From: Xavier Noria <fxn@...>
Date: 2007-01-05T05:23:32+09:00
Subject: Re: What does "extend self" do?

On Jan 4, 2007, at 9:09 PM, Jeff wrote:

> I happened to be reading dependencies.rb in the Rails source, and it
> starts like this:
>
> require 'set'
> require File.dirname(__FILE__) + '/core_ext/module/ 
> attribute_accessors'
> require File.dirname(__FILE__) + '/core_ext/load_error'
> require File.dirname(__FILE__) + '/core_ext/kernel'
>
> module Dependencies #:nodoc:
>   extend self
> ...
>
>
> What is the "extend self" doing?  I thought at the top a module,  
> 'self'
> was pretty much an empty context at that point... but I guess not,
> since the writer obviously thinks self contains something worth
> extending...?

It extends the very module object. That's one-liner to add all the  
module instance methods as module functions. That is

   module Foo
     extend self
     def foo
       'foo'
     end
   end

allows the call Foo.foo.

To do it by hand you'd add a

   module_function :method

for each method.

-- fxn