- reset: documentation ( source)
- array_shift: documentation ( source)
<?php
$memoize = function ($fn, $cacheKeyFn = null, $limit = null) {
$cache = array();
return function () use ($fn, $cacheKeyFn, $limit, & $cache) {
$args = func_get_args();
if ($cacheKeyFn) {
$key = call_user_func_array($cacheKeyFn, $args);
} else {
$key = reset($args);
}
if (isset($cache[$key])) {
return $cache[$key];
}
$result = call_user_func_array($fn, $args);
if ($limit !== null && count($cache) === $limit) {
array_shift($cache);
}
$cache[$key] = $result;
return $result;
};
};
$numCalls = 0;
$memoFib = $memoize(
function ($n) use (& $memoFib, & $numCalls) {
$numCalls++;
if ($n === 1 || $n === 2) return 1;
return $memoFib($n - 1) + $memoFib($n - 2);
}
);
echo $memoFib(0) . PHP_EOL;
echo $memoFib(1) . PHP_EOL;