Re: [RFC] Union Types v2

On Wed, Sep 4, 2019 at 10:26 AM Nikita Popov <nikita.ppv@gmail.com> wrote: > Hi internals, > > I'd like to start the discussion on union types again, with a new proposal: > > Pull Request: https://github.com/php/php-rfcs/pull/1 > Rendered Proposal: > Œ1 > 6"sýãÌãG̱&Nhttps://github.com/nikic/php-rfcs/blob/union-types/rfcs/0000-union-types-v2.md > > As an experiment, I'm submitting this RFC as a GitHub pull request, to > evaluate whether this might be a better medium for RFC proposals in the > future. It would be great if we could keep the discussion to the GitHub > pull request for the purpose of this experiment (keep in mind that you can > also create comments on specific lines in the proposal, not just the > overall discussion thread!) Of course, you can also reply to this mail > instead. The final vote will be held in the wiki as usual. > > Relatively to the previous proposal by Bob&Levi ( > https://wiki.php.net/rfc/union_types), I think the main > differences in > this proposal are: > * Updated to specify interaction with new language features, like full > variance and property types. > * Updated for the use of the ?Type syntax rather than the Type|null > syntax. > * Only supports "false" as a pseudo-type, not "true". > * Slightly simplified semantics for the coercive typing mode. > > Regards, > Nikita > Heads up, two weeks have passed, so this may now go to voting... I believe relative to my original draft the main change that has happened as a result of the discussion is the use of T1|T2|null syntax instead of ?(T1|T2) syntax for nullable types. ?T becomes an alias for T|null. People felt fairly strongly that while ?T is a nice shorthand for a common case, unions should use the T1|T2|null syntax that both reads better and is already well-established from phpdoc. I figured I should mentioned this for people who haven't been following the GitHub thread... Nikita