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Date: Fri, 22 Mar 2024 21:05:58 +0100
Message-ID: <CAPzBOBMRNW7DjnYaGDu9u7V1iTL4s3sa-4XXX4s29d9=qN+eiw@mail.gmail.com>
Subject: Re: [PHP-DEV] Proposal: AS assertions
To: "Rowan Tommins [IMSoP]" <imsop.php@rwec.co.uk>
Cc: Claude Pache <claude.pache@gmail.com>, internals@lists.php.net
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From: landers.robert@gmail.com (Robert Landers)

On Fri, Mar 22, 2024 at 8:02=E2=80=AFPM Rowan Tommins [IMSoP]
<imsop.php@rwec.co.uk> wrote:
>
> On Fri, 22 Mar 2024, at 17:38, Claude Pache wrote:
>
>
> Le 22 mars 2024 =C3=A0 16:18, Rowan Tommins [IMSoP] <imsop.php@rwec.co.uk=
> a =C3=A9crit :
>
> $optionalExpiryDateTime =3D $expiry as ?DateTimeInterface else some_other=
_function($expiry);
> assert($optionalExpiryDateTime is ?DateTimeInterface); // cannot fail, al=
ready asserted by the "as"
>
>
> I think that the `is` operator is all we need; the `as` operator adds syn=
tax complexity for little gain. Compare:
>
> $optionalExpiryDateTime =3D $expiry as ?DateTimeInterface else some_other=
_function($expiry);
>
> vs
>
> $optionalExpiryDateTime =3D $expiry is ?DateTimeInterface ? $expiry : som=
e_other_function($expiry);
>
>
>
> I agree, it doesn't add much; and that's what the draft RFC Ilija linked =
to says as well.
>
> But the point of that particular example is that after the "is" version, =
you don't actually know the type of $optionalExpiryDateTime without looking=
 up the return type of some_other_function()
>
> With the "as" version, you can see at a glance that after that line, $opt=
ionalExpiryDateTime is *guaranteed* to be DateTimeInterface or null, which =
I understood to be the intention of Robert's original proposal on this thre=
ad.
>
> --
> Rowan Tommins
> [IMSoP]
>

Indeed, "as" is to pattern matching like the fn is to function. You
can live with one or the other, but having both is much more useful.