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Foreach with ampersand (&) ​

When iterating through an array of items, changes you make to the as value are not reflected in the original array. e.g. if you iterate through your array as in foreach ($cars as $car) any changes to $car will not be reflected in $cars.

The following code shows the problem if you don't use the ampersand(&).

php

$correlations = [
  [
    'completion_status' => 'complete',
  ],
  [
    'completion_status' => 'incomplete',
  ],
  [
    'completion_status' => 'incomplete',
  ],
];

foreach ($correlations as $correlation) {
  $correlation['action_status'] = ($correlation['completion_status'] == 'complete') ? 'no-action-required' : 'action-required';
}
var_dump($correlations);

// Notice the use of the ampersand below.
foreach ($correlations as &$correlation) {
  $correlation['action_status'] = $correlation['completion_status'] == 'complete' ? 'no-action-required' : 'action-required';
}
var_dump($correlations);

And here is the output. Notice that the first var_dump shows no sign of the action_status items. With the ampersand(&) the expected variable appears.

array(3) {
  [0]=>
  array(1) {
    ["completion_status"]=>
    string(8) "complete"
  }
  [1]=>
  array(1) {
    ["completion_status"]=>
    string(10) "incomplete"
  }
  [2]=>
  array(1) {
    ["completion_status"]=>
    string(10) "incomplete"
  }
}
array(3) {
  [0]=>
  array(2) {
    ["completion_status"]=>
    string(8) "complete"
    ["action_status"]=>
    string(18) "no-action-required"
  }
  [1]=>
  array(2) {
    ["completion_status"]=>
    string(10) "incomplete"
    ["action_status"]=>
    string(15) "action-required"
  }
  [2]=>
  &array(2) {
    ["completion_status"]=>
    string(10) "incomplete"
    ["action_status"]=>
    string(15) "action-required"
  }
}

Here is Copilot's take on the problem:

The code you provided is iterating over the $correlations array and updating each $correlation item's action_status based on its completion_status. However, this code doesn't actually update the original $correlations array because $correlation is a copy of the original item in the array, not a reference.

To refactor this code and make sure the original $correlations array is updated, you should use the & symbol to pass $correlation by reference:

php
foreach ($correlations as &$correlation) {
    $correlation['action_status'] = $correlation['completion_status'] == 'complete' ? 'no-action-required' : 'action-required';
}
unset($correlation); // Unset reference to avoid unexpected behavior

This way, any changes made to $correlation inside the loop will be reflected in the original $correlations array. The unset($correlation) line is added after the loop to break the reference with the last element, as recommended in the PHP documentation to avoid unexpected behavior.

Deep merge arrays with numeric keys ​

While searching for a way to merge two arrays with numeric keys, I found this information on PHP.net. Unfortunately array_merge_recursive() does not work with numeric keys. The following code (from 12 years ago) is a solution to the problem. I did have to get ChatGPT to modernize the code a bit so it would work with PHP 8.

php
function array_merge_recursive_new(array $base, array $array1, array ...$arrays): array {
  array_unshift($arrays, $array1);

  foreach ($arrays as $array) {
    foreach ($array as $key => $value) {
      if (is_array($value) && isset($base[$key]) && is_array($base[$key])) {
        $base[$key] = array_merge_recursive_new($base[$key], $value);
      } else {
        $base[$key] = $value;
      }
    }
  }
  return $base;
}

// Define some test arrays
$array1 = ['a' => 1, 'b' => 2, 'c' => ['d' => 3]];
$array2 = ['a' => 2, 'c' => ['e' => 4]];
$array3 = ['f' => 5, 'c' => ['g' => 6]];

// Merge the arrays
$result = array_merge_recursive_new($array1, $array2, $array3);

// Print the result
print_r($result);

Here is the output:

Array
(
    [a] => 2
    [b] => 2
    [c] => Array
        (
            [d] => 3
            [e] => 4
            [g] => 6
        )
    [f] => 5
)

Reference ​