Operators as method parameters in C#

Question

I don't think it's possible to use operators as a parameters to methods in C# 3.0 but is there a way to emulate that or some syntactic sugar that makes it seem like that's what's going on?

I ask because I recently implemented the thrush combinator in C# but while translating Raganwald's Ruby example

(1..100).select(&:odd?).inject(&:+).into { |x| x * x }

Which reads "Take the numbers from 1 to 100, keep the odd ones, take the sum of those, and then answer the square of that number."

I fell short on the Symbol#to_proc stuff. That's the &: in the select(&:odd?) and the inject(&:+) above.

Answer 1

Well, in simple terms you can just use a lambda:

public void DoSomething(Func<int, int, int> op)
{
    Console.WriteLine(op(5, 2));
}

DoSomething((x, y) => x + y);
DoSomething((x, y) => x * y);
// etc

That's not very exciting though. It would be nice to have all those delegates prebuilt for us. Of course you could do this with a static class:

public static class Operator<T>
{
     public static readonly Func<T, T, T> Plus;
     public static readonly Func<T, T, T> Minus;
     // etc

     static Operator()
     {
         // Build the delegates using expression trees, probably
     }
}

Indeed, Marc Gravell has done something very similar in MiscUtil, if you want to look. You could then call:

DoSomething(Operator<int>.Plus);

It's not exactly pretty, but it's the closest that's supported at the moment, I believe.

I'm afraid I really don't understand the Ruby stuff, so I can't comment on that...

Answer 2

The following is direct, literal (as much as possible) C# translation:

(Func<int>)(x => x * x)(
    Enumerable.Range(1, 100)
        .Where(x => x % 2 == 1)
        .Aggregate((x, y) => x + y))

Specifically:

• blocks: {||} - become lambdas: =>
• select becomes Where
• inject becomes Aggregate
• into becomes a direct call on a lambda instance