From: dblack@...
Date: 2003-01-11T03:18:19+09:00
Subject: Re: attr_reader/writer vs. attr_accessor w/ access control

Hi --

On Sat, 11 Jan 2003, Mauricio [iso-8859-1] Fern�ndez wrote:

> On Fri, Jan 10, 2003 at 08:38:50AM +0900, Tom Sawyer wrote:
> > On Thursday 09 January 2003 03:57 pm, Mauricio Fern�ndez wrote:
> > > That would not happen if accessors were, say, protected by default. But
> > > then you'd have to 'publicize' them anyway, and the situation wouldn't
> > > be that different from the current one.
> > >
> > > OTOH if instance variables were private (not accessible by subclasses)
> > > all this would be much more relevant. I really felt that this was
> > > The Right Thing but matz doesn't [55201]. I think the main point was
> > > that inheritance is anyway a very strong relationship, so this apparent
> > > breach in data hiding is not that important.
> >
> > that's it! that's it! i've been pulling my hair out since the beginning of my
> > rubyist days deciding when it is the Right Thing to use @var vs. self.var.
> > And finally it has become clear! the answer is simple: NEVER USE @ OUTSIDE A
> > GETTER OR SETTER METHOD. what, you say? indeed! in fact, with use of the
>
> Then take into account that this goes against matz's word [55201], for
> if @var were never to be used, it would not exist in the language and
> instance vars. would be class-local by default.
> I have to ponder about this some more, but I have the feeling @iv is
> needed sometimes.

  ruby-1.6.8$ grep "^[[:space:]]\+@[A-Za-z_]\+ \?= \?" \
              `find . -name '*.rb'` | wc -l
              1026

:-)

In fact, I tend to think the attr_* shortcuts, while very useful,
sometimes lead to the impression that there's a closer connection
between attribute accessor methods and instance variables than there
really is.  The presence of such methods, and the use of instance
variables, can vary independently.

For example:

  class A
    def some_attribute
      100
    end
  end

or

  class B
    def some_attribute
      @var
    end
  end

or

  class C
    attr_reader :some_attribute
    def some_attribute=(x)
      @some_attribute = x * 10
    end
  end

and so on.


David

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