module Extlib
  def self.class_inheritable_reader(klass, *ivars)
    instance_reader = ivars.pop[:reader] if ivars.last.is_a?(Hash)
    
    ivars.each do |ivar|
      klass.class_eval <<-RUBY, __FILE__, __LINE__ + 1
        def self.#{ivar}
          return @#{ivar} if self == #{klass} || defined?(@#{ivar})
          ivar = superclass.#{ivar}
          return nil if ivar.nil? && !#{klass}.instance_variable_defined?("@#{ivar}")
          @#{ivar} = ivar && !ivar.is_a?(Module) && !ivar.is_a?(Numeric) ? ivar.dup : ivar
        end
      RUBY
      unless instance_reader == false
        klass.class_eval <<-RUBY, __FILE__, __LINE__ + 1
          def #{ivar}
            self.class.#{ivar}
          end
        RUBY
      end
    end
  end
  
  def self.class_inheritable_writer(klass, *ivars)
    instance_writer = ivars.pop[:instance_writer] if ivars.last.is_a?(Hash)
    ivars.each do |ivar|
      klass.class_eval <<-RUBY, __FILE__, __LINE__ + 1
        def self.#{ivar}=(obj)
          @#{ivar} = obj        
        end
      RUBY
      unless instance_writer == false
        klass.class_eval <<-RUBY, __FILE__, __LINE__ + 1
          def #{ivar}=(obj) self.class.#{ivar} = obj end
        RUBY
      end
    end
  end
  
  def self.class_inheritable_accessor(klass, *syms)
    class_inheritable_reader(klass, *syms)
    class_inheritable_writer(klass, *syms)
  end
end
 
module Merb; end
 
class Merb::Controller
  Extlib::class_inheritable_accessor self, :_form_class
end
 
class Merb::Mailer
  Extlib::class_inheritable_accessor self, :config
 
  def initialize
    self.config = 'hello' if config.nil?
  end
end
 
puts Merb::Mailer.new.config #=> 'hello'