From: Michael Fellinger <m.fellinger@...>
Date: 2010-06-20T01:20:26+09:00
Subject: Re: General Ruby OOP question

On Sun, Jun 20, 2010 at 12:37 AM, Ammar Ali <ammarabuali@gmail.com> wrote:
> On Sat, Jun 19, 2010 at 4:56 PM, Paul A. <cyril.staff@gmail.com> wrote:
>> But is it ethics? I mean, is that lawful under the principles of
>> object-oriented programming. Maybe this is so much power, to pass self
>> inside person instance inside its home... 'cause it's almost as if there
>> was no class, no partitioning.
>
> There is nothing wrong from an OOP point of view with one object
> containing a reference to another object. Even in the real world, it
> makes sense that a person knows where their home is.
>
> In some languages, like C++, this can introduce some typing and API
> complications, but not in Ruby where methods are invoked by sending
> messages to the objects.
>
> The problems that you might have with this approach are related to
> design requirements. For example, what if one person can, optionally,
> have more than one home?

I think I'd model it somewhat like this (untested):

class Window
  attr_accessor :open
end

class Home
  attr_accessor :window

  def initialize
    @window = Window.new
  end
end

class Person
  attr_accessor :location

  def enter(location)
    self.location = location
  end

  def open_window
    if location.window.respond_to?(:open=)
      location.window.open = true
    else
      raise("The location doesn't have any windows you can open")
    end
  end
end

guy = Person.new
home = Home.new
guy.enter(home)
guy.open_window

-- 
Michael Fellinger
CTO, The Rubyists, LLC