update a global array within a function - php

Question

I have a global array in which I am trying to update a value (remain persistent) and then display it.
I get no error but the array never gets updated.
<?php
$anchor = 'bird';
$stuff = array('apple', 'bird', 'frog');
function insert($anchor, $stuff){
foreach($stuff as $part){
$new_array = array($anchor => rand());
if($part == $anchor){
array_push($stuff, $new_array);
}
}
}
for($x = 0; $x < 2; $x++){
insert($anchor, $stuff);
var_dump($stuff);
}
output:
array(3) {
[0]=>
string(5) "apple"
[1]=>
string(4) "bird"
[2]=>
string(4) "frog"
}
array(3) {
[0]=>
string(5) "apple"
[1]=>
string(4) "bird"
[2]=>
string(4) "frog"
}
expected output:
{'bird' => 674568765}
{'bird' => 986266261}
How do I update an array within a function, so that the changes are reflected globally (persistent)?

Answer 1

Pass the variable $stuff by reference. Note the & in the function parameters.
function insert($anchor, &$stuff){ // note the & mark
foreach($stuff as $part){
$new_array = array($anchor => rand());
if($part == $anchor){
array_push($stuff, $new_array);
}
}
}

Answer 2

As others have mentioned: by default, PHP function arguments are passed by value, meaning that a value changed inside a function does not change outside of the function.
I suggest returning the new $stuff value from your function:
<?php
$anchor = 'bird';
$stuff = array('apple', 'bird', 'frog');
function insert($anchor, $stuff){
foreach($stuff as $part){
$new_array = array($anchor => rand());
if($part == $anchor){
array_push($stuff, $new_array);
}
}
return $stuff;
}
for($x = 0; $x < 2; $x++){
$stuff=insert($anchor, $stuff);
}
echo"<pre>".print_r($stuff,true)."</pre>";
?>
Array
(
[0] => apple
[1] => bird
[2] => frog
[3] => Array
(
[bird] => 618490127
)
[4] => Array
(
[bird] => 1869073273
)
)
Other solutions propose passing by reference, to which I'm not opposed. But I have definitely run into buggy code in which it wasn't immediately clear that a function was changing a value, and I've been confused by unexpected loop behavior. As a result, I generally prefer arguably more readable/maintainable code that returns a new value.
See When to pass-by-reference in PHP.
Get technical with Sara Golemon.

Answer 3

If you want changes to a variable that you pass to a function to persist after the function ends, pass the variable by reference:
Change:
function insert($anchor, $stuff)
To
function insert($anchor, &$stuff)