Reflecting Generics

I had an interesting problem today, how do you find out if an object is a subclass of a generic type? If you've simply got an instance of a generic type...

List<int> myobject = new List<int>();

You can find that myobject is a List<> by using the method GetGenericTypeDefinition():

if(myobject.GetType().GetGenericTypeDefinition() == typeof(List<>)) { ... }

But say you've got a type that inherits from a generic type:

public class A : List<int> { }

Now if you've got an instance of A:

A myA = new A();

You can't call GetGenericTypeDefinition(), it complains that myA.GetType() is in an incorrect state. Similarly, asking this:

myA.GetType().IsSubclassOf(typeof(List<>))

returns false because myA is a subclass of List<int>, but not List<>. I couldn't find any way of doing this without manually walking up the class hierarchy. In the end I gave in and wrote a this little recursive function:

public bool IsDerivedFromGenericType(Type givenType, Type genericType)
{
    Type baseType = givenType.BaseType;
    if (baseType == null) return false;
    if (baseType.IsGenericType)
    {
        if (baseType.GetGenericTypeDefinition() == genericType) return true;
    }
    return IsDerivedFromGenericType(baseType, genericType);
}

I guess where I was going wrong was thinking that List<int> 'inherits' from List<>, but of course it doesn't. It's an entirely unrelated hierarchy. Generics are not inheritance. I spent some time digging through the newsgroups looking for an answer to this and there's quite a lot of confusion around this issue. A really common misconception is to think that, for example, List<int> inherits from List<object> and that you can downcast like this..

List<int> myIntList = new List<int>();
List<object> myObjectList = (List<object>)myIntList;

It doesn't work.