From: Robert Klemme <bob.news@...>
Date: 2005-04-16T18:29:34+09:00
Subject: Re: Why specify module names redundantly in Modules?


"Paul Battley" <pbattley@gmail.com> schrieb im Newsbeitrag 
news:2ab6a502050415181312665afb@mail.gmail.com...
>> All that class and extend stuff some people are doing here is 
>> unnecessary,
>> as far as I can tell.
>
> Once you have three or more methods, 'extend self' once makes for less
> typing than 'self.' prepended to each method name.  Is that a good
> reason?  You choose.

It's different from a semantical point of view: if you make a module extend 
itself then you have those methods as instance methods (i.e. instances of 
classes that include this module) as well as class methods.  If you just 
define them using def "sef.foo()..." then there are no instance methods.

Personal note: I don't like the idiom "module X; ... extend self end" 
because it mixes module usage as mixin and namespace.  You define instance 
methods only to conveniently define them as class methods.  Using "module X; 
class<<self; def ... end end" or using "def self.foo..." is only slightly 
more verbose but avoids this problem.  I normally use a module *either* as 
mix in (in that case I define instance methods) *or* as a namespace (in that 
case I define class methods and classes inside the module).

# note the spelling "module" not "Module".
module Foo
   def bar() "instance" end

   # note: self == Foo, so these
   # two are equivalent:
   def self.bar() "class" end
   def Foo.bar() "class" end
end

class X
  include Foo
end

in IRB:

>> Foo.bar
=> "class"
>> X.new.bar
=> "instance"

HTH

Kind regards

    robert