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<?php class User { protected $profile; public function setProfile(Profile $profile) { $this->profile = $profile; } } class Profile { protected $user; public function __construct(User $user) { $this->user = $user; $user->setProfile($this); } } $user1 = new User(); $profile1 = new Profile($user1); $user2 = new User(); $profile2 = new Profile($user2); var_dump($profile1 == $profile2);

preferences:
37.87 ms | 402 KiB | 5 Q