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In JavaScript I can do the following:

  • File of some framework defines a class. (It called a prototype, but in general terms it is a class anyway)
  • I can add methods in that class and overload some its methods without changing the source file with the class definition.

Can I do the same in Ruby? Python?

I'm choosing a new platform for server-side development. I need something easy for AOP.


// Base file
function Foo() {}
Foo.prototype = {
    bar: function() {

// Module, which wants to extend the base
(function() {
    var original = Foo.prototype.bar;
    Foo.prototype.bar = function() {
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I believe that is possible in Ruby, there's also an AOP framework for Ruby: aquarium.rubyforge.org –  FrustratedWithFormsDesigner Jul 15 '11 at 14:27
@FrustratedWithFormsDesigner: your comment is a good answer. –  kevin cline Jul 15 '11 at 14:56
@kevin cline: I posted as a comment beacuse I really wasn't sure, as I'm not really a Ruby programmer, just someone who thinks it's neat but never gets much chance to work in in. ;) –  FrustratedWithFormsDesigner Jul 15 '11 at 14:56
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3 Answers

up vote 1 down vote accepted

I know you can in Ruby, all classes are open. So if you have class Foo in Foo.rb all you would have to do is declare the class like normal and then add your methods.

require 'Foo'
class Foo
    def addedFunctionality
          "This does nothing!"

Hopefully that is what you are looking for.

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Yes, you can do this in both Ruby and Python. I prefer Ruby, but my Python experience is limited. Programming Ruby is excellent, and contains complete, well-written documentation of Ruby meta-programming.

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The functionality that you are describing can be achieved in any language: for example in Java you could define your "prototype" as a HashMap, store objects inside it that implement your function and update those function objects from another part of the code base. Not particularly elegant, but it works.....

In Clojure (my current favourite language for server-side dev) you could do:

(def base-prototype-object 
     (fn [some-parameter] (do-whatever-you-like-with some-parameter))}

;; later in the code
(def extended-object-using-prototype
      (fn [some-parameter] (do-something-different-with some-parameter))}

Overall, I wouldn't make this capability the primary factor for choosing a language - library support, community, performance, robustness of platform, cross-platform portability, ability to leverage existing skills in the team etc. are are far more important.

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Although this functionality is indeed implementable in any language, the HashMap-based "object" implementation is really limited for languages such as Java and C++, where this is not the usual method for writing classes and most (if not all existing code) is not written with this support in mind. If you require extending core library classes (e.g. you're doing AOP), then I would choose a language with direct or native support for this (e.g. Python, Ruby, Clojure, ...). –  André Caron Jul 15 '11 at 14:52
@Andre - yes I agree, prototyped-based inheritance is rather unidiomatic in statically typed languages like Java/C++. I'm only trying to make clear that it isn't impossible (which some people think....) –  mikera Jul 15 '11 at 15:00
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