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

On Sun, Dec 20, 2020 at 2:43 AM tyson andre <tysonandre775@hotmail.com> wrote: > 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) > I probably brought this up in a previous thread, but I think it's worth considering again here, given recent changes to the RFC: I think it would make more sense to introduce this as `function array_is_list(array $array): bool`. That is, a function that only accepts arrays in the first place and determines whether the given array is a list. Your RFC does mention this possibility, but I think the argument it makes against it is not particularly strong, especially given the recent rename. The argument is that is_array_and_list($array) is shorter than writing out is_array($array) && array_is_list($array) -- that's still true, but with the new name, it's really not that much shorter anymore. On the other hand, is_array($array) && array_is_list($array) cleanly separates out the two predicates. If we take into account the fact that in the vast majority of cases we will know a-priori that the input is an array, just not whether it is a list, making the function array_is_list($array) is both clearer and more concise. function foo(array $array) { assert(array_is_list($array)); // Already know it's an array... } if (is_array($value)) { if (array_is_list($value)) { // Already know it's an array... return serialize_as_list($value); } else { return serialize_as_dict($value); } } Regards, Nikita