From: dblack@...
Date: 2003-08-17T09:33:03+09:00
Subject: Re: Newbie Q: Data encapsulation with Ruby

Hi --

On Sun, 17 Aug 2003, Joe Cheng wrote:

> > Ruby is good this way: objects can choose to expose their state
> > directly, *but then they can change to having more complex method-based
> > access.* [emphasis added]
>
> Once again, Dave Thomas hits the nail on the head.  The reason attr_reader
> and attr_writer are OO-approved (at least, to the degree that Java getX and
> setX accessors are) is because you can override their behavior later.  The
> same would not be true of making Java fields public, since there is no way
> you can "intercept" direct field access and no way to write methods that
> look like direct field access.  (I think the same is true in C++?)

Ruby also has the #private method (referred to wrongly by me, earlier,
as a keyword), so you could do for example:

  class C
    attr_reader :a
    private
    attr_writer :a
    def something
      # you can use #a= here
    end
  end

  C.new.a = 1    # error -- private method called

In other words, you can layer access levels on top of the
attr_*-generated methods (and others, of course).


David

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