From: Bret Pettichord <bret@...>
Date: 2005-09-07T13:38:39+09:00
Subject: Class constant methods

In several cases, i find myself wanting to create constants for a set of 
related classes. Each class has a different value, defined once, and then 
have the methods of the "abstract" class be able to reference the "classes" 
value.

I've tried doing this thing with methods and class variables and class 
constants, but the only one that works is methods. Like support_types in 
the following code from Watir:

     class TextField < Element
         def locate
             if @how == :from_object
                 ole_object = @what
             else
                 ole_object = @container.getObject(@how, @what, 
supported_types)
             end
             @o = ole_object
         end
         def supported_types
             return ["text", "password", "textarea"]
         end
         private :supported_types
    ...

     class Hidden < TextField
         def initialize(container,  how, what)
             super
         end
         def supported_types
             return ["hidden"]
         end

I've found that the only way to get the behavior that i want is to use 
these kinds of "constant" methods. These seems inelegant, and i am 
wondering if there is a cleaner way of doing this kind of thing?

Here's another example of where i've done this kind of thing:

     class SelectLists < ElementCollections
         include CommonCollection
         def element_class; SelectList; end
         def element_tag; 'SELECT'; end
     end

Any suggestions. If i recall correctly, class constants didn't work because 
it wouldn't get the right scope. And class variables didn't have separate 
values for each of the classes.

Anyway, it seemed kludgy to have to use a method, when a constant or 
variable would do. Comments?

Bret


_____________________
  Bret Pettichord
  www.pettichord.com