From: ptkwt@... (Phil Tomson)
Date: 2005-11-23T18:47:26+09:00
Subject: Re: pattern: auto-running module init code

In article <3736dd30511230027i2d31677aw4f36c01d289636f0@mail.gmail.com>,
Sean O'Halpin  <sean.ohalpin@gmail.com> wrote:
>Hi Phil,
>
>You can also use super:
>
>class Bar
>  def initialize(*args, &block)
>    puts "in Bar"
>    super
>  end
>end
>
>class Foo < Bar
>  def initialize(*args, &block)
>    puts "in Foo"
>    super
>  end
>end
>
>f =3D Foo.new
>
>module Mod
>  def initialize(*args, &block)
>    puts "in Mod"
>    super
>  end
>end
>
>class Foo
>  include Mod
>end
>
>f =3D Foo.new


Ah, that would be too simple ;-)  And the user of the module has to remember 
to call 'super' somewhere in the constructor, I was trying for something more 
automatic :)  

Hmmm...This brings up another thought:  Just like C++ programmers are often 
advised to go ahead and make their methods virtual in case someone comes along 
and subclasses, should we be generally calling super in our constructors in case 
someone comes along and mixes-in a module with an 'initialize' method defined? 



>
>--- OUTPUT ---
>in Foo
>in Bar
# after the 2nd f.new:
>in Foo
>in Mod
>in Bar
>
>or Module.included
>
>class Bar
>  def initialize(*args, &block)
>    puts "in Bar"
>    super
>  end
>end
>
>class Foo < Bar
>  def initialize(*args, &block)
>    puts "in Foo"
>    super
>  end
>end
>
>module Mod
>  def self.included(obj)
>    puts "in Mod"
>  end
>end

Perhaps, but isn't 'obj' in this case actually the including class? 

to make it more clear, change to:
  module Mod
    def self.included(obj)
      pus "in Mod: obj is: #{obj} #{obj.class}"
    end
  end

>
>class Foo
>  include Mod
>end
>

Then the output will be:

  in Mod: obj is: Foo Class

and it is called even before there is any instance of Foo created.  So any 
initialization code you want to run by using 'included' will be class-level 
initialization, not instance-level.  That may or may not be what you want.

Phil