From: "David A. Black" <dblack@...>
Date: 2008-09-30T18:32:59+09:00
Subject: Re: extend keyword in class definition

Hi --

On Tue, 30 Sep 2008, ruud grosmann wrote:

> Hi list,
>
> I am reading the book 'design patterns in ruby'. On page 201 I find
> this code example:
>
> require 'forwardable'
>
> class WriterDecorator
>    extend Forwardable
>
>    def_delegators :@real_writer, :write_line, :rewind, :pos, :close
>
>    def initialize (real_writer)
>       @real_writer = real_writer
>    end
> end
>
>
> I am a bit surprised by the 'extend Forwardable' line. Can anybody
> explain me what this is? Is it the same as 'include Forwardable' or is
> it the same as 'class WriterDecorator < Forwardable'?

It's like a per-object include operation.

   module M
     def speak
       puts "Hi!"
     end
   end

   obj = Object.new
   obj.extend(M)
   obj.speak       # "Hi!"

The example you've got extends the class object WriterDecorator. It's
like this:

   class C
     extend M
   end

   C.speak         # "Hi!"


David

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