Strange behavior for arrays passed by reference - php

Question

I've just got an unexpected result for a simple function which has an argument passed by reference.
Let's presume we have the following arrays:
$arr = array(
'Test' => 1,
'OtherKey' => 2,
);
$keyTranslation = array(
'OtherKey' => 'other_key',
'Test' => 'test',
);
The $keyTranslation array might not have the keys defined in the same order as the $arr. This is just to explain the need of the function.
and the following function:
function test(&$arr, $keyTranslation) {
foreach ($arr as $key => $value) {
$arr[$keyTranslation[$key]] = $value;
unset($arr[$key]);
}
}
The unexpected result is when simply call the function having the arrays above as arguments:
test($arr, $keyTranslation);
What I was expected?
array(2) {
["test"]=>
int(1)
["other_key"]=>
int(2)
}
What I've got?
NOTICE Undefined index: test on line number 10
NOTICE Undefined index: other_key on line number 10
NOTICE Undefined index: on line number 10
array(0) { }
Why was this happened?
Because each time I am adding a new value to the passed by reference array, the loop is iterating also over that value and unset it.
The question
Is this normal? or it is a bug in PHP?

Answer 1

This is what I would use as it seems a bit dodgy to be setting & unsetting elements of an array while foreaching through it...
function test(&$arr, $keyTranslation) {
$newarr = array();
foreach ($arr as $key => $value) {
$newarr[$keyTranslation[$key]] = $value;
}
$arr = $newarr; // Not sure if you'd have to unset $arr first...
}

Answer 2

Make sure you test if the translated key exists :
<?php
$arr = [ 'Foo' => 1, 'Bar' => 2 , 'dont_change' => 3, ];
$trans = [ 'Foo' => 'bar', 'Bar' => 'foo', 'Foobar' => 'foobar', ];
function test(&$arr, $trans) {
foreach($arr as $key => $value) {
if (!isset($trans[$key])) continue;
$arr[$trans[$key]] = $value;
unset($arr[$key]);
}
}
test($arr, $trans);
print_r($arr);

Answer 3

No Bug here. First of all the keys in $arr are 'Test' and 'OtherKey'. In your function you try to access $arr['test'] and $arr['other_key'], which do not exist, hence the notices. Then you unset the key and therefore the result is that $arr is null after the function call, as you passed $arr by reference.