From: Robert Dober <robert.dober@...>
Date: 2008-06-28T01:59:43+09:00
Subject: Re: Is it ellegant to use a global variable to store a Logger object?

On Fri, Jun 27, 2008 at 11:40 AM, Robert Dober <robert.dober@gmail.com> wrote:
> On Fri, Jun 27, 2008 at 10:17 AM, Shot (Piotr Szotkowski) <shot@hot.pl> wrote:
>> Iñaki Baz Castillo:
>>
>>> El Jueves, 26 de Junio de 2008, Shot (Piotr Szotkowski) escribió:
>>
>>>> module MyProgram
>>>>   class Logger
>>>>   class << self
>>>>     def debug …
>>>>       …
>>>>     end
>>>>   end
>>>>   end
>>>> end
>>
>>> Ok, this seems really ellegant and I've tested that I can call
>>> "Logger.debug..." in any submodule/subclass into the program :)
>>
>> :)
>>
>>> Just a question: Logger must use an instance of a class (real
>>> class Logger), so to store it I think the best option is using
>>> a @@class_variable into Logger module
>>
>> No – by using class << self, you're operating on the Logger object
>> (an instance of the class Class), and you can access its *instance*
>> variables.
> <snip>
> Amen
>
> grep --recursive '@@' lib && echo "Classvariables are the root of all evil ;)"
>
> Cheers
> Robert
>


They are shared by all subclasses, look at this
irb(main):006:0> class A
irb(main):007:1> @@a = self
irb(main):008:1> end
=> A
irb(main):009:0> class B < A
irb(main):010:1> @@a = self
irb(main):011:1> end
=> B
irb(main):013:0> A.send :class_variable_get, :@@a
=> B

this was bad enough for me never wanting have to do with them again,
now look at this

irb(main):014:0> class A
irb(main):015:1> @a = self
irb(main):016:1> end
=> A
irb(main):017:0> class B < A
irb(main):018:1> @a = self
irb(main):019:1> end
=> B
irb(main):020:0> A.instance_variable_get :@a
=> A
irb(main):021:0> B.instance_variable_get :@a
=> B

HTH
Robert




-- 
http://ruby-smalltalk.blogspot.com/

---
AALST (n.) One who changes his name to be further to the front
D.Adams; The Meaning of LIFF