From: Sean O'Halpin <sean.ohalpin@...>
Date: 2005-10-07T03:02:05+09:00
Subject: Re: techniques for module to contribute to initialize() of its including classes

On 10/6/05, ES <ruby-ml@magical-cat.org> wrote:
> Robert Klemme wrote:
> > itsme213 wrote:
> >
> >>What are good design techniques for this e.g. if the module adds some
> >>instance variables to its included class?
> >>
> >>module M
> >>  def f
> >>    @f
> >>  end
> >>  # how to initialize @f ?
> >>end
> >>
> >>class A
> >>  include M
> >>end
> >>Thanks.
> >
> >
> > Do it like this and the module initialite will seamlessly integrate into
> > the class inheritance chain:
> >
> > module M
> >   def initialize(*a,&b)
> >     super
> >     @f = 10
> >   end
> > end
>
> This does not work directly if the class itself defines an #initialize
> as it will take precedence over the module version.
>
It works if you call super from within the class initialize. The
module is inserted into the inheritance chain before any superclasses.

module M
  def f
    @f
  end
  # how to initialize @f ?
  def initialize(*args, &block)
    puts "in M.initialize"
    super
    @f = 10
  end
end

class A
  def initialize(*args, &block)
    puts "in A.initialize"
    super
  end
end

class B < A
  include M
  def initialize(*args, &block)
    puts "in B.initialize"
    super
  end
end

b = B.new
p b.f

__END__
in B.initialize
in M.initialize
in A.initialize
10

Sean