // multi dimensional
                {
                    for (var i = 0; i < elems.Count; i++)
                        if (!TryEmit(elems[i], paramExprs, il, ref closure, parent, i))
                            return false;

                    il.Emit(OpCodes.Newobj, arrayType.GetTypeInfo().DeclaredConstructors.GetFirst());
                    return true;
                }

                il.Emit(OpCodes.Newarr, elemType);

                var isElemOfValueType = elemType.IsValueType();

                for (int i = 0, n = elems.Count; i < n; i++)
                {
                    il.Emit(OpCodes.Dup);
                    EmitLoadConstantInt(il, i);

                    // loading element address for later copying of value into it.
                    if (isElemOfValueType)
                        il.Emit(OpCodes.Ldelema, elemType);

                    if (!TryEmit(elems[i], paramExprs, il, ref closure, parent))
                        return false;

                    if (isElemOfValueType)
                        il.Emit(OpCodes.Stobj, elemType); // store element of value type by array element address
                    else
                        il.Emit(OpCodes.Stelem_Ref);
                }

                return true;
            }

            private static bool TryEmitArrayIndex(Type exprType, ILGenerator il)
            {
                if (exprType.IsValueType())
                    il.Emit(OpCodes.Ldelem, exprType);
                else
                    il.Emit(OpCodes.Ldelem_Ref);
                return true;
            }

            private static bool EmitMemberInit(MemberInitExpression expr,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure, ParentFlags parent)
            {
                var valueVarIndex = -1;
                if (expr.Type.IsValueType())
                    valueVarIndex = il.GetNextLocalVarIndex(expr.Type);

                var newExpr = expr.NewExpression;
                if (newExpr == null)
                {
                    if (!TryEmit(expr.Expression, paramExprs, il, ref closure, parent))
                        return false;
                }
                else
                {
                    var argExprs = newExpr.Arguments;
                    for (var i = 0; i < argExprs.Count; i++)
                        if (!TryEmit(argExprs[i], paramExprs, il, ref closure, parent, i))
                            return false;

                    var ctor = newExpr.Constructor;
                    // ReSharper disable once ConditionIsAlwaysTrueOrFalse
                    if (ctor != null)
                        il.Emit(OpCodes.Newobj, ctor);
                    else if (newExpr.Type.IsValueType())
                    {
                        if (valueVarIndex == -1)
                            valueVarIndex = il.GetNextLocalVarIndex(expr.Type);
                        EmitLoadLocalVariableAddress(il, valueVarIndex);
                        il.Emit(OpCodes.Initobj, newExpr.Type);
                    }
                    else
                        return false; // null constructor and not a value type, better to fallback
                }

                var bindings = expr.Bindings;
                for (var i = 0; i < bindings.Count; i++)
                {
                    var binding = bindings[i];
                    if (binding.BindingType != MemberBindingType.Assignment)
                        return false;

                    if (valueVarIndex != -1) // load local value address, to set its members
                        EmitLoadLocalVariableAddress(il, valueVarIndex);
                    else
                        il.Emit(OpCodes.Dup); // duplicate member owner on stack

                    if (!TryEmit(((MemberAssignment)binding).Expression, paramExprs, il, ref closure, parent) ||
                        !EmitMemberAssign(il, binding.Member))
                        return false;
                }

                if (valueVarIndex != -1)
                    EmitLoadLocalVariable(il, valueVarIndex);
                return true;
            }

            private static bool EmitMemberAssign(ILGenerator il, MemberInfo member)
            {
                if (member is PropertyInfo prop)
                {
                    var method = prop.DeclaringType.FindPropertySetMethod(prop.Name);
                    if (method == null)
                        return false;

                    il.Emit(method.IsVirtual ? OpCodes.Callvirt : OpCodes.Call, method);
                    return true;
                }

                if (member is FieldInfo field)
                {
                    il.Emit(field.IsStatic ? OpCodes.Stsfld : OpCodes.Stfld, field);
                    return true;
                }

                return false;
            }

            private static bool TryEmitIncDecAssign(UnaryExpression expr,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure, ParentFlags parent)
            {
                var operandExpr = expr.Operand;
                
                MemberExpression memberAccess;
                var useLocalVar = false;
                int localVarIndex, paramIndex = -1;

                var isParameterOrVariable = operandExpr.NodeType == ExpressionType.Parameter;
                var usesResult = (parent & ParentFlags.IgnoreResult) == 0;
                if (isParameterOrVariable)
                {
                    localVarIndex = closure.GetDefinedLocalVarOrDefault((ParameterExpression)operandExpr);
                    if (localVarIndex != -1)
                    {
                        EmitLoadLocalVariable(il, localVarIndex);
                        useLocalVar = true;
                    }
                    else
                    {
                        paramIndex = paramExprs.Count - 1;
                        while (paramIndex != -1 && !ReferenceEquals(paramExprs[paramIndex], operandExpr))
                            --paramIndex;
                        if (paramIndex == -1)
                            return false;
                        il.Emit(OpCodes.Ldarg, paramIndex + 1);
                    }

                    memberAccess = null;

                }
                else if (operandExpr.NodeType == ExpressionType.MemberAccess)
                {
                    memberAccess = (MemberExpression)operandExpr;

                    if (!TryEmitMemberAccess(memberAccess, paramExprs, il, ref closure, parent | ParentFlags.DupMemberOwner))
                        return false;

                    useLocalVar = memberAccess.Expression != null && (usesResult || memberAccess.Member is PropertyInfo);
                    localVarIndex = useLocalVar ? il.GetNextLocalVarIndex(operandExpr.Type) : -1;
                }
                else
                    return false;

                switch (expr.NodeType)
                {
                    case ExpressionType.PreIncrementAssign:
                        il.Emit(OpCodes.Ldc_I4_1);
                        il.Emit(OpCodes.Add);
                        StoreIncDecValue(il, usesResult, isParameterOrVariable, localVarIndex);
                        break;

                    case ExpressionType.PostIncrementAssign:
                        StoreIncDecValue(il, usesResult, isParameterOrVariable, localVarIndex);
                        il.Emit(OpCodes.Ldc_I4_1);
                        il.Emit(OpCodes.Add);
                        break;

                    case ExpressionType.PreDecrementAssign:
                        il.Emit(OpCodes.Ldc_I4_1);
                        il.Emit(OpCodes.Sub);
                        StoreIncDecValue(il, usesResult, isParameterOrVariable, localVarIndex);
                        break;

                    case ExpressionType.PostDecrementAssign:
                        StoreIncDecValue(il, usesResult, isParameterOrVariable, localVarIndex);
                        il.Emit(OpCodes.Ldc_I4_1);
                        il.Emit(OpCodes.Sub);
                        break;
                }

                if (isParameterOrVariable && paramIndex != -1)
                    il.Emit(OpCodes.Starg_S, paramIndex + 1);
                else if (isParameterOrVariable || useLocalVar && !usesResult) 
                    EmitStoreLocalVariable(il, localVarIndex);

                if (isParameterOrVariable)
                    return true;

                if (useLocalVar && !usesResult)
                    EmitLoadLocalVariable(il, localVarIndex);

                if (!EmitMemberAssign(il, memberAccess.Member))
                    return false;

                if (useLocalVar && usesResult)
                    EmitLoadLocalVariable(il, localVarIndex);

                return true;
            }

            private static void StoreIncDecValue(ILGenerator il, bool usesResult, bool isVar, int localVarIndex)
            {
                if (!usesResult)
                    return;

                if (isVar || localVarIndex == -1)
                    il.Emit(OpCodes.Dup);
                else
                {
                    EmitStoreLocalVariable(il, localVarIndex);
                    EmitLoadLocalVariable(il, localVarIndex);
                }
            }

            private static bool TryEmitAssign(BinaryExpression expr,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure, ParentFlags parent)
            {
                var left = expr.Left;
                var right = expr.Right;
                var leftNodeType = expr.Left.NodeType;
                var nodeType = expr.NodeType;

                // if this assignment is part of a single body-less expression or the result of a block
                // we should put its result to the evaluation stack before the return, otherwise we are
                // somewhere inside the block, so we shouldn't return with the result
                var flags = parent & ~ParentFlags.IgnoreResult;
                switch (leftNodeType)
                {
                    case ExpressionType.Parameter:
                        var leftParamExpr = (ParameterExpression)left;

                        var paramIndex = paramExprs.Count - 1;
                        while (paramIndex != -1 && !ReferenceEquals(paramExprs[paramIndex], leftParamExpr))
                            --paramIndex;

