Path: csiph.com!x330-a1.tempe.blueboxinc.net!feeder1.hal-mli.net!weretis.net!feeder4.news.weretis.net!feeds.phibee-telecom.net!talisker.lacave.net!lacave.net!not-for-mail
From: 7stud -- <bbxx789_05ss@yahoo.com>
Newsgroups: comp.lang.ruby
Subject: Re: What do you do when you need to attach data to an object instance?
Date: Thu, 14 Apr 2011 18:15:08 -0500
Organization: Service de news de lacave.net
Lines: 76
Message-ID: <24ba002d74b2765157d36054768e8e73@ruby-forum.com>
References: <BANLkTinVjc-Lv4LYB6ODXCRDnrDOQj+2uA@mail.gmail.com>
NNTP-Posting-Host: bristol.highgroove.com
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
X-Trace: talisker.lacave.net 1302822950 2581 65.111.164.187 (14 Apr 2011 23:15:50 GMT)
X-Complaints-To: abuse@lacave.net
NNTP-Posting-Date: Thu, 14 Apr 2011 23:15:50 +0000 (UTC)
In-Reply-To: <BANLkTinVjc-Lv4LYB6ODXCRDnrDOQj+2uA@mail.gmail.com>
X-Received-From: This message has been automatically forwarded from the ruby-talk mailing list by a gateway at comp.lang.ruby. If it is SPAM, it did not originate at comp.lang.ruby. Please report the original sender, and not us. Thanks! For more details about this gateway, please visit: http://blog.grayproductions.net/categories/the_gateway
X-Mail-Count: 381578
X-Ml-Name: ruby-talk
X-Rubymirror: Yes
X-Ruby-Talk: <24ba002d74b2765157d36054768e8e73@ruby-forum.com>
Xref: x330-a1.tempe.blueboxinc.net comp.lang.ruby:2891

Aaron D. Gifford wrote in post #992841:
> What do you do when you see a need to be able to attach some data to
> an object instance for later use somewhere else in a body of code?
> Lately I've resorted to this:
>
> ## Generic utility to allow one to attach data with a getter/setter to
> ## any instance of any object so long as there isn't a method name
> ## collision:
> def attach_data(obj, name, data)
>   getter = name.to_sym
>   setter = (name.to_s + '=').to_sym
>   raise "method name collision for #{obj.class} instance" if
> obj.respond_to?(getter) || obj.respond_to?(setter)
>   ## The 'value' local variable will remain in existence in the lambda
> closures below:
>   value = data
>   meta = class << obj ; self ; end
>   meta.send(:define_method, getter, lambda { value })            ##
> Getter closure
>   meta.send(:define_method, setter, lambda {|val| value = val }) ##
> Setter closure
>   value
> end
>
> For example, in an application using SSH keys, I didn't want to create
> a new subclass, nor use an array or hash container instance just to
> carry an OpenSSL::PKey::RSA object instance around the code.  But I
> needed to associate a user ID (user@host) to a key so it could be
> accessed somewhere else.  I figured it was easiest to just attach it
> to the OpenSSL::PKey::RSA instance (see code above) directly.  That
> made the code cleaner, portions that only required the RSA key
> directly, yet still gave the benefit of the key instance containing
> the additional meta data I required.
>
> What do you do when you need stuff like that?  Monkey patch?  Use a
> container and pass it around instead?  Or?
>

How about a decorator pattern?


> Is there a module version of OpenStruct that one can just include in
> whatever class one wants to attach additional arbitrary data to?  So I
> could have done this instead:
>
> require 'ostructmod'
> class OpenSSL::PKey
>   include OpenStructModule
> end
>
> ???
>
> Aaron out.

class SSL
  def talk
    puts 'hi'
  end
end

class MyWrapper
  def initialize(ssl_obj, key)
    @ssl_obj = ssl_obj
    @key = key
  end

  attr_accessor :ssl_obj, :key

  def method_missing(name, *args)
    @ssl_obj.send(name, *args)
  end
end

-- 
Posted via http://www.ruby-forum.com/.