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Date: Fri, 22 Mar 2024 11:58:30 +0000
To: internals@lists.php.net
Subject: Re: [PHP-DEV] Proposal: AS assertions
Content-Type: text/plain
From: imsop.php@rwec.co.uk ("Rowan Tommins [IMSoP]")

On Fri, 22 Mar 2024, at 10:05, Robert Landers wrote:
> After asking an AI for some examples and usages, the most compatible
> one would be C#'s. In actuality, I think it could be hugely simplified
> if we simply return null instead of throwing. There'd be no special
> case for |null, and it would move the decision making to the
> programmer:
>
> $x = $a as int ?? throw new LogicException();

It might be relevant that C# has only recently introduced the concept of explicitly nullable reference types, with a complex migration process for existing code: https://learn.microsoft.com/en-us/dotnet/csharp/nullable-migration-strategies So in most C# code, there isn't actually a difference between "expect a DateTime" and "expect a DateTime or null"

PHP, however, strictly separates those two, and always has; so this would be surprising:

$x = $a as DateTime;
assert($x instanceof DateTime); // will fail if $x has defaulted to null!


That's why I suggested that with an explcit default, the default would be automatically asserted as matching the specified type:

$x = $a as DateTime else 'No date given'; // TypeError: string given, DateTime expected
$x = $a as DateTime|string else 'No date given'; // OK

$x = $a as DateTime else null; // TypeError: null given, DateTime expected
$x = $a as ?DateTime else null; // OK

If the statement runs without error, $x is guaranteed to be of the type (or pattern) given to the "as" operator.


Regards,
-- 
Rowan Tommins
[IMSoP]