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Jonathan Swartz


CHI::Memoize - Make functions faster with memoization, via CHI


version 0.02


    use CHI::Memoize qw(:all);
    # Straight memoization in memory
    # Memoize an anonymous function
    $anon = memoize($anon);
    # Memoize based on the second and third argument to func
    memoize('func', key => sub { $_[1], $_[2] });
    # Memoize only in certain cases
    memoize('func', key => sub { $_[0] eq 'variable' ? NO_MEMOIZE : @_ });
    # Expire after one hour
    memoize('func', expires_in => '1h');
    # Store a maximum of 10 results with LRU discard
    memoize('func', max_size => 10);
    # Store raw references instead of serializing/deserializing (faster, more risky)
    memoize('func', driver => 'RawMemory');
    # Store in memcached instead of memory
    memoize('func', driver => 'Memcached', servers => [""]);
    # See what's been memoized for a function
    my @keys = memoized('func')->cache->get_keys;
    # Clear memoize results for a function
    my @keys = memoized('func')->cache->clear;
    # Use an explicit cache instead of autocreating one
    my $cache = CHI->new(driver => 'Memcached', servers => [""]);
    memoize('func', cache => $cache);
    # Unmemoize function, restoring it to its original state


"`Memoizing' a function makes it faster by trading space for time. It does this by caching the return values of the function in a table. If you call the function again with the same arguments, memoize jumps in and gives you the value out of the table, instead of letting the function compute the value all over again." -- quoted from the original Memoize

CHI::Memoize provides the same facility as Memoize, but backed by CHI. This means, among other things, that you can


All of these are importable; only memoize is imported by default. use Memoize qw(:all) will import them all as well as the NO_MEMOIZE constant.

memoize ($func, option => value, ...)

Creates a new function wrapped around $func that caches results based on passed arguments.

$func can be a function name (with or without a package prefix) or an anonymous function. In the former case, the name is rebound to the new function. In either case a code ref to the new wrapper function is returned.

By default, the cache key is formed from combining the full function name, the calling context ("L" or "S"), and all the function arguments with canonical JSON (sorted hash keys). e.g. these arguments will generate the same cache key:

    memoized_function(a => 5, b => 6, c => { d => 7, e => 8 });
    memoized_function(b => 6, c => { e => 8, d => 7 }, a => 5);

but these will use a different cache key because of context:

     my $scalar = memoized_function(5);
     my @list = memoized_function(5);

By default, the cache namespace is formed from the full function name or the stringified code reference. This allows you to introspect and clear the memoized results for a particular function.

memoize throws an error if $func is already memoized.

memoized ($func)

Returns a CHI::Memoize::Info object if $func has been memoized, or undef if it has not been memoized.

    # The CHI cache where memoize results are stored
    my $cache = memoized($func)->cache;

    # Code references to the original function and to the new wrapped function
    my $orig = memoized($func)->orig;
    my $wrapped = memoized($func)->wrapped;
unmemoize ($func)

Removes the wrapper around $func, restoring it to its original unmemoized state. Also clears the memoize cache if possible (not supported by all drivers, particularly memcached). Throws an error if $func has not been memoized.


The following options can be passed to "memoize".


Specifies a code reference that takes arguments passed to the function and returns a cache key. The key may be returned as a list, list reference or hash reference; it will automatically be serialized to JSON in canonical mode (sorted hash keys). e.g. this uses the second and third argument to the function as a key:

    memoize('func', key => sub { @_[1..2] });

Regardless of what key you specify, it will automatically be prefixed with the full function name and the calling context ("L" or "S").

If the function returns CHI::Memoize::NO_MEMOIZE (or NO_MEMOIZE if you import it), this call won't be memoized. This is useful if you have a cache of limited size or if you know certain arguments will yield nondeterministic results.

set and get options

You can pass any of CHI's set options (e.g. expires_in, expires_variance) or get options (e.g. expire_if, busy_lock). e.g.

    # Expire after one hour
    memoize('func', expires_in => '1h');
    # Expire when a particular condition occurs
    memoize('func', expire_if => sub { ... });
cache options

Any remaining options will be passed to the CHI constructor to generate the cache:

    # Store in memcached instead of memory
    memoize('func', driver => 'Memcached', servers => [""]);

Unless specified, the namespace is generated from the full name of the function being memoized.

You can also specify an existing cache object:

    # Store in memcached instead of memory
    my $cache = CHI->new(driver => 'Memcached', servers => [""]);
    memoize('func', cache => $cache);


By default CHI, and thus CHI::Memoize, returns a deep clone of the stored value. e.g. in this code

    # func returns a list reference
    my $ref1 = func();
    my $ref2 = func();

$ref1 and $ref2 will be references to two completely different lists which have the same contained values. More specifically, the value is serialized by Storable on set and deserialized (hence cloned) on get.

The advantage here is that it is safe to modify a reference returned from a memoized function; your modifications won't affect the cached value.

    my $ref1 = func();
    push(@$ref1, 3, 4, 5);
    my $ref2 = func();
    # $ref2 does not have 3, 4, 5

The disadvantage is that it takes extra time to serialize and deserialize the value, and that some values like code references may be more difficult to store. And cloning may not be what you want at all, e.g. if you are returning objects.

Alternatively you can use CHI::Driver::RawMemory, which will store raw references the way Memoize does. Now, however, any modifications to the contents of a returned reference will affect the cached value.

    memoize('func', driver => 'RawMemory');
    my $ref1 = func();
    push(@$ref1, 3, 4, 5);
    my $ref2 = func();
    # $ref1 eq $ref2
    # $ref2 has 3, 4, 5


The caveats of Memoize apply here as well. To summarize:

  • Do not memoize a function whose behavior depends on program state other than its own arguments, unless you explicitly capture that state in your computed key.

  • Do not memoize a function with side effects, as the side effects won't happen on a cache hit.

  • Do not memoize a very simple function, as the costs of caching will outweigh the costs of the function itself.


A number of modules address a subset of the problems addressed by this module, including:


Questions and feedback are welcome, and should be directed to the perl-cache mailing list:


Bugs and feature requests will be tracked at RT:


The latest source code can be browsed and fetched at:

    git clone git://github.com/jonswar/perl-chi-memoize.git


CHI, Memoize


Jonathan Swartz <swartz@pobox.com>


This software is copyright (c) 2011 by Jonathan Swartz.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.