Reimplementing attr_accessor as an exercise in The Compleat Rubyist

properties.rb

module Properties
  def property(property_name)
    define_method(property_name) do
      instance_variable_get("@#{property_name}".to_sym)
    end
    
    define_method("#{property_name}=".to_sym) do |value|
      instance_variable_set("@#{property_name}".to_sym, value)
    end
  end

  module InstanceMethods
    def method_missing(method_name, *args)
      @attrs ||= {}
      md = method_name.to_s.match(/(set|get)_(.+)/)
      if md
        if md[1] == "set"
          @attrs[md[2]] = args.first
        else
          @attrs[md[2]]
        end
      else
        super(method_name, args)
      end
    end
  end
  
  def self.extended(klass)
    klass.send(:include, InstanceMethods)
  end
end

class Foo
  extend Properties
  property :bar
end