Generic constraint ignores co-variance

Question

Let\'s say we have an interface like

public interface IEnumerable
{ /*...*/ }

that is co-variant in T.

Answer 1

Change your GenericMethod and add generic constraint class:

public void GenericMethod<T>(IEnumerable<T> p) where T : class, ISomeInterface
{
    IEnumerable<ISomeInterface> e = p;
    // or
    TestMethod(p);
}

Covariance does not support structs, so we need to tell that we want to use classes only.