PHP: rfc:mb_levenshtein

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====== PHP RFC: Multibyte for levenshtein, mb_levenshtein function ======
  * Version: 0.1
  * Date: 2024-09-25
  * Author: Yuya Hamada, youkidearitai@gmail.com
  * Status: Declined
  * First Published at: http://wiki.php.net/rfc/mb_levenshtein

===== Introduction =====
Multibyte levenshtein distances have feature requests in the past. Therefore, we would like to create the mb_levenshtein function to implement this.

ref: [[https://github.com/php/php-src/issues/10180]]

====== Levenshtein distance difference mb_levenshtein vs grapheme_levenshtein =====
The mb_levenshtein function is the Levenshtein distance in code points.
This is useful for comparing Unicode code points. For example, this can be used to compare concatenated characters.  

<code>
var_dump(mb_levenshtein("\u{0065}\u{0301}", "\u{00e9}")); // "é" result is 1.
</code>

Surely, There are times when I want to consider this to be the same. In that case, I will propose grapheme_levenshtein separately.

===== Proposal =====
Add mb_levenshtein function.

<code>
function mb_levenshtein(string $string1, string $string2, int $insertion_cost = 1, int $replacement_cost = 1, int $deletion_cost = 1, ?string $encoding = null): int {}
</code>

===== 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 mb_levenshtein() to the mbstring 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/10180

===== 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 mb_levenshtein function" auth="Yuya Hamada" voteType="single" closed="true" closeon="2025-03-08T00:00:00Z">
   * Yes
   * No
</doodle>

===== Implementation =====
https://github.com/php/php-src/pull/16043

===== References =====
Userland implementation is here:
  * https://github.com/KEINOS/mb_levenshtein



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