Question

Let’s say I have a generic class:

public class MyGenericClass<T> { 
  ...
}

Now inside this class, I want to have a method that allows me to interact with another generic, which could be of generic type T or any superclass of T, for example:

public void DoSomething<T1>(List<T1> things) 
  where T : T1 // of course this won't compile
{
  ...
}

How would you do this?

Answer 1

You can’t, I’m afraid. The closest you could come would be to have a method in a non-generic class – possibly an extension method:

public static MyGenericClassExtensions
{
    public static void DoSomething<T, T1>(this MyGenericClass<T> @this,
                                          List<T1> things)
        where T : T1
    {
        ...
    }
}

That’s fine, because it’s introducing both type parameters at the same time.

Of course, an alternative would be to keep the method as an instance method within MyGenericClass<T>, without the constraint, and check the constraint at execution time. That would be unfortunate in terms of the compile-time safety and general declarative nature of generics, but it may end up working out better for you.