Question

I have the following class A.

public class A
{
    public string Name { get; set; }
}

I need to emit a dynamic proxy using Reflection.Emit to override Equals.

// This class must be generated by Reflection.Emit.
public class AProxy : A
{
    private bool equalsHasBeenCalled;

    public override bool Equals(object obj)
    {
        if (this.equalsHasBeenCalled)
        {
            return base.Equals(obj);
        }

        this.equalsHasBeenCalled = true;

        return CaseInsensitiveComparer.Equals(this, obj); // Demo.
    }
}

However, the actual generated code (viewed with Reflector) is:

public class AProxy : A
{
    private bool equalsHasBeenCalled;

    public override bool Equals(object obj)
    {
        if (base.equalsHasBeenCalled)
        {
            return base.Equals(obj);
        }

        base.equalsHasBeenCalled = true;

        return CaseInsensitiveComparer.Equals(this, obj);
    }
}

..which of course throws a System.FieldAccessException (since no such member exists). The correct is to call this.equalsHasBeenCalled (not base.equalsHasBeenCalled).

I am using the Reflection.Emit add-in for Reflector to generate the code (field1 is the FieldInfo for the “equalsHasBeenCalled” field):

        // Writing body
        gen.Emit(OpCodes.Nop);

        // I suspect it has to be around here.
        gen.Emit(OpCodes.Ldarg_0);
        gen.Emit(OpCodes.Ldfld, field1);
        gen.Emit(OpCodes.Ldc_I4_0);

        gen.Emit(OpCodes.Ceq);
        gen.Emit(OpCodes.Stloc_1);
        gen.Emit(OpCodes.Ldloc_1);
        gen.Emit(OpCodes.Brtrue_S, label25);
        gen.Emit(OpCodes.Nop);
        gen.Emit(OpCodes.Ldarg_0);
        gen.Emit(OpCodes.Ldarg_1);
        gen.Emit(OpCodes.Call, method2);
        gen.Emit(OpCodes.Stloc_0);
        gen.Emit(OpCodes.Br_S, label42);
        gen.MarkLabel(label25);

        // ..and probably here also?
        gen.Emit(OpCodes.Ldarg_0);
        gen.Emit(OpCodes.Ldc_I4_1);
        gen.Emit(OpCodes.Stfld, field1);

        gen.Emit(OpCodes.Ldarg_0);
        gen.Emit(OpCodes.Ldarg_1);
        gen.Emit(OpCodes.Call, method3);
        gen.Emit(OpCodes.Stloc_0);
        gen.Emit(OpCodes.Br_S, label42);
        gen.MarkLabel(label42);
        gen.Emit(OpCodes.Ldloc_0);
        gen.Emit(OpCodes.Ret);

Answer 1

Why dont you write what you need in C#, decompile to IL and see how it’s set up? Also, if you need to do any more of things like this in your project, I suggest you look into Castle DynamicProxy.