• January 11, 2012
• in net, geek
• 2 min read

Implicits instead of Extension Methods?

After the latest round of scala is teh complex, I started thinking a bit more about the similar roles implicit conversions in scala play to extension methods in C#. I can't objectively comment on whether Extension Methods are simpler (they are still a discoverability issue), but I can comment that the idea of implicit conversion to attach new functionality to existing code really intrigued me. It does seem less obvious but also a lot more powerful.

Then i thought, wait, C# has implicit.. Did they just invent extension methods without needing to? I've never used implicit conversion in C# for anything but automatic casting, but maybe I was just not imaginative enough. So here goes nothing:

public class RichInt {
  public readonly int Value;

  public static implicit operator RichInt(int i) {
    return new RichInt(i);
  }

  public static implicit operator int(RichInt i) {
    return i.Value;
  }

  private RichInt(int i) {
    Value = i;
  }

  public IEnumerable<int> To(int upper) {
    for(int i = Value;i<=upper;i++) {
      yield return i;
    }
  }
}

Given the above I was hoping I could mimic scala's RichInt to() method and write code like this:

foreach(var i in 10.To(20)) {
  Console.WriteLine(i);
}

Alas that won't compile. Implicit conversion only works on assignment, so i had to write

foreach(var i in ((RichInt)10).To(20)) {
  Console.WriteLine(i);
}

So I do have to use an extension method to create To() in C#.

And, yes, i'm grossly simplifying what scala's implicts can accomplish. Also, I wish I could have block scope using statements to import extension methods for just a block the way scala's import allows you to handle local scope implicits.