I’m Wrong Because Ruby and Powershell Are Mainstream

Brad Wilson and Scott Hanselman took me to task for my comment the other day that no “mainstream” language had implemented extension methods:

How mainstream is Ruby on Rails for you? Ruby is a full fledged dynamic language. No hacks for “extension methods” (Brad)

Ya, I kind of blanched at that statement too…method_missing is pretty mainstream… (Scott)

They’re right, Ruby does support the addition (and redefinition I think) of methods on a class at any time. There’s a sample of this in the Classes and Objects chapter of Programming Ruby (aka the pick-axe book) where they add a basic documentation facility “available to any module or class” in Ruby by adding a doc instance method to the Module class.


class Module 
  @@docs = Hash.new(nil) 
  def doc(str) 
    @@docs[self.name] = str 
  def Module::doc(aClass) 
    # If we’re passed a class or module, convert to string
    # (‘<=’ for classes checks for same class or subtype)
    aClass = aClass.name if aClass.type <= Module 
    @@docs[aClass] || “No documentation for #{aClass}”

Given how Ruby classes are defined, I think the newly added methods have access to the private data of the class. Extension methods in C#3/VB9 only have access the public interface of the object. But that’s a fairly minor difference.


FYI, Powershell can do this as well, though not as succinctly as Ruby. Scott has an example how you can add a DatePhotoTaken property to System.IO.FileInfo using Omar Shahine’sPhotoLibrary project.

Chalk this up to my continuing ignorance of dynamic languages. I’m working on it, albeit slowly.

4 thoughts on “I’m Wrong Because Ruby and Powershell Are Mainstream

  • Anonymous

    The biggest questions is – why invent another language for PowerShell if there are so many great popular languages already in existance?

  • Jeffrey Snover

    > The biggest questions is – why invent another language for PowerShell if > there are so many great popular languages already in existance?

    Try it and you’ll see. I’m not aware of a language that has as wide a dynamic range as PowerShell (Please point one out if you know of one). Bruce Payette’s book, PowerShell in Action provides both a great language reference as well as the reasoning behind the decisions we made in producing PowerShell (Bruce is the dev lead for the language).

    Jeffrey Snover [MSFT]
    Windows PowerShell/MMC Architect
    Visit the Windows PowerShell Team blog at: http://blogs.msdn.com/PowerShell
    Visit the Windows PowerShell ScriptCenter at: http://www.microsoft.com/technet/scriptcenter/hubs/msh.mspx

  • DevHawk

    orchmid, Ruby not only allows you to inject methods into objects, but into classes as well. Extension Methods in C#3/VB9 act at the class level. Javascript doesn’t really have classes and I don’t know Python well enough to comment.

    As for why to invent another language, I certainly don’t think a single lanugage feature is enough to argue for or against the existence of the PowerShell language. I fraking love PowerShell, and it has nothing to do with the ability to add new methods to classes.

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