Out parameters for generic classes | Downcasting for generic

[RomanSoloweow]

Why is out not supported for parameters?

With the current implementation, we cannot do this:

class A {}
class B:A {}

class C<T> where T: A {}

C<B> t1 = new C<B>();

C<A> t2 = t1; //we cannot perform such a conversion

[HaloFour]

Generic variance does not extend to classes. B may inherit from A, but C<B> does not inherit from C<A>. If you could cast List<B> to List<A> you could be permitted to add values to it that are not B which would break type safety.

[0x0737]

#2498?