public function reject($callback)
    {
        if (is_callable($callback))
        {
            return $this->copy()->filter(function($item) use ($callback)
            {
                return ! $callback($item);
            });
        }

        $callback = $this->getStringable($callback);

        return $this->copy()->filter(function($item) use ($callback)
        {
            return $item != $callback;
        });
    }