From: Ron Fox <fox@...>
Date: 2008-07-02T20:42:03+09:00
Subject: Re: Ruby Idiom for dynamic programming? (request for comments)

@@ffunccache is a class variable, not an object variable.
It is shared amongst all instance sof the class Module.

RF

Lars Christensen wrote:
> Random idea i had...
> 
> I sometimes make custom classes/method for caching output of
> functions, i.e. for dynamic programming. To generalise this, i though
> it would be possible to implement it like this:
> 
> class A
>   def func(a, b, *c)
>     puts "Computing... #{[a,b,c].inspect}"
>     return [a,b,c].hash
>   end
>   cached :func
> end
> 
> My 'cached' directive is defined as:
> 
> class Module
>   def cached(method, cache = (@@funccache ||= {}))
>     orig = "uncached_#{method}"
>     alias_method orig, method
>     define_method method do |*args|
>       key = [ method, args ]
>       @@funccache[key] ||= send(orig, *args)
>     end
>   end
> end
> 
> What's the scope of @@funccache? (What 'object' holds it?). Is there a
> better way to do it?
> 
> Lars


-- 
Ron Fox
NSCL
Michigan State University
East Lansing, MI 48824-1321