php对象数组式访问接口（ArrayAccess）

提供给对象可以像访问数组一样访问对象的接口

class obj implements arrayaccess {
    private $container = array();
    public function __construct() {
        $this->container = array(
            'one'   => 1,
            'two'   => 2,
            'three' => 3,
        );
    }
    
    // 检查索引是否存在
    public function offsetExists($offset) {
        return isset($this->container[$offset]);
    }
    // 删除指定索引的值
    public function offsetUnset($offset) {
        unset($this->container[$offset]);
    }
    // 获取指定索引的值
    public function offsetGet($offset) {
        return isset($this->container[$offset]) ? $this->container[$offset] : null;
    }
    // 设置指定索引的值
    public function offsetSet($offset, $value) {
        if (is_null($offset)) {
            $this->container[] = $value;
        } else {
            $this->container[$offset] = $value;
        }
    }
}

$obj = new obj;

var_dump(isset($obj['two']));
var_dump($obj['two']);
unset($obj['two']);
var_dump(isset($obj['two']));
$obj['two'] = 'A value';
var_dump($obj['two']);
$obj[] = 'Append 1';
$obj[] = 'Append 2';
$obj[] = 'Append 3';
print_r($obj);