舉個例子

class Test implements ArrayAccess
{
    private $testData = [];

    public function offsetExists($offset)
    {
        echo 'call ' . __METHOD__ . "\r\n";
        return isset($this->testData[$offset]);
    }

    public function offsetGet($offset)
    {
        echo 'call ' . __METHOD__ . "\r\n";
        return $this->testData[$offset];
    }

    public function offsetSet($offset, $value)
    {
        echo 'call ' . __METHOD__ . "\r\n";
        return $this->testData[$offset] = $value;
    }

    public function offsetUnset($offset)
    {
        echo 'call ' . __METHOD__ . "\r\n";
        unset($this->testData[$offset]);
    }

}

$obj = new Test();

if (!isset($obj['name'])) { //call Test::offsetExists
$obj['name'] = 'zhangsan'; //call Test::offsetSet
}
echo $obj['name'] . "\r\n"; //call Test::offsetGet

var_dump($obj);

$obj['age'] = 18; //call Test::offsetSet

echo $obj['age'] . "\r\n"; //call Test::offsetGet

unset($obj['address']); //call Test::offsetUnset

ArrayAccess（數組式訪問）接口