Re: Proposal: AS assertions

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]