From: Brian Candler <B.Candler@...>
Date: 2003-08-09T17:14:14+09:00
Subject: Re: Ruby and OOP-design (question of an old "procedural person" ;)

On Sat, Aug 09, 2003 at 04:47:10PM +0900, Meino Christian Cramer wrote:
>  Then I read about the new sort_by feature. This is exactly what I
>  need!
>  
>  But sort_by needs an array as input.
> 
>  And my "list"-object is an object (or a duck, which quaks ;) holding
>  and array...or what...or .... I got confused here.

  class List
    def sort!
      @list = @list.sort_by { |x| [x.freq, x.time] }
    end
  end

In other words, since you've wrapped Array in your List object, then you
give your List object a sort! method which sorts itself. This is an example
of the "has_a" / "delegation" design pattern: List contains (has_a) Array
instance, and List#sort passes on (delegates) the sort request to the object
it contains.

This is an excellent way of composing systems, but in this simple case you
might just want to use an Array directly and drop the List class. It depends
how much extra functionality you want to bundle in there. If there's not
much in 'List' on top of a standard Array, an alternative is to make class
methods which perform the specific operations you want on an array of your
special objects:

   class Broadcaster
     def Broadcaster.sort_by_freq(arr)
       arr.sort_by { |x| [x.freq, x.time] }
     end
   end

   stations = []                       # generic array
   stations << Broadcaster.new(...)
   ...
   stations = Broadcaster.sort_by_freq(stations)

>  Is this "design" ok (in the sense of OOP)?

I'd say it looks pretty sound (no pun intended!)

Regards,

Brian.