public function getDocumentIdentifier($document)
    {
        return isset($this->documentIdentifiers[spl_object_hash($document)]) ?
            $this->documentIdentifiers[spl_object_hash($document)] : null;
    }
public function getDocumentIdentifier($document)
    {
        return isset($this->documentIdentifiers[spl_object_hash($document)]) ?
            $this->documentIdentifiers[spl_object_hash($document)] : null;
    }
public function getDocumentIdentifier ( $ document ) { return isset ( $ this -> documentIdentifiers [ spl_object_hash ( $ document ) ] ) ? $ this -> documentIdentifiers [ spl_object_hash ( $ document ) ] : null ; }
Gets the identifier of a document.

@param object $document

@return Identifier|null The identifier instance for the document
Gets the identifier of a document .