C# Covariance on subclass return types

Question

Does anyone know why covariant return types are not supported in C#? Even when attempting to use an interface, the compiler complains that it is not allowed. See the followi

Answer 1

Eric Lippert has written a few posts on this site about return method covariance on method overrides, without as far as I can see addressing why the feature is unsupported. He has mentioned, though, that there are no plans to support it: https://stackoverflow.com/a/4349584/385844

Eric is also fond of saying that the answer to "why isn't X supported" is always the same: because nobody has designed, implemented, and tested (etc.) X. An example of that is here: https://stackoverflow.com/a/1995706/385844

There may be some philosophical reason for the lack of this feature; perhaps Eric will see this question and enlighten us.

EDIT

As Pratik pointed out in a comment:

interface IBuilder 
{ 
    T Build(); 
} 

should be

interface IBuilder 
{ 
    T Build(); 
} 

That would allow you to implement PastryOrder : IBuilder, and you could then have

IBuilder builder = new PastryOrder();

There are probably two or three approaches you could use to solve your problem, but, as you note, return method covariance is not one of those approaches, and none of this information answers the question of why C# doesn't support it.