From: "David A. Black" <dblack@...>
Date: 2005-09-21T20:57:05+09:00
Subject: Re: Problem with constants

Hi --

On Wed, 21 Sep 2005, HaPK wrote:

> Kroeger Simon (ext) wrote:
>
>> I'm puzzled:
>> -----------------------
>> class X
>>  A = 1
>>  def X.a
>>    A
>>  end
>> end
>> 
>> class Y < X
>>  A = 2
>> end
>> 
>> class Z < X
>>  A = 3
>>  def Z.a
>>    A
>>  end
>> end
>> 
>> p X.a #=> 1
>> p Y.a #=> 1
>> p Z.a #=> 3
>> -----------------------
>> (ruby 1.8.2 (2004-12-25) [i386-mswin32])
>> 
>> Shouldn't this yield at least a warning?
>> Is this a feature?
>> 
> Since A is not a class variable (it's a local variable) it's saved in "X.a" 
> closure. In Y class it doesn't exist, so it can't influence on "X.a" method.

Actually A is a constant, not a local variable, and method definitions
aren't closures.  I'm pretty sure that what's happening is that the
constant references are being resolved at compile-time, so that by the time
Y.a is run, the reference inside X.a has been permanently resolved to
X::A.

See what happens when you make this change:

   def X.a
     const_get("A")
   end

Now the constant is being resolved dynamically, and you'll get 1/2/3
in the output.


David

-- 
David A. Black
dblack@wobblini.net