using System;

using System.Runtime.CompilerServices;

public class Program {

    private interface IMath<T> {

        internal T Add (T value1, T value2);

        internal T Negate (T value);

    }

​

    private class Math<T> : IMath<T> {

        internal static readonly IMath<T> P = Math.P as IMath<T> ?? new Math<T>();

        T IMath<T>.Add (T a, T b) => NoSupport(); 

        T IMath<T>.Negate (T a) => NoSupport(); 

        private static T NoSupport ([CallerMemberName] string op = "") =>

            throw new NotSupportedException($"{op} not supported for type {typeof(T).Name}.");

    }

​

    private class Math : IMath<int>, IMath<float> {

        internal static Math P = new Math();

        int IMath<int>.Add (int a, int b) => a + b;

        int IMath<int>.Negate (int value) => -value;

        float IMath<float>.Add (float a, float b) => a + b;

        float IMath<float>.Negate (float value) => -value;

    }

    // ---- test code ----

    static T Negate <T> (T value) => Math<T>.P.Negate(value);

​

    public static void Main()

    {

        Console.WriteLine(Negate(42));

        Console.WriteLine(Negate(3.0f));

        Console.WriteLine(Negate(2.0));

    }

}