Symfony\Component\DependencyInjection\ContainerBuilder::hasAlias PHP Method

    public function hasAlias($id)
    {
        return isset($this->aliasDefinitions[strtolower($id)]);
    }

 /**
  * @param string $id
  * @return string
  */
 public function definitionClass(string $id) : string
 {
     if ($this->builder->hasAlias($id)) {
         return $this->builder->getDefinition((string) $this->builder->getAlias($id))->getClass()->getClass();
     }
     return $this->builder->getDefinition($id)->getClass();
 }