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

On Sun, Jan 3, 2021 at 8:56 PM Larry Garfield <larry@garfieldtech.com> wrote: > On Sun, Jan 3, 2021, at 12:17 PM, tyson andre wrote: > > > 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. > > > Possible alternative that's less clumsy: is_packed_array? Hi Tyson, Thanks for the proposal and implementation. I've wanted a function that does this on numerous occasions, so I think it will be a good addition to the standard library. If I may chime in with Larry's suggestion: I think is_packed_array would a better name than is_array_and_list. The latter is potentially confusing since it sounds like the value has more than one type. is_packed_array makes it clearer that the function checks whether the value is an array matching certain criteria. I think it also reads better when used along with other functions. For example: function is_associative_array(mixed $value) { return is_array($value) && !is_packed_array($value); // vs. return is_array($value) && !is_array_and_list($value); } Best regards, Theodore