protected function resolve(string $handler)
    {
        $handler = $this->split($handler);

        if (is_string($handler)) {
            return function_exists($handler) ? $handler : $this->createClass($handler);
        }

        list($class, $method) = $handler;

        if ((new ReflectionMethod($class, $method))->isStatic()) {
            return $handler;
        }

        return [$this->createClass($class), $method];
    }