From: Sean O'Dell <sean@...>
Date: 2004-06-10T04:55:34+09:00
Subject: Re: [ANN] Ruby/Interface

I decided the library wasn't "Ruby" enough and I got some ideas from Daniel 
Berger's interface library, so I made a lot of changes.

Homepage: http://interface.rubyforge.org/
Rubyforge Project Homepage: http://rubyforge.org/projects/interface/
Download: http://rubyforge.org/frs/?group_id=266&release_id=529

Code Snippet:

	require "celsoft.com/interface" 

	HashInterface = Interface.new

	HashInterface.add_class_patterns(Hash, :[], :[]=)
	HashInterface.add_pattern(:each_pair, proc{||})

	class Hash
	  implements HashInterface
	end

	class<<ENV
	  implements HashInterface
	end

	p Hash.new.implements?(HashInterface) == true
	p ENV.implements?(HashInterface) == true

	HashInterface.add_pattern(:each_pair, proc{|a|}) # method param changed

	p ENV.implements?(HashInterface) == false

How It Works

Method patterns are stored with each Interface object and are used to check 
against the methods of any given object. The name and number of parameters 
are important. If an object never claims to implement an interface, it will 
always report that it does not implement a given interface, even if it may be 
capable of it. When an object claims to implement an interface, a thorough 
check is performed to verify that it actually does. This check is only 
performed when necessary for efficiency, when implements? is called. The 
result of the check is cached and returned quickly on subsequent calls to 
implements?. If either the interface definition changes, or methods are 
changed in the class of the object, the cache is dumped and the thorough 
check is performed the next time implements? is called, and the answer is 
then again cached.