csharp11.7.cs

// Interface specifies static properties and operators
interface IAddable<T> where T : IAddable<T>
{
    static abstract T Zero { get; }
    static abstract T operator +(T t1, T t2);
}

// Classes and structs (including built-ins) can implement interface
struct Int32 : …, IAddable<Int32>
{
// Explicit
    static Int32 I.operator +(Int32 x, Int32 y) => x + y; 
// Implicit
    public static int Zero => 0;                          
}

// Generic algorithms can use static members on T
public static T AddAll<T>(T[] ts) where T : IAddable<T>
{
// Call static operator    
    T result = T.Zero;
// Use `+`                   
    foreach (T t in ts) { result += t; } 
    return result;
}

// Generic method can be applied to built-in and user-defined types
int sixtyThree = AddAll(new [] { 1, 2, 4, 8, 16, 32 });