动态类型的Msil Emit静态数组

Question

I'm trying to create a new type using Reflection.Emit (in c#).

The code I want to create is something similar to

public class 
{
   public static int[] A = new int[] {1, 2, 3};
}

I first tried to define a field, and then set its value:

var fb = tb.DefineField("A", FieldAttributes.Public | FieldAttributes.Static);
fb.SetValue(null, new int[] {1, 2, 3});

but it doesn't work, since setValue is only supported for simple types (int, float, ...).

Now I'm trying to use DefineInitializedData (much longer code which doesn't work...), but it does not generate any valid IL code.

Answer 1

setValue is only supported for simple types (int, float, ...)

No, it's not. FieldBuilder inherits SetValue() from FieldInfo , but it doesn't make sense for FieldBuilder .

There is FieldBuilder.SetConstant() , but it only works for const fields. And you can't have const fields of reference types with values other than null .

What you need to do is the same thing any compiler would have to do: create a static constructor, create the array there and then assign it to the field:

var fb = tb.DefineField("A", typeof(int[]), FieldAttributes.Public | FieldAttributes.Static);

var ctor = tb.DefineTypeInitializer();

var il = ctor.GetILGenerator();

// new int[3]
il.Emit(OpCodes.Ldc_I4_3);
il.Emit(OpCodes.Newarr, typeof(int));

// array[0] = 1
il.Emit(OpCodes.Dup);
il.Emit(OpCodes.Ldc_I4_0);
il.Emit(OpCodes.Ldc_I4_1);
il.Emit(OpCodes.Stelem_I4);

// array[1] = 2
il.Emit(OpCodes.Dup);
il.Emit(OpCodes.Ldc_I4_1);
il.Emit(OpCodes.Ldc_I4_2);
il.Emit(OpCodes.Stelem_I4);

// arr[2] = 3
il.Emit(OpCodes.Dup);
il.Emit(OpCodes.Ldc_I4_2);
il.Emit(OpCodes.Ldc_I4_3);
il.Emit(OpCodes.Stelem_I4);

// A = array
il.Emit(OpCodes.Stsfld, fb);

il.Emit(OpCodes.Ret);

If you look at the decompiled code generated by the C# compiler, you might see different IL, using something like <PrivateImplementationDetails>.__StaticArrayInitTypeSize=12 and RuntimeHelpers.InitializeArray() . That's an optimization and I think that if you're writing IL by hand, it's going to be simpler to use the normal method I showed above.