From: "David A. Black" <dblack@...>
Date: 2004-04-24T01:14:07+09:00
Subject: Re: attr_accessor vs. local variable

Hi --

On Sat, 24 Apr 2004, Its Me wrote:

> Ruby not seem to predictably recognize attribute accessors (including
> setters) as such unless preceded by "self.attr".  But it recognizes other
> self messages fine. I suspect this has something to do with its rule on what
> is deemed a local variable.

That's correct, except that there's nothing unpredictable about it, and
it's not specific to methods defined with the attr_* family.  

> What rule / ambiguity causes this?
> 
> class A
>   attr_accessor :x, :y
> 
>   def initialize
>     p x      # local or @x?

Strictly speaking, neither; in your example, it's a call to the method
x (which you happen to have defined as <def x; @x; end>, but could
have defined in many different ways).

>     x=5      # does not call self.x=

If it looks like a local variable assignment, then Ruby will define a
local variable of that name at compile time, and will execute the
assignment at runtime.  Since all bare "var = value" expressions get
claimed by this process, the way to insulate calls to '=' methods is
to make the receiver explicit:

>     self.y=5      # sets @y

which means it can no longer be interpreted as a variable assignment.


David

-- 
David A. Black
dblack@wobblini.net