From: Robert Dober <robert.dober@...>
Date: 2010-11-02T04:51:51+09:00
Subject: Re: the dark side of inherited methods

On Mon, Nov 1, 2010 at 12:49 AM, James Edward Gray II
<james@graysoftinc.com> wrote:
> On Oct 31, 2010, at 5:30 PM, timr wrote:
<snip>
> It is a problem with inheritance and another reason why inheritance is almost never what we want.

Completely agree with this. Apart of the code you suggested I would
like to tackle the problem on a conceptional level. Enumerable#map
returns arrays Period. What OP might want to do is something like this

module Sequence
  include Enumerable
  # A sequence is defined by
  # (i) How to traverse it
  #   def each &blk
  # making sure that blk is called with exactly all elements of the
sequence in the
  # predefined order
  # (ii) How to append elements to it
  #   def add new_element
  # creating a new sequence (or modifying in place)
  def map &blk
    inject(self.class.new) do | result, ele |
      result.add blk.( ele )
    end
  end
end # module Sequence

If OP had had this available the delegation would have worked quite well.

class Vector
   include Sequence
   def each; # as he needs (must yield all elements)
   def add;  # as he needs (must return a Sequence)

No inheritance and yet quite some effective decomposition :P

HTH
R.

-- 
There are worse things than having people misunderstand your work. A
worse danger is that you will yourself misunderstand your work.
-- Paul Graham