SplStorageObjects

The SplObjectStorage class provides a list for objects: it may also the values with the same object, making it an efficient object set.

<?php

    // As an object set
    $s = new SplObjectStorage();

    $o1 = new stdClass;
    $o2 = new stdClass;
    $o3 = new stdClass;

    $s->attach($o1);
    $s->attach($o2);

    var_dump($s->contains($o1)); // true
    var_dump($s->contains($o2)); // true
    var_dump($s->contains($o3)); // false

?>

Documentation

See also SplObjectStorage Class.

Related : Object, SplObjectStorage, Weakmap