[ruby-talk:12014] ANN: Memoize 0.1.2

Hi,

This is to announce Memoize: "for speeding up methods/functions by caching
their results; on subsequent calls the cached result is returned instead
of being recalculated".

This has speeded up some of my calculation-intensive stuff and at the
recent GOTRUG meeting Aleksi encouraged me to submit it to RAA. So, here
it is...

You'll find the README below.

Regards,

Robert


*************************************************
* Memoize - caching method results for speed-up *
*************************************************

Version: 0.1.2
Release date: 2001-03-05
Available from: http://www.ce.chalmers.se/~feldt/ruby/extensions/memoize
Donwload: http://www.ce.chalmers.se/~feldt/ruby/extensions/memoize/memoize-0-1-2.tar.gz
Author: Robert Feldt, [e-mail]
README version: $Id: README,v 1.3 2001/03/05 13:59:46 feldt Exp $

What is it?
-----------
Directive for making your functions faster by trading space for time. When
you "memoize" a method/function its results are cached so that later calls
with the same arguments returns results in the cache instead of
recalculating them.

Synopsis
--------
	require 'memoize'

	# From top-level
	memoize(:my_slow_function)

	# In class def
	class C
	  def m
    	    # Heavy calc
	  end
	  memoize :m
	end

	# my_slow_function and C#m may now return results faster

Optionally you can supply a cache to be used for caching results:

	memoize(:my_slow_function, BoundedLruCache.new(50))

Cache is any object that responds to [] and []= (basically Hashes). 

You can implement different expiration policies by doing your own cache.
One example is in resultcache.rb:
  * BoundedLruCache - Hash with fixed size, that will delete 
      least-recently-used values when full.

Installation?
-------------
1. unpack tarball (if you haven't already)
2. install: ruby install.rb
3. If you've got RubyUnit installed you can also run some tests...

Requirements?
-------------
None; plain Ruby >= 1.6.2.

I've successfully used Memoize with Ruby 1.7.0 (2001-01-23) and 
cygwin 1.1.8 (gcc version 2.95.2-6) on Windows NT 4.0 Workstation.

NOTE THAT THIS IS AN ALPHA RELEASE SO THERE WILL LIKELY BE BUGS.

RubyUnit is needed to run unit tests.

Known bugs?
-----------
* Does not work on class methods. Pretty easy to fix. Will be soon...
* Blocks/procs do not work as expected since Ruby will create unique block
    for each method call? So following won't give no speed-up even though
    the same block is passed both times:

       p = proc{|i| 2*i}
       r1 = my_memoized_method(&p)
       r2 = my_memoized_method(&p)

    (matz will fix this in future Ruby version, see ruby-talk:12001)

Special things to note?
-----------------------
DO NOT memoize METHODS THAT
    * have side effects (printing output, altering files etc.),
    * depend on state other than its arguments
    * return a data structure that is modified by its caller

It mostly makes sense to use on "stand-alone", computationally expensive 
(especially recursive) methods. However, we might alleviate some of these 
situations in the future by incorporating a normalization proc to use to 
get a hash for the arguments.

License and legal issues?
-------------------------
Memoize is copyright (c) 2001 Robert Feldt, [e-mail].
All rights reserved.

Memoize is distributed under LGPL. See LICENSE and COPYING-LESSER.

Acknowledgements?
-----------------
Thanks to Aleksi Niemelfor pointing out that what I called "result
caching"
has been called "memoize" in the perl community and that there is a
Memoize 
extension to perl in CPAN. I'm still not sure "memoize" is a better name
than
"result caching" but if the former is already in use I'll comply... ;-)

Do you have comments or questions?
----------------------------------
I'd appreciate if you drop me a note if you're successfully using 
Memoize. If there are some known users I'll be more motivated to packing 
up additions / new versions and post them to RAA.
Please give feedback!

Happy coding!

Robert Feldt, [e-mail]