C# casting an inherited Generic interface

Question

I\'m having some trouble getting my head around casting an interface I\'ve come up with. It\'s an MVP design for C# Windows Forms. I have an IView class which I implement o

Answer 1

The problem is the generic type parameter. If you make the interface parameter covariant then the cast will work.

This is accomplished by adding the out keyword, like so:

interface IPresenter where V : IView
{
    void PresBlah();

}

You can learn more about how this works with the following MSDN article: Covariance and Contravariance in Generics. The section Generic Interfaces with Covariant Type Parameters specifically applies to your question.

Update: Make sure you check the comments between @phoog and me. If your actual code accepts a V as an input, you will be unable to make it covariant. The referenced article and @phoog's answer explains this case in further detail.