I want to make a contract about static methods/properties in order to use them in a generic setting. Like this:

interface IAnimal {
    static string Sound;
}

class Dog : IAnimal {
    static string Sound => "woof";
}

class Cat : IAnimal {
    static string Sound => "meow";
}

class AnimalSoundExplainer<T> where T : IAnimal {

    // This does not work (but I would like it to):
    internal static void Explain() =>
        Console.WriteLine("Every "   typeof(T).Name   " makes "   T.Sound);
}

I would use it like this:

AnimalSoundExplainer<Dog>.Explain(); // should write "Every Dog makes woof"
AnimalSoundExplainer<Cat>.Explain(); // should write "Every Cat makes meow"

1. How can I make that contract (so that I get compile errors if I do not fulfill the contract)? C#'s static interface members do not work that way; C# will always just use the (provided or not) implementation of IAnimal. It does allow implementing/overriding static members analog to non-static members.

2. How can I make use of that contract inside a generic setting, i.e. how can I access theses members from a given generic type argument

• without needing to generate instances and
• without using reflection methods that make my program slow? (If there are reflection methods that do not make my program slow, I'd be okay with them.)

CodePudding user response：

This functionality is called "static abstract members", and it is currently in preview in .NET 6.

If you're happy enabling preview functionality, the following works in .NET 6 preview:

interface IAnimal {
    static abstract string Sound { get; }
}

class Dog : IAnimal {
    public static string Sound => "woof";
}

class Cat : IAnimal {
    public static string Sound => "meow";
}

class AnimalSoundExplainer<T> where T : IAnimal {

    internal static void Explain() =>
        Console.WriteLine("Every "   typeof(T).Name   " makes "   T.Sound);
}

See it on SharpLab.