Functional\Exceptions\InvalidArgumentException::assertCallback PHP Method

    public static function assertCallback($callback, $callee, $parameterPosition)
    {
        if (!is_callable($callback)) {
            if (!is_array($callback) && !is_string($callback)) {
                throw new static(sprintf('%s() expected parameter %d to be a valid callback, no array, string, closure or functor given', $callee, $parameterPosition));
            }
            $type = gettype($callback);
            switch ($type) {
                case 'array':
                    $type = 'method';
                    $callback = array_values($callback);
                    $sep = '::';
                    if (is_object($callback[0])) {
                        $callback[0] = get_class($callback[0]);
                        $sep = '->';
                    }
                    $callback = join($callback, $sep);
                    break;
                default:
                    $type = 'function';
                    break;
            }
            throw new static(sprintf("%s() expects parameter %d to be a valid callback, %s '%s' not found or invalid %s name", $callee, $parameterPosition, $type, $callback, $type));
        }
    }

/**
 * Memoizes callbacks and returns their value instead of calling them
 *
 * @param callable $callback Callable closure or function
 * @param array $arguments Arguments
 * @param array|string $key Optional memoize key to override the auto calculated hash
 * @return mixed
 */
function memoize($callback, array $arguments = array(), $key = null)
{
    static $storage = array();
    if ($callback === null) {
        $storage = array();
        return null;
    }
    InvalidArgumentException::assertCallback($callback, __FUNCTION__, 1);
    static $keyGenerator = null;
    if (!$keyGenerator) {
        $keyGenerator = function ($value) use(&$keyGenerator) {
            $type = gettype($value);
            if ($type === 'array') {
                $key = join(':', map($value, $keyGenerator));
            } elseif ($type === 'object') {
                $key = get_class($value) . ':' . spl_object_hash($value);
            } else {
                $key = (string) $value;
            }
            return $key;
        };
    }
    if ($key === null) {
        $key = $keyGenerator(array_merge(array($callback), $arguments));
    } else {
        $key = $keyGenerator($key);
    }
    if (!isset($storage[$key]) && !array_key_exists($key, $storage)) {
        $storage[$key] = call_user_func_array($callback, $arguments);
    }
    return $storage[$key];
}