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To: Rowan Tommins <rowan.collins@gmail.com>, "internals@lists.php.net"
	<internals@lists.php.net>
CC: Nikita Popov <nikita.ppv@gmail.com>
Thread-Topic: [PHP-DEV] [RFC] [Vote] Deprecate functions with overloaded
 signatures
Thread-Index: AQHZqDNOzscc7EYmMEqrpB8lsTz/k6+dZgkAgAAWZYCAAFdR/4AAsh6AgANtoEk=
Date: Thu, 29 Jun 2023 16:51:21 +0000
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Subject: Re: [PHP-DEV] [RFC] [Vote] Deprecate functions with overloaded
 signatures
From: theodorejb@outlook.com (Theodore Brown)

On Tue, June 27, 2023, 6:33 Rowan Tommins wrote:=0A=
> On 27/06/2023 02:25, Theodore Brown wrote:=0A=
> > Currently the following code returns only the array keys that loosely e=
qual null:=0A=
> >=0A=
> >      array_keys($array, null)=0A=
> >=0A=
> > If the function is changed to a single signature with $filter_value def=
aulting to null (with an argument count check to preserve the above functio=
nality), its behavior becomes a lot more surprising/unexpected. If a parame=
ter defaults to null, as a user I don't expect the function to work differe=
ntly when I explicitly pass the default value.=0A=
> =0A=
> =0A=
> An alternative solution to this situation is to introduce a new dummy=0A=
> value for such parameters, similar to how JavaScript uses the special=0A=
> "Symbol" type to have keys that can't collide with any userland value.=0A=
> In this context, this could be achieved with a single-value enum, i.e.:=
=0A=
> =0A=
> enum ArrayKeys { case IncludeAll; }=0A=
> =0A=
> function array_keys(array $array, mixed $filter_value =3D=0A=
> ArrayKeys::IncludeAll, bool $strict =3D false): array {}=0A=
> =0A=
> That way, the optional parameter has a real default value, distinct from=
=0A=
> any value the user might wish to filter by, including null, and full=0A=
> compatibility is maintained with existing code.=0A=
> =0A=
> I don't know whether this is a direction we want to go, but thought I'd=
=0A=
> throw it out there.=0A=
=0A=
=0A=
That's an interesting idea, but I'm not sure it would make the behavior any=
 less confusing. Are single-value enums used like this anywhere else in PHP=
? As a user my expectation when seeing `ArrayKeys::IncludeAll` as the defau=
lt is that there must be other `ArrayKeys` enum values for additional optio=
ns.=0A=
=0A=
Note that currently there is a draft RFC to support objects in array keys. =
[1] If that feature is accepted, would it not be allowed to filter array ke=
ys by the `ArrayKeys::IncludeAll` enum value? That would also be surprising=
/unexpected.=0A=
=0A=
Based on the current vote tally, `array_keys` looks like it will be the onl=
y remaining function in PHP 9 with an overloaded signature, which would mak=
e it all the more strange.=0A=
=0A=
[1]: https://wiki.php.net/rfc/object_keys_in_arrays=