From: Gene Tani <gene.tani@...>
Date: 2005-12-09T12:27:36+09:00
Subject: Re: Transparent Caching Idiom


Daniel Schierbeck wrote:
> beng wrote:
> > I've made good use of this idiom recently, and wanted to share it.
> >
> > Once this code is active, any method named with a "_c" suffix is
> > automatically cached. The method is assumed to follow a simple
> > contract: It performs no side-effects / mutations, and it's arguments
> > properly implement "Object.hash".
> >
> > This is specifically useful for expensive but functional calculations.
> > Enjoy!
> >
> > --Ben (b@gimpert.com)
> >
> > # <code>
> > class Class
> >
> >     alias old_new new
> >     def new(*args, &block)
> >         Class.defc_wrap(old_new(*args, &block))
> >     end
> >
> >     def Class.defc_wrap(obj)
> >         klass = obj.class
> >         defc_methods = obj.methods.select { |n| n =~ /_c$/ }
> >         defc_methods.each do |name|
> >             meth = obj.method(name)
> >             wrapped_name = Class.defc_next_name(klass)
> >             cache = klass.class_eval("@#{wrapped_name} = {}")
> >             wrapper = Proc.new do |*args_a|
> >                 arg_hash = args_a.hash
> >                 if cache.has_key?(arg_hash)
> >                     cache[arg_hash]
> >                 else
> >                     cache[arg_hash] = meth.call(*args_a)
> >                 end
> >             end
> >             klass.send(:alias_method, wrapped_name, name)
> >             klass.send(:define_method, name, wrapper)
> >         end
> >         obj
> >     end
> >
> >     def Class.defc_next_name(obj)
> >         klass = obj.class
> >         i = 1
> >         i += 1 while obj.respond_to?("_defc_#{i}") ||
> > obj.instance_variables.member?("@_defc_#{i}")
> >         "_defc_#{i}"
> >     end
> >
> > end
> > </code>
> >
>
> Neat. Though it would be cool if the methods that were to be cached were
> chosen through a class method rather than a method name suffix.
>
>    class Klass
>      def foo; end
>      def bar; end
>      cached_method :foo, :bar
>    end
>
>
> Cheers,
> Daniel
I got this bookmarked, When i get time, i'll have to compare to prior
thread on memozing
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/155159
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/155170