Defining an extension method on IEnumerable<T> where T is specific kind of type?

Question

I want a method to only work on types which implement the /, +, -, * operators. Is there any "clean" way to do this?

Answer 1

You can define constraints on Type Parameters. So you can require T to implement an interface:

public static class Classy
{
    public static void Extension<T>(this IEnumerable<T> Ninjas) 
        where T : IMathStuff
    {

    }
}

This requires all T to implement IMathStuff. Now, if you can't fit the operators into the interface IMathStuff, you can leave the interface blank as a Marker Interface and only apply it to classes that do implement the operators.

This kind of assumes you're working with all custom classes and not the built-in types. It's a workaround for something that isn't exactly supported.

Answer 2

There is not a clean way to do this. You will need to implement IEnumberable<int>, IEnumberable<float>... etc

Answer 3

Not at compile-time. You'd have to use reflection, I think.

A lot of those are value types such as int and long, "where T : struct" but there is no interface or base type that is common to them.

Answer 4

This would require an interface, such as IArithmetic.

Unfortunately, this doens't work currently. This is a highly requested feature, however.

There are some workarounds, usually requiring working with a second generic parameter, but most wouldn't work with IEnumerator<T>.