From: dblack@...
Date: 2003-08-17T01:28:22+09:00
Subject: Re: Newbie Q: Data encapsulation with Ruby

Hi --

On Sun, 17 Aug 2003, Mauricio [iso-8859-1] Fern�ndez wrote:

> On Sun, Aug 17, 2003 at 01:02:45AM +0900, Dan Doel wrote:
> >
> > P.S.: It's also the case that people can add methods to your class to
> > access private data
> > you don't want them to. That's just a part of ruby.  I believe the
> > #freeze method prevents
> > that, though.
>
> They can also use instance_eval, or add singleton methods to the object.
> Now, if you cannot trust the people you're working with not to break
> your design you're screwed, no matter the language or the technology.

The one sort of "innocent" area where the Ruby attribute conventions
can also cause breakage is in the return values of reader methods --
those values being, of course, references:

  class C
    attr_accessor :s
  end

  c = C.new
  c.s = "hello"
  s = c.s
  s << " there"     # looks innocently local, but....
  p c.s             # "hello there"

One can get around this with dup'ing and/or freeze'ing, but I think it
may just be that the referential nature of Ruby variables and the
concept of an object being in charge of its own state are somewhat
in conflict.

(One can also get around this by not doing it, but for some reason it
strikes me as something that could happen inadvertently.)


David

-- 
David Alan Black
home: dblack@superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav