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Date: Fri, 22 Mar 2024 09:46:22 +0000
To: internals@lists.php.net
Subject: Re: [PHP-DEV] Proposal: AS assertions
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From: imsop.php@rwec.co.uk ("Rowan Tommins [IMSoP]")

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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 that `??` catches the type error and returns the right-hand expression instead:
> 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 parameter, 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 = $description as string|null ?? (string)$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 = $description as string|null else (string)$description;
// or
$descString = $description as string|null catch (string)$description;
// or
$descString = $description as string|null default (string)$description;


I actually think there are quite a lot of scenarios where that idiom would be useful:

$optionalExpiryDateTime = $expiry as ?DateTimeInterface else new DateTimeImmutable($expiry);
$optionalUnixTimestamp = $time as ?int else strotime((string)$time);
$optionalUnicodeName = $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 = $name as ?string else null;

Regards,
-- 
Rowan Tommins
[IMSoP]
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<!DOCTYPE html><html><head><title></title><style type=3D"text/css">p.Mso=
Normal,p.MsoNoSpacing{margin:0}</style></head><body><div>On Fri, 22 Mar =
2024, at 08:17, Jordi Boggiano wrote:<br></div><blockquote type=3D"cite"=
 id=3D"qt" style=3D""><div class=3D"qt-moz-cite-prefix">We perhaps could=
 make sure that as does not throw if used with
      `??`, or that `??` catches the type error and returns the
      right-hand expression instead:<br></div><p>So to do a nullable typ=
ecast you would do:<br></p><p>&nbsp;&nbsp;&nbsp; $a as int|float ?? null=
<br></p></blockquote><div><br></div><div>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.<br></div><=
div><br></div><div><br></div><div>As a concrete example, imagine you hav=
e an optional $description parameter, and want to ensure any non-null va=
lues are converted to string, but keep null unchanged.<br></div><div><br=
></div><div>At first sight, it looks like you could write this:<br></div=
><div><br></div><div>$descString =3D $description as string|null ?? (str=
ing)$description;<br></div><div><br></div><div>But this won't work - the=
 ?? swallows the null and turns it into an empty string, which isn't wha=
t you wanted. You need some syntax that catches the TypeError, but prese=
rves the null:<br></div><div><br></div><div>$descString =3D $description=
 as string|null else (string)$description;<br></div><div>// or<br></div>=
<div>$descString =3D $description as string|null catch (string)$descript=
ion;<br></div><div>// or<br></div><div>$descString =3D $description as s=
tring|null default (string)$description;<br></div><div><br></div><div><b=
r></div><div>I actually think there are quite a lot of scenarios where t=
hat idiom would be useful:<br></div><div><br></div><div>$optionalExpiryD=
ateTime =3D $expiry as ?DateTimeInterface else new DateTimeImmutable($ex=
piry);<br></div><div>$optionalUnixTimestamp =3D $time as ?int else strot=
ime((string)$time);<br></div><div>$optionalUnicodeName =3D $name as ?Uni=
codeString else new UnicodeString( $name );<br></div><div>etc<br></div><=
div><br></div><div>And once you have that, you don't need anything speci=
al for the null case, it's just:<br></div><div><br></div><div>$nameStrin=
g =3D $name as ?string else null;<br></div><div><br></div><div>Regards,<=
br></div><div>-- <br></div><div>Rowan Tommins<br></div><div>[IMSoP]<br><=
/div></body></html>
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