Question

I have run into a problem with generics and new members. I wrote a generic class which operates on an object of type ObjectA. ObjectB derives from ObjectA and hides a few of ObjectA’s members. When I supply the type of ObjectB as the type parameter to the generic class, I would expect that when I call any of the members hidden by ObjectB, I would be calling ObjectB’s implementation. However, the CLR still calls the hidden members (ObjectA’s implementation). This seems illogical because I explicitly provided the type of ObjectB to the generic class. Is this a problem with generics themselves, or am I doing something wrong?

Edit: Unfortunately, I do not have access to ObjectA’s source code and the member I want to override is not virtual. If I had access to ObjectA’s source code, I would make the member virtual, but as I cannot do so, my only option for ‘overriding’ the member is through the ‘new’ keyword.

class GenericClass<T> where T : ObjectA   {       public void DoWork(T item)       {           // When type parameter 'T' is ObjectB, should get ObjectB's implementation           item.Invoke();       }   }    class ObjectA   {     public void Invoke()       {           // A's implementation...       }   }  class ObjectB : ObjectA   {     public new void Invoke()       {           // B's implementation...       }   }  static void Main()   {       GenericClass<ObjectB> genericClass = new GenericClass<ObjectB>();       ObjectB objectB = new ObjectB();       genericClass.DoWork(objectB);   } 

Answer 1

No. The calls generated by the compiler are to the members it knows about at compile-time. That’s the members exposed by ObjectA.

Any reason you’re not using normal inheritance, with virtual/overridden methods?

Here’s another example of the same kind of thing, by the way – the overloaded == operator for strings isn’t used, even though T is string in the call to Foo:

using System;  class Test {     static bool Foo<T>(T first, T second)         where T : class     {         return first == second;     }      static void Main()     {         string x = 'hello';         string y = new string(x.ToCharArray());          Console.WriteLine(Foo(x, y));     } }