使PHP对象的行为类似于数组？

class MyArray implements ArrayAccess, Iterator, Countable {
    private $container = array();
    private $position = 0;

    public function offsetSet($offset, $value) {
        if (is_null($offset)) {
            $this->container[] = $value;
        } else {
            $this->container[$offset] = $value;
        }
    }

    public function offsetExists($offset) {
        return isset($this->container[$offset]);
    }

    public function offsetUnset($offset) {
        unset($this->container[$offset]);
    }

    public function offsetGet($offset) {
        return isset($this->container[$offset]) ? $this->container[$offset] : null;
    }

    public function rewind() {
        $this->position = 0;
    }

    public function current() {
        return $this->container[$this->position];
    }

    public function key() {
        return $this->position;
    }

    public function next() {
        ++$this->position;
    }

    public function valid() {
        return isset($this->container[$this->position]);
    }

    public function count() {
        return count($this->container);
    }
}

$obj = new MyArray();
$obj[] = 'value1';
$obj[] = 'value2';

foreach ($obj as $key => $value) {
    echo $key . ': ' . $value . PHP_EOL;
}

echo 'Count: ' . count($obj) . PHP_EOL;