It seems to me that we should have an RFC for this. Either https://wiki.php.net/rfc/array_key_first_last_index should be updated respectively, or a new RFC should be pursued.

I've requested a PHP.net wiki account at http://news.php.net/php.internals/102225 to create a new RFC due to the different functional scope of this PR in comparison to the existing RFC.

EDIT:
Link to the RFC for this PR: https://wiki.php.net/rfc/array_key_first_last

According to your RFC, NULL will be returned if nothing was found. Does this work?

$array = [null => true];
if (null !== array_key_first($array) && null !== array_key_last($array)) {
    echo 'hi';
}

Reading the code, I would expect that there is a collision in the return value. I know it's an edge-case, but I've seen this code being written before. The var_dump output of this gives an empty string though, so it's different behavior than you'd expect when reading the code as a new developer.

$array = [null => true];
var_dump($array);

array(1) { [""] => bool(true) }

The functions will return null only for empty arrays. The provided array is not empty and thus a given key will be returned. As a key initialized with null will be casted to an empty string, the empty string will be returned:

$array = [null => true];
var_dump(array_key_first($array));

string(0) ""

In the code example you provided the code inside the if will be executed and "hi" will be echoed.

It's an unexpected behavior at first glance but it's an already existing PHP behavior, see array_keys for example:

var_dump(array_keys([null => true]));

array(1) {
  [0]=>
  string(0) ""
}

We could even propose an RFC to deprecate null as a key assignment, WDYT?

deprecate null as an array key could help to avoid errors. But I think it would be a huge deal to update large legacy applications due to something like

$array[$randomVariable] = $bla;

where $randomVariable is not always defined. Have seen it sometimes.

Should be feasible with an appropriate time as a warning.

Yep, that's the goal of a deprecation: just send a E_DEPRECATED error without breaking the script 😉

As I extended the scope of the RFC to provide a complete set of functions for handling the outer array elements I updated the PR to also implement and add tests for the methods

$firstValue = array_value_first($array);
$lastValue = array_value_last($array);

Is the _value part added due to backward compatibility? It would make sense as these two functions are often implemented in the user land. Otherwise I think it would be neat to have just short names array_first and array_last as the _value part is nowhere to be seen in other array functions. Replacing user defined functions with the same functionality shouldn't be a big issue.

Primary I've chosen the names to have consistent function names for the group of functions to handle array keys/values:

array_keys();
array_key_first();
array_key_last();

array_values();
array_value_first();
array_value_last();

In my opinion array_value_first describes the function better than array_first which provides less context if used in user land code and may be mistaken as array_key_first.

array_value_first() returning NULL is still ambiguous though, because the first value could be NULL, or the array could be empty. :/

Comment on behalf of cmb at php.net:

Thanks! Applied via 50516a6.