yii\caching\ApcCache::init PHP Method

    public function init()
    {
        parent::init();
        $extension = $this->useApcu ? 'apcu' : 'apc';
        if (!extension_loaded($extension)) {
            throw new InvalidConfigException("ApcCache requires PHP {$extension} extension to be loaded.");
        }
    }

 public function init()
 {
     $this->useApcu = true;
     parent::init();
 }