Newsgroups: php.internals
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Xref: news.php.net php.internals:113831
Date: Sun, 28 Mar 2021 16:54:19 +0200 (CEST)
To: internals <internals@lists.php.net>
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Thread-Topic: Proposal: add IntlDateTimePatternGenerator
Subject: Proposal: add IntlDateTimePatternGenerator
From: mel@dafert.at (Mel Dafert)

Hello Internals,

I would like to propose an addition to the intl extension, IntlDateTimePatternGenerator.
ICU exposes the DateTimePatternGenerator class that allows generating a formatting pattern from a given "skeleton" for a given locale. (see https://unicode-org.github.io/icu-docs/apidoc/dev/icu4c/classicu_1_1DateTimePatternGenerator.html)
This allows more flexibility than the current $format argument of IntlDateFormatter::format(), which takes either a few pre-defined constants or a hard-coded format.
This functionality also has been requested in the past. (see https://bugs.php.net/bug.php?id=70377)

For example, if an application requires a format that will always use the long version of a year, but the short version of a month (eg. "MM/dd/YYYY" for "en_US", or "dd.MM.YYYY" for "de_DE"), one is out of luck.
IntlDateFormatter::SHORT will use the short year for "de_DE" ("dd.MM.YY"), and IntlDateFormatter::MEDIUM will use the long version of a month for "en_US" ("MMM dd, YYYY").

With IntlDateTimePatternGenerator::getBestPattern(), a skeleton can be provided to generate the appropriate pattern for a given locale.
In the use-case given above, the skeleton "YYYYMMdd" will generate the desired patterns for each locale, which can then be passed to IntlDateFormatter::format().

Proposed Signature:
```
class IntlDateTimePatternGenerator
{
    public function __construct(?string $locale = null) {}

    public static function create(?string $locale = null): ?IntlDateTimePatternGenerator {}

    public function getBestPattern(string $skeleton): string|false {}
}
```

Example use-case:
```
$date = new \DateTime();
$skeleton = "YYYYMMdd";
$dtpg = new \IntlDateTimePatternGenerator(); // uses default locale if not specified
$format = $dtpg->getBestPattern($skeleton);

echo \IntlDateFormatter::formatObject($date, $format); // outputs "28.03.2020" for "de_DE" locale

```

The proposed implementation can be found here: https://github.com/php/php-src/pull/6771
I assume that this will require an RFC, in which case I request the karma to create one. My wiki account is deltragon.

Regards,
Mel Dafert