From: "nicholasmabry@..." <nicholasmabry@...>
Date: 2008-06-11T11:49:46+09:00
Subject: Re: storing values for later use

Hey Tom,

The previous responders were right on. Memoization is the concept of
caching the results of a function call. Googling 'ruby memoization'
will yield far better descriptions than mine, but here's a simple
example using the ruby gem Memoize. When it is mixed-in to a class
definition, it adds the method memoize() to instances of the class.
When you want to begin storing results of a calculation, call memoize
on the object with the symbol name (the colon string) of the method
you'd like to begin caching.

require 'memoize'

class CalcLibrary
  include Memoize
  def call_c(function_name, *args_array)
    # This method calls into the C extension (I assume)
    # And returns an array (we'll just return randoms)
    return_array = []
    srand Time.now.usec
    return_array << rand(10000)
    return_array << rand(10000)
  end
end

# A quick test
puts "-- No memoize() call yet --"
clib = CalcLibrary.new

puts "Result one:"
puts clib.call_c("rand")[1]
puts "Result two:"
puts clib.call_c("rand")[1]
puts "Result three:"
puts clib.call_c("rand", 2)[1]

puts "-- Memoized --"
clib.memoize :call_c

puts "Result one:"
puts clib.call_c("rand")[1]
puts "Result two:"             # Should be the same as result 1 if
cached
puts clib.call_c("rand")[1]
puts "Result three:"
puts clib.call_c("rand", 2)[1]


The Memoize module also includes the ability to store and load caches
out to a file, but it's easy to get into trouble that way without
diving into how it's working under-the-hood. Good luck with your
project!