k3n / PHP-Memoize

PHP Memoization via userland code

PHP Memoize

Userland implementation written in PHP 5.4, but easily downgraded to 5.3 (by removing both callable type hints).

Wikipedia: Memoization

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function memoize ( callable $fnOrig, callable $fnHash )

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fnOrig

The first argument is your function to optimize.

fnHash

The second argument is your hashing function, which will receive a single argument: an array representing 
the parameters. Your hash function should return a value that can safely be used an array key.

* Note: both arguments will be invoked as the first argument to call_user_func().

Return Values

The return value is an anonymous function that you can substitute in place of your original function call.

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Demo

We will use this simple factorial function to demonstrate the reduction in required invocations:

function factorial($n) {
    if ($n == 0) return 1;
    return factorial($n - 1);
}

First, the long way

$i = pow(10, 4);
while (--$i) {
    factorial(10);
}

This requires 109989 invocations of factorial().

Now, memoized

$fact = memoize('factorial', function($args) {
    return $args[0];
});
$i = pow(10, 4);
while (--$i) {
    $fact(10);
}

Here, 11 invocations of factorial().

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Variations

This function is extremely flexible:

$fact = memoize('factorial', 'your_hasher');

$fact = memoize('math::factorial', 'lib::hash');

$apiGetUserData = memoize(
    [new Api, 'getUserData'],
    [new Hasher, 'hashUserData']
);

$Logger = new Logger;
$toJson = memoize(function ($user, $action) use ($Logger) {
    $Logger->warn('cache miss');
    return json_encode(['user' => $user, 'action' => $action]);
}, function ($args) use ($Logger) {
    $Logger->info('cache lookup');
    return vsprintf("%d:%s", $args);
});