Aslak Hellesoy's uncommon sense - Annotations in Ruby

Annotations in Ruby

[ Aslak Hellesoy ] 06:05, Friday, 25 February 2005

A couple of days ago I wished there was a way to use annotations in Ruby. I'm writing a Ruby on Rails application that renders a lot of objects in HTML. Many of these objects are "editable" via the web interface, and in order to make it easier for the user, I wanted the web interface to have both an explanatory text and a HTML tooltip for each object's field.

Because I like simple things I also like to keep things in one place (I don't want to maintain this metadata in a separate RHTML template).

Ruby doesn't support annotations out of the box, so I opened up the Class class and added support for annotations. Now I can do:

require 'rscm/annotations'

  class EmailSender
    ann :description => "IP address of the mail server", :tip => "Use 'localhost' if you have a good box, sister!"
    attr_accessor :server
  end

The class' annotations can then be accessed like this:

  EmailSender.server[:description] # => "IP address of the mail server"

It took the Java community forever to do stuff like this. First a couple of years of XDoclet, then JSR175. And tons of code too. In Ruby it's 1 hour's work and 25 lines of code. Go figure.

For more info see http://rscm.rubyforge.org/classes/Class.html

And oh, here's the code:

class Class
  def ann(anns)
    @@anns ||= {}
    def self.method_missing(sym, *args) #:nodoc:
      @@anns[sym]
    end
    $attr_anns ||= {}
    $attr_anns.merge!(anns)
  end

  alias old_attr_reader attr_reader #:nodoc:
  def attr_reader(*syms) #:nodoc:
    syms.each do |sym|
      @@anns[sym] = $attr_anns
    end
    $attr_anns = nil
    old_attr_reader(*syms)
  end

  def attr_accessor(*syms) #:nodoc:
    attr_reader(*syms)
    attr_writer(*syms)
  end
end

UPDATE (March 3 2005) An updated version of the Ruby annotations library is available at rafb

Please don't be intimidated by ignorants like John. Javablogs is interesting because many technological discussions appear there, even if the main scope is java.
Java does not exist in a vacuum and posts like this helps put the language and platform into context.
Javablogs will be a poorer place if everything not strictly related to java was removed.

I for one hope you and others will continue to publish these things to javablogs.

so to John, please use the javablogs filters to ban blogs that you do not care for i do this with most non-english blogs), but otherwise STFU.

--Morten Wilken, February 25, 2005 10:20 AM

Eu:

What's unlogical or wrong about my example? Are you suggesting it's better to introduce more complexity to get things "right", even if a low-fi solution works?

I care more whether code is readable, simple and maintainable than whether it's following a pattern or a spec.

If you evaluate a technical approach with a Java mindset (which you seem to be doing - Ruby doesn't have interfaces), most code written in other languages will seem "wrong".

--Aslak Hellesoy, February 25, 2005 04:09 PM

1 full hour? You could have said the truth (10 minutes at most, if you're quite sloppy at meta-programming), I don't think these javaheads would bite you for that. They sort of managed to put up with DHH after all...

Besides, the implementation is flawed. You should have used class instance variables.

You could make it at least thread-safe with a Class granularity very easily. But I can understand that most railers won't care about that.

--blergh, March 9, 2005 05:55 PM