# TITLE:
#
#   Inheritor
#
# SUMMARY:
#
#   Prototype-like class design.
#
# COPYRIGHT:
#
#   Copyright (c) 2005 Thomas Sawyer
#
# LICENSE:
#
#   Ruby License
#
#   This module is free software. You may use, modify, and/or redistribute this
#   software under the same terms as Ruby.
#
#   This program is distributed in the hope that it will be useful, but WITHOUT
#   ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
#   FOR A PARTICULAR PURPOSE.
#
# AUTHORS:
#
#   - Thomas Sawyer

#require 'facets/module/class_extension'
require 'facets/class_extension'

# = Inheritor
#
# Inheritor providse a means to store and inherit data via
# the class heirarchy. An inheritor creates two methods
# one named after the key that provides a reader. And one
# named after key! which provides the writer. (Because of
# the unique nature of inheritor the reader and writer
# can't be the same method.)
#
#   class X
#     inheritor :foo, [], :+
#   end
#
#   class Y < X
#   end
#
#   X.x! << :a
#   X.x => [:a]
#   Y.x => [:a]
#
#   Y.x! << :b
#   X.x => [:a]
#   Y.x => [:a, :b]
#
# It is interesting to note that the only reason inheritor is needed at all
# is becuase Ruby does not allow modules to be inherited at the class-level, or
# conversely that the "class-levels" of classes are not modules instead.

class Object

  # Create an inheritor "class attribute".
  def inheritor( key, obj, op=nil )

    # inhertiance operator
    op = op ? op.to_sym : :add

    # inheritor store a this level
    instance_variable_set("@#{key}", obj)

    #base = self
    deflambda = lambda do

      define_method( key ) do
        defined?(super) ? super.__send__(op,obj) : obj.dup
      end

      define_method( "#{key}!" ) do
        instance_variable_get("@#{key}") || inheritor( key, obj.class.new, op )
        #if instance_variables.include?("@#{key}")
        #  instance_variable_get("@#{key}")
        #else
        #  if self != base
        #    inheritor( key, obj.class.new, op )
        #  end
        #end
      end
    end

    # TODO This is an issue if you try to include a module
    # into Module or Class itself. How to fix?

    # if the object is a module (not a class or other object)
    if self == Class or self == Module
      class_eval &deflambda
    elsif is_a?(Class)
      (class << self; self; end).class_eval &deflambda
    elsif is_a?(Module)
      #class_inherit &deflambda
      extend class_extension( &deflambda )
    else # other Object
      (class << self; self; end).class_eval &deflambda
    end

    obj
  end

end