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To: php internals <internals@lists.php.net>, tyson andre
	<tysonandre775@hotmail.com>
Thread-Topic: [PHP-DEV] Re: [RFC] Add is_list(mixed $value): bool to check for
 list-like arrays
Thread-Index: AQHW1m7vogEIYJkiwEyrC80th3/gm6oWSyBggACSbgCAATCMVQ==
Date: Mon, 4 Jan 2021 21:44:50 +0000
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Subject: Re: [PHP-DEV] Re: [RFC] Add is_list(mixed $value): bool to check for
 list-like arrays
From: theodorejb@outlook.com (Theodore Brown)

On Sun, Jan 3, 2021 at 8:56 PM Larry Garfield <larry@garfieldtech.com> wrot=
e:=0A=
=0A=
> On Sun, Jan 3, 2021, at 12:17 PM, tyson andre wrote:=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=0A=
> > > return true if the type of $value is array and the array keys are=0A=
> > > `0 .. count($value)-1` in that order.=0A=
> > >=0A=
> > > It's well-known that PHP's `array` data type is rare among=0A=
> > > programming languages in that it supports both integer and string=0A=
> > > keys and that iteration order is important and guaranteed. (it is=0A=
> > > used for overlapping use cases - in many other languages, both=0A=
> > > vectors/lists/arrays and hash maps are available)=0A=
> > >=0A=
> > > While it is possible to efficiently check that something is an=0A=
> > > array, that array may still have string keys, not start from 0,=0A=
> > > have missing array offsets, or contain out of order keys.=0A=
> > >=0A=
> > > It can be useful to verify that the assumption that array keys=0A=
> > > are consecutive integers is correct, both for data that is being=0A=
> > > passed into a module or for validating data before returning it=0A=
> > > from a module. However, because it's currently inconvenient to do=0A=
> > > that, this has rarely been done in my experience.=0A=
> > >=0A=
> > > In performance-sensitive serializers or data encoders, it may=0A=
> > > also be useful to have an efficient check to distinguish lists=0A=
> > > from associative arrays. For example, json_encode does this when=0A=
> > > 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=0A=
> > > ability to efficiently check if a PHP `array` has sequential=0A=
> > > 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=0A=
> > > optimized array improvements=94=0A=
> > > Implementation: https://github.com/php/php-src/pull/6070=0A=
> > > (some discussion is in the linked PR it was based on)=0A=
> >=0A=
> >=0A=
> > Due to concerns about naming causing confusion with theoretical=0A=
> > potential future changes to the language,=0A=
> > I've updated https://wiki.php.net/rfc/is_list to use the name=0A=
> > `is_array_and_list(mixed $value): bool` instead.=0A=
> > (e.g. what if php used the reserved word `list` to add an actual list=
=0A=
> > 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=
>=0A=
> Possible alternative that's less clumsy: is_packed_array?=0A=
=0A=
=0A=
Hi Tyson,=0A=
=0A=
Thanks for the proposal and implementation. I've wanted a function=0A=
that does this on numerous occasions, so I think it will be a good=0A=
addition to the standard library.=0A=
=0A=
If I may chime in with Larry's suggestion: I think `is_packed_array`=0A=
would  a better name than `is_array_and_list`. The latter is potentially=0A=
confusing since it sounds like the value has more than one type.=0A=
`is_packed_array` makes it clearer that the function checks whether=0A=
the value is an array matching certain criteria. I think it also reads=0A=
better when used along with other functions. For example:=0A=
=0A=
    function is_associative_array(mixed $value) {=0A=
        return is_array($value) && !is_packed_array($value);=0A=
        // vs.=0A=
        return is_array($value) && !is_array_and_list($value);=0A=
    }=0A=
=0A=
Best regards,  =0A=
Theodore=