Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:126725
Message-ID: <3C61F33E-7399-45F2-8DFD-AAC3443E519F@garsi.de>
Content-Type: multipart/alternative;
	boundary="Apple-Mail=_9C8594CA-7189-4A3E-B3DD-B837D0CB773E"
Precedence: bulk
Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3826.400.131.1.6\))
Subject: Re: [PHP-DEV] [RFC] [Discussion] Never parameters
Date: Wed, 12 Mar 2025 10:17:45 +0100
In-Reply-To: <CALaXqqRWL8ygMGoA5xnMtt7w6rE-5WJJZ5P9oiO3vHgqvod=Fw@mail.gmail.com>
Cc: PHP Internals <internals@lists.php.net>
To: Daniel Scherzer <daniel.e.scherzer@gmail.com>
References: <CALaXqqRWL8ygMGoA5xnMtt7w6rE-5WJJZ5P9oiO3vHgqvod=Fw@mail.gmail.com>
From: alwin@garsi.de (Yogarine)


--Apple-Mail=_9C8594CA-7189-4A3E-B3DD-B837D0CB773E
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain;
	charset=utf-8

On 10 Mar 2025, at 20:07, Daniel Scherzer <daniel.e.scherzer@gmail.com> =
wrote:
> Hi internals,
>=20
> I'd like to start discussion on a new RFC about allowing `never` for =
parameter types when declaring a method.
>=20
> * RFC: https://wiki.php.net/rfc/never-parameters-v2
> * Implementation: https://github.com/php/php-src/pull/18016
>=20
> -Daniel

Hi Daniel,

To begin, I'm all for a `never` bottom type, and I use it regularly when =
I need to write TypeScript.

However, I think the example offered in this RFC =E2=80=93 while a valid =
one, for now =E2=80=93 isn't the most appropriate use case for a `never` =
type. A bottom type is more often used when defining conditional types, =
or to assert that the default for a switch/match expression should never =
be reached without raising an error that the switch/match cases are not =
exhaustive.

As such, a `never` type provides a lot of value for static analysis =
tools and IDEs, and as a matter of fact both PHPStan[1] and PhpStorm[2] =
provide ways to declare a bottom type. Furthermore, when conditional =
return types and/or generics are finally implemented in PHP, never will =
become even more valuable if not essential.

But, when generics eventually do make their way to PHP, it also means =
the provided example no longer applies, because you would just be able =
to use generic types:

```php
interface BackedEnum<T> extends UnitEnum {
  public T $value;
=20
  public static function from(T $value): static;
  public static function tryFrom(T $value): ?static;
}
```

So I think it may help sell your RFC if you provide some additional =
context illustrating the use of the `never` type in generics and static =
analysis. Otherwise I fear that some people may interpret `never` as a =
stopgap solution until we get generics.

Alwin


[1] https://phpstan.org/writing-php-code/phpdoc-types#bottom-type
[2] =
https://github.com/JetBrains/phpstorm-attributes/blob/master/README.md#nor=
eturn


--Apple-Mail=_9C8594CA-7189-4A3E-B3DD-B837D0CB773E
Content-Transfer-Encoding: quoted-printable
Content-Type: text/html;
	charset=utf-8

<html><head><meta http-equiv=3D"content-type" content=3D"text/html; =
charset=3Dutf-8"></head><body style=3D"overflow-wrap: break-word; =
-webkit-nbsp-mode: space; line-break: after-white-space;"><meta =
http-equiv=3D"content-type" content=3D"text/html; charset=3Dutf-8"><div =
dir=3D"auto"><div dir=3D"ltr"></div><div dir=3D"ltr">On 10 Mar 2025, at =
20:07, Daniel Scherzer &lt;daniel.e.scherzer@gmail.com&gt; =
wrote:</div><blockquote type=3D"cite"><div dir=3D"ltr"><div dir=3D"ltr">Hi=
 internals,<div><br></div><div>I'd like to start discussion on a new RFC =
about allowing `never` for parameter types when declaring a =
method.</div><div><br></div><div>* RFC:&nbsp;<a =
href=3D"https://wiki.php.net/rfc/never-parameters-v2">https://wiki.php.net=
/rfc/never-parameters-v2</a></div><div>* Implementation:&nbsp;<a =
href=3D"https://github.com/php/php-src/pull/18016">https://github.com/php/=
php-src/pull/18016</a></div><div><br></div><div>-Daniel</div></div>
</div></blockquote><br><div>Hi Daniel,</div><div><br></div><div>To =
begin, I'm all for a `never` bottom type, and I use it regularly when I =
need to write TypeScript.</div><div><br></div><div>However, I think the =
example offered in this RFC =E2=80=93 while a valid one, for now =E2=80=93=
 isn't the most appropriate use case for a `never` type. A bottom type =
is more often used when defining conditional types, or to assert that =
the default for a switch/match expression should never be reached =
without raising an error that the switch/match cases are not =
exhaustive.</div><div><br></div><div>As such, a `never` type provides a =
lot of value for static analysis tools and IDEs, and as a matter of fact =
both PHPStan[1] and PhpStorm[2] provide ways to declare a bottom type. =
Furthermore, when conditional return types and/or generics are finally =
implemented in PHP, never will become even more valuable if not =
essential.</div><div><br></div><div>But, when generics eventually do =
make their way to PHP, it also means the provided example no longer =
applies, because you would just be able to use generic =
types:</div><div><br></div><div>```php</div><div><div>interface =
BackedEnum&lt;T&gt; extends UnitEnum {</div><div>&nbsp; public T =
$value;</div><div>&nbsp;</div><div>&nbsp; public static function from(T =
$value): static;</div><div>&nbsp; public static function tryFrom(T =
$value): =
?static;</div><div>}</div></div><div>```</div><div><br></div><div>So I =
think it may help sell your RFC if you provide some additional context =
illustrating the use of the `never` type in generics and static =
analysis. Otherwise I fear that some people may interpret `never` as a =
stopgap solution until we get =
generics.</div><div><br></div><div>Alwin</div><div><br></div><div><br></di=
v><div>[1]&nbsp;<a =
href=3D"https://phpstan.org/writing-php-code/phpdoc-types#bottom-type">htt=
ps://phpstan.org/writing-php-code/phpdoc-types#bottom-type</a></div><div>[=
2]&nbsp;<a =
href=3D"https://github.com/JetBrains/phpstorm-attributes/blob/master/READM=
E.md#noreturn">https://github.com/JetBrains/phpstorm-attributes/blob/maste=
r/README.md#noreturn</a></div><div><br></div></div></body></html>=

--Apple-Mail=_9C8594CA-7189-4A3E-B3DD-B837D0CB773E--