                        var arithmeticNodeType = nodeType;
                        switch (nodeType)
                        {
                            case ExpressionType.AddAssign:
                                arithmeticNodeType = ExpressionType.Add;
                                break;
                            case ExpressionType.AddAssignChecked:
                                arithmeticNodeType = ExpressionType.AddChecked;
                                break;
                            case ExpressionType.SubtractAssign:
                                arithmeticNodeType = ExpressionType.Subtract;
                                break;
                            case ExpressionType.SubtractAssignChecked:
                                arithmeticNodeType = ExpressionType.SubtractChecked;
                                break;
                            case ExpressionType.MultiplyAssign:
                                arithmeticNodeType = ExpressionType.Multiply;
                                break;
                            case ExpressionType.MultiplyAssignChecked:
                                arithmeticNodeType = ExpressionType.MultiplyChecked;
                                break;
                            case ExpressionType.DivideAssign:
                                arithmeticNodeType = ExpressionType.Divide;
                                break;
                            case ExpressionType.ModuloAssign:
                                arithmeticNodeType = ExpressionType.Modulo;
                                break;
                            case ExpressionType.PowerAssign:
                                arithmeticNodeType = ExpressionType.Power;
                                break;
                            case ExpressionType.AndAssign:
                                arithmeticNodeType = ExpressionType.And;
                                break;
                            case ExpressionType.OrAssign:
                                arithmeticNodeType = ExpressionType.Or;
                                break;
                            case ExpressionType.ExclusiveOrAssign:
                                arithmeticNodeType = ExpressionType.ExclusiveOr;
                                break;
                            case ExpressionType.LeftShiftAssign:
                                arithmeticNodeType = ExpressionType.LeftShift;
                                break;
                            case ExpressionType.RightShiftAssign:
                                arithmeticNodeType = ExpressionType.RightShift;
                                break;
                        }

                        if (paramIndex != -1)
                        {
                            // shift parameter index by one, because the first one will be closure
                            if ((closure.Status & ClosureStatus.ShouldBeStaticMethod) == 0)
                                ++paramIndex;

                            if (leftParamExpr.IsByRef)
                            {
                                if (paramIndex == 0)
                                    il.Emit(OpCodes.Ldarg_0);
                                else if (paramIndex == 1)
                                    il.Emit(OpCodes.Ldarg_1);
                                else if (paramIndex == 2)
                                    il.Emit(OpCodes.Ldarg_2);
                                else if (paramIndex == 3)
                                    il.Emit(OpCodes.Ldarg_3);
                                else
                                    il.Emit(OpCodes.Ldarg_S, (byte)paramIndex);
                            }

                            if (arithmeticNodeType == nodeType)
                            {
                                if (!TryEmit(right, paramExprs, il, ref closure, flags))
                                    return false;
                            }
                            else if (!TryEmitArithmetic(expr, arithmeticNodeType, paramExprs, il, ref closure, parent))
                                return false;

                            if ((parent & ParentFlags.IgnoreResult) == 0)
                                il.Emit(OpCodes.Dup); // duplicate value to assign and return

                            if (leftParamExpr.IsByRef)
                                EmitByRefStore(il, leftParamExpr.Type);
                            else
                                il.Emit(OpCodes.Starg_S, paramIndex);

                            return true;
                        }
                        else if (arithmeticNodeType != nodeType)
                        {
                            var localVarIdx = closure.GetDefinedLocalVarOrDefault(leftParamExpr);
                            if (localVarIdx != -1)
                            {
                                if (!TryEmitArithmetic(expr, arithmeticNodeType, paramExprs, il, ref closure, parent))
                                    return false;

                                EmitStoreLocalVariable(il, localVarIdx);
                                return true;
                            }
                        }

                        // if parameter isn't passed, then it is passed into some outer lambda or it is a local variable,
                        // so it should be loaded from closure or from the locals. Then the closure is null will be an invalid state.
                        // if it's a local variable, then store the right value in it
                        var localVariableIdx = closure.GetDefinedLocalVarOrDefault(leftParamExpr);
                        if (localVariableIdx != -1)
                        {
                            if (!TryEmit(right, paramExprs, il, ref closure, flags))
                                return false;

                            if ((right as ParameterExpression)?.IsByRef == true)
                                il.Emit(OpCodes.Ldind_I4);

                            if ((parent & ParentFlags.IgnoreResult) == 0) // if we have to push the result back, duplicate the right value
                                il.Emit(OpCodes.Dup);

                            EmitStoreLocalVariable(il, localVariableIdx);
                            return true;
                        }

                        // check that it's a captured parameter by closure
                        var nonPassedParams = closure.NonPassedParameters;
                        var nonPassedParamIndex = nonPassedParams.Length - 1;
                        while (nonPassedParamIndex != -1 &&
                               !ReferenceEquals(nonPassedParams[nonPassedParamIndex], leftParamExpr))
                            --nonPassedParamIndex;
                        if (nonPassedParamIndex == -1)
                            return false; // what??? no chance

                        il.Emit(OpCodes.Ldarg_0); // closure is always a first argument

                        if ((parent & ParentFlags.IgnoreResult) == 0)
                        {
                            if (!TryEmit(right, paramExprs, il, ref closure, flags))
                                return false;

                            var valueVarIndex = il.GetNextLocalVarIndex(expr.Type); // store left value in variable
                            EmitStoreLocalVariable(il, valueVarIndex);

                            // load array field and param item index
                            il.Emit(OpCodes.Ldfld, ArrayClosureWithNonPassedParamsField);
                            EmitLoadConstantInt(il, nonPassedParamIndex);
                            EmitLoadLocalVariable(il, valueVarIndex);
                            if (expr.Type.IsValueType())
                                il.Emit(OpCodes.Box, expr.Type);
                            il.Emit(OpCodes.Stelem_Ref); // put the variable into array
                            EmitLoadLocalVariable(il, valueVarIndex);
                        }
                        else
                        {
                            // load array field and param item index
                            il.Emit(OpCodes.Ldfld, ArrayClosureWithNonPassedParamsField);
                            EmitLoadConstantInt(il, nonPassedParamIndex);

                            if (!TryEmit(right, paramExprs, il, ref closure, flags))
                                return false;

                            if (expr.Type.IsValueType())
                                il.Emit(OpCodes.Box, expr.Type);
                            il.Emit(OpCodes.Stelem_Ref); // put the variable into array
                        }

                        return true;

                    case ExpressionType.MemberAccess:
                        var assignFromLocalVar = right.NodeType == ExpressionType.Try;

                        var resultLocalVarIndex = -1;
                        if (assignFromLocalVar)
                        {
                            resultLocalVarIndex = il.GetNextLocalVarIndex(right.Type);

                            if (!TryEmit(right, paramExprs, il, ref closure, ParentFlags.Empty))
                                return false;

                            EmitStoreLocalVariable(il, resultLocalVarIndex);
                        }

                        var memberExpr = (MemberExpression)left;
                        var objExpr = memberExpr.Expression;
                        if (objExpr != null && 
                            !TryEmit(objExpr, paramExprs, il, ref closure, flags | ParentFlags.MemberAccess | ParentFlags.InstanceAccess))
                            return false;

                        if (assignFromLocalVar)
                            EmitLoadLocalVariable(il, resultLocalVarIndex);
                        else if (!TryEmit(right, paramExprs, il, ref closure, ParentFlags.Empty))
                            return false;

                        var member = memberExpr.Member;
                        if ((parent & ParentFlags.IgnoreResult) != 0)
                            return EmitMemberAssign(il, member);

                        il.Emit(OpCodes.Dup);

                        var rightVarIndex = il.GetNextLocalVarIndex(expr.Type); // store right value in variable
                        EmitStoreLocalVariable(il, rightVarIndex);

                        if (!EmitMemberAssign(il, member))
                            return false;

                        EmitLoadLocalVariable(il, rightVarIndex);
                        return true;

                    case ExpressionType.Index:
                        var indexExpr = (IndexExpression)left;

                        var obj = indexExpr.Object;
                        if (obj != null && !TryEmit(obj, paramExprs, il, ref closure, flags))
                            return false;

                        var indexArgExprs = indexExpr.Arguments;
                        for (var i = 0; i < indexArgExprs.Count; i++)
                            if (!TryEmit(indexArgExprs[i], paramExprs, il, ref closure, flags, i))
                                return false;

                        if (!TryEmit(right, paramExprs, il, ref closure, flags))
                            return false;

                        if ((parent & ParentFlags.IgnoreResult) != 0)
                            return TryEmitIndexAssign(indexExpr, obj?.Type, expr.Type, il);

                        var varIndex = il.GetNextLocalVarIndex(expr.Type); // store value in variable to return
                        il.Emit(OpCodes.Dup);
                        EmitStoreLocalVariable(il, varIndex);

                        if (!TryEmitIndexAssign(indexExpr, obj?.Type, expr.Type, il))
                            return false;

                        EmitLoadLocalVariable(il, varIndex);
                        return true;

                    default: // todo: not yet support assignment targets
                        return false;
                }
            }

            private static void EmitByRefStore(ILGenerator il, Type type)
            {
                if (type == typeof(int) || type == typeof(uint))
                    il.Emit(OpCodes.Stind_I4);
                else if (type == typeof(byte))
                    il.Emit(OpCodes.Stind_I1);
                else if (type == typeof(short) || type == typeof(ushort))
                    il.Emit(OpCodes.Stind_I2);
                else if (type == typeof(long) || type == typeof(ulong))
                    il.Emit(OpCodes.Stind_I8);
                else if (type == typeof(float))
                    il.Emit(OpCodes.Stind_R4);
                else if (type == typeof(double))
                    il.Emit(OpCodes.Stind_R8);
                else if (type == typeof(object))
                    il.Emit(OpCodes.Stind_Ref);
                else if (type == typeof(IntPtr) || type == typeof(UIntPtr))
                    il.Emit(OpCodes.Stind_I);
                else
                    il.Emit(OpCodes.Stobj, type);
            }

            private static bool TryEmitIndexAssign(IndexExpression indexExpr, Type instType, Type elementType, ILGenerator il)
            {
                if (indexExpr.Indexer != null)
                    return EmitMemberAssign(il, indexExpr.Indexer);

                if (indexExpr.Arguments.Count == 1) // one dimensional array
                {
                    if (elementType.IsValueType())
                        il.Emit(OpCodes.Stelem, elementType);
                    else
                        il.Emit(OpCodes.Stelem_Ref);
                    return true;
                }

