PHP: rfc:grapheme_str_split

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====== PHP RFC: Grapheme cluster for str_split function: grapheme_str_split ======
  * Version: 0.1
  * Date: 2024-03-04
  * Author: Yuya Hamada, youkidearitai@gmail.com
  * Status: Implemented
  * Target Version: PHP 8.4
  * Implementation: https://github.com/php/php-src/pull/13580
  * First Published at: http://wiki.php.net/rfc/grapheme_str_split

===== Introduction =====
I noticed PHP does not have a grapheme cluster based str_split function. So I think need str_split for grapheme cluster, grapheme_str_split function using [[https://unicode-org.github.io/icu/userguide/icu4c/|ICU]]. Creating this function in the Intl extension would provide stronger support for grapheme clusters. This feature will allow to correctly handle emoji and Variation Selectors.

grapheme_str_split function is correctly support for grapheme cluster.

<code>
$ sapi/cli/php -r 'var_dump(grapheme_str_split("🙇‍♂️"));'
array(1) {
  [0]=>
  string(13) "🙇‍♂️"
}
</code>

For example, compare to mb_str_split function, mb_str_split function is str_split for Unicode codepoint. (Of course, sometimes this is more convenient.)

<code>
$ sapi/cli/php -r 'var_dump(mb_str_split("🙇‍♂️"));'
array(4) {
  [0]=>
  string(4) "🙇"
  [1]=>
  string(3) "‍" // U+200D Zero Width Joinner
  [2]=>
  string(3) "♂"
  [3]=>
  string(3) "️" // U+FE0F VARIATION SELECTOR
}
</code>

Until now, PCRE functions were required to support grapheme clusters.

<code>
$ sapi/cli/php -r  'preg_match_all("/(\X)/u", "🙇‍♂️", $matches, PREG_OFFSET_CAPTURE); var_dump($matches[1]);'
array(1) {
  [0]=>
  array(2) {
    [0]=>
    string(13) "🙇‍♂️"
    [1]=>
    int(0)
  }
}
</code>

Examples of other languages. Ruby is already support grapheme clusters as [[https://ruby-doc.org/3.2.2/String.html#method-i-grapheme_clusters|String#grapheme_clusters]]

<code>
s = "\u0061\u0308-pqr-\u0062\u0308-xyz-\u0063\u0308" # => "ä-pqr-b̈-xyz-c̈"
s.grapheme_clusters
# => ["ä", "-", "p", "q", "r", "-", "b̈", "-", "x", "y", "z", "-", "c̈"]
</code>

grapheme_str_split support to grapheme clusters (variation selectors).

<code>
$ sapi/cli/php -r 'var_dump(grapheme_str_split("ä-pqr-b̈-xyz-c̈"));'
array(13) {
  [0]=>
  string(2) "ä"
  [1]=>
  string(1) "-"
  [2]=>
  string(1) "p"
  [3]=>
  string(1) "q"
  [4]=>
  string(1) "r"
  [5]=>
  string(1) "-"
  [6]=>
  string(3) "b̈"
  [7]=>
  string(1) "-"
  [8]=>
  string(1) "x"
  [9]=>
  string(1) "y"
  [10]=>
  string(1) "z"
  [11]=>
  string(1) "-"
  [12]=>
  string(3) "c̈"
}
</code>

===== Proposal =====
Add grapheme_str_split function.

<code>
function grapheme_str_split(string $string, int $length = 1): array|false {}
</code>

$string is only support UTF-8. $length is the length of the grapheme cluster per element of the array.

===== Backward Incompatible Changes =====
This could break a function existing in userland with the same name.


===== Proposed PHP Version(s) =====
PHP 8.4

===== RFC Impact =====
==== To SAPIs ====

To SAPIs Will add the aforementioned functions to all PHP environments.


==== To Existing Extensions ====

Add grapheme_str_split() to the intl extension.


==== To Opcache ====
No effect.

==== New Constants ====
No new constants.

==== php.ini Defaults ====
No changed php.ini settings.

===== Open Issues =====
No issues

===== Future Scope =====
This section details areas where the feature might be improved in future, but that are not currently proposed in this RFC.

===== Proposed Voting Choices =====
<doodle title="Add grapheme cluster for str_split function: grapheme_str_split" auth="youkidearitai" voteType="single" closed="false" closeon="2024-04-10T00:00:00Z">
   * Yes
   * No
</doodle>


===== Implementation =====
https://github.com/php/php-src/pull/13580


===== Rejected Features =====
Keep this updated with features that were discussed on the mail lists.
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