Introduction to Type Classes for .NET Developers, Number interface

number.cs

public interface Number<T>
{
    T Add(T a, T b);

    T Subtract(T a, T b);
}

public class Integer : Number<int>
{
    public int Add(int a, int b) => a + b;

    public int Subtract(int a, int b) => a - b;
}

public class Double : Number<double>
{
    public double Add(double a, double b) => a + b;

    public double Subtract(double a, double b) => a - b;
}