The way to make this work is to iterate over the list and cast the elements. This can be done using ConvertAll: List<A> listOfA = new List<C>().ConvertAll(x => (A)x); You could also use Linq: List<A> listOfA = new List<C>().Cast<A>().ToList();
The out keyword in generics is used to denote that the type T in the interface is covariant. See Covariance and contravariance for details. The classic example is IEnumerable<out T>. Since IEnumerable<out T> is covariant, you’re allowed to do the following: IEnumerable<string> strings = new List<string>(); IEnumerable<object> objects = strings; The second line above would … Read more