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Subject: Re: [PHP-DEV] RFC: Marking return values as important (#[\NoDiscard])
Date: Thu, 30 Jan 2025 18:48:39 +0100
In-Reply-To: <da1854112a3acb434e43868b431fe9e9@bastelstu.be>
Cc: php internals <internals@lists.php.net>
To: =?utf-8?Q?Tim_D=C3=BCsterhus?= <tim@bastelstu.be>
References: <a995ac24905030e168e7f6006b996cd5@bastelstu.be>
 <a3d14e31-53eb-4a04-8fb2-01f58809fec1@app.fastmail.com>
 <3f170549-cfd6-441e-b892-cf51d726dbe8@bastelstu.be>
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 <FC48217C-7934-4957-9DC9-6C5576B78DA8@rwec.co.uk>
 <da1854112a3acb434e43868b431fe9e9@bastelstu.be>
From: claude.pache@gmail.com (Claude Pache)


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> Le 30 janv. 2025 =C3=A0 16:51, Tim D=C3=BCsterhus <tim@bastelstu.be> a =
=C3=A9crit :
>=20
> Hi
>=20
> Am 2025-01-30 10:02, schrieb Rowan Tommins [IMSoP]:
>> I think it would be good to explore alternatives - for instance, I =
think C# has a reserved _ variable to assign discarded results to, but =
may be misremembering.
>=20
> A quick search confirms that C# supports the `_` variable. It's also =
supported with Rust.
>=20
> We are open to possible alternatives to the `(void)` cast, this was =
also something we discussed while drafting the RFC. However we opted for =
the `(void)` with out proposal for the following reasons:
>=20
> - `$_ =3D func();` is already working as a regular variable (see my =
reply to Rob regarding lifetimes), thus repurposing it as a =E2=80=9Cdisca=
rd pile=E2=80=9D would cause backwards compatibility issues.
> - `_ =3D func();` would introduce new syntax (just like `(void)`), but =
does not look and feel like PHP to us.
> - `(void)func();` has precedent in other languages (just like `_ =3D`) =
and looks and feels like PHP. In fact in earlier PHP versions there =
already was an `(unset)` cast to unconditionally turn an expression into =
`null`. We opted for `(void)` instead of bringing back `(unset)` for the =
following reasons: (1) Possible confusion about a deprecated + removed =
feature coming back (e.g. avoiding old blog articles). (2) More cleanly =
enforcing that `(void)` is a statement, rather than an expression. (3) =
The similarity with the `void` return type to indicate that =
=E2=80=9Cnothing=E2=80=9D is returned.

A possible alternative is: `! func();`, that already =E2=80=9Cworks=E2=80=9D=
 as of today, modulo possible optimisation.

In any case, I think that `(void) func();` is not self-explanatory, and =
in the event I want to ignore a result I am not supposed to ignore, I =
will probably write something more explicit like, `$unused =3D =
func();`(possibly decorated with an annotation telling static analysers =
not to complain that $unused is unused), or `forget(func())`

BTW,  the RFC says that introducing the `(void)` cast is a backward =
compatible change, which is incorrect; see: https://3v4l.org/iN7OY

=E2=80=94Claude


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<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;"><br =
id=3D"lineBreakAtBeginningOfMessage"><div><br><blockquote =
type=3D"cite"><div>Le 30 janv. 2025 =C3=A0 16:51, Tim D=C3=BCsterhus =
&lt;tim@bastelstu.be&gt; a =C3=A9crit :</div><br =
class=3D"Apple-interchange-newline"><div><div>Hi<br><br>Am 2025-01-30 =
10:02, schrieb Rowan Tommins [IMSoP]:<br><blockquote type=3D"cite">I =
think it would be good to explore alternatives - for instance, I think =
C# has a reserved _ variable to assign discarded results to, but may be =
misremembering.<br></blockquote><br>A quick search confirms that C# =
supports the `_` variable. It's also supported with Rust.<br><br>We are =
open to possible alternatives to the `(void)` cast, this was also =
something we discussed while drafting the RFC. However we opted for the =
`(void)` with out proposal for the following reasons:<br><br>- `$_ =3D =
func();` is already working as a regular variable (see my reply to Rob =
regarding lifetimes), thus repurposing it as a =E2=80=9Cdiscard pile=E2=80=
=9D would cause backwards compatibility issues.<br>- `_ =3D func();` =
would introduce new syntax (just like `(void)`), but does not look and =
feel like PHP to us.<br>- `(void)func();` has precedent in other =
languages (just like `_ =3D`) and looks and feels like PHP. In fact in =
earlier PHP versions there already was an `(unset)` cast to =
unconditionally turn an expression into `null`. We opted for `(void)` =
instead of bringing back `(unset)` for the following reasons: (1) =
Possible confusion about a deprecated + removed feature coming back =
(e.g. avoiding old blog articles). (2) More cleanly enforcing that =
`(void)` is a statement, rather than an expression. (3) The similarity =
with the `void` return type to indicate that =E2=80=9Cnothing=E2=80=9D =
is returned.<br></div></div></blockquote><div><br></div><div>A possible =
alternative is: `! func();`, that already =E2=80=9Cworks=E2=80=9D as of =
today, modulo possible optimisation.</div><div><br></div><div>In any =
case, I think that `(void) func();` is not self-explanatory, and in the =
event I want to ignore a result I am not supposed to ignore, I will =
probably write something more explicit like, `$unused =3D =
func();`(possibly decorated with an annotation telling static analysers =
not to complain that $unused is unused), or =
`forget(func())`</div><div><br></div><div>BTW, &nbsp;the RFC says that =
introducing the `(void)` cast is a backward compatible change, which is =
incorrect; see:&nbsp;<a =
href=3D"https://3v4l.org/iN7OY">https://3v4l.org/iN7OY</a></div><div><br><=
/div><div>=E2=80=94Claude</div><div><br></div></div></body></html>=

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