PHP: rfc:grapheme_levenshtein

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====== PHP RFC: Grapheme cluster for levenshtein, grapheme_levenshtein function ======
  * Version: 0.1
  * Date: 2024-10-14
  * Author: Yuya Hamada, youkidearitai@gmail.com
  * Status: Implemented
  * First Published at: http://wiki.php.net/rfc/grapheme_levenshtein

===== Introduction =====
I creating mb_levenshtein [[https://wiki.php.net/rfc/mb_levenshtein]]. However, there was some discussion that the Levenshtein function for each grapheme cluster might be more logical, and I thought so too, so I created a PoC.

ref: [[https://github.com/php/php-src/issues/16428]]

For example, combined character is works fine.

<code>
var_dump(grapheme_levenshtein("\u{0065}\u{0301}", "\u{00e9}")); // Result is 0 when use grapheme_levenshtein. mb_levenshtein is not works well.
</code>

Also, variable selector is works fine.

<code>
// variable $nabe and $nabe_E0100 is seems nothing different.
// However, $nabe_E0100 is variable selector in U+908A U+E0100.
// So grapheme_levenshtein result is maybe 0.
$nabe = '邊';
$nabe_E0100 = "邊󠄀";
var_dump(grapheme_levenshtein($nabe, $nabe_E0100)); // Result is 0 when use grapheme_levenshtein. mb_levenshtein result is 1 that it's not works fine.
</code>

===== Proposal =====
Add grapheme_levenshtein function.

<code>
function grapheme_levenshtein(string $string1, string $string2, int $insertion_cost = 1, int $replacement_cost = 1, int $deletion_cost = 1): int|false {}
</code>

$string1 and $string2 must be valid UTF-8. Returns false if either string fails to parse as UTF-8.

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


===== Proposed PHP Version(s) =====
PHP 8.5

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


==== To Existing Extensions ====
Adds grapheme_levenshtein() to the intl extension. 

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

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

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

===== Open Issues =====
https://github.com/php/php-src/issues/16428

===== 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 =====
Include these so readers know where you are heading and can discuss the proposed voting options.


===== Voting =====
<doodle title="Add grapheme_levenshtein function" auth="youkidearitai" voteType="single" closed="true" closeon="2025-04-16T00:00:00Z">
   * Yes
   * No
</doodle>

===== Implementation =====
https://github.com/php/php-src/pull/18087

===== References =====
Nothing.

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