Comments on: Remedial Scala: Emulating C# Extension Methods

By: dave

dave — Thu, 22 Jan 2009 22:51:51 +0000

Thanks. I also enjoyed your article. For some reason the line “Try to ignore the static, people!” made me laugh. Anyway, as the title suggests, I’m still learning Scala, but my impression is that Scala’s implicit conversions, like extension methods, are bound at compile time (Scala doesn’t have a static keyword). However, the conversion method may return an object of any type it wishes and the method is actually called on that returned object. I think this is why Ricky says that C#’s extension methods are less flexible above. I’m still learning. This post seems to give an example of more powerful usage, but it’s assumes a pretty good knowledge of Scala.

Thanks again for the comment.

By: Ruben Verborgh

Ruben Verborgh — Thu, 22 Jan 2009 20:15:14 +0000

Hi,

Interesting article. I just blogged about the problems associated with the static binding of extension methods. (http://ruben.3click.be/blog/extension-methods-silent-static-slaves)

I’m not familiar with Scala, but the code of the stringToWords function makes it look like the binding happens at runtime, as I don’t see a “static” keyword. Is that correct? If so, it would mean that this technique is actually a lot better then extension methods.

By: dave

dave — Wed, 21 Jan 2009 12:42:30 +0000

Thanks for the tip. I originally wrote WordCounter as a separate class, but changed it when I found this less verbose version. I wouldn’t have guessed that that “anonymous” type would result in reflection. Do you think a case like this is an instance of a compiler that just isn’t smart enough yet, or is it by design? If Scala were more widely adopted, I’d really worry about performance hits like this being hidden in the concision of the language. My software is already usually really slow :)

By: Ricky Clarkson

Ricky Clarkson — Wed, 21 Jan 2009 08:27:37 +0000

Calls to wordCounts will use reflection (as that uses structural typing). It’s better to create a named type containing wordCounts:

implicit def stringToWordCounter(s: String) = WordCounter(s)
case class WordCounter(s: String) {
def wordCounts…
}

Yes, it’s more repetitive, but it’s faster. C#’s extension methods have no runtime overhead, are simpler to write and much less flexible.