How to change a value in a repeated item

[shiningstarpxx]

for example

1 message UserItem
2 {
3 repeated int32 nums = 1;
4 }
5
6 message User
7 {
8 repeated int32 data = 1;
9 optional UserItem item = 2;
10 }

12 include('test.proto.php');
13
14 $u = new User();
15
16 for( $i = 0; $i < 2; $i++ )
17 {
18 $u->appendData($i);
19 }
20 echo $u->getData(1)."\n"; // 1
21 echo $u->getData(0)."\n"; // 0

if I want to change $u->data[1] = 100, what should i do?
I have no idea, and i am looking forward to your answer