type_cast.rb

# Usage
#
# class Rectangle
#   include TypeCast
#
#   ...
#   
#   attr_accessor :width, :height, :fill
#   type_cast :width, :height, :method => :to_f
#   type_cast :fill, :allow_nil => false, :method => lambda { |value| !!value }
#
#   ...
#
#   def area
#     width * height
#   end
#
#   def draw
#     ...
#     fill_with_color(color) if fill
#     ...
#   end
# end
#
#
# r = Rectangle.new :width => "10", :height => 12, :fill => "yes"
# r.width     #=> 10.0
# r.height    #=> 12.0
# r.fill      #=> true


module TypeCast
  extend ActiveSupport::Concern

  module ClassMethods
    def type_cast(*args)
      options = args.extract_options!
      options[:allow_nil] = true if options[:allow_nil].nil?
      raise ArgumentError, "Undefined method for type casting" if options[:method].nil?
      raise ArgumentError, "Undefined attribute for type casting" if args.empty?

        
      args.each do |attr|
        define_method "#{attr}_with_type_cast=" do |value|
          value = if value.nil? && options[:allow_nil]
                    nil
                  else 
                    options[:method].is_a?(Proc) ? options[:method].call(value) : value.send(options[:method])
                  end
          send("#{attr}_without_type_cast=", value)
        end
        alias_method_chain :"#{attr}=", :type_cast
      end
    end
  end
end