Added "key" parameter to array_reduce callback

[Bilge]

This changes the signature of the array_reduce callback from:

callback(mixed $carry, mixed $item): mixed

to:

callback(mixed $carry, mixed $item, int|string $key): mixed

[divinity76]

guess it's worth mentioning that it can easily be built in userland?

function array_reduce_with_key(array $array, callable $callback, mixed $initial = null): mixed
{
    $result = $initial;
    foreach ($array as $key => $value) {
        $result = $callback($result, $value, $key);
    }
    return $result;
}

[Bilge]

I don't think that's worth mentioning, unless you can justify why it precludes the usefulness of having it in core?

[divinity76]

well there is a backwards-compatibility concern, for example

$array = [[1, 2], [3, 4], [5, 6]];
$flattened_array = array_reduce($array, array_merge(...), []);

today generates

array(1,2,3,4,5,6)

but in your branch presumably generates

Fatal error: Uncaught TypeError: array_merge(): Argument #3 must be of type array, int given

it might not be worth the BC break to do it in core (i don't know)

edit: would not affect the vast majority of code in the wild (as you said in the ML, most functions don't care about an extra argument.. but exceptions exist)

[nielsdos]

This would indeed require an RFC because there's a BC concern, even though the BC impact is likely limited.

[divinity76]

the bc problem could be resolved by adding a 4th argument bool $callback_with_key = false to array_reduce