private function createUniqPlaceholder($key)
    {
        if ($key instanceof RawSqlFragment) {
            $placeholder = $key->getFragment();
        } else if ($key instanceof RawBindingInterface) {
            $placeholder = $key->getTarget();
        } else {
            // Create unique placeholder
            $placeholder = $this->getUniqPlaceholder();

            // Bind to the global stack
            $this->bind($placeholder, $key);
        }

        return $placeholder;
    }