                // multi dimensional array
                return EmitMethodCall(il, instType?.FindMethod("Set"));
            }

            private static bool TryEmitMethodCall(Expression expr,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure, ParentFlags parent)
            {
                var flags = parent & ~ParentFlags.IgnoreResult | ParentFlags.Call;
                var callExpr = (MethodCallExpression)expr;
                var objExpr = callExpr.Object;
                var method = callExpr.Method;
                var methodParams = method.GetParameters();
                var objIsValueType = false;
                if (objExpr != null)
                {
                    if (!TryEmit(objExpr, paramExprs, il, ref closure, flags | ParentFlags.InstanceAccess))
                        return false;

                    objIsValueType = objExpr.Type.IsValueType();
                    if (objIsValueType && objExpr.NodeType != ExpressionType.Parameter && !closure.LastEmitIsAddress)
                        EmitStoreLocalVariableAndLoadItsAddress(il, objExpr.Type);
                }

                var fewArgCount = callExpr.FewArgumentCount;
                if (fewArgCount >= 0)
                {
                    if (fewArgCount == 1)
                    {
                        if (!TryEmit(((OneArgumentMethodCallExpression)callExpr).Argument, paramExprs, il, ref closure, flags, methodParams[0].ParameterType.IsByRef ? 0 : -1))
                            return false;
                    }
                    else if (fewArgCount == 2)
                    {
                        var twoArgsExpr = (TwoArgumentsMethodCallExpression)callExpr;
                        if (!TryEmit(twoArgsExpr.Argument0, paramExprs, il, ref closure, flags, methodParams[0].ParameterType.IsByRef ? 0 : -1) ||
                            !TryEmit(twoArgsExpr.Argument1, paramExprs, il, ref closure, flags, methodParams[1].ParameterType.IsByRef ? 1 : -1))
                            return false;
                    }
                    else if (fewArgCount == 3)
                    {
                        var threeArgsExpr = (ThreeArgumentsMethodCallExpression)callExpr;
                        if (!TryEmit(threeArgsExpr.Argument0, paramExprs, il, ref closure, flags, methodParams[0].ParameterType.IsByRef ? 0 : -1) ||
                            !TryEmit(threeArgsExpr.Argument1, paramExprs, il, ref closure, flags, methodParams[1].ParameterType.IsByRef ? 1 : -1) ||
                            !TryEmit(threeArgsExpr.Argument2, paramExprs, il, ref closure, flags, methodParams[2].ParameterType.IsByRef ? 2 : -1))
                            return false;
                    }
                    else if (fewArgCount == 4)
                    {
                        var fourArgsExpr = (FourArgumentsMethodCallExpression)callExpr;
                        if (!TryEmit(fourArgsExpr.Argument0, paramExprs, il, ref closure, flags, methodParams[0].ParameterType.IsByRef ? 0 : -1) ||
                            !TryEmit(fourArgsExpr.Argument1, paramExprs, il, ref closure, flags, methodParams[1].ParameterType.IsByRef ? 1 : -1) ||
                            !TryEmit(fourArgsExpr.Argument2, paramExprs, il, ref closure, flags, methodParams[2].ParameterType.IsByRef ? 2 : -1) ||
                            !TryEmit(fourArgsExpr.Argument3, paramExprs, il, ref closure, flags, methodParams[3].ParameterType.IsByRef ? 3 : -1))
                            return false;
                    }
                    else if (fewArgCount == 5)
                    {
                        var fiveArgsExpr = (FiveArgumentsMethodCallExpression)callExpr;
                        if (!TryEmit(fiveArgsExpr.Argument0, paramExprs, il, ref closure, flags, methodParams[0].ParameterType.IsByRef ? 0 : -1) ||
                            !TryEmit(fiveArgsExpr.Argument1, paramExprs, il, ref closure, flags, methodParams[1].ParameterType.IsByRef ? 1 : -1) ||
                            !TryEmit(fiveArgsExpr.Argument2, paramExprs, il, ref closure, flags, methodParams[2].ParameterType.IsByRef ? 2 : -1) ||
                            !TryEmit(fiveArgsExpr.Argument3, paramExprs, il, ref closure, flags, methodParams[3].ParameterType.IsByRef ? 3 : -1) ||
                            !TryEmit(fiveArgsExpr.Argument4, paramExprs, il, ref closure, flags, methodParams[4].ParameterType.IsByRef ? 4 : -1))
                            return false;
                    }

                    if (objIsValueType && method.IsVirtual)
                        il.Emit(OpCodes.Constrained, objExpr.Type);
                    il.Emit(method.IsVirtual ? OpCodes.Callvirt : OpCodes.Call, method);
                    if (parent.IgnoresResult() && method.ReturnType != typeof(void))
                        il.Emit(OpCodes.Pop);
                    closure.LastEmitIsAddress = false;
                    return true;
                }

                var args = callExpr.Arguments;
                for (var i = 0; i < methodParams.Length; i++)
                    if (!TryEmit(args[i], paramExprs, il, ref closure, flags, methodParams[i].ParameterType.IsByRef ? i : -1))
                        return false;

                if (objIsValueType && method.IsVirtual)
                    il.Emit(OpCodes.Constrained, objExpr.Type);
                il.Emit(method.IsVirtual ? OpCodes.Callvirt : OpCodes.Call, method);
                if (parent.IgnoresResult() && method.ReturnType != typeof(void))
                    il.Emit(OpCodes.Pop);

                closure.LastEmitIsAddress = false;
                return true;
            }

            private static bool TryEmitMemberAccess(MemberExpression expr,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure, ParentFlags parent)
            {
                if (expr.Member is PropertyInfo prop)
                {
                    var instanceExpr = expr.Expression;
                    if (instanceExpr != null)
                    {
                        if (!TryEmit(instanceExpr, paramExprs, il, ref closure,
                            ~ParentFlags.IgnoreResult & ~ParentFlags.DupMemberOwner &
                            (parent | ParentFlags.Call | ParentFlags.MemberAccess | ParentFlags.InstanceAccess)))
                            return false;

                        if ((parent & ParentFlags.DupMemberOwner) != 0)
                            il.Emit(OpCodes.Dup);

                        // Value type special treatment to load address of value instance in order to access a field or call a method.
                        // Parameter should be excluded because it already loads an address via `LDARGA`, and you don't need to.
                        // And for field access no need to load address, cause the field stored on stack nearby
                        if (!closure.LastEmitIsAddress &&
                            instanceExpr.NodeType != ExpressionType.Parameter && instanceExpr.Type.IsValueType())
                            EmitStoreLocalVariableAndLoadItsAddress(il, instanceExpr.Type);
                    }

                    closure.LastEmitIsAddress = false;
                    var propGetter = prop.DeclaringType.FindPropertyGetMethod(prop.Name);
                    if (propGetter == null)
                        return false;

                    il.Emit(propGetter.IsVirtual ? OpCodes.Callvirt : OpCodes.Call, propGetter);
                    return true;
                }

                if (expr.Member is FieldInfo field)
                {
                    var instanceExpr = expr.Expression;
                    if (instanceExpr != null)
                    {
                        if (!TryEmit(instanceExpr, paramExprs, il, ref closure,
                            ~ParentFlags.IgnoreResult & ~ParentFlags.DupMemberOwner &
                            (parent | ParentFlags.MemberAccess | ParentFlags.InstanceAccess)))
                            return false;

                        if ((parent & ParentFlags.DupMemberOwner) != 0)
                            il.Emit(OpCodes.Dup);

                        closure.LastEmitIsAddress = field.FieldType.IsValueType() && (parent & ParentFlags.InstanceAccess) != 0;
                        il.Emit(closure.LastEmitIsAddress ? OpCodes.Ldflda : OpCodes.Ldfld, field);
                    }
                    else if (field.IsLiteral)
                    {
                        var fieldValue = field.GetValue(null);
                        if (fieldValue != null)
                            return TryEmitNotNullConstant(false, field.FieldType, fieldValue, il, ref closure);

                        il.Emit(OpCodes.Ldnull);
                    }
                    else
                    {
                        il.Emit(OpCodes.Ldsfld, field);
                    }

                    return true;
                }

                return false;
            }

            // ReSharper disable once FunctionComplexityOverflow
            private static bool TryEmitNestedLambda(LambdaExpression lambdaExpr,
                IReadOnlyList<ParameterExpression> outerParamExprs, ILGenerator il, ref ClosureInfo closure)
            {
                // First, find in closed compiled lambdas the one corresponding to the current lambda expression.
                // Situation with not found lambda is not possible/exceptional,
                // it means that we somehow skipped the lambda expression while collecting closure info.
                var outerNestedLambdas = closure.NestedLambdas;
                var outerNestedLambdaIndex = outerNestedLambdas.Length - 1;
                while (outerNestedLambdaIndex != -1 && 
                       !ReferenceEquals(outerNestedLambdas[outerNestedLambdaIndex].LambdaExpression, lambdaExpr))
                    --outerNestedLambdaIndex;
                if (outerNestedLambdaIndex == -1)
                    return false;

                var nestedLambdaInfo = closure.NestedLambdas[outerNestedLambdaIndex];
                var nestedLambda = nestedLambdaInfo.Lambda;
                var nestedLambdaInClosureIndex = outerNestedLambdaIndex + closure.Constants.Count;

                var varIndex = nestedLambdaInfo.UsageCountOrVarIndex - 1;
                if (varIndex > 0)
                    EmitLoadLocalVariable(il, varIndex);
                else
                {
                    il.Emit(OpCodes.Ldloc_0);
                    EmitLoadConstantInt(il, nestedLambdaInClosureIndex);
                    il.Emit(OpCodes.Ldelem_Ref); // load the array item object
                }

