From: Lars Olsson <lasso@...>
Date: 2011-04-12T17:30:41+09:00
Subject: Re: Copying parameters to singleton class

On 12 Apr, 09:00, Robert Klemme <shortcut...@googlemail.com> wrote:
> On Tue, Apr 12, 2011 at 4:48 AM, 7stud -- <bbxx789_0...@yahoo.com> wrote:
> > ...but then you could do this:
>
> > module ClassFactory
> >  def ClassFactory.included(includer)
> >    includer.extend(ClassMethods)
> >  end
>
> >  module ClassMethods
>
> >    def using(hash)
> >      Class.new do
> >        @options = hash
> >        class << self
> >          attr_reader :options
> >        end
> >      end
> >    end
>
> >  end
> > end
>
> > class Opportunities
> >  include ClassFactory
> > end
>
> I think we can do this simpler if you want to reuse that options
> creation functionality:
>
> module ClassFactory
>   attr_reader :options
>
>   def using(opts)
>     Class.new(self).tap do |cl|
>       cl.instance_variable_set '@options', opts.freeze
>     end
>   end
> end
>
> class Opportunities
>   extend ClassFactory
> end
>
> irb(main):020:0> foo = Opportunities.using(foo: 1, bar: 2)
> => #<Class:0x10952bc0>
> irb(main):021:0> foo.options
> => {:foo=>1, :bar=>2}
> irb(main):022:0> foo.ancestors
> => [#<Class:0x10952bc0>, Opportunities, Object, Kernel, BasicObject]
>
>
>
> > I really wanted to write that like below, but it doesn't work??
>
> > module ClassFactory
> >  def ClassFactory.included(includer)
> >    includer.extend(ClassMethods)
> >  end
>
> >  module ClassMethods
>
> >    def using(hash)
> >      Class.new do
> >        @options = hash
> >      end
> >    end
>
> >    def options
> >      @options
> >    end
>
> >  end
> > end
>
> > class Opportunities
> >  include ClassFactory
> > end
>
> > Foo = Opportunities.using({one: 1, two: 2, three: 3})
> > Bar = Opportunities.using({four: 4, five: 5, six: 6})
>
> > p Foo.options
> > p Bar.options
>
> > --output:--
> > prog.rb:28:in `<main>': undefined method `options' for Foo:Class
> > (NoMethodError)
>
> Your new class does not inherit module ClassMethods, that's why.
>
> Kind regards
>
> robert
>
> --
> remember.guy do |as, often| as.you_can - without endhttp://blog.rubybestpractices.com/

Hello again!

I've now incorporated your solution into my code and it works very
well. I still have a small question though. What's the reason for
freezing the options? I can see no obvious explanation for it except
that one might not want to change them by accident. Or is there
another reason for this?

/lasso