From: Gavin Kistner <gavin@...>
Date: 2005-07-13T12:30:41+09:00
Subject: Initialization via a Module

I have a module that needs to set a few instance variables on the  
instances it is used with, during initialization.

I wrote a library that did this a while ago, and I really thought it  
was working fine when I left it. It had code like this:

module Foo
   attr_reader :foo
   def initialize
     @foo = 'foo'
     super
   end
end

class Bar
   include Foo
   attr_reader :bar
   def initialize
     @bar = 'bar'
   end
end

b = Bar.new
p b.foo

...but Foo#initialize is not being called. Am I wrong? Did I leave my  
library in a broken state, despite calling it 1.0.3 and releasing it  
and using it? Or did the above used to work? (In 1.8.1 or 2 or so?)


Anyhow, I cobbled the following together, and it works, but...is  
there a better/cleaner way to do the following:

module Foo
   attr_reader :foo
   def self.included( klass )
     klass.instance_eval{
       alias_method :_pre_foo_initialize, :initialize
       define_method( :initialize ){ |*args|
         _setup_foo
         _pre_foo_initialize( *args )
       }
     }
   end

   def self.extended( obj )
     obj.instance_eval{ _setup_foo }
   end

   private
     def _setup_foo
       @foo = 'foo'
     end
end

class Bar
   attr_reader :bar
   def initialize( bar )
     @bar = bar
   end
   include Foo
end

class Cow
   attr_reader :cow
   def initialize
     @cow = 'cow'
   end
end

b = Bar.new( 'bar' )
p b.bar
p b.foo

c = Cow.new
c.extend( Foo )
p c.cow
p c.foo

--
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