Re: [RFC] Add is_list(mixed $value): bool to check for list-like arrays

Hi internals, > I've created the RFC https://wiki.php.net/rfc/is_list > > This adds a new function is_list(mixed $value): bool that will > return true > if the type of $value is array and the array keys are 0 .. > count($value)-1 in that order. > > It's well-known that PHP's array data type is rare > among programming 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, both vectors/lists/arrays and > hash maps are available) > > While it is possible to efficiently check that something is an array, > that array may still have string keys, not start from 0, have missing array offsets, > or contain out of order keys. > > It can be useful to verify that the assumption that array keys are consecutive integers is > correct, > both for data that is being passed into a module or for validating data before returning it > from a module. > However, because it's currently inconvenient to do that, this has rarely been done in my > experience. > > In performance-sensitive serializers or data encoders, it may also be useful to have an > efficient check to distinguish lists from associative arrays.. > For example, json_encode does this when deciding to serialize a value as [0, 1, 2] instead of > {“0”:0,“2”:1,“1”:1} > for arrays depending on the key orders. > > Prior email threads/PRs have had others indicate interest in the ability to efficiently check > if a PHP array has sequential ordered keys starting from 0 > > https://externals.io/message/109760 “Any interest in a list > type?” > https://externals.io/message/111744 “Request for couple > memory optimized array improvements” > Implementation: https://github.com/php/php-src/pull/6070 (some > discussion is in the linked PR it was based on) Due to concerns about naming causing confusion with theoretical potential future changes to the language, I've updated https://wiki.php.net/rfc/is_list to use the name is_array_and_list(mixed $value): bool instead. (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.) I plan to start voting on the RFC in a few days. Thanks, - Tyson