Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:115479
MIME-Version: 1.0
Date: Mon, 19 Jul 2021 10:41:23 +0200
Message-ID: <CAOWwgpm+PPhW6A5=Oi1tpdkQh9COGw5dQLE+Ek1p0BZ6T-xQsA@mail.gmail.com>
To: PHP Internals List <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="000000000000a6542b05c775e769"
Subject: intersection types and null for defaults, properties and return types
From: nicolas.grekas@gmail.com (Nicolas Grekas)

--000000000000a6542b05c775e769
Content-Type: text/plain; charset="UTF-8"

Hi all,

I want to bring your attention to a behavior that was mostly overlooked:

   1. it is not possible to use an intersection type with an argument that
   defaults to null
   2. it is not possible to use an intersection type with a nullable
   property (nor to make it default to null)
   3. it is not possible to use an intersection type with a nullable return
   type

Actually, 2. was possible until it was "closed" in
https://github.com/php/php-src/pull/7254

I reported these behavior and you might find some discussion about it in
https://bugs.php.net/81268

Looking at the past discussion on this list (
https://externals.io/message/113712) and at the rfc itself (
https://wiki.php.net/rfc/pure-intersection-types), this was mostly
overlooked.

That's why I'm posting this message. So that we can have that missing
discussion here.

To me, we are going to need (userland "we") these capabilities.

It's quite surprising to be "forced" to return something, or "forced" to
pass a value, when all other types in PHP allow "null". I know about the
null pattern, but it is quite uncommon in PHP, because "null" works just
great usually.

I feel like we "just" need to agree on a syntax to make this possible. It
was first suggested in the related PR to use "?A&B" (see
https://github.com/php/php-src/pull/6799#issuecomment-804761117)

This was rejected by the author with the reasoning that (?A)&B could mean
(?A)&B or ?(A&B) or even (?A)|B.

I personally don't think this ambiguity exists: (?A)|B is strictly the same
as A&B, thus ?A&B cannot also mean A&B, and I don't get how one could take
?A&B for  (?A)|B.

Another argument is that ?A&B might collide with a future syntax. But I
fail to see how. For sure we create examples of such collisions, but they
all look constructed to me.

Shouldn't we allow ?A&B ? Intersection types look unfinished to me without
compat with nullables.

Cheers,
Nicolas

--000000000000a6542b05c775e769--