Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:112741
User-Agent: Cyrus-JMAP/3.3.1-61-gb52c239-fm-20201210.001-gb52c2396
Mime-Version: 1.0
Message-ID: <3fe86a3a-7aaa-48c0-b1fa-2f5266e3bdf2@www.fastmail.com>
In-Reply-To: 
 <DM6PR07MB6618ACE23A04BBE30EE67D8BF9D30@DM6PR07MB6618.namprd07.prod.outlook.com>
References: 
 <DM6PR07MB6618468A8C4A49818C4E2EB0F9C10@DM6PR07MB6618.namprd07.prod.outlook.com>
 <DM6PR07MB6618ACE23A04BBE30EE67D8BF9D30@DM6PR07MB6618.namprd07.prod.outlook.com>
Date: Sun, 03 Jan 2021 20:56:34 -0600
To: "php internals" <internals@lists.php.net>
Content-Type: text/plain;charset=utf-8
Content-Transfer-Encoding: quoted-printable
Subject: =?UTF-8?Q?Re:_[PHP-DEV]_Re:_[RFC]_Add_is=5Flist(mixed_$value):_bool_to_c?=
 =?UTF-8?Q?heck_for_list-like_arrays?=
From: larry@garfieldtech.com ("Larry Garfield")

On Sun, Jan 3, 2021, at 12:17 PM, tyson andre wrote:
> Hi internals,
>=20
> > I've created the RFC https://wiki.php.net/rfc/is_list
> >=20
> > This adds a new function `is_list(mixed $value): bool` that will ret=
urn true
> > if the type of $value is array and the array keys are `0 .. count($v=
alue)-1` in that order.
> >
> > It's well-known that PHP's `array` data type is rare among programmi=
ng languages
> > in that it supports both integer and string keys
> > and that iteration order is important and guaranteed.
> > (it is used for overlapping use cases - in many other languages, bot=
h vectors/lists/arrays and hash maps are available)
> >=20
> > While it is possible to efficiently check that something is an array=
,
> > that array may still have string keys, not start from 0, have missin=
g array offsets,
> > or contain out of order keys.
> >=20
> > It can be useful to verify that the assumption that array keys are c=
onsecutive integers is correct,
> > both for data that is being passed into a module or for validating d=
ata before returning it from a module.
> > However, because it's currently inconvenient to do that, this has ra=
rely been done in my experience.
> >=20
> > In performance-sensitive serializers or data encoders, it may also b=
e useful to have an efficient check to distinguish lists from associativ=
e arrays.
> > For example, json_encode does this when deciding to serialize a valu=
e as [0, 1, 2] instead of {=E2=80=9C0=E2=80=9D:0,=E2=80=9C2=E2=80=9D:1,=E2=
=80=9C1=E2=80=9D:1}
> > for arrays depending on the key orders.
> >=20
> > Prior email threads/PRs have had others indicate interest in the abi=
lity to efficiently check
> > if a PHP `array` has sequential ordered keys starting from 0
> >=20
> > https://externals.io/message/109760 =E2=80=9CAny interest in a list =
type?=E2=80=9D
> > https://externals.io/message/111744 =E2=80=9CRequest for couple memo=
ry optimized array improvements=E2=80=9D
> > Implementation: https://github.com/php/php-src/pull/6070 (some discu=
ssion is in the linked PR it was based on)
>=20
> Due to concerns about naming causing confusion with theoretical=20
> potential future changes to the language,
> I've updated https://wiki.php.net/rfc/is_list to use the name=20
> `is_array_and_list(mixed $value): bool` instead.
> (e.g. what if php used the reserved word `list` to add an actual list=20=

> type in the future, and is_list() returned false for that.)
>=20
> I plan to start voting on the RFC in a few days.

Possible alternative that's less clumsy: is_packed_array?

--Larry Garfield