class Module
  # has and after do not exist in Ruby OOTB, so we define them here:
  def has(options)
      options.each_pair do |k, v|
        singleton_class.send(:attr_accessor, k)
        instance_variable_set("@#{k}", v)
    end
  end

  def after(meth, &after_block)
    old_meth = instance_method(meth)
    define_method(meth) do |*args, &block|
      old_meth.bind(self).(*args, &block)
      after_block.(self.class)
    end
  end
end

module CountingModule
  def self.extended(c)
    c.has :count => 0
    c.after(:initialize) do |klass|
      puts "construction finished"
      klass.count += 1
    end
  end
end

class Foo
  extend CountingModule
end

Foo.new #=> "construction finished"
Foo.new #=> "construction finished"

puts Foo.count #=> 2