Generic List of Generic Interfaces not allowed, any alternative approaches?

Question

I am trying to find the right way to use a Generic List of Generic Interfaces as a variable.

Here is an example. It is probably not the best, but hopefully you will get

Answer 1

You say it won't work because you don't define T. So define it:

public class Holder<T>
{
    public List<IPrimitive<T>> Primitives {get;set;}
}

Answer 2

John is correct.

Might I also suggest (if you are using C# 4) that you make your interface covariant?

public interface IPrimitive<out T>
{
     T Value { get; }
}

This could save you some trouble later when you need to get things out of the list.

Answer 3

public interface IPrimitive
{

}

public interface IPrimitive<T> : IPrimitive
{
     T Value { get; }
}

public class Star : IPrimitive<T> //must declare T here
{

}

Then you should be able to have

List<IPrimitive> primitives = new List<IPrimitive>;

primitives.Add(new Star());   // Assuming Star implements IPrimitive
primitives.Add(new Sun());    // Assuming Sun implements IPrimitive