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Date: Wed, 20 Jun 2018 15:24:34 +0100
Message-ID: <CALKiJKok2KOCprhQPAA_+_3cQsUn_LiHJUwGCgqLFBC1wLXTHw@mail.gmail.com>
To: Levi Morrison <levim@php.net>
Cc: enno.woortmann@web.de, internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="000000000000d9b57a056f138ed0"
Subject: Re: [PHP-DEV] [RFC][Under Discussion] Add functions
 array_key_first()and array_key_last()
From: rowan.collins@gmail.com (Rowan Collins)

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On 20 June 2018 at 15:10, Levi Morrison <levim@php.net> wrote:

> On Wed, Jun 20, 2018 at 8:09 AM Rowan Collins <rowan.collins@gmail.com>
> wrote:
> >
> > On 20 June 2018 at 14:55, Levi Morrison <levim@php.net> wrote:
> >>
> >>
> >>     if ([$key, $value] = array_last($input) {
> >>         // do something
> >>     }
> >>
> >
> >
> > Unfortunately, this won't work. I didn't know list() could even be used
> as an expression, but apparently if it is, it evaluates to the whole array
> on its right-hand side, which makes sense.
> >
> > So, if array_last([]) returns [null, null], then [$key,
> $value]=array_last([]) will also evaluate to [null, null]. Since that's not
> an empty array (it has two elements in it), it will evaluate to true.
> https://3v4l.org/lIEa1
> >
> > If, on the other hand, array_last([]) returned something empty, like [],
> the list() assignment would throw Notices for the implicit access to
> elements [0] and [1] of the empty array. https://3v4l.org/qhq5R
>
> It returns `?array`. So either `null` or `[$key, $value]`. There are
> no notices; sorry for the lack of detail.
>


Ah, OK, you learn something every day! For anyone else like me who was
unaware of this, list() apparently silently accepts any non-array value on
the right of the assignment, assigns all variables in the list() to null,
and evaluates to the assigned (but otherwise unused) value. So
$x=list($a,$b)=42; will set $a and $b to NULL, and $x to 42, without any
notices.

I don't think I would ever have expected that behaviour, but apparently
it's been that way forever, so I guess it's fine to exploit it.

Incidentally, there's no mention of this on the manual page, which is also
missing information on the short-hand syntax and key-based destructuring
introduced in PHP 7.1: http://php.net/list

Regards,
-- 
Rowan Collins
[IMSoP]

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