Question

I have been reading here at stackoverflow how to write to a class var member using reflection. I use something like:

typeof(MyClass).GetField("myvar", BindingFlags.Public | BindingFlags.Instance).SetValue(instancie, 10);

This works for classes but if I do the same for a Struct instead of a class when reading myvar I allways get 0 (default construction value for int). This is the code I use:

struct MyStruct
{
    public int myvar;
}

MyStruct instance=new MyStruct();

typeof(MyStruct).GetField("myvar", BindingFlags.Public | BindingFlags. BindingFlags.Instance).SetValue(instance, 10);

Do anybody know why could this be hapenning?

Answer 1

When you pass in “instance”, that is a box – which is a wrapped clone of the data, that you later discard.

To use reflection here:

object obj = instance; // box
blah.SetValue(obj, value); // mutate inside box
instance = (YourType)obj; // unbox