Pass by reference php - php

Question

So im learning about passing by reference, what i dont understand is this, do i need to use pass by reference on functions? Like this
$items = [1,2,3,4,5];
function my_func(&$items) {
$items[] = 6;
}
my_func($items);
var_dump($items);
It will output
array(6) { [0]=> int(1) [1]=> int(2) [2]=> int(3) [3]=> int(4) [4]=> int(5) [5]=> int(6) }
I have seen people adding values to array by reference like this
class play {
public function test() {
$items = [1,2,3,4,5];
foreach($items as &$item) {
$item[] = 6;
}
return $items;
}
}
$play = new play;
$play->test();
then i get Warning:
Cannot use a scalar value as an array in
Is there a way in a loop to add a value by reference outside a function?

Answer 1

You don't need a function to use reference variables. You can do it with ordinary assignment.
$items = [1,2,3,4,5];
$alias = &$items;
$alias[] = 6;
print_r($items);

Answer 2

It seems you misunderstand what the code is doing...
You have an array...
$array = [1,2,3,4,5,6];
...which can be re-written as...
$array = [
0 => 1,
1 => 2,
2 => 3,
3 => 4,
4 => 5,
5 => 6,
];
// Hint: try print_r($array);
...the numbers on the left are the keys and the numbers on the right are the values.
Your loop loops through the array one row at a time:
foreach ($array as $item) {
echo $item;
}
// Output: 123456
Now, if you add the "pass by reference" operator then you can edit the value of $item; for example we could turn each item in the array to 1...
foreach ($array as &$item) {
$item = 1;
}
print_r($array);
/* Output:
Array
(
[0] => 1
[1] => 1
[2] => 1
[3] => 1
[4] => 1
[5] => 1
)
*/
Without the & in front of $item the code above would only change the value of $item inside of the foreach loop. The original array would not be touched.
The reason that you get an error is because you're assigning a value to $item as though it were an array. Where as, in fact, the $item variable is an integer. So all you need to do to make it work is remove the [] in your assignment line:
$item[] = 6;
// Becomes...
$item = 6;
If, instead of replacing a value you want to add a value then you can do that. But you need to add a value to the array which is $items NOT $item:
$items[] = 6;
Of course, doing that in a loop will add the value once for each item in the array...

Answer 3

I figured it out!
$result['books'][0] = ['id' => 1];
$result['books'][1] = ['id' => 2];
foreach ($result['books'] as &$book) { // use a reference
$book['new_index'] = 'new value';
$book['new_book_id'] = '29929292';
}
//unset($book); // unset the reference
echo "<pre>";
print_r($result);
echo "</pre>";