Why doesn't this C# casting example work?

Question

I'm trying to understand why this cast doesn't work:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace CastTest {

    class Foo {}

    // I want to use this kind of like a typedef, to avoid writing List<Foo> everywhere.
    class FooList : List<Foo> {}

    class Program {
        static void Main(string[] args) {
            FooList list = (FooList) Program.GetFooList();
        }

        // Suppose this is some library method, and i don't have control over the return type
        static List<Foo> GetFooList() {
            return new List<Foo>();
        }
    }
}

This generates a runtime error:

InvalidCastException: Unable to cast object of type 'System.Collections.Generic.List`1[CastTest.Foo]' to type 'CastTest.FooList'.

Can anyone explain why this doesn't work, and whether I can get around this somehow?

Answer 1

Just because your FooList is a List doesn't make the List a FooList.