protocols.rb

class Module
  def protocol(proto_name)
    @current_protocol = proto_name.to_sym
  end

  def protocols
    @protocols ||= Hash.new{|h,k| h[k] = []}
  end

  def method_added(name)
    return nil if name == :method_added
    protocols[@current_protocol || :instance_methods] << name
  end

end

class Testing

  def name
    "Testing object"
  end

protocol :accessors

  attr_reader :size
  attr_accessor :role

protocol :drawing

  def moveto
  end
end

puts Testing.protocols.inspect