memcached - php数组缓存和memcache缓存 一道面试题，帮忙理下思路

<code>// example:
// get_cache('foo');
// get_cache(['foo', 'bar']);
function get_cache($keys) {
    static $cache = [];
    static $memcached;

    $keys = (array)$keys;

    $result = $missing = [];
    foreach ($keys as $key) {
        if (isset($cache[$key])) {
            $result[$key] = $cache[$key];
        } else {
            $missing[] = $key;
        }
    }

    if (!$missing) {
        return $result;
    }

    if (!$memcached) {
        $memcached = new Memcached;
    }

    $mresult = $memcached->getMulti($missing);
    if ($mresult) {
        foreach ($mresult as $key => $value) {
            $result[$key] = $cache[$key] = $value;
        }
    }

    return $result;
}</code>