From: "Ara.T.Howard" <Ara.T.Howard@...>
Date: 2005-07-12T07:59:03+09:00
Subject: Re: class_attr_accessor

On Tue, 12 Jul 2005, Jeffrey Moss wrote:

> I think it only gets tricky like you've pointed out if you're trying to do
> default variable initialization values, but on the other hand this is
> probably 99% of the useful purposes of a class_attr is with a default value
> set.  So your point is well taken.

right you are.  it bit me a few times and was ending up writing things like

   class A
     class << self
       attr 'a'
       attr 'b'
       def init
         self.a = 42
         self.b = 'forty-two'
       end
       def inherited subklass
         subklass.init
         super
       end
     end
     self.init
   end

   class B < A
     self.b = 42.0
   end

all over the place.

which starts being kinda ugly.  i found that i almost always wanted class
varibles to essentially call 'super' when not over-ridden - in otherwords to
get a reasonable value from the parent class - but this is not possible with
either @@vars or @vars without some trickery.  so i wrote it once and called
it traits.  ;-)


btw.  one of the things i like most about traits is that combination
getter/setter reads so well for exactly the case of class inheritence/default
values:

   require 'traits'

   class Package
     class << self
       trait 'size' => 42
       trait 'weight' => 42
     end
   end

   class LightPackage
     weight 4.2
   end

   class HeavyPackage
     weight 420
   end

and this works like it looks - all still have size 42.

cheers.

-a
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