[PHP-NOTES] note 130531 added to control-structures.foreach

Definitely relevant for PHP 7+

1. You can't change array during iteration

Foreach WILL NOT LOOP through new values added to the array 
<?php
while inside the loop.
$a = [1, 2, 3];
foreach ($a as $k => $v) {
    echo $v;

    if ($v === 2) {
        $v[] = 4;
    }
}
?>
Output: 123
But the original array was modified: [1, 2, 3, 4]

Foreach WILL LOOP through values deleted from the array while inside the loop.
<?php
$a = [1, 2, 3];
foreach ($a as $k => $v) {
    echo $v;

    if ($v === 2) {
        unset($a[2]);
    }
}
?>
Output: 123
But the original array was modified: [1, 2]

2. But If you iterate by reference using foreach ($arr as &$v) then $arr is turned into a reference and you can change it during iteration

Foreach WILL LOOP through new values added to the array while inside the loop.
<?php
$a = [1, 2, 3];
foreach ($v as &$v) {
    echo $v;

    if ($v === 2) {
        $v[] = 4;
    }
}
?>
Output: 1234

Foreach WILL NOT LOOP through values deleted from the array while inside the loop.
<?php
$a = [1, 2, 3];
foreach ($a as $k => &$v) {
    echo $v;

    if ($v === 2) {
        unset($a[2]);
    }
}
?>
Output: 12
----
Server IP: 45.112.84.4
Probable Submitter: 80.90.5.137 (proxied: 2a03:d000:184:35c:31bd:5811:9420:ede6)
----
Manual Page -- https://php.net/manual/en/control-structures.foreach.php
Edit        -- https://main.php.net/note/edit/130531
Del: integrated  -- https://main.php.net/note/delete/130531/integrated
Del: useless     -- https://main.php.net/note/delete/130531/useless
Del: bad code    -- https://main.php.net/note/delete/130531/bad+code
Del: spam        -- https://main.php.net/note/delete/130531/spam
Del: non-english -- https://main.php.net/note/delete/130531/non-english
Del: in docs     -- https://main.php.net/note/delete/130531/in+docs
Del: other reasons-- https://main.php.net/note/delete/130531
Reject      -- https://main.php.net/note/reject/130531
Search      -- https://main.php.net/manage/user-notes.php