From: Francis Cianfrocca <garbagecat10@...>
Date: 2006-05-23T05:32:28+09:00
Subject: Re: initializing instance variables in a module

You still have to call it every time you use the variable.

On 5/22/06, dblack@wobblini.net <dblack@wobblini.net> wrote:
> Hi --
>
> On Tue, 23 May 2006, Jeff Rose wrote:
>
> > Well, it took a while but I found the answer.  This is done in ActiveRecord
> > to wrap a possible setup method in the unit tests for auto-instrumentation of
> > fixtures.  Once I knew what to look for, however, I found an old post by
> > Florian Gross that lays out the exact answer nicely:
> >
> > http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/129834
> >
> > For educational purposes though, I'll explain a few things I found...
> >
> > 1) The append_features method is deprecated, and the included method is now
> > the preferred callback.  This method is called when a module is included, and
> > it is passed the module that has done the including.
> >
> > 2) There is another callback, method_added, which is a meta-class method that
> > is called every time a new method is defined for its class, and the symbol
> > for the method name is passed.
> >
> > So, the trick is to add a custom method_added method to the meta-class of the
> > class that does the including by extending it in the included callback.  The
> > custom method_added needs to redefine initialize after it is added so that it
> > does the custom setup, then calls the original.
> >
> > Phew...  Too bad we can't just have another callback that lets us do this
> > easily.  Maybe that feels too much like multiple inheritance or something?
> >
> > module Foo
> >  def module_initialize
> >    @myvar = Hash.new {|k,v| k[v] = []}
> >  end
> >
> >  def bar(key)
> >    @mybar[key]
> >  end
> > end
> >
> > Isn't this a common thing to want?
>
> I'm probably being thick but what's wrong with just writing a method
> that wraps @myvar and initializes it if necessary, and then returns
> it?
>
>
> David
>
> --
> David A. Black (dblack@wobblini.net)
> * Ruby Power and Light, LLC (http://www.rubypowerandlight.com)
>    > Ruby and Rails consultancy and training
> * Author of "Ruby for Rails" from Manning Publications!
>    > http://www.manning.com/black
>
>