                // If lambda does not use any outer parameters to be set in closure, then we're done
                ref var nestedClosureInfo = ref nestedLambdaInfo.ClosureInfo;
                var nestedNonPassedParams = nestedClosureInfo.NonPassedParameters;
                if (nestedNonPassedParams.Length == 0)
                    return true;

                //-------------------------------------------------------------------
                // For the lambda with non-passed parameters (or variables) in closure
                // we have loaded `NestedLambdaWithConstantsAndNestedLambdas` pair.
                if (varIndex > 0)
                {
                    // we are already have variable loaded
                    il.Emit(OpCodes.Ldfld, NestedLambdaWithConstantsAndNestedLambdas.NestedLambdaField);
                    EmitLoadLocalVariable(il, varIndex); // load the variable for the second time
                    il.Emit(OpCodes.Ldfld, NestedLambdaWithConstantsAndNestedLambdas.ConstantsAndNestedLambdasField);
                }
                else
                {
                    var nestedLambdaAndClosureItemsVarIndex = il.GetNextLocalVarIndex(typeof(NestedLambdaWithConstantsAndNestedLambdas));
                    EmitStoreLocalVariable(il, nestedLambdaAndClosureItemsVarIndex);

                    // - load the `NestedLambda` field
                    EmitLoadLocalVariable(il, nestedLambdaAndClosureItemsVarIndex);
                    il.Emit(OpCodes.Ldfld, NestedLambdaWithConstantsAndNestedLambdas.NestedLambdaField);

                    // - load the `ConstantsAndNestedLambdas` field
                    EmitLoadLocalVariable(il, nestedLambdaAndClosureItemsVarIndex);
                    il.Emit(OpCodes.Ldfld, NestedLambdaWithConstantsAndNestedLambdas.ConstantsAndNestedLambdasField);
                }

                // - create `NonPassedParameters` array
                EmitLoadConstantInt(il, nestedNonPassedParams.Length); // size of array
                il.Emit(OpCodes.Newarr, typeof(object));

                // - populate the `NonPassedParameters` array
                var outerNonPassedParams = closure.NonPassedParameters;
                for (var nestedParamIndex = 0; nestedParamIndex < nestedNonPassedParams.Length; ++nestedParamIndex)
                {
                    var nestedParam = nestedNonPassedParams[nestedParamIndex];

                    // Duplicate nested array on stack to store the item, and load index to where to store
                    il.Emit(OpCodes.Dup);
                    EmitLoadConstantInt(il, nestedParamIndex);

                    var outerParamIndex = outerParamExprs.Count - 1;
                    while (outerParamIndex != -1 && !ReferenceEquals(outerParamExprs[outerParamIndex], nestedParam))
                        --outerParamIndex;
                    if (outerParamIndex != -1) // load parameter from input outer params
                    {
                        // Add `+1` to index because the `0` index is for the closure argument
                        if (outerParamIndex == 0)
                            il.Emit(OpCodes.Ldarg_1);
                        else if (outerParamIndex == 1)
                            il.Emit(OpCodes.Ldarg_2);
                        else if (outerParamIndex == 2)
                            il.Emit(OpCodes.Ldarg_3);
                        else
                            il.Emit(OpCodes.Ldarg_S, (byte)(1 + outerParamIndex));

                        if (nestedParam.Type.IsValueType())
                            il.Emit(OpCodes.Box, nestedParam.Type);
                    }
                    else // load parameter from outer closure or from the local variables
                    {
                        if (outerNonPassedParams.Length == 0)
                            return false; // impossible, better to throw?

                        var variableIdx = closure.GetDefinedLocalVarOrDefault(nestedParam);
                        if (variableIdx != -1) // it's a local variable
                        {
                            EmitLoadLocalVariable(il, variableIdx);
                        }
                        else // it's a parameter from the outer closure
                        {
                            var outerNonPassedParamIndex = outerNonPassedParams.Length - 1;
                            while (outerNonPassedParamIndex != -1 && !ReferenceEquals(outerNonPassedParams[outerNonPassedParamIndex], nestedParam))
                                --outerNonPassedParamIndex;
                            if (outerNonPassedParamIndex == -1)
                                return false; // impossible

                            // Load the parameter from outer closure `Items` array
                            il.Emit(OpCodes.Ldarg_0); // closure is always a first argument
                            il.Emit(OpCodes.Ldfld, ArrayClosureWithNonPassedParamsField);
                            EmitLoadConstantInt(il, outerNonPassedParamIndex);
                            il.Emit(OpCodes.Ldelem_Ref);
                        }
                    }

                    // Store the item into nested lambda array
                    il.Emit(OpCodes.Stelem_Ref);
                }

                // - create `ArrayClosureWithNonPassedParams` out of the both above
                il.Emit(OpCodes.Newobj, ArrayClosureWithNonPassedParamsConstructor);

                // - call `Curry` method with nested lambda and array closure to produce a closed lambda with the expected signature
                var lambdaTypeArgs = nestedLambda.GetType().GetTypeInfo().GenericTypeArguments;

                var closureMethod = nestedLambdaInfo.LambdaExpression.ReturnType == typeof(void)
                    ? CurryClosureActions.Methods[lambdaTypeArgs.Length - 1].MakeGenericMethod(lambdaTypeArgs)
                    : CurryClosureFuncs.Methods[lambdaTypeArgs.Length - 2].MakeGenericMethod(lambdaTypeArgs);

                il.Emit(OpCodes.Call, closureMethod);
                return true;
            }

            private static bool TryEmitInvoke(InvocationExpression expr,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure, ParentFlags parent)
            {
                var lambda = expr.Expression;
                if (!TryEmit(lambda, paramExprs, il, ref closure, parent & ~ParentFlags.IgnoreResult))
                    return false;

                var argExprs = expr.Arguments;
                for (var i = 0; i < argExprs.Count; i++)
                    if (!TryEmit(argExprs[i], paramExprs, il, ref closure,
                        parent & ~ParentFlags.IgnoreResult & ~ParentFlags.InstanceAccess,
                        argExprs[i].Type.IsByRef ? i : -1))
                        return false;

                var delegateInvokeMethod = lambda.Type.FindDelegateInvokeMethod();
                il.Emit(OpCodes.Call, delegateInvokeMethod);

                if ((parent & ParentFlags.IgnoreResult) != 0 && delegateInvokeMethod.ReturnType != typeof(void))
                    il.Emit(OpCodes.Pop);

                return true;
            }

            private static bool TryEmitSwitch(SwitchExpression expr,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure, ParentFlags parent)
            {
                // todo:
                //- use switch statement for int comparison (if int difference is less or equal 3 -> use IL switch)
                //- TryEmitComparison should not emit "CEQ" so we could use Beq_S instead of Brtrue_S (not always possible (nullable))
                //- if switch SwitchValue is a nullable parameter, we should call getValue only once and store the result.
                //- use comparison methods (when defined)

                var endLabel = il.DefineLabel();
                var labels = new Label[expr.Cases.Count];
                for (var index = 0; index < expr.Cases.Count; index++)
                {
                    var switchCase = expr.Cases[index];
                    labels[index] = il.DefineLabel();

                    foreach (var switchCaseTestValue in switchCase.TestValues)
                    {
                        if (!TryEmitComparison(expr.SwitchValue, switchCaseTestValue, ExpressionType.Equal, paramExprs, il,
                            ref closure, parent))
                            return false;
                        il.Emit(OpCodes.Brtrue, labels[index]);
                    }
                }

                if (expr.DefaultBody != null)
                {
                    if (!TryEmit(expr.DefaultBody, paramExprs, il, ref closure, parent))
                        return false;
                    il.Emit(OpCodes.Br, endLabel);
                }

                for (var index = 0; index < expr.Cases.Count; index++)
                {
                    var switchCase = expr.Cases[index];
                    il.MarkLabel(labels[index]);
                    if (!TryEmit(switchCase.Body, paramExprs, il, ref closure, parent))
                        return false;

                    if (index != expr.Cases.Count - 1)
                        il.Emit(OpCodes.Br, endLabel);
                }

                il.MarkLabel(endLabel);

                return true;
            }

            private static bool TryEmitComparison(Expression exprLeft, Expression exprRight, ExpressionType expressionType,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure, ParentFlags parent)
            {
                var leftOpType = exprLeft.Type;
                var leftIsNullable = leftOpType.IsNullable();
                var rightOpType = exprRight.Type;
                if (exprRight is ConstantExpression c && c.Value == null && exprRight.Type == typeof(object))
                    rightOpType = leftOpType;

                int lVarIndex = -1, rVarIndex = -1;
                if (!TryEmit(exprLeft, paramExprs, il, ref closure, parent & ~ParentFlags.IgnoreResult & ~ParentFlags.InstanceAccess))
                    return false;

                if (leftIsNullable)
                {
                    lVarIndex = EmitStoreLocalVariableAndLoadItsAddress(il, leftOpType);
                    il.Emit(OpCodes.Call, leftOpType.FindNullableGetValueOrDefaultMethod());
                    leftOpType = Nullable.GetUnderlyingType(leftOpType);
                }

                if (!TryEmit(exprRight, paramExprs, il, ref closure, parent & ~ParentFlags.IgnoreResult & ~ParentFlags.InstanceAccess))
                    return false;

                if (leftOpType != rightOpType)
                {
                    if (leftOpType.IsClass() && rightOpType.IsClass() &&
                        (leftOpType == typeof(object) || rightOpType == typeof(object)))
                    {
                        if (expressionType == ExpressionType.Equal)
                        {
                            il.Emit(OpCodes.Ceq);
                            if ((parent & ParentFlags.IgnoreResult) != 0)
                                il.Emit(OpCodes.Pop);
                        }
                        else if (expressionType == ExpressionType.NotEqual)
                        {
                            il.Emit(OpCodes.Ceq);
                            il.Emit(OpCodes.Ldc_I4_0);
                            il.Emit(OpCodes.Ceq);
                        }
                        else
                            return false;

