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Re: [SG16] Agenda for the 2021-12-01 SG16 telecon

From: Tom Honermann <tom_at_[hidden]>
Date: Wed, 1 Dec 2021 14:13:30 -0500
On 11/28/21 5:22 AM, Jens Maurer wrote:
> On 28/11/2021 10.42, Corentin Jabot via SG16 wrote:
>> On Sun, Nov 28, 2021, 01:31 Tom Honermann via SG16 <sg16_at_[hidden] <mailto:sg16_at_[hidden]>> wrote:
>> 2. If the estimated width of the fill character is greater than 1, then alignment to the end of the available space might not be possible. The choice here is whether to under-fill or over-fill the available space. This possibility is avoided if fill characters are restricted to characters with an estimated width of exactly 1.
>> std::format("{:🤡>4}", 123);
>> Is there value in specifying it? Neither solutions are great nor terrible, i think saying unspecified would be fine, so would underfilling i guess.
>> Hopefully, we are consistent and choose option 1 among those specified in the lwg issue
>> For P2286R3 <https://wg21.link/p2286r3>, LEWG requested <https://lists.isocpp.org/sg16/2021/11/2845.php> that SG16 consider the ramifications for support of user defined delimiters. We should also discuss the "?" specifier proposed to explicitly opt in to quoted and escaped formats for std::string, std::string_view, and arrays of char/wchar_t.
>> Not sure the quoted thing is in our purview.
>> For the delimiter, we should support codepoints, to be consistent with everything else. The issue is the we don't have experience with that afaik.
> But the compile-time format string parser might not necessarily understand
> the details of the literal encoding, so it's unclear how codepoints map to
> code units. Or are you saying that the rest of std::format already requires
> detailed understanding, anyway?

I believe the compile-time format string parser is already required to
understand such details. For example, if the literal encoding is
Shift-JIS, then the parser would need to be able to differentiate byte
values that appear as lead code units vs trailing code units (since, for
example, a 0x5C code unit denotes the '\' character if it is a lead code
unit, but that value may also appear as a trailing code unit for a
double byte character).

I agree with Corentin that delimiters should be restricted to code
points. That is consistent with the direction we have already advocated
for fill characters in LWG3576 <https://cplusplus.github.io/LWG/issue3576>.


Received on 2021-12-01 13:13:34