From: ara.t.howard@...
Date: 2006-01-01T10:28:17+09:00
Subject: Re: Memoization, files and Marshal?

On Sun, 1 Jan 2006, Daniel Berger wrote:

> Hi all,
>
> Inspired by a recent blog entry by Mauricio Fernandez, I decided to try
> to add a method to the memoize package that would allow users to
> memoize using a file based approach rather than memory, either to
> conserve memory or for persistance.
>
> However, I'm not sure it's possible.  If it is, I'd love to know how.
> If it's not, well, pstore it is.
>
> Here's what I tried:
>
> def memoize_to_file(name, file)
>   meth = method(name)
>   cache = Hash.new.update(Marshal.load(File.read(file))) rescue nil
>   cache ||= {}
>   (class << self; self; end).class_eval do
>      define_method(name) do |*args|
>         if cache.has_key?(args)
>            cache[args]
>         else
>            cache[args] ||= meth.call(*args)
>            File.open(file, "wb+"){ |f| Marshal.dump(cache, f) }
>         end
>      end
>   end
>   cache
> end
>
> # Code snippet
> include Memoize
> def fib(n)
>   return n if n < 2
>   fib(n-1) + fib(n-2)
> end
> memoize_to_file(:fib, "temp.txt")
> fib(10)
>
> However, running that gives me this error: in `fib': undefined method
> `+' for #<File:temp.txt (closed)> (NoMethodError)
>
> Any ideas?
>
> Thanks,


   harp:~ > cat a.rb
   def memoize_to_file(name, file)
     cache = Hash.new.update(Marshal.load(File.read(file))) rescue {}
     (class << self; self; end).class_eval do
        define_method(name) do |*args|
           unless cache.has_key?(args)
             cache[args] = method(name).call(*args)
             File.open(file, "wb+"){|f| Marshal.dump(cache, f) }
           end
           cache[args]
        end
     end
   end

   def fib(n)
    return n if n < 2
    fib(n-1) + fib(n-2)
   end

   memoize_to_file "fib", "fib.cache"
   n = fib 10
   p n



   harp:~ > ruby a.rb
   55


regards.

-a
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