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Date: Wed, 18 Sep 2019 15:33:01 +0200
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To: PHP internals <internals@lists.php.net>
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Subject: Re: [RFC] Union Types v2
From: nikita.ppv@gmail.com (Nikita Popov)

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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:
> https://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

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