From: Gavin Kistner <gavin@...>
Date: 2005-10-02T03:10:37+09:00
Subject: Creating a Class factory

As noted in another thread, I'm looking at ways of creating a Struct- 
like class; one that is a factory for creating classes. I did it one  
way by using Struct itself, but I'm not wild about it. I'd like to  
write my own, that sets true instance variables instead of struct's  
members thing. Is Struct using C magic during its initialize to cause  
"Struct.new" to return class objects, or is it just doing the  
equivalent of the following:

class Foo
     def self.new
         klass = Class.new( self )
         # setup klass here
         klass
     end
end

Is there a better way to make a class that creates 'instances' which  
are also classes?

Erps, except that the above doesn't work, because if you ask the new  
class to inherit from the factory, then 'new' is overridden and  
doesn't call initialize. For example:

class KeywordClass
     def self.new( property_hash )
         klass = Class.new( self )
         code = <<-ENDCODE
             attr_accessor #{property_hash.keys.map{|k| 
k.to_s.intern.inspect}.join(', ')}
             def initialize( values={} )
                 #{property_hash.map{ |prop,default|
                     "@#{prop} = values[#{prop.inspect}] || # 
{default.inspect}"
                 }.join("\n")}
             end
         ENDCODE
         klass.class_eval code
         klass
     end
     def foo
         "whoa"
     end
end

People = KeywordClass.new :cat=>true
puts People.new.cat
#=> ArgumentError: wrong number of arguments (0 for 1)