From: Lars Olsson <lasso@...>
Date: 2011-04-11T18:55:23+09:00
Subject: Re: Copying parameters to singleton class

On 11 Apr, 11:36, Jesús Gabriel y Galán <jgabrielyga...@gmail.com>
wrote:
> On Mon, Apr 11, 2011 at 11:20 AM, Lars Olsson <la...@lassoweb.se> wrote:
> > Hi list!
>
> > I have a metaprogramming question that is driving me mad. I though I
> > understood how to do it, but obviously I didn't. This is what I want
> > to do:
>
> > I want to create a class method that takes a bunch of options and
> > returns a singleton class with those options set,
>
> > class Opportunities
> >  def self.using(options)
> >    # Store options in singleton class variable @options and then
> > return singleton class
> >  end
> >  def self.options
> >    return @options
> >  end
> > end
>
> > So that I can use:
>
> > foo = Opportunities.using({:one => 1, :two: => 2, :three => 3})
> > bar = Opportunities.using({:four => 4, :five: => 5, :six => 6})
>
> > and then
>
> > foo.options => {:one => 1, :two: => 2, :three => 3}
> > bar.options => {:four => 4, :five: => 5, :six => 6}
>
> > Please note that I don't want instances of the Opportunities class, I
> > want two separate classes that shares the same behavior except for
> > that they return different values for the Opportunities.options call.
>
> If you don't want instances of Opportunities, of which class you want instances?
> Where is the common behaviour of those objects defined?
>
> > This really should be possible with ruby, right?
>
> I'm not sure if I understand what you want, can you tell us why this
> doesn't fit your requirements:
>
> ruby-1.8.7-p334 :005 > class Opportunities
> ruby-1.8.7-p334 :006?>   attr_reader :options
> ruby-1.8.7-p334 :007?>   def initialize options
> ruby-1.8.7-p334 :008?>     @options = options
> ruby-1.8.7-p334 :009?>     end
> ruby-1.8.7-p334 :010?>   def self.using options
> ruby-1.8.7-p334 :011?>     new(options)
> ruby-1.8.7-p334 :012?>     end
> ruby-1.8.7-p334 :013?>   end
>  => nil
> ruby-1.8.7-p334 :014 > foo = Opportunities.using({:a => 3, :b => 4})
>  => #<Opportunities:0xb7496418 @options={:b=>4, :a=>3}>
> ruby-1.8.7-p334 :015 > foo.options
>  => {:b=>4, :a=>3}
> ruby-1.8.7-p334 :016 > bar = Opportunities.using({:a => 5, :b => 10})
>  => #<Opportunities:0xb748e22c @options={:b=>10, :a=>5}>
> ruby-1.8.7-p334 :017 > bar.options
>  => {:b=>10, :a=>5}
>
> Jesus.

Actually, I don't want any instances at all. I would have preferred to
use instances myself, but since my task involves calling a framework
method that takes a class and not an "ordinary" instance I needed a
hack to be override the options method. Robert's solution does exactly
what I need.

Thank you for your speedy answers!

/lasso