Why does this change in assignment order change the variables contents?

Question

Explain this please :)

If I run

$custId = getExternalId();
echo $custId . "\n"; // Prints foobar_16262499_1
$serial = '';

$custId = explode('_', $custId);
var_dump($custId);
$custId = $custId[1];
$serial = $custId[2];

die("custId: $custId serial: $serial\n");

I get

custId: 16262499 serial: 2

This is not correct. Serial should be 1. But if I change the order of assignment to

$custId = getExternalId();
echo $custId . "\n"; // Prints foobar_16262499_1
$serial = '';

$custId = explode('_', $custId);
var_dump($custId);
$serial = $custId[2];   // Change order here!!!
$custId = $custId[1];

die("custId: $custId serial: $serial\n");

It works and gives me

custId: 16262499 serial: 1

WHY?

In both cases the var_dump of the array produces the same output:

array(3) {
  [0]=>
  string(4) "foobar"
  [1]=>
  string(8) "16262499"
  [2]=>
  string(1) "1"
}

I'm running PHP/5.3.3 ZendServer

SMACKS HEAD... How could I miss the obvious :)...

Answer 1

you override

$custId 

when you write this line

$custId = $custId[1];

so after that you get something you do not expect

$serial = $custId[2];

so do like this

list($custId,$serial) = array($custId[1],$custId[2]); 

Answer 2

1.    $custId = $custId[1];
2.    $serial = $custId[2]; // **

** this really means, ($custId[1])[2] of the original getExternalId();

Because the variable $custId after line 1 is no longer the result of

$custId = getExternalId();

But rather only the 2nd element (index [1]) from it.

You can add to your debugging by dumping just one more time

$custId = explode('_', $custId);
var_dump($custId);
$custId = $custId[1];
var_dump($custId);
$serial = $custId[2];