// thinkbeforecoding

C# Static interfaces - Take 2

2009-10-22T13:11:07 / jeremie chassaing

As Romain was pointing in the comments, I totally missed to tell where I wanted to go with this static interface things. Need more sleep these days…

So here it is.

No I don’t want to do this

The point was not to enable something like this :

   int value = ICountable.Count;

Static interfaces have no implementation exactly like interfaces.

With interfaces, you need an instance (usually in a variable or member) to find the actual implementation and call it. With static interfaces, you need a type.

There are two ways to specify a type:

  • with its type name (Sample4.Count)
  • with a generic type parameter (T.Count)

I was also proposing a way to specify a type for extension methods.

Where it would be useful - operators

The reason why everybody is asking for static members in interfaces is ultimately to have operators in interfaces.

Imagine :

    public static interface IArithmetic<T>


        static T operator +(T x, T y);

        static T operator -(T x, T y);

        static T operator *(T x, T y);

        static T operator /(T x, T y);


Now you can write generic code like :

        public static T Power<T>(this T value, int count) where T : IArithmetic<T>


            var result = T.Identity;


            for (int i=0;i<count;i++)

                result = result*value;


            return result;


Cool !

This way, no need for the 20 overloads of Enumerable.Sum, it would work for any type presenting the expected static interface.