using extension methods on int

Question

I'm reading about extension methods, and monkeying around with them to see how they work, and I tried this:

namespace clunk {
    public static class oog {
        public static int doubleMe(this int x) {
            return 2 * x;
        }
    }

    class Program {
        static void Main() {
            Console.WriteLine(5.doubleMe());
        }
    }
}

and it worked as expected, successfully extending int with the doubleMe method, printing 10.

Next, being an old C guy, I wondered if I could do this:

namespace clunk {
    public static class BoolLikeC {
        public static bool operator true(this int i)  { return i != 0; }
        public static bool operator false(this int i) { return i == 0; }
    }

    class Program {
        static void Main() {
            if ( 7 ) {
                Console.WriteLine("7 is so true");
            }
        }
    }
}

I would think if the former would work, then the latter ought to work to make it such that an int used in a boolean context would call the extension method on int, check to see that 7 is not equal to 0, and return true. But instead, the compiler doesn't even like the later code, and puts the red squiggly lines under the two this's and says "Type expected". Why shouldn't this work?

Answer 1

Very clever! A nice attempt, but regrettably we did not implement "extension everything", just extension methods.

We considered implementing extension properties, extension operators, extension events, extension constructors, extension interfaces, you name it, but most of them were not compelling enough to make it into C# 4 or the upcoming version of C#. We got as far as designing a syntax for the sort of thing you mention. We got rather farther on extension properties; we almost got extension properties into C# 4 but it ended up not working out. The sad story is here.

http://blogs.msdn.com/b/ericlippert/archive/2009/10/05/why-no-extension-properties.aspx

So, long story short, no such feature, but we'll consider it for hypothetical future releases of the language.

You can of course make a "ToBool()" extension method on int if you really do like the retro C convention that non-zero-means-true.