                        if ((parent & ParentFlags.IgnoreResult) != 0)
                            il.Emit(OpCodes.Pop);

                        return true;
                    }
                }

                if (rightOpType.IsNullable())
                {
                    rVarIndex = EmitStoreLocalVariableAndLoadItsAddress(il, rightOpType);
                    il.Emit(OpCodes.Call, rightOpType.FindNullableGetValueOrDefaultMethod());
                    // ReSharper disable once AssignNullToNotNullAttribute
                    rightOpType = Nullable.GetUnderlyingType(rightOpType);
                }

                var leftOpTypeInfo = leftOpType.GetTypeInfo();
                if (!leftOpTypeInfo.IsPrimitive && !leftOpTypeInfo.IsEnum)
                {
                    var methodName
                        = expressionType == ExpressionType.Equal ? "op_Equality"
                        : expressionType == ExpressionType.NotEqual ? "op_Inequality"
                        : expressionType == ExpressionType.GreaterThan ? "op_GreaterThan"
                        : expressionType == ExpressionType.GreaterThanOrEqual ? "op_GreaterThanOrEqual"
                        : expressionType == ExpressionType.LessThan ? "op_LessThan"
                        : expressionType == ExpressionType.LessThanOrEqual ? "op_LessThanOrEqual"
                        : null;

                    if (methodName == null)
                        return false;

                    // todo: for now handling only parameters of the same type
                    var methods = leftOpTypeInfo.DeclaredMethods.AsArray();
                    for (var i = 0; i < methods.Length; i++)
                    {
                        var m = methods[i];
                        if (m.IsSpecialName && m.IsStatic && m.Name == methodName &&
                            IsComparisonOperatorSignature(leftOpType, m.GetParameters()))
                        {
                            il.Emit(OpCodes.Call, m);
                            return true;
                        }
                    }

                    if (expressionType != ExpressionType.Equal && expressionType != ExpressionType.NotEqual)
                        return false;

                    il.Emit(OpCodes.Call, _objectEqualsMethod);

                    if (expressionType == ExpressionType.NotEqual) // invert result for not equal
                    {
                        il.Emit(OpCodes.Ldc_I4_0);
                        il.Emit(OpCodes.Ceq);
                    }

                    if (leftIsNullable)
                        goto nullCheck;

                    if ((parent & ParentFlags.IgnoreResult) > 0)
                        il.Emit(OpCodes.Pop);

                    return true;
                }

                // handle primitives comparison
                switch (expressionType)
                {
                    case ExpressionType.Equal:
                        il.Emit(OpCodes.Ceq);
                        break;

                    case ExpressionType.NotEqual:
                        il.Emit(OpCodes.Ceq);
                        il.Emit(OpCodes.Ldc_I4_0);
                        il.Emit(OpCodes.Ceq);
                        break;

                    case ExpressionType.LessThan:
                        il.Emit(OpCodes.Clt);
                        break;

                    case ExpressionType.GreaterThan:
                        il.Emit(OpCodes.Cgt);
                        break;

                    case ExpressionType.GreaterThanOrEqual:
                    case ExpressionType.LessThanOrEqual:
                        var ifTrueLabel = il.DefineLabel();
                        if (rightOpType == typeof(uint) || rightOpType == typeof(ulong) ||
                            rightOpType == typeof(ushort) || rightOpType == typeof(byte))
                            il.Emit(expressionType == ExpressionType.GreaterThanOrEqual ? OpCodes.Bge_Un_S : OpCodes.Ble_Un_S, ifTrueLabel);
                        else
                            il.Emit(expressionType == ExpressionType.GreaterThanOrEqual ? OpCodes.Bge_S : OpCodes.Ble_S, ifTrueLabel);

                        il.Emit(OpCodes.Ldc_I4_0);
                        var doneLabel = il.DefineLabel();
                        il.Emit(OpCodes.Br_S, doneLabel);

                        il.MarkLabel(ifTrueLabel);
                        il.Emit(OpCodes.Ldc_I4_1);

                        il.MarkLabel(doneLabel);
                        break;

                    default:
                        return false;
                }

            nullCheck:
                if (leftIsNullable)
                {
                    var leftNullableHasValueGetterMethod = exprLeft.Type.FindNullableHasValueGetterMethod();

                    EmitLoadLocalVariableAddress(il, lVarIndex);
                    il.Emit(OpCodes.Call, leftNullableHasValueGetterMethod);

                    // ReSharper disable once AssignNullToNotNullAttribute
                    EmitLoadLocalVariableAddress(il, rVarIndex);
                    il.Emit(OpCodes.Call, leftNullableHasValueGetterMethod);

                    switch (expressionType)
                    {
                        case ExpressionType.Equal:
                            il.Emit(OpCodes.Ceq); // compare both HasValue calls
                            il.Emit(OpCodes.And); // both results need to be true
                            break;

                        case ExpressionType.NotEqual:
                            il.Emit(OpCodes.Ceq);
                            il.Emit(OpCodes.Ldc_I4_0);
                            il.Emit(OpCodes.Ceq);
                            il.Emit(OpCodes.Or);
                            break;

                        case ExpressionType.LessThan:
                        case ExpressionType.GreaterThan:
                        case ExpressionType.LessThanOrEqual:
                        case ExpressionType.GreaterThanOrEqual:
                            il.Emit(OpCodes.Ceq);
                            il.Emit(OpCodes.Ldc_I4_1);
                            il.Emit(OpCodes.Ceq);
                            il.Emit(OpCodes.And);
                            break;

                        default:
                            return false;
                    }
                }

                if ((parent & ParentFlags.IgnoreResult) > 0)
                    il.Emit(OpCodes.Pop);

                return true;
            }

            private static bool IsComparisonOperatorSignature(Type t, ParameterInfo[] pars) =>
                pars.Length == 2 && pars[0].ParameterType == t && pars[1].ParameterType == t;

            private static bool TryEmitArithmetic(BinaryExpression expr, ExpressionType exprNodeType,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure,
                ParentFlags parent)
            {
                var flags = parent & ~ParentFlags.IgnoreResult & ~ParentFlags.InstanceCall | ParentFlags.Arithmetic;

                var leftNoValueLabel = default(Label);
                var leftExpr = expr.Left;
                var lefType = leftExpr.Type;
                var leftIsNullable = lefType.IsNullable();
                if (leftIsNullable)
                {
                    leftNoValueLabel = il.DefineLabel();
                    if (!TryEmit(leftExpr, paramExprs, il, ref closure, flags | ParentFlags.InstanceCall))
                        return false;

                    if (!closure.LastEmitIsAddress) 
                        EmitStoreLocalVariableAndLoadItsAddress(il, lefType);

                    il.Emit(OpCodes.Dup);
                    il.Emit(OpCodes.Call, lefType.FindNullableHasValueGetterMethod());

                    il.Emit(OpCodes.Brfalse, leftNoValueLabel);
                    il.Emit(OpCodes.Call, lefType.FindNullableGetValueOrDefaultMethod());
                }
                else if (!TryEmit(leftExpr, paramExprs, il, ref closure, flags))
                    return false;

                var rightNoValueLabel = default(Label);
                var rightExpr = expr.Right;
                var rightType = rightExpr.Type;
                var rightIsNullable = rightType.IsNullable();
                if (rightIsNullable)
                {
                    rightNoValueLabel = il.DefineLabel();
                    if (!TryEmit(rightExpr, paramExprs, il, ref closure, flags | ParentFlags.InstanceCall))
                        return false;

                    if (!closure.LastEmitIsAddress)
                        EmitStoreLocalVariableAndLoadItsAddress(il, rightType);

                    il.Emit(OpCodes.Dup);
                    il.Emit(OpCodes.Call, rightType.FindNullableHasValueGetterMethod());
                    il.Emit(OpCodes.Brfalse, rightNoValueLabel);
                    il.Emit(OpCodes.Call, rightType.FindNullableGetValueOrDefaultMethod());
                }
                else if (!TryEmit(rightExpr, paramExprs, il, ref closure, flags))
                    return false;

                var exprType = expr.Type;
                if (!TryEmitArithmeticOperation(expr, exprNodeType, exprType, il))
                    return false;

