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Date: Thu, 16 Apr 2020 15:00:40 +0200
Message-ID: <CAC5V6gjU4X8KsREiaF+kB4rGVHPQ2Up5DuUPgmaK+0arpSkH4Q@mail.gmail.com>
To: Enno Woortmann <enno.woortmann@web.de>
Cc: internals@lists.php.net
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Subject: Re: [PHP-DEV] Type hints in array destructuring expressions
From: guilliam.xavier@gmail.com (Guilliam Xavier)

On Thu, Apr 16, 2020 at 12:20 PM Enno Woortmann <enno.woortmann@web.de> wrote:
>
> Hi together,
>
> as the voting for the "Type casting in array destructuring expressions"
> shows a clear direction to be declined (sad faces on my side, I really
> would've liked it as a feature completion of the casting feature set
> without the need for a really new syntax, as the parser also already
> coverred it, but ok, time to continue :D ), combined with a strong
> interest for the topic "type checks in array destructuring expressions"
> (as well in the discussion as in the vote) I've set up a first draft of
> an RFC covering this topic:
>
> https://wiki.php.net/rfc/typehint_array_desctructuring
>
> The discussion around the casting in array destructuring brought up the
> idea to perform regular type checks in array destructuring expressions.
> This RFC proposes a new syntax to type hint a variable inside an array
> destructuring expression:
>
> $data = [42, 'Example', 2002];
> [int $id, string $data, int $year] = $data;
>
> The type hints behave identically to the type hints used in method
> signatures (compare https://wiki.php.net/rfc/scalar_type_hints_v5). This
> especially includes a behaviour depending on the strict_types directive.
>
> Additionally to scalar type hints also object type hints are possible.
>
> I've not yet started an implementation draft but I think this one will
> be more tricky than the type cast implementation approach. As the parser
> re-uses the array definition for array destructuring expressions (which
> also leads to the type cast implementation without touching the parser)
> adding type hints to the definition would also affect other parts of the
> language eg. something like:
>
> $x = [int $a, string $b];
>
> would be parsed by the parser. I'm currently not able to grasp the
> impact of such a change. But that's another topic.
>
> Let's focus on the idea itself instead of the implementation first.
> Thoughts on the first draft?
>
> Cheers, Enno
>
> --
> PHP Internals - PHP Runtime Development Mailing List
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>

Hi, thanks for proposing,

I guess it could be useful (or convenient at least). Just 2 thoughts:

- It has been requested several times on this list to stop using the
wording "type hint" and instead write "type declaration" ;)

- When I see this example in the RFC:
```
$years = [["now", 2020], ["future", 2021]];
foreach ($years as [string $description, int $year]) {
```
I immediately think of a similar:
```
$years = ["now" => 2020, "future" => 2021];
foreach ($years as string $description => int $year) {
```
or:
```
$foos = [new Foo("one"), new Foo("two")];
foreach ($foos as Foo $foo) {
```
Now I remember this has already been requested (e.g.
https://externals.io/message/104485#104488), but that's not really the
same use case, so I don't know if it could/should be included...

Regards,

-- 
Guilliam Xavier