On Sun, 8 Sep 2019 at 09:52, Billy O'Neal (VC LIBS) <bion_at_[hidden]>
wrote:

> > I agree that EGCS is the best option. That doesn't drag locale
>
>
>
> Because we don’t get to assume that we’re talking about Unicode at all, it
> absolutely drags in locale.
>

Sorry, I should have been more specific.
There is a non-tailored Unicode EGCS boundary algorithm (but it can be
tailored)
I didn't mean to imply that text manipulation can be done without knowing
its encoding and never use "locale" to mean encoding.

EGCS are only defined for text whose character repertoire is Unicode, other
encodings deal with codepoints




>
>
> Billy3
>
>
> ------------------------------
> *From:* Lib <lib-bounces_at_[hidden]> on behalf of Corentin via Lib <
> lib_at_[hidden]>
> *Sent:* Saturday, September 7, 2019 11:08:25 PM
> *To:* Library Working Group <lib_at_[hidden]>
> *Cc:* Corentin <corentin.jabot_at_[hidden]>; Victor Zverovich <
> victor.zverovich_at_[hidden]>; Tom Honermann <tom_at_[hidden]>;
> unicode_at_[hidden] <unicode_at_[hidden]>
> *Subject:* Re: [isocpp-lib] New issue: Are std::format field widths code
> units, code points, or something else?
>
>
>
> On Sun, Sep 8, 2019, 5:30 AM Tom Honermann via Lib <lib_at_[hidden]>
> wrote:
>
>> On 9/7/19 10:44 PM, Victor Zverovich wrote:
>>
>> > Is field width measured in code units, code points, or something else?
>>
>> I think the main consideration here is that width should be
>> locale-independent by default for consistency with the rest of
>> std::format's design.
>>
>> I agree with that goal, but...
>>
>> If we can say that width is measured in grapheme clusters or code points
>> based on the execution encoding (or whatever the standardese term) without
>> querying the locale then I suggest doing so.
>>
>> I don't know how to do that. From my response to Zach, if code units
>> aren't used, then behavior should be different for LANG=C vs LANG=C.UTF-8.
>>
>> I have slight preference for grapheme clusters since those correspond to
>> user-perceived characters, but only have implementