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Thread-Topic: [RFC] Add is_list(mixed $value): bool to check for list-like
 arrays
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Date: Sun, 3 Jan 2021 18:17:44 +0000
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Subject: Re: [RFC] Add is_list(mixed $value): bool to check for list-like
 arrays
From: tysonandre775@hotmail.com (tyson andre)

Hi internals,=0A=
=0A=
> I've created the RFC https://wiki.php.net/rfc/is_list=0A=
> =0A=
> This adds a new function `is_list(mixed $value): bool` that will return t=
rue=0A=
> if the type of $value is array and the array keys are `0 .. count($value)=
-1` in that order.=0A=
>=0A=
> It's well-known that PHP's `array` data type is rare among programming la=
nguages=0A=
> in that it supports both integer and string keys=0A=
> and that iteration order is important and guaranteed.=0A=
> (it is used for overlapping use cases - in many other languages, both vec=
tors/lists/arrays and hash maps are available)=0A=
> =0A=
> While it is possible to efficiently check that something is an array,=0A=
> that array may still have string keys, not start from 0, have missing arr=
ay offsets,=0A=
> or contain out of order keys.=0A=
> =0A=
> It can be useful to verify that the assumption that array keys are consec=
utive integers is correct,=0A=
> both for data that is being passed into a module or for validating data b=
efore returning it from a module.=0A=
> However, because it's currently inconvenient to do that, this has rarely =
been done in my experience.=0A=
> =0A=
> In performance-sensitive serializers or data encoders, it may also be use=
ful to have an efficient check to distinguish lists from associative arrays=
.=0A=
> For example, json_encode does this when deciding to serialize a value as =
[0, 1, 2] instead of {=930=94:0,=932=94:1,=931=94:1}=0A=
> for arrays depending on the key orders.=0A=
> =0A=
> Prior email threads/PRs have had others indicate interest in the ability =
to efficiently check=0A=
> if a PHP `array` has sequential ordered keys starting from 0=0A=
> =0A=
> https://externals.io/message/109760 =93Any interest in a list type?=94=0A=
> https://externals.io/message/111744 =93Request for couple memory optimize=
d array improvements=94=0A=
> Implementation: https://github.com/php/php-src/pull/6070 (some discussion=
 is in the linked PR it was based on)=0A=
=0A=
Due to concerns about naming causing confusion with theoretical potential f=
uture changes to the language,=0A=
I've updated https://wiki.php.net/rfc/is_list to use the name `is_array_and=
_list(mixed $value): bool` instead.=0A=
(e.g. what if php used the reserved word `list` to add an actual list type =
in the future, and is_list() returned false for that.)=0A=
=0A=
I plan to start voting on the RFC in a few days.=0A=
=0A=
Thanks,=0A=
- Tyson=