Re: [RFC] Transform void into an alias for null
| From: | Ilija Tovilo | Date: | Mon, 02 Jun 2025 23:46:07 +0000 |
| Subject: | Re: [RFC] Transform void into an alias for null | ||
| References: | 1 | Groups: | php.internals |
| Request: | Send a blank email to internals+get-127544@lists.php.net to get a copy of this message | ||
Hi Gina
On Mon, Jun 2, 2025 at 6:28 PM Gina P. Banyard <internals@gpb.moe> wrote:
>
> RFC: https://wiki.php.net/rfc/void-as-null
After a read, I think I fundamentally disagree with the proposal. It
says (regarding the status-quo):
> * void is not a subtype of a function with a mixed return type
This is laid out as a downside, but I don't think it is. Consider this
example under the specified behavior:
interface MapInterface {
public function set(string $key, mixed $value): void;
}
class Map implements MapInterface {
public function set(string $key, mixed $value): void {
// Store the key/value pair _somehow_
}
}
Let's assume the return type
MapInterface::set() mixed instead,
where the intention is for set() to return the previous value, or
null if there was none. This change will go completely unnoticed by
Map::set(), because void is now just null, which is a subtype
of
mixed. This is a bug that would previously have been caught,
notifying you that you're supposed to return _something_.
Similarly, the code function foo(): void { return null; } is now
proposed to be valid, and I assume the inverse for void/return; is
also true. In this example, we now update Map::set() to the new
return type.
class Map implements MapInterface {
public function set(string $key, mixed $value): mixed {
$oldValue = /* Fetch old value _somehow_ */;
// Store the key/value pair _somehow_
if (!$this->observers) {
return; // This line was here before.
}
$this->observers->notify($key, $oldValue, $value);
return $oldValue;
}
}
Good examples are hard, but imagine Map::set() would allow notifying
a list of observers about changes to the map. Previously, the
return; would have prevented an erroneous call to notify() on
null. However, now it is missing the returning of $oldValue. This
is another bug that would previously have been caught. In fact, even a
missing trailing return $something; would not be caught anymore.
IMO, these checks are useful enough not to be removed.
Please let me know if I'm missing anything.
Ilija