<?php /* Bridge between PHP versions by jms/metadata */ trait SerializationHelper { /**  * @deprecated Use serializeToArray  *  * @return string  */ public function serialize() { return serialize($this->serializeToArray()); } /**  * @deprecated Use unserializeFromArray  *  * @param string $str  *  * @return void  */ public function unserialize($str) { $this->unserializeFromArray(unserialize($str)); } public function __serialize(): array { return [$this->serialize()]; } public function __unserialize(array $data): void { $this->unserialize($data[0]); } } class ClassMetadata implements \Serializable { use SerializationHelper; /**  * @var array  */ private $indexMetadatas = []; public function addIndexMetadata($contextName, IndexMetadata $indexMetadata) { $indexMetadata->setClassMetadata($this); $this->indexMetadatas[$contextName] = $indexMetadata; } public function serializeToArray(): array { return [$this->indexMetadatas,]; } public function unserializeFromArray(array $data): void { list($indexMetadata) = $data; $this->indexMetadatas = $indexMetadata; } } class IndexMetadata { /**  * @var ClassMetadata  */ private $classMetadata; public function getClassMetadata() { return $this->classMetadata; } public function setClassMetadata(ClassMetadata $classMetadata) { $this->classMetadata = $classMetadata; } } $classMetadata = new ClassMetadata(); $indexMetadata = new IndexMetadata(); $classMetadata->addIndexMetadata('test', $indexMetadata); var_dump(serialize($classMetadata));