From: dblack@...
Date: 2006-03-12T13:35:55+09:00
Subject: Re: Adding methods to a singleton dynamically

Hi --

On Sun, 12 Mar 2006, Mike Austin wrote:

> I'm building a view hierarchy from a file, and I would like it to add getter 
> methods for every subview created.  For example, I should be able to write:
>
> window.bottom_panel.save_button.left = 20
>
> I played around with singleton classes and define_method, am I close?  I 
> wonder if it is illegal to do 'class << self end' within a method - I get the 
> error 'class definition in method body'
>
> hierarchy.each do |key, value|
>  view = Object::const_get( key[1] ).new
>
>  class << self end
>
>  self.class.class_eval do
>    define_method( key[1] ) do
>      return view
>    end
>  end
> end
>
> hierarchy = {
>  [:bottom_panel, :Panel] => {
>    [:save_button, :Button] => {}
>  }
> }

I just *know* there's a way to do this with inject... :-)  But
meanwhile, see if this is of any use.  It's a whole little
self-contained simulation.

def cascade_from_hierarchy(base,hierarchy)
   label, kind = *hierarchy.keys[0]
   rest = hierarchy.values[0]
   view = kind.new

   (class << base; self; end).class_eval do
     define_method(label) { view }
   end

   cascade_from_hierarchy(view,rest) unless rest.empty?
end

class Panel; end
class Button; end
class Window; end

window = Window.new
hierarchy = {
   [:bottom_panel, Panel] => {
     [:save_button, Button] => {}
   }
}

cascade_from_hierarchy(window,hierarchy)

p window.bottom_panel.save_button # #<Button:0x1ceb58>

__END__


David
-- 
David A. Black (dblack@wobblini.net)
Ruby Power and Light, LLC (http://www.rubypowerandlight.com)

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