From: GOTO Kentaro <gotoken@...>
Date: 2002-08-08T05:05:09+09:00
Subject: Re: Inherited question

At Thu, 8 Aug 2002 04:17:17 +0900,
Alan Chen wrote:

> I'm playing around with the inherited hook and I'm having some problems.
> The following code is running on "ruby 1.6.7 (2002-03-19) [i386-linux]".
> It works fine when I leave the inherited def out, and explicitly register
> the child class.  However, if I attempt the same with the hook, I get the
> following error:
> 
> check-inherited.rb:9:in `initialize': wrong # of arguments(0 for 1) (ArgumentError)
> 	from check-inherited.rb:9:in `new'
> 	from check-inherited.rb:9:in `register'
> 	from check-inherited.rb:5:in `inherited'
> 	from check-inherited.rb:20

> ### check-inherited.rb
> 
> class Base
>   @@childitems = {}
>   
> #   def self.inherited(subclass)
> # 	self.register(subclass)
> #   end
> 
>   def self.register(subclass)
> 	item = subclass.new
> 	@@childitems[item.name] = item
>   end	
> 
>   attr_reader :name
>   
>   def initialize(name)
> 	@name = name
>   end
> end
> 
> class Sub1 < Base
>   def initialize
> 	super('child_sub1')
>   end
> end
> 
> # not called when testing with self.inherited commented-in
> Base.register(Sub1)
> 
> ### end of file

Class#inherited would be called when the line "class Sub1 < Base" is
evaluated.  In the time, Base#initialize is not defined yet and the
arity (i.e. # of args) of Sub1.new is 1, which is same to Base.new's
because the arity of Base#initialize is 1.

The following sketches the problem. 

  class A
    def initialize(x) end
  end

  class B < A
  end

# p B.new # uncomment and will get ArgumentError

  class B
    def initialize() end
  end

  p B.new

-- Gotoken