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Date: Thu, 21 Mar 2024 00:05:07 +0100
Message-ID: <CAPzBOBPDVE-xtQoFUOXchwNAo_iJTGs=RKcnoq1mOtKF70eeLA@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 Wed, Mar 20, 2024 at 8:30=E2=80=AFPM Rowan Tommins [IMSoP]
<imsop.php@rwec.co.uk> wrote:
>
>
>
> On 20 March 2024 12:51:15 GMT, Robert Landers <landers.robert@gmail.com> =
wrote:
>
> >Oh and there isn't any difference between:
> >
> >$x as ?Type
> >
> >or
> >
> >$x as Type|null
>
>
> I'm not sure if I've misunderstood your example, or you've misunderstood =
mine.
>
> I'm saying that this should be an error, because the value is neither an =
instance of Foo nor null:
>
> $a =3D 42;
> $b =3D $a as Foo|null;
>
> Your earlier example implies that would make $b equal null, which feels w=
rong to me, because it means it wouldn't match this:
>
> $a =3D 42;
> $b =3D $a as Foo|Bar;
>
> If we want a short-hand for "set to null on error" that should be separat=
e from the syntax for a nullable type.
>
>
> Regards,
> Rowan Tommins
> [IMSoP]

Interesting. I'm not sure there's a better way to say "set to null on
error" since it would be barely sensical to give a nullable type on
the right hand side anyway; so we might as well use it. In other
words, I can't think of a case where you'd actually want a Type|null
and you wouldn't have to check for null anyway.

If you think about it, in this proposal, you could use it in a match:

// $a is TypeA|TypeB|null

match (true) {
  $a as ?TypeA =3D> 'a',
  $a as ?TypeB =3D> 'b',
  $a =3D=3D=3D null =3D> 'null',
}

No matter what, you're going to have to check for null if you want to
handle all cases and throwing an error when you ask for a nullable
type would render a ton of utility moot (i.e., this match statement
wouldn't work). It's probably better to say, "I want what is on the
right-hand side of `as` or an error." Including `null` in that type
seems to be that you would get null if no other type matches, since
any variable can be `null`.

Robert Landers
Software Engineer
Utrecht NL