TYPO3.Flow

The doc comment for \TYPO3\FLOW3\Persistence\PersistenceManagerInterface::getIdentifierByObject() says, that the return type is "mixed".
Usually that is the UUID of the object (string).
If the object has an @Id property, that will be returned insted.
In case the object has multiple @Id properties, only the first of those is returned.

Example:
Mode:

class ObjectPathMapping {

    /**
     * @var string
     * @Id
     */
    protected $objectType;

    /**
     * @var string
     * @Id
     */
    protected $uriPattern;

    /**
     * @var string
     * @Id
     */
    protected $pathSegment;
[...]
}

Now, only the value of $objectType would be returned. Instead I'd expect an array that contains the Id properties - or a serialized representation!?