From: Kent Dahl <kentda+news@...>
Date: 2004-04-04T23:45:34+09:00
Subject: Re: good module use?

Bauduin Raphael wrote:
> I thought to create a module to add an instance variable representing 
> the connection to a database:
> 
> module MyDbModule

   class <<self
       attr :conn
   end

>       require "postgres"
>       pghost="localhost"
>       pgport=nil
>       pgoptions=nil
>       pgtty=nil
>       dbname="mydb"
>       user='mylogin'
>       password='mypassword'
>      
> @conn=PGconn.connect(pghost,pgport,pgoptions,pgtty,dbname,user,password)
> 
> end
> 
> However, this doesn't work. The Pickaxe describes modules as a group of 
> calsses, methods, constants, which my modules doens't respect (no method 
> defined).

The reason is that Module#attr creates accessor methods for the 
instances of the module (in reality, the instances of classes including 
the module). The @conn instance variable belongs to the MyDbModule 
object itself, so attr needs to be called in the scope the class of 
MyDbModule. It's due to a metaclass hierachy headache.

> Is there a way to achieve what I'm trying, and in the case that it would 
> be possible, is it a good approach?

I'd be more inclined to use singleton, and delay connecting to the 
database until it is needed.

-- 
(\[ Kent Dahl ]/)_    _~_    _____[ http://www.pvv.org/~kentda/ ]_____/~
  ))\_student_/((  \__d L b__/     Master of Science in Technology     )
( \__\_�|�_/__/ ) _)  Industrial economics and technology management (
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