best-mixin-stratgey.rb

#! /usr/bin/env ruby

# this is best practice for writing mixins.  the deferred evaluation is more
# powerful that the approach of ClassMethods/InstanceMethods as modules too
#

  module Mixin
  # put your class level code in here
  #
    ClassMethods = proc do
    # if you do anything with constants you'll need dynamic scoping since,
    # otherwise, a const's scope is determined lexically...
    #
      const_set(:Const, self.name)

      def foo
        const_get(:Const)
      end
    end

  # put your instance methods here
  #
    InstanceMethods = proc do
      def bar
        self.class.name.downcase
      end
    end

  # trigger on mixin.  the order may need reversed for ruby 1.9.2
  #
    def Mixin.included(other)
      super
    ensure
      other.send(:instance_eval, &ClassMethods)
      other.send(:module_eval, &InstanceMethods)
    end
  end




# sample usage
#

if $0 == __FILE__
  class A
    include Mixin
  end

  class B
    include Mixin
  end

  p A.foo     #=> "A"
  p A.new.bar #=> "a"

  p B.foo     #=> "B"
  p B.new.bar #=> "b"
end