From: 7stud -- <bbxx789_05ss@yahoo.com>
Newsgroups: comp.lang.ruby
Subject: Re: Making a simple parser
Date: Mon, 18 Apr 2011 15:22:05 -0500
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7stud -- wrote in post #993588:
>
> Note that when inherited() is called, the methods of the subclass are
> not defined yet, so if you create objects of the subclass inside
> inherited(), the initialize() method in the parent is called.
>

And you can get around that problem by letting InputFormat#parse create 
the objects:

class InputFormat
  @children = []

  def self.children
    @children
  end

  def initialize(input)
    @input = input
  end

  def parse
    InputFormat.children.each { |child|
      instance = child.new
      instance.parse(@input) if instance.supported?
    }
  end

  def self.inherited(sub_class)
    @children << sub_class
  end
end



class InputFormatA < InputFormat
  def initialize
    puts "Initializing instance of #{self.class}"
  end

  def supported?
    true
  end

  def parse(str)
    puts "InputFormatA is parsing #{str}"
  end
end

class InputFormatB < InputFormat
  def initialize
    puts "Initializing instance of #{self.class}"
  end

  def supported?
    true
  end

  def parse(str)
    puts "InputFormatB is parsing #{str}"
  end
end



input = InputFormat.new('hello world')
input.parse

--output:--
Initializing instance of InputFormatA
InputFormatA is parsing hello world
Initializing instance of InputFormatB
InputFormatB is parsing hello world

-- 
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