Hi Morgan,
Thanks for the support!
> my partition functions also map passes and rejects to true and false
> respectively (so the result is a mapping from booleans to array values).
>
> [true => $passed, false => $rejected] = array_partition(...);
I looked at this, and the catch is that boolean array keys are cast to
integers, so true => 1 and false => 0. A boolean-keyed result would
therefore have to put the rejected elements at index 0, and then
positional destructuring silently gives the opposite of what it reads:
[$adults, $minors] = array_partition($users, fn($u) => $u->age >= 18);
// with a bool-keyed result, $adults would hold the minors
Whichever layout is chosen, one of the two idioms ends up swapped. I'd
rather keep "matching first" at index 0, since that's what Ruby, Kotlin,
Rust, Haskell and Laravel all return, and it makes the plain
[$matching, $rest] destructuring work. I'll document the pitfall
explicitly in the RFC, with your example, so nobody reaches for
[true => ..., false => ...] expecting it to work.
> I would also prefer the callback parameter to be named $predicate, to
> emphasise that it is supposed to return a boolean.
I agree it's more descriptive in isolation. But every other array
function taking a callback names it $callback, including array_filter()
and the recent array_find(), array_find_key(), array_any() and
array_all(), which are also predicates. With named arguments I think
it's more valuable that callback: works the same way across the whole
family, so I'd prefer to keep $callback for consistency. I'll mention
it in the RFC as a considered alternative.
Thanks,
Ayoub
On Sat, Oct 24, 2026 at 4:47 AM Morgan <[email protected]> wrote:
>
> On 2026-10-24 12:16, mickmackusa wrote:
> > Hi Ayoub,
> >
> > - It feels unintuitive that `true` callback outcomes map to the `0` key
> > and `false` outcomes map to `1`.
> I'm also in support, and this would have been my only observation: my
> partition functions also map passes and rejects to true and false
> respectively (so the result is a mapping from booleans to array values).
>
> If that mapping were retained, it could be documented in code as
>
> [true => $passed, false => $rejected] = array_partition(...);
>
> or
>
> $adult_tested = array_partition(...);
>
> $adults = $adult_tested[true];
> $minors = $adult_tested[false];
>
>
>
>
>
>
> I would also prefer the callback parameter to be named $predicate, to
> emphasise that it is supposed to return a boolean. $callback doesn't
> convey as much about what it's for - the same name is used, for example,
> in usort(), where it's a comparator. It didn't matter until named
> parameters became a thing.
>
