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Date: Fri, 22 Mar 2024 13:58:54 +0100
Message-ID: <CAPzBOBPvMu7NRocrAJHWULpjvJyk_SC4+MFs5d-7dQpdMuSahg@mail.gmail.com>
Subject: Re: [PHP-DEV] Proposal: AS assertions
To: "Rowan Tommins [IMSoP]" <imsop.php@rwec.co.uk>
Cc: internals@lists.php.net
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From: landers.robert@gmail.com (Robert Landers)

On Fri, Mar 22, 2024 at 12:01=E2=80=AFPM Rowan Tommins [IMSoP]
<imsop.php@rwec.co.uk> wrote:
>
> On Fri, 22 Mar 2024, at 08:17, Jordi Boggiano wrote:
>
> We perhaps could make sure that as does not throw if used with `??`, or t=
hat `??` catches the type error and returns the right-hand expression inste=
ad:
>
> So to do a nullable typecast you would do:
>
>     $a as int|float ?? null
>
>
> While this limits the impact to only expressions combining as with ?? it =
still has the same fundamental problem: you can't meaningfully use it with =
a nullable type.
>
>
> As a concrete example, imagine you have an optional $description paramete=
r, and want to ensure any non-null values are converted to string, but keep=
 null unchanged.
>
> At first sight, it looks like you could write this:
>
> $descString =3D $description as string|null ?? (string)$description;
>
> But this won't work - the ?? swallows the null and turns it into an empty=
 string, which isn't what you wanted. You need some syntax that catches the=
 TypeError, but preserves the null:
>
> $descString =3D $description as string|null else (string)$description;
> // or
> $descString =3D $description as string|null catch (string)$description;
> // or
> $descString =3D $description as string|null default (string)$description;
>
>
> I actually think there are quite a lot of scenarios where that idiom woul=
d be useful:
>
> $optionalExpiryDateTime =3D $expiry as ?DateTimeInterface else new DateTi=
meImmutable($expiry);
> $optionalUnixTimestamp =3D $time as ?int else strotime((string)$time);
> $optionalUnicodeName =3D $name as ?UnicodeString else new UnicodeString( =
$name );
> etc
>
> And once you have that, you don't need anything special for the null case=
, it's just:
>
> $nameString =3D $name as ?string else null;
>
> Regards,
> --
> Rowan Tommins
> [IMSoP]

I'm not sure I can grok what this does...

$optionalExpiryDateTime =3D ($expiry =3D=3D=3D null || $expiry instanceof
DateTimeInterface) ? $expiry : new DateTimeImmutable($expiry)

Maybe? What would be the usefulness of this in real life code? I've
never written anything like it in my life.

Personally, this is much more readable (assuming I got the logic right):

using always null if not match, and handle the case for when $expiry
isn't a string:

$optionalExpiryDateTime =3D $expiry =3D=3D null ? $expiry : $expiry as
DateTimeInterface ?? new DateTimeImmutable($expiry as string ?? "now")

But I can't think of why you'd want null ... null would apply to all
types and have a dedicated branch, no matter what any other type is.

Robert Landers
Software Engineer
Utrecht NL