C# variance problem: Assigning List as List<Base>

Question

Look at the following example (partially taken from MSDN Blog):

class Animal { }
class Giraffe : Animal { }

static void Main(string[] args)
{
    // Array a         


        

Answer 1

In terms of List, I'm afraid you're out of luck. However, .NET 4.0/C# 4.0 adds support for covariant/contravariant interfaces. Specifically, IEnumerable is now defined as IEnumerable, which means that the type parameter is now covariant.

This means you can do something like this in C# 4.0...

// implicit casting
IEnumerable animalsList = new List();

// explicit casting
IEnumerable animalsList2 = (IEnumerable) new List();

Note: Array types have also been covariant (at least since .NET 1.1).

I think it's a shame that variance support wasn't added for IList and other similar generic interfaces (or generic classes even), but oh well, at least we have something.