Re: [RFC] Allow null as standalone type

On Mon, Oct 4, 2021 at 5:33 AM Levi Morrison via internals < internals@lists.php.net> wrote: > On Sat, Oct 2, 2021 at 9:07 AM G. P. B. <george.banyard@gmail.com> wrote: > > > > Hello internals, > > > > I'm proposing a new RFC to make 'null' usable as a standalone type. > > > > RFC: https://wiki.php.net/rfc/null-standalone-type > > GitHub PR: https://github.com/php/php-src/pull/7546 > > > > Best regards, > > > > George P. Banyard > > I don't see the word void in the RFC. I think there ought > to be > something said about how naked null is different or not > different > than void. > Right. To quote the original union types RFC, this was the motivation for the current limitation: > The null type is only allowed as part of a union, and can not be used as a standalone type. Allowing it as a standalone type would make both function foo(): void and function foo(): null legal function signatures, with similar but not identical semantics. This would negatively impact teachability for an unclear benefit. I'm not opposed to making null usable as a standalone type though. I think the fact that a "void" function must use "return;" instead of "return null;" and a "null" function conversely must use "return null;" instead of "return;" will probably be sufficient disambiguation. If we make this change, I would however suggest to also support "false" as a standalone type. I think this change primarily has benefits from a typesystem completeness perspective rather than a strong practical need. From that angle, it would be nice if all types that are usable in a union are also usable as standalone types, rather than shifting the special case from null to false. Regards, Nikita