What is the real reason for that limitation? Is it just work that had to be done? Is it conceptually hard? Is it impossible?
Sure, one couldn't use the type parameters in fields, because they are allways read-write. But that can't be the answer, can it?
The reason for this question is that I'm writing an article on variance support in C# 4, and I feel that I should explain why it is restricted to delegates and interfaces. Just to inverse the onus of proof.
Update: Eric asked about an example.
What about this (don't know if that makes sense, yet :-))
public class Lookup<out T> where T : Animal {
public T Find(string name) {
Animal a = _cache.FindAnimalByName(name);
return a as T;
}
}
var findReptiles = new Lookup<Reptile>();
Lookup<Animal> findAnimals = findReptiles;
The reason for having that in one class could be the cache that is held in the class itself. And please don't name your different type pets the same!
BTW, this brings me to optional type parameters in C# 5.0 :-)
Update 2: I'm not claiming the CLR and C# should allow this. Just trying to understand what led to that it doesnt.