From: David Alan Black <dblack@...>
Date: 2004-04-08T12:24:18+09:00
Subject: Re: Preferred Instance Variable Access Method

Hi --

Jean-Hugues ROBERT <jean_hugues_robert@yahoo.com> writes:

> Hi,
> 
> At 05:34 08/04/2004 +0900, you wrote:
> What's the preferred way of accessing a class's instance variables?
> 
> I tend to use @var instead of self.var (I guess var() would work, and
> var too).
> 
> I see two advantages:
>    1) Faster (I never benchmarked however)
>    2) Lines starting with @ are like methods with ! at the end =>
>          Draw the attention to probable side effect on obj's state.

Don't forget, though, that these techniques (@var vs. self.var) are
only equivalent in certain simple (and common, but not unique) cases.
If you're doing anything more complex, like:

  def var=(x)
    @var = x.to_s.upcase
  end

then you don't have a choice; you have to go through the method
(self.var = y) rather than just doing @var = y, elsewhere in the
class.  

(The original question involved another level of remove (wrapping the
attr_* methods themselves in "var_get" and "var_modify" methods, but
wherever they occur, @var = and self.var= are not automatically
equivalent.)

This also points to a constraint on Eric's point about not wanting to
worry about forgetting the 'self' -- namely, that you can only do that
when you know for sure that #var= is a simple set method for @var.
Also, the @var = y technique could come back to bite you if you
reimplement the setter method and haven't routed your assignments
through it:

  attr_accessor :var
  def initialize(y)
    @var = y        # OK until you reimplement #var= to do something
  end               # non-simple, at which point you have to remember
                    # that you assigned directly to @var here.

(I would have quoted Eric directly except I'm posting directly to
comp.lang.ruby, because of the gateway problems, and Eric's posts
don't seem to be making it here :-(


David

-- 
David A. Black
dblack@wobblini.net