Generate dynamic method to set a field of a struct instead of using reflection

Question

Let\'s say I have the following code which update a field of a struct using reflection. Since the struct instance is copied into the DynamicUpdate

Answer 1

After some experiments:

public delegate void ClassFieldSetter(T target, TValue value) where T : class;

public delegate void StructFieldSetter(ref T target, TValue value) where T : struct;

public static class FieldSetterCreator
{
    public static ClassFieldSetter CreateClassFieldSetter(FieldInfo field)
        where T : class
    {
        return CreateSetter>(field);
    }

    public static StructFieldSetter CreateStructFieldSetter(FieldInfo field)
        where T : struct
    {
        return CreateSetter>(field);
    }

    private static TDelegate CreateSetter(FieldInfo field)
    {
        return (TDelegate)(object)CreateSetter(field, typeof(T), typeof(TValue), typeof(TDelegate));
    }

    private static Delegate CreateSetter(FieldInfo field, Type instanceType, Type valueType, Type delegateType)
    {
        if (!field.DeclaringType.IsAssignableFrom(instanceType))
            throw new ArgumentException("The field is declared it different type");
        if (!field.FieldType.IsAssignableFrom(valueType))
            throw new ArgumentException("The field type is not assignable from the value");

        var paramType = instanceType.IsValueType ? instanceType.MakeByRefType() : instanceType;
        var setter = new DynamicMethod("", typeof(void),
                                        new[] { paramType, valueType },
                                        field.DeclaringType.Module, true);

        var generator = setter.GetILGenerator();
        generator.Emit(OpCodes.Ldarg_0);
        generator.Emit(OpCodes.Ldarg_1);
        generator.Emit(OpCodes.Stfld, field);
        generator.Emit(OpCodes.Ret);

        return setter.CreateDelegate(delegateType);
    }
}

The main difference from the expression tree approach is that readonly fields can also be changed.