                if (leftIsNullable || rightIsNullable)
                {
                    var valueLabel = il.DefineLabel();
                    il.Emit(OpCodes.Br, valueLabel);

                    if (rightIsNullable)
                        il.MarkLabel(rightNoValueLabel);
                    il.Emit(OpCodes.Pop);

                    if (leftIsNullable)
                        il.MarkLabel(leftNoValueLabel);
                    il.Emit(OpCodes.Pop);

                    if (exprType.IsNullable())
                    {
                        var endL = il.DefineLabel();
                        var locIndex = InitValueTypeVariable(il, exprType);
                        EmitLoadLocalVariable(il, locIndex);
                        il.Emit(OpCodes.Br_S, endL);
                        il.MarkLabel(valueLabel);
                        il.Emit(OpCodes.Newobj, exprType.GetTypeInfo().DeclaredConstructors.GetFirst());
                        il.MarkLabel(endL);
                    }
                    else
                    {
                        il.Emit(OpCodes.Ldc_I4_0);
                        il.MarkLabel(valueLabel);
                    }
                }

                return true;
            }

            private static bool TryEmitArithmeticOperation(BinaryExpression expr,
                ExpressionType exprNodeType, Type exprType, ILGenerator il)
            {
                if (!exprType.IsPrimitive())
                {
                    if (exprType.IsNullable())
                        exprType = Nullable.GetUnderlyingType(exprType);

                    if (!exprType.IsPrimitive())
                    {
                        MethodInfo method = null;
                        if (exprType == typeof(string))
                        {
                            var paraType = typeof(string);
                            if (expr.Left.Type != expr.Right.Type || expr.Left.Type != typeof(string))
                                paraType = typeof(object);

                            var methods = typeof(string).GetTypeInfo().DeclaredMethods.AsArray();
                            for (var i = 0; i < methods.Length; i++)
                            {
                                var m = methods[i];
                                if (m.IsStatic && m.Name == "Concat" && 
                                    m.GetParameters().Length == 2 && m.GetParameters()[0].ParameterType == paraType)
                                {
                                    method = m;
                                    break;
                                }
                            }
                        }
                        else
                        {
                            var methodName
                                = exprNodeType == ExpressionType.Add ? "op_Addition"
                                : exprNodeType == ExpressionType.AddChecked ? "op_Addition"
                                : exprNodeType == ExpressionType.Subtract ? "op_Subtraction"
                                : exprNodeType == ExpressionType.SubtractChecked ? "op_Subtraction"
                                : exprNodeType == ExpressionType.Multiply ? "op_Multiply"
                                : exprNodeType == ExpressionType.MultiplyChecked ? "op_Multiply"
                                : exprNodeType == ExpressionType.Divide ? "op_Division"
                                : exprNodeType == ExpressionType.Modulo ? "op_Modulus"
                                : null;

                            if (methodName != null)
                            {
                                var methods = exprType.GetTypeInfo().DeclaredMethods.AsArray();
                                for (var i = 0; method == null && i < methods.Length; i++)
                                {
                                    var m = methods[i];
                                    if (m.IsSpecialName && m.IsStatic && m.Name == methodName)
                                        method = m;
                                }
                            }
                        }

                        if (method == null)
                            return false;

                        il.Emit(method.IsVirtual ? OpCodes.Callvirt : OpCodes.Call, method);
                        return true;
                    }
                }

                switch (exprNodeType)
                {
                    case ExpressionType.Add:
                    case ExpressionType.AddAssign:
                        il.Emit(OpCodes.Add);
                        return true;

                    case ExpressionType.AddChecked:
                    case ExpressionType.AddAssignChecked:
                        il.Emit(exprType.IsUnsigned() ? OpCodes.Add_Ovf_Un : OpCodes.Add_Ovf);
                        return true;

                    case ExpressionType.Subtract:
                    case ExpressionType.SubtractAssign:
                        il.Emit(OpCodes.Sub);
                        return true;

                    case ExpressionType.SubtractChecked:
                    case ExpressionType.SubtractAssignChecked:
                        il.Emit(exprType.IsUnsigned() ? OpCodes.Sub_Ovf_Un : OpCodes.Sub_Ovf);
                        return true;

                    case ExpressionType.Multiply:
                    case ExpressionType.MultiplyAssign:
                        il.Emit(OpCodes.Mul);
                        return true;

                    case ExpressionType.MultiplyChecked:
                    case ExpressionType.MultiplyAssignChecked:
                        il.Emit(exprType.IsUnsigned() ? OpCodes.Mul_Ovf_Un : OpCodes.Mul_Ovf);
                        return true;

                    case ExpressionType.Divide:
                    case ExpressionType.DivideAssign:
                        il.Emit(OpCodes.Div);
                        return true;

                    case ExpressionType.Modulo:
                    case ExpressionType.ModuloAssign:
                        il.Emit(OpCodes.Rem);
                        return true;

                    case ExpressionType.And:
                    case ExpressionType.AndAssign:
                        il.Emit(OpCodes.And);
                        return true;

                    case ExpressionType.Or:
                    case ExpressionType.OrAssign:
                        il.Emit(OpCodes.Or);
                        return true;

                    case ExpressionType.ExclusiveOr:
                    case ExpressionType.ExclusiveOrAssign:
                        il.Emit(OpCodes.Xor);
                        return true;

                    case ExpressionType.LeftShift:
                    case ExpressionType.LeftShiftAssign:
                        il.Emit(OpCodes.Shl);
                        return true;

                    case ExpressionType.RightShift:
                    case ExpressionType.RightShiftAssign:
                        il.Emit(OpCodes.Shr);
                        return true;

                    case ExpressionType.Power:
                        il.Emit(OpCodes.Call, typeof(Math).FindMethod("Pow"));
                        return true;
                }

                return false;
            }

            private static bool TryEmitLogicalOperator(BinaryExpression expr,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure, ParentFlags parent)
            {
                if (!TryEmit(expr.Left, paramExprs, il, ref closure, parent))
                    return false;

                var labelSkipRight = il.DefineLabel();
                il.Emit(expr.NodeType == ExpressionType.AndAlso ? OpCodes.Brfalse : OpCodes.Brtrue, labelSkipRight);

                if (!TryEmit(expr.Right, paramExprs, il, ref closure, parent))
                    return false;

                var labelDone = il.DefineLabel();
                il.Emit(OpCodes.Br, labelDone);

                il.MarkLabel(labelSkipRight); // label the second branch
                il.Emit(expr.NodeType == ExpressionType.AndAlso ? OpCodes.Ldc_I4_0 : OpCodes.Ldc_I4_1);
                il.MarkLabel(labelDone);

                return true;
            }

            private static bool TryEmitConditional(ConditionalExpression expr,
                IReadOnlyList<ParameterExpression> paramExprs, ILGenerator il, ref ClosureInfo closure, ParentFlags parent)
            {
                var testExpr = TryReduceCondition(expr.Test);

                // detect a special simplistic case of comparison with `null`
                var comparedWithNull = false;
                if (testExpr is BinaryExpression b)
                {
                    if (b.NodeType == ExpressionType.Equal || b.NodeType == ExpressionType.NotEqual ||
                        !b.Left.Type.IsNullable() && !b.Right.Type.IsNullable())
                    {
                        if (b.Right is ConstantExpression r && r.Value == null)
                        {
                            // the null comparison for nullable is actually a `nullable.HasValue` check,
                            // which implies member access on nullable struct - therefore loading it by address
                            if (b.Left.Type.IsNullable())
                                parent |= ParentFlags.MemberAccess;
                            comparedWithNull = TryEmit(b.Left, paramExprs, il, ref closure, parent & ~ParentFlags.IgnoreResult);
                        }
                        else if (b.Left is ConstantExpression l && l.Value == null)
                        {
                            // the null comparison for nullable is actually a `nullable.HasValue` check,
                            // which implies member access on nullable struct - therefore loading it by address
                            if (b.Right.Type.IsNullable())
                                parent |= ParentFlags.MemberAccess;
                            comparedWithNull = TryEmit(b.Right, paramExprs, il, ref closure, parent & ~ParentFlags.IgnoreResult);
                        }
                    }
                }

                if (!comparedWithNull)
                {
                    if (!TryEmit(testExpr, paramExprs, il, ref closure, parent & ~ParentFlags.IgnoreResult))
                        return false;
                }

                var labelIfFalse = il.DefineLabel();
                il.Emit(comparedWithNull && testExpr.NodeType == ExpressionType.Equal ? OpCodes.Brtrue : OpCodes.Brfalse, labelIfFalse);

                var ifTrueExpr = expr.IfTrue;
                if (!TryEmit(ifTrueExpr, paramExprs, il, ref closure, parent & ParentFlags.IgnoreResult))
                    return false;

                var ifFalseExpr = expr.IfFalse;
                if (ifFalseExpr.NodeType == ExpressionType.Default && ifFalseExpr.Type == typeof(void))
                {
                    il.MarkLabel(labelIfFalse);
                    return true;
                }

                var labelDone = il.DefineLabel();
                il.Emit(OpCodes.Br, labelDone);

                il.MarkLabel(labelIfFalse);
                if (!TryEmit(ifFalseExpr, paramExprs, il, ref closure, parent & ParentFlags.IgnoreResult))
                    return false;

                il.MarkLabel(labelDone);
                return true;
            }

            private static Expression TryReduceCondition(Expression testExpr)
            {
                if (testExpr is BinaryExpression b)
                {
                    if (b.NodeType == ExpressionType.OrElse || b.NodeType == ExpressionType.Or)
                    {
                        if (b.Left is ConstantExpression l && l.Value is bool lb)
                            return lb ? b.Left : TryReduceCondition(b.Right);

                        if (b.Right is ConstantExpression r && r.Value is bool rb && rb == false)
                            return TryReduceCondition(b.Left);
                    }
                    else if (b.NodeType == ExpressionType.AndAlso || b.NodeType == ExpressionType.And)
                    {
                        if (b.Left is ConstantExpression l && l.Value is bool lb)
                            return !lb ? b.Left : TryReduceCondition(b.Right);

                        if (b.Right is ConstantExpression r && r.Value is bool rb && rb)
                            return TryReduceCondition(b.Left);
                    }
                }

                return testExpr;
            }

            private static bool EmitMethodCall(ILGenerator il, MethodInfo method, ParentFlags parent = ParentFlags.Empty)
            {
                if (method == null)
                    return false;

                il.Emit(method.IsVirtual ? OpCodes.Callvirt : OpCodes.Call, method);

                if ((parent & ParentFlags.IgnoreResult) != 0 && method.ReturnType != typeof(void))
                    il.Emit(OpCodes.Pop);
                return true;
            }

            private static void EmitLoadConstantInt(ILGenerator il, int i)
            {
                switch (i)
                {
                    case -1:
                        il.Emit(OpCodes.Ldc_I4_M1);
                        break;
                    case 0:
                        il.Emit(OpCodes.Ldc_I4_0);
                        break;
                    case 1:
                        il.Emit(OpCodes.Ldc_I4_1);
                        break;
                    case 2:
                        il.Emit(OpCodes.Ldc_I4_2);
                        break;
                    case 3:
                        il.Emit(OpCodes.Ldc_I4_3);
                        break;
                    case 4:
                        il.Emit(OpCodes.Ldc_I4_4);
                        break;
                    case 5:
                        il.Emit(OpCodes.Ldc_I4_5);
                        break;
                    case 6:
                        il.Emit(OpCodes.Ldc_I4_6);
                        break;
                    case 7:
                        il.Emit(OpCodes.Ldc_I4_7);
                        break;
                    case 8:
                        il.Emit(OpCodes.Ldc_I4_8);
                        break;
                    default:
                        if (i > -129 && i < 128)
                            il.Emit(OpCodes.Ldc_I4_S, (sbyte)i);
                        else
                            il.Emit(OpCodes.Ldc_I4, i);
                        break;
                }
            }

            private static void EmitLoadLocalVariableAddress(ILGenerator il, int location)
            {
                if (location < 256)
                    il.Emit(OpCodes.Ldloca_S, (byte)location);
                else
                    il.Emit(OpCodes.Ldloca, location);
            }

            private static void EmitLoadLocalVariable(ILGenerator il, int location)
            {
                if (location == 0)
                    il.Emit(OpCodes.Ldloc_0);
                else if (location == 1)
                    il.Emit(OpCodes.Ldloc_1);
                else if (location == 2)
                    il.Emit(OpCodes.Ldloc_2);
                else if (location == 3)
                    il.Emit(OpCodes.Ldloc_3);
                else if (location < 256)
                    il.Emit(OpCodes.Ldloc_S, (byte)location);
                else
                    il.Emit(OpCodes.Ldloc, location);
            }

            private static void EmitStoreLocalVariable(ILGenerator il, int location)
            {
                if (location == 0)
                    il.Emit(OpCodes.Stloc_0);
                else if (location == 1)
                    il.Emit(OpCodes.Stloc_1);
                else if (location == 2)
                    il.Emit(OpCodes.Stloc_2);
                else if (location == 3)
                    il.Emit(OpCodes.Stloc_3);
                else if (location < 256)
                    il.Emit(OpCodes.Stloc_S, (byte)location);
                else
                    il.Emit(OpCodes.Stloc, location);
            }

            private static int EmitStoreLocalVariableAndLoadItsAddress(ILGenerator il, Type type)
            {
                var varIndex = il.GetNextLocalVarIndex(type);
                if (varIndex == 0)
                {
                    il.Emit(OpCodes.Stloc_0);
                    il.Emit(OpCodes.Ldloca_S, (byte)0);
                }
                else if (varIndex == 1)
                {
                    il.Emit(OpCodes.Stloc_1);
                    il.Emit(OpCodes.Ldloca_S, (byte)1);
                }
                else if (varIndex == 2)
                {
                    il.Emit(OpCodes.Stloc_2);
                    il.Emit(OpCodes.Ldloca_S, (byte)2);
                }
                else if (varIndex == 3)
                {
                    il.Emit(OpCodes.Stloc_3);
                    il.Emit(OpCodes.Ldloca_S, (byte)3);
                }
                else if (varIndex < 256)
                {
                    il.Emit(OpCodes.Stloc_S, (byte)varIndex);
                    il.Emit(OpCodes.Ldloca_S, (byte)varIndex);
                }
                else
                {
                    il.Emit(OpCodes.Stloc, varIndex);
                    il.Emit(OpCodes.Ldloca, varIndex);
                }

                return varIndex;
            }
        }
    }

    // Helpers targeting the performance. Extensions method names may be a bit funny (non standard), 
    // in order to prevent conflicts with YOUR helpers with standard names
    internal static class Tools
    {
        internal static bool IsValueType(this Type type) => type.GetTypeInfo().IsValueType;
        internal static bool IsPrimitive(this Type type) => type.GetTypeInfo().IsPrimitive;
        internal static bool IsClass(this Type type) => type.GetTypeInfo().IsClass;

        internal static bool IsUnsigned(this Type type) =>
            type == typeof(byte) || type == typeof(ushort) || type == typeof(uint) || type == typeof(ulong);

        internal static bool IsNullable(this Type type) =>
            type.GetTypeInfo().IsGenericType && type.GetTypeInfo().GetGenericTypeDefinition() == typeof(Nullable<>);

        internal static MethodInfo FindMethod(this Type type, string methodName)
        {
            var methods = type.GetTypeInfo().DeclaredMethods.AsArray();
            for (var i = 0; i < methods.Length; i++)
                if (methods[i].Name == methodName)
                    return methods[i];

            return type.GetTypeInfo().BaseType?.FindMethod(methodName);
        }

        internal static MethodInfo DelegateTargetGetterMethod = typeof(Delegate).FindPropertyGetMethod("Target");

        internal static MethodInfo FindDelegateInvokeMethod(this Type type) => type.FindMethod("Invoke");

        internal static MethodInfo FindNullableGetValueOrDefaultMethod(this Type type)
        {
            var methods = type.GetTypeInfo().DeclaredMethods.AsArray();
            for (var i = 0; i < methods.Length; i++)
            {
                var m = methods[i];
                if (m.GetParameters().Length == 0 && m.Name == "GetValueOrDefault")
                    return m;
            }

            return null;
        }

        internal static MethodInfo FindValueGetterMethod(this Type type) =>
            type.FindPropertyGetMethod("Value");

        internal static MethodInfo FindNullableHasValueGetterMethod(this Type type) =>
            type.FindPropertyGetMethod("HasValue");

        internal static MethodInfo FindPropertyGetMethod(this Type propHolderType, string propName)
        {
            var methods = propHolderType.GetTypeInfo().DeclaredMethods.AsArray();
            for (var i = 0; i < methods.Length; i++)
            {
                var method = methods[i];
                if (method.IsSpecialName)
                {
                    var methodName = method.Name;
                    if (methodName.Length == propName.Length + 4 && methodName[0] == 'g' && methodName[3] == '_')
                    {
                        var j = propName.Length - 1;
                        while (j != -1 && propName[j] == methodName[j + 4]) --j;
                        if (j == -1)
                            return method;
                    }
                }
            }

            return propHolderType.GetTypeInfo().BaseType?.FindPropertyGetMethod(propName);
        }

        internal static MethodInfo FindPropertySetMethod(this Type propHolderType, string propName)
        {
            var methods = propHolderType.GetTypeInfo().DeclaredMethods.AsArray();
            for (var i = 0; i < methods.Length; i++)
            {
                var method = methods[i];
                if (method.IsSpecialName)
                {
                    var methodName = method.Name;
                    if (methodName.Length == propName.Length + 4 && methodName[0] == 's' && methodName[3] == '_')
                    {
                        var j = propName.Length - 1;
                        while (j != -1 && propName[j] == methodName[j + 4]) --j;
                        if (j == -1)
                            return method;
                    }
                }
            }

            return propHolderType.GetTypeInfo().BaseType?.FindPropertySetMethod(propName);
        }

        internal static MethodInfo FindConvertOperator(this Type type, Type sourceType, Type targetType)
        {
            var methods = type.GetTypeInfo().DeclaredMethods.AsArray();
            for (var i = 0; i < methods.Length; i++)
            {
                var m = methods[i];
                if (m.IsStatic && m.IsSpecialName && m.ReturnType == targetType)
                {
                    var n = m.Name;
                    // n == "op_Implicit" || n == "op_Explicit"
                    if (n.Length == 11 && 
                        n[2] == '_' && n[5] == 'p' && n[6] == 'l' && n[7] == 'i' && n[8] == 'c' && n[9] == 'i' && n[10] == 't' && 
                        m.GetParameters()[0].ParameterType == sourceType)
                        return m;
                }
            }

            return null;
        }

        internal static ConstructorInfo FindSingleParamConstructor(this Type type, Type paramType)
        {
            var ctors = type.GetTypeInfo().DeclaredConstructors.AsArray();
            for (var i = 0; i < ctors.Length; i++)
            {
                var ctor = ctors[i];
                var parameters = ctor.GetParameters();
                if (parameters.Length == 1 && parameters[0].ParameterType == paramType)
                    return ctor;
            }

            return null;
        }

        public static T[] AsArray<T>(this IEnumerable<T> xs)
        {
            if (xs is T[] array)
                return array;
            return xs == null ? null : xs.ToArray();
        }

        private static class EmptyArray<T>
        {
            public static readonly T[] Value = new T[0];
        }

        public static T[] Empty<T>() => EmptyArray<T>.Value;

        public static T[] WithLast<T>(this T[] source, T value)
        {
            if (source == null || source.Length == 0)
                return new[] { value };
            if (source.Length == 1)
                return new[] { source[0], value };
            if (source.Length == 2)
                return new[] { source[0], source[1], value };
            var sourceLength = source.Length;
            var result = new T[sourceLength + 1];
            Array.Copy(source, 0, result, 0, sourceLength);
            result[sourceLength] = value;
            return result;
        }

        public static Type[] GetParamTypes(IReadOnlyList<ParameterExpression> paramExprs)
        {
            if (paramExprs == null || paramExprs.Count == 0)
                return Empty<Type>();

            if (paramExprs.Count == 1)
                return new[] { paramExprs[0].IsByRef ? paramExprs[0].Type.MakeByRefType() : paramExprs[0].Type };

            var paramTypes = new Type[paramExprs.Count];
            for (var i = 0; i < paramTypes.Length; i++)
            {
                var parameterExpr = paramExprs[i];
                paramTypes[i] = parameterExpr.IsByRef ? parameterExpr.Type.MakeByRefType() : parameterExpr.Type;
            }

            return paramTypes;
        }

        public static Type GetFuncOrActionType(Type[] paramTypes, Type returnType)
        {
            if (returnType == typeof(void))
            {
                switch (paramTypes.Length)
                {
                    case 0: return typeof(Action);
                    case 1: return typeof(Action<>).MakeGenericType(paramTypes);
                    case 2: return typeof(Action<,>).MakeGenericType(paramTypes);
                    case 3: return typeof(Action<,,>).MakeGenericType(paramTypes);
                    case 4: return typeof(Action<,,,>).MakeGenericType(paramTypes);
                    case 5: return typeof(Action<,,,,>).MakeGenericType(paramTypes);
                    case 6: return typeof(Action<,,,,,>).MakeGenericType(paramTypes);
                    case 7: return typeof(Action<,,,,,,>).MakeGenericType(paramTypes);
                    default:
                        throw new NotSupportedException(
                            $"Action with so many ({paramTypes.Length}) parameters is not supported!");
                }
            }

            switch (paramTypes.Length)
            {
                case 0: return typeof(Func<>).MakeGenericType(returnType);
                case 1: return typeof(Func<,>).MakeGenericType(paramTypes[0], returnType);
                case 2: return typeof(Func<,,>).MakeGenericType(paramTypes[0], paramTypes[1], returnType);
                case 3: return typeof(Func<,,,>).MakeGenericType(paramTypes[0], paramTypes[1], paramTypes[2], returnType);
                case 4: return typeof(Func<,,,,>).MakeGenericType(paramTypes[0], paramTypes[1], paramTypes[2], paramTypes[3], returnType);
                case 5: return typeof(Func<,,,,,>).MakeGenericType(paramTypes[0], paramTypes[1], paramTypes[2], paramTypes[3], paramTypes[4], returnType);
                case 6: return typeof(Func<,,,,,,>).MakeGenericType(paramTypes[0], paramTypes[1], paramTypes[2], paramTypes[3], paramTypes[4], paramTypes[5], returnType);
                case 7: return typeof(Func<,,,,,,,>).MakeGenericType(paramTypes[0], paramTypes[1], paramTypes[2], paramTypes[3], paramTypes[4], paramTypes[5], paramTypes[6], returnType);
                default:
                    throw new NotSupportedException(
                        $"Func with so many ({paramTypes.Length}) parameters is not supported!");
            }
        }

        public static T GetFirst<T>(this IEnumerable<T> source)
        {
            // This is pretty much Linq.FirstOrDefault except it does not need to check
            // if source is IPartition<T> (but should it?)

            if (source is IList<T> list)
                return list.Count == 0 ? default : list[0];
            using (var items = source.GetEnumerator())
                return items.MoveNext() ? items.Current : default;
        }

        public static T GetFirst<T>(this IList<T> source)
        {
            return source.Count == 0 ? default : source[0];
        }

        public static T GetFirst<T>(this T[] source)
        {
            return source.Length == 0 ? default : source[0];
        }
    }

    /// Hey
    public static class ILGeneratorHacks
    {
        /*
        // Original methods from ILGenerator.cs
        
        public virtual LocalBuilder DeclareLocal(Type localType)
        {
            return this.DeclareLocal(localType, false);
        }

        public virtual LocalBuilder DeclareLocal(Type localType, bool pinned)
        {
            MethodBuilder methodBuilder = this.m_methodBuilder as MethodBuilder;
            if ((MethodInfo)methodBuilder == (MethodInfo)null)
                throw new NotSupportedException();
            if (methodBuilder.IsTypeCreated())
                throw new InvalidOperationException(SR.InvalidOperation_TypeHasBeenCreated);
            if (localType == (Type)null)
                throw new ArgumentNullException(nameof(localType));
            if (methodBuilder.m_bIsBaked)
                throw new InvalidOperationException(SR.InvalidOperation_MethodBaked);
            this.m_localSignature.AddArgument(localType, pinned);
            LocalBuilder localBuilder = new LocalBuilder(this.m_localCount, localType, (MethodInfo)methodBuilder, pinned);
            ++this.m_localCount;
            return localBuilder;
        }
        */

        /// Not allocating the LocalBuilder class
        /// emitting this:
        /// il.m_localSignature.AddArgument(type);
        /// return PostInc(ref il.LocalCount);
        public static Func<ILGenerator, Type, int> CompileGetNextLocalVarIndex()
        {
            if (LocalCountField == null || LocalSignatureField == null || AddArgumentMethod == null)
                return (i, t) => i.DeclareLocal(t).LocalIndex;

            var method = new DynamicMethod(string.Empty,
                typeof(int), new[] { typeof(ExpressionCompiler.ArrayClosure), typeof(ILGenerator), typeof(Type) },
                typeof(ExpressionCompiler.ArrayClosure), skipVisibility: true);

            var il = method.GetILGenerator();

            il.Emit(OpCodes.Ldarg_1); // load `il` argument
            il.Emit(OpCodes.Ldfld, LocalSignatureField);
            il.Emit(OpCodes.Ldarg_2); // load `type` argument
            il.Emit(OpCodes.Ldc_I4_0); // load `pinned: false` argument
            il.Emit(OpCodes.Call, AddArgumentMethod);

            il.Emit(OpCodes.Ldarg_1); // load `il` argument
            il.Emit(OpCodes.Ldflda, LocalCountField);
            il.Emit(OpCodes.Call, PostIncMethod);

            il.Emit(OpCodes.Ret);

            return (Func<ILGenerator, Type, int>)method.CreateDelegate(typeof(Func<ILGenerator, Type, int>), ExpressionCompiler.EmptyArrayClosure);
        }

        internal static int PostInc(ref int i) => i++;

        public static readonly MethodInfo PostIncMethod = typeof(ILGeneratorHacks).GetTypeInfo()
            .GetDeclaredMethod(nameof(PostInc));

        /// Get via reflection
        public static readonly FieldInfo LocalSignatureField = typeof(ILGenerator).GetTypeInfo()
            .GetDeclaredField("m_localSignature");

        /// Get via reflection
        public static readonly FieldInfo LocalCountField = typeof(ILGenerator).GetTypeInfo()
            .GetDeclaredField("m_localCount");

        /// Get via reflection
        public static readonly MethodInfo AddArgumentMethod = typeof(SignatureHelper).GetTypeInfo()
            .GetDeclaredMethods(nameof(SignatureHelper.AddArgument)).First(m => m.GetParameters().Length == 2);

        private static readonly Func<ILGenerator, Type, int> _getNextLocalVarIndex = CompileGetNextLocalVarIndex();

        /// Does the job
        public static int GetNextLocalVarIndex(this ILGenerator il, Type t) => _getNextLocalVarIndex(il, t);
    }

    internal struct LiveCountArray<T>
    {
        public int Count;
        public T[] Items;

        public LiveCountArray(T[] items)
        {
            Items = items;
            Count = items.Length;
        }

        public ref T PushSlot()
        {
            if (++Count > Items.Length)
                Items = Expand(Items);
            return ref Items[Count - 1];
        }

        public void PushSlot(T item)
        {
            if (++Count > Items.Length)
                Items = Expand(Items);
            Items[Count - 1] = item;
        }

        public void Pop() => --Count;

        private static T[] Expand(T[] items)
        {
            if (items.Length == 0)
                return new T[4];

            var count = items.Length;
            var newItems = new T[count << 1]; // count x 2
            Array.Copy(items, 0, newItems, 0, count);
            return newItems;
        }
    }
}
#endif