DelegateHelpers.cs

using System;
using System.Collections.Generic;
using System.Reflection;
using System.Reflection.Emit;
using System.Runtime.CompilerServices;
using Platform.Exceptions;

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

namespace Platform.Reflection
{
    /// <summary>
    /// <para>
    /// Represents the delegate helpers.
    /// </para>
    /// <para></para>
    /// </summary>
    public static class DelegateHelpers
    {
        /// <summary>
        /// <para>
        /// Compiles the or default using the specified emit code.
        /// </para>
        /// <para></para>
        /// </summary>
        /// <typeparam name="TDelegate">
        /// <para>The delegate.</para>
        /// <para></para>
        /// </typeparam>
        /// <param name="emitCode">
        /// <para>The emit code.</para>
        /// <para></para>
        /// </param>
        /// <param name="typeMemberMethod">
        /// <para>The type member method.</para>
        /// <para></para>
        /// </param>
        /// <returns>
        /// <para>The delegate.</para>
        /// <para></para>
        /// </returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static TDelegate CompileOrDefault<TDelegate>(Action<ILGenerator> emitCode, bool typeMemberMethod)
            where TDelegate : Delegate
        {
            var @delegate = default(TDelegate);
            try
            {
                @delegate = typeMemberMethod ? CompileTypeMemberMethod<TDelegate>(emitCode) : CompileDynamicMethod<TDelegate>(emitCode);
            }
            catch (Exception exception)
            {
                exception.Ignore();
            }
            return @delegate;
        }

        /// <summary>
        /// <para>
        /// Compiles the or default using the specified emit code.
        /// </para>
        /// <para></para>
        /// </summary>
        /// <typeparam name="TDelegate">
        /// <para>The delegate.</para>
        /// <para></para>
        /// </typeparam>
        /// <param name="emitCode">
        /// <para>The emit code.</para>
        /// <para></para>
        /// </param>
        /// <returns>
        /// <para>The delegate</para>
        /// <para></para>
        /// </returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static TDelegate CompileOrDefault<TDelegate>(Action<ILGenerator> emitCode) where TDelegate : Delegate => CompileOrDefault<TDelegate>(emitCode, false);

        /// <summary>
        /// <para>
        /// Compiles the emit code.
        /// </para>
        /// <para></para>
        /// </summary>
        /// <typeparam name="TDelegate">
        /// <para>The delegate.</para>
        /// <para></para>
        /// </typeparam>
        /// <param name="emitCode">
        /// <para>The emit code.</para>
        /// <para></para>
        /// </param>
        /// <param name="typeMemberMethod">
        /// <para>The type member method.</para>
        /// <para></para>
        /// </param>
        /// <returns>
        /// <para>The delegate.</para>
        /// <para></para>
        /// </returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static TDelegate Compile<TDelegate>(Action<ILGenerator> emitCode, bool typeMemberMethod)
            where TDelegate : Delegate
        {
            var @delegate = CompileOrDefault<TDelegate>(emitCode, typeMemberMethod);
            if (EqualityComparer<TDelegate>.Default.Equals(@delegate, default))
            {
                @delegate = new NotSupportedExceptionDelegateFactory<TDelegate>().Create();
            }
            return @delegate;
        }

        /// <summary>
        /// <para>
        /// Compiles the emit code.
        /// </para>
        /// <para></para>
        /// </summary>
        /// <typeparam name="TDelegate">
        /// <para>The delegate.</para>
        /// <para></para>
        /// </typeparam>
        /// <param name="emitCode">
        /// <para>The emit code.</para>
        /// <para></para>
        /// </param>
        /// <returns>
        /// <para>The delegate</para>
        /// <para></para>
        /// </returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static TDelegate Compile<TDelegate>(Action<ILGenerator> emitCode) where TDelegate : Delegate => Compile<TDelegate>(emitCode, false);

        /// <summary>
        /// <para>
        /// Compiles the dynamic method using the specified emit code.
        /// </para>
        /// <para></para>
        /// </summary>
        /// <typeparam name="TDelegate">
        /// <para>The delegate.</para>
        /// <para></para>
        /// </typeparam>
        /// <param name="emitCode">
        /// <para>The emit code.</para>
        /// <para></para>
        /// </param>
        /// <returns>
        /// <para>The delegate</para>
        /// <para></para>
        /// </returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static TDelegate CompileDynamicMethod<TDelegate>(Action<ILGenerator> emitCode)
        {
            var delegateType = typeof(TDelegate);
            delegateType.GetDelegateCharacteristics(out Type returnType, out Type[] parameterTypes);
            var dynamicMethod = new DynamicMethod(GetNewName(), returnType, parameterTypes);
            emitCode(dynamicMethod.GetILGenerator());
            return (TDelegate)(object)dynamicMethod.CreateDelegate(delegateType);
        }

        /// <summary>
        /// <para>
        /// Compiles the type member method using the specified emit code.
        /// </para>
        /// <para></para>
        /// </summary>
        /// <typeparam name="TDelegate">
        /// <para>The delegate.</para>
        /// <para></para>
        /// </typeparam>
        /// <param name="emitCode">
        /// <para>The emit code.</para>
        /// <para></para>
        /// </param>
        /// <returns>
        /// <para>The delegate</para>
        /// <para></para>
        /// </returns>
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static TDelegate CompileTypeMemberMethod<TDelegate>(Action<ILGenerator> emitCode)
        {
            AssemblyName assemblyName = new AssemblyName(GetNewName());
            var assembly = AssemblyBuilder.DefineDynamicAssembly(assemblyName, AssemblyBuilderAccess.Run);
            var module = assembly.DefineDynamicModule(GetNewName());
            var type = module.DefineType(GetNewName());
            var methodName = GetNewName();
            type.EmitStaticMethod<TDelegate>(methodName, emitCode);
            var typeInfo = type.CreateTypeInfo();
            return (TDelegate)(object)typeInfo.GetMethod(methodName).CreateDelegate(typeof(TDelegate));
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static string GetNewName() => Guid.NewGuid().ToString("N");
    }
}