#1,041 – Adding New Type Parameters when You Derive from a Generic Class

You can define a generic class that inherits from another generic class, for example:

public class ListPlus<T> : List<T>

You can also add new type parameters in the new class being defined.  In the example below, ListPlus derives from List<T> and adds a second type parameter.

        public class ListPlus<T, TShadow> : List<T>
        {
            private List<TShadow> shadowList = new List<TShadow>();

            public void AddItem(T mainItem, TShadow shadowItem)
            {
                base.Add(mainItem);
                shadowList.Add(shadowItem);
            }
        }

When we construct the type, we need to provide type arguments for both type parameters.

            ListPlus<Dog, Cat> myListPlus = new ListPlus<Dog, Cat>();
            Dog fido = new Dog("Fido");
            Cat puff = new Cat("Puff");
            myListPlus.AddItem(fido, puff);