From: Jos Backus <jos@...>
Date: 2004-12-02T16:21:04+09:00
Subject: Re: Accessing class constants from within a module?

On Thu, Dec 02, 2004 at 01:56:49PM +0900, Michael C. Libby wrote:
> You probably don't want to do that anyway. If you change to Debug::DEBUG
> in the class definitions, you'll be modifying a constant which can only
> have one value at a time. You want two different values (and you can't
> really tell the module to figure out which class constant is which
> without a lot of headaches), so maybe just set it as a default instance
> variable in your new objects?
 
Joel's solution was what I was looking for originally (thanks Joel!) but your
solution admittedly works well too. Thanks for that, Michael.

Another approach I tried was using a class variable but that doesn't work
either, presumably because it is likewise trying to find @@debug in Debug, not
the including class:

lizzy:~% cat n
module Debug
  def debug(level, msg)
    puts msg unless level > @@debug
  end
end

class C1
  @@debug = 1
  include Debug
  def foo
    debug(1, "this is foo")
  end
end

class C2
  @@debug = 1
  include Debug
  def bar
    debug(2, "this is bar")
  end
end

C1.new.foo
C2.new.bar
lizzy:~% ruby n
n:3:in `debug': uninitialized class variable @@debug in Debug (NameError)
        from n:11:in `foo'
        from n:23
lizzy:~% 

Cheers,
-- 
Jos Backus                       _/  _/_/_/      Sunnyvale, CA
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jos at catnook.com        _/_/   _/_/_/          require 'std/disclaimer'