public function getIndexProviders($index)
    {
        if (!isset($this->providers[$index])) {
            throw new \InvalidArgumentException(sprintf('No providers were registered for index "%s".', $index));
        }

        $providers = [];
        foreach ($this->providers[$index] as $type => $providerId) {
            $providers[$type] = $this->getProvider($index, $type);
        }

        return $providers;
    }