如何发射新结构

Question

var instanceType = typeof(T);            
LocalBuilder instanceBuilder = il.DeclareLocal(instanceType);// T 
if (instanceType.IsValueType)
{
    il.Emit(OpCodes.Ldloca, instanceBuilder);
    il.Emit(OpCodes.Initobj, instanceBuilder);
    il.Emit(OpCodes.Stloc_S, instanceBuilder);
}
else
{
    il.Emit(OpCodes.Newobj, instanceType.GetConstructor(Type.EmptyTypes));
    il.Emit(OpCodes.Stloc_S, instanceBuilder);
}
il.Emit(OpCodes.Ldstr, "Test");
il.Emit(OpCodes.Call, typeof(Console).GetMethod("WriteLine", new Type[] { TypeUtil._StringType }));
il.Emit(OpCodes.Ldloc, instanceBuilder);
il.Emit(OpCodes.Call, typeof(Console).GetMethod("WriteLine", new Type[] { TypeUtil._ObjectType }));

任何人都可以告诉我如何通过默认构造函数发射新的结构？

Answer 1

您所需要的只是ldloca(或ldflda/ldsflda(和initobj。没有什么可存储的(stloc_s是不必要的(。initobj的第二个参数是 type 令牌，而不是地址：

using System;
using System.Reflection.Emit;
static class Program
{
    static void Main()
    {
        var method = new DynamicMethod("create", typeof(Foo), new[] { typeof(int) });
        var il = method.GetILGenerator();
        var local = il.DeclareLocal(typeof(Foo));
        // initialize the local (essentially: the default ctor)
        il.Emit(OpCodes.Ldloca_S, local);
        il.Emit(OpCodes.Initobj, typeof(Foo));
        // assign the parameter value to the property
        il.Emit(OpCodes.Ldloca_S, local);
        il.Emit(OpCodes.Ldarg_0);
        il.Emit(OpCodes.Call,
            typeof(Foo).GetProperty(nameof(Foo.Id)).GetSetMethod());
        // load, box, and call CWL
        il.Emit(OpCodes.Ldloc_S, local);
        il.Emit(OpCodes.Box, typeof(Foo));
        il.Emit(OpCodes.Call, typeof(Console).GetMethod(
            nameof(Console.WriteLine), new[] { typeof(object) }));
        // return the value of the 
        il.Emit(OpCodes.Ldloc_S, local);
        il.Emit(OpCodes.Ret);
        // call the emitted method
        var del = (Func<int, Foo>)method.CreateDelegate(typeof(Func<int, Foo>));
        var foo = del(42);
    }
}
public struct Foo
{
    public int Id { get; set; } // not usually a good idea, note
    public override string ToString() => Id.ToString();
}