From: Daniel Schierbeck <daniel.schierbeck@...>
Date: 2006-04-23T21:10:01+09:00
Subject: Metaprogramming Conventions

Recently, there was a post on news:comp.lang.ruby[1] by Avdi Grimm, who 
asked if there were any conventions when using metaprogramming. He gave 
this example:

   require 'memoize'
   require 'validate'

   class Foo
     attr_accessor :bar
     memoize :bar
     validate :bar do |value|
       value.include? "Johnny Walker Black Label"
     end
   end

Disregard the fact that you rarely want to memoize a writer method.

How do I know if memoize and validate play nicely together?

There has already been a proposal that would make it very easy to add 
metaprogramming capabilities without treading on each other's toes[2], 
but it would be a very big step.

A simpler solution would be to add a special method definition (an 
advice), that had a `super' that called the *previous* definition of 
that method.

   class Foo
     attr_accessor :bar

     advice bar
       '[' + super + ']'
     end

     advice bar
       '{' + super + '}'
     end
   end

   foo = Foo.new
   foo.bar = 'baz'
   foo.bar        #=> {[baz]}

That way, the user could choose in which order the wrapper methods 
should be called.


Cheers,
Daniel Schierbeck


[1] 
<http://groups.google.com/group/comp.lang.ruby/browse_thread/thread/e5be2e3b8a9d9614/6b3ab3e56f3a82cd>
[2] <http://www.rcrchive.net/rcr/show/321>