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Subject: Re: Alternative approach for LWG3565 "Handling of encodings in localized chrono formatting"
From: Victor Zverovich (victor.zverovich_at_[hidden])
Date: 2021-06-22 17:21:57


Hi Peter and other unicoders,

This is an interesting idea but as Corentin already pointed out the name is
just a convention so I'm not sure how it is supposed to work. The
transcoding solution on the other hand is implementable, possibly in
multiple ways. I initially implemented it for MSVC/Windows but someone
contributed an implementation for libstdc++ where transcoding is normally
unnecessary but it's still cool that it works. The proposed resolution
should probably say something for the case when transcoding is impossible
which can happen with weird user-defined locales. A simple solution is to
fallback to no transcoding.

Cheers,
Victor

On Thu, Jun 17, 2021 at 1:57 PM Peter Brett via SG16 <sg16_at_[hidden]>
wrote:

> Hi all,
>
> The current proposed resolution for LWG3565 (https://wg21.link/LWG3565)
> involves transcoding from the locale encoding to UTF-8. This makes me a
> little uncomfortable.
>
> Is it possible instead to say that, if the string literal encoding is
> UTF-8, then the effective locale is _as if_ the specified or global
> locale was modified by replacing the associated codeset with UTF-8?
>
> So, the following code:
>
> std::locale l1("Russian.1251");
> auto s = std::format(l1, "День недели: {:L}", std::chrono::Monday);
>
> Would behave as if replaced by:
>
> std::locale l1("Russian.1251");
> std::locale l2(l1, std::locale("Russian.UTF-8"), locale::time);
> auto s = std::format(l2, "День недели: {:L}", std::chrono::Monday);
>
> This would permit an implementation that has UTF-8 locale data available
> to use it directly, rather than being required to use the 1251 codeset
> locale data and transcode in order to conform to the standard.
>
> Peter
>
> P.S. How would one go about writing a locale object that customizes
> chrono formatting with std::format? Does anyone have a code sample?
> --
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