Contrawhatywho – nicer generics in C# 4.0

Everyone probably knows this already, but it’s probably easy to miss as *stuff now just works*. Contravariance, or covariance is now improved to make working with generics that little bit simpler.

The following code now compiles fine in .net 4, but won’t compile against .net 3.5:

class Program
{
static void Main(string[] args)
{
Animal a = new Animal();
Bear b = new Bear();
IList<Bear> bears = new List<Bear>();
bears.Add(b);
IEnumerable<IAnimal> animals = bears;
}

class Animal : IAnimal
{
public override string ToString()
{
return “I am an animal”;
}
}

   class Bear : IAnimal
   {
       public override string ToString()
       {
           return "I am a bear";
       }
    } 

    internal interface IAnimal
    {
    }
}