From: Daniel Berger <djberg96@...>
Date: 2006-01-01T09:22:56+09:00
Subject: Memoization, files and Marshal?

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,

Dan