simple collection based upon SplObjectStorage.php

<?php
class Collection extends SplObjectStorage {
    
    public function __construct($mixed = array()) {
        if ($mixed) {
            $this->add($mixed);
        }
    }
    
    public function add($mixed) {
        if (is_object($mixed)) {
            $this->attach($mixed);
        }
        if (is_array($mixed)) {
            foreach ($mixed as $obj) {
                $this->attach($obj);
            }
        }
    }
    
}

class Tag_Collection extends Collection {
        
    public function attach(Tag $tag) {
        parent::attach($tag);
    }
}

class Tag {
    
    public $title;
    
    public function __construct($title) {
        $this->title = $title;
    }
    
}

$tag1 = new Tag("One");
$tag2 = new Tag("Two");
$tag3 = new Tag("5ive");

$tag3Clone = clone $tag3;

$collection = new Tag_Collection(array($tag1, $tag2, $tag3));
$collection->add(new Tag("Six"));
$collection->add(new Tag("Six"));
$collection->add($tag3Clone);

foreach ($collection as $obj) {
    echo $obj->title . "\n";
}

echo "===================\n";

$collection->detach($tag3Clone);

foreach ($collection as $obj) {
    echo $obj->title . "\n";
}
?>