PHP SPL SplObjectStorage是用来存储一组对象的，特别是当你需要唯一标识对象的时候。
PHP SPL SplObjectStorage类实现了Countable,Iterator,Serializable,ArrayAccess四个接口。可实现统计、迭代、序列化、数组式访问等功能。
看下面一个简单的例子：
class A {
public $i;
public function __construct($i) {
$this->i = $i;
}
}
$a1 = new A(1);
$a2 = new A(2);
$a3 = new A(3);
$a4 = new A(4);
$container = new SplObjectStorage();
//SplObjectStorage::attach 添加对象到Storage中
$container->attach($a1);
$container->attach($a2);
$container->attach($a3);
//SplObjectStorage::detach 将对象从Storage中移除
$container->detach($a2);
//SplObjectStorage::contains用于检查对象是否存在Storage中
var_dump($container->contains($a1)); //true
var_dump($container->contains($a4)); //false
//遍历
$container->rewind();
while($container->valid()) {
var_dump($container->current());
$container->next();
}
