Stack<T> implements ICollection, but has methods from ICollection<T>

Question

I'm trying to create a custom collection based on Stack<T>. When I look at Stack<T> [from metadata] in visual studio, it shows that Stack<T> implements ICollection, which would require it to implement ICollection's CopyTo(Array array, index) method, but instead, it is shown as having ICollection<T>'s CopyTo(T[] array, index) method. Can someone explain why this is the case?

I'm trying to create a collection that mimics Stack<T> pretty heavily. When I implement ICollection as stack does, it requires me to use the CopyTo(Array array, index) method, but what I really want is to use the CopyTo(T[] array, index) method, like Stack<T> does. Is there a way to achieve this without implementing ICollection<T>?

Janitress

The methods are implemented explicitly. Explicitly implemented methods are not public and therefore would not show up in the metadata (which only lists public properties). – Directorate

You might try .NET Reflector to see the actual complete source code of Stack<T>, including private methods. – Cowles

@JeffMercado Wow... I can't believe it was that easy. I always wondered what "Explicitly Implement suchnsuch" meant. Thanks. – Janitress

Posted the .NET 4.0 implementation of Stack<T> if you want to take a look. pastebin.com/p2k4URtU – Actuary

@SPFiredrake, how did you get that?! – Devaughn

@JeffMercado you should probably post that as an answer and briefly explain how to explicitly implement an interface so you can get the credit. – Outdoor

@JeffMercado - your answer, which is good, is more useful as an answer than a comment. Strangely, I've seen more and more people use comments to answer questions lately. Go figure. – Cordovan

@C.E: I'm swamped at work right now and would have otherwise provided a full answer. The best that I could do with the time I have is to throw in a comment. It's hard to force myself to put in a sub-standard answer (by my standards). – Directorate

@Devaughn - downloading Framework source from within VS has been around for a while. Take a look at this article: blogs.msdn.com/b/rscc/archive/2010/08/16/… – Cordovan

Answer 1

As others have written, you can use explicit interface implementation to satisfy your non-generic interface:

void ICollection.CopyTo(Array array, int arrayIndex)
{
  var arrayOfT = array as T[];
  if (arrayOfT == null)
    throw new InvalidOperationException();
  CopyTo(arrayOfT, arrayIndex); // calls your good generic method
}

Solitary

Answer 2

I guess the method CopyTo(Array array, index) is implemented explicitly. This means, you will only see that method if you see the object as an ICollection:

var collection = (ICollection)stack;
collection.CopyTo(array, 0);

Angulation