/*
 * ArrayAccess ：Interface to provide accessing objects as arrays.
 * 用访问数组的方式访问对象的
 */

class Foo implements ArrayAccess
{
    private $container = [];

    public function __construct()
    {
        $this->container = [
            ‘a‘=>1,
            ‘b‘=>2,
            ‘c‘=>3
        ];
    }

    public function offsetExists($offset)
    {
        // TODO: Implement offsetExists() method.
        return isset($this->container[$offset]);
    }

    public function offsetGet($offset)
    {
        // TODO: Implement offsetGet() method.
        return $this->container[$offset]??null;
    }

    public function offsetSet($offset, $value)
    {
        // TODO: Implement offsetSet() method.
        $this->container[$offset] = $value;
    }

    public function offsetUnset($offset)
    {
        // TODO: Implement offsetUnset() method.
        unset($this->container[$offset]);
    }

}

$foo = new Foo();
$foo[‘d‘] = 321;
$foo[‘a‘] = 123;
var_dump(isset($foo[‘ae‘]));//bool(false)
var_dump(isset($foo[‘a‘]));//bool(true)