Why and when to use &$result in PHP? - php

Question

We are trying to call the same function from within the function but it won't work.
We belive that there is a &$result variable that should be placed somewhere , we have seen it in other parts of our code that another person has written, but we don't know where and how it works.
Could someone please explain?
Here is our code if you want to have a look:
$parentID = $_POST['id'];
$choosenCategory = $_POST['choosenCategory'];
$count = 0;
function count_child($parentID, $choosenCategory){
foreach($parentID as $thisID){
foreach($_SESSION['items'][$thisID]['Children'] as $ChildID){
$DatabaseID = $ChildID;
$ItemCategory = $_SESSION['items'][$DatabaseID]['ItemCategory'];
$ItemName = $_SESSION['items'][$DatabaseID]['ItemName'];
$ItemStatus = $_SESSION['items'][$DatabaseID]['ItemStatus'];
$ParentID = $_SESSION['items'][$thisID]['DatabaseID'];
$Children = $_SESSION['items'][$DatabaseID]['Children'];
$Dependencies = $_SESSION['items'][$DatabaseID]['Dependencies'];
if($ItemCategory == $choosenCategory){
$count++;
}
if($ItemCategory !== "RWP" && $ItemCategory !== "US" && $levels === "all"){
$array = array();
count_child($ChildID, $choosenCategory);
}
}
}
}
count_child($parentID, $choosenCategory);
$json = json_encode($count);
echo $json;
It always output 0, regardless of what input we give.

Answer 1

Try to return $count from the function;
Like this:
$parentID = $_POST['id'];
$choosenCategory = $_POST['choosenCategory'];
function count_child($parentID, $choosenCategory){
$count = 0;
foreach ($parentID as $thisID){
$aChild = &$_SESSION['items'][$thisID]['Children'];
foreach ($aChild as $ChildID){
$DatabaseID = $ChildID;
$ItemCategory = $_SESSION['items'][$DatabaseID]['ItemCategory'];
$ItemName = $_SESSION['items'][$DatabaseID]['ItemName'];
$ItemStatus = $_SESSION['items'][$DatabaseID]['ItemStatus'];
$ParentID = $_SESSION['items'][$thisID]['DatabaseID'];
$Children = $_SESSION['items'][$DatabaseID]['Children'];
$Dependencies = $_SESSION['items'][$DatabaseID]['Dependencies'];
if ($ItemCategory == $choosenCategory){
$count++;
}
if ($ItemCategory !== "RWP" && $ItemCategory !== "US" && $levels === "all"){
$array = array();
paint_child($ChildID, $choosenCategory);
}
}
}
return $count;
}
$count = count_child($parentID, $choosenCategory);
$json = json_encode($count);
echo $json;

Answer 2

Depending on the php version and which datatype you are using, php creates a copy of your data when you call the function. that copy is used within that function. when you are now modify the data then the copy is modify. Later when your call is finished, the copy will be deleted (in each function call in every recursion step). That & operation avoids a copy and sends a reference. No copy will be created. The reference operator can used in function parameters also at return values, but it's more common in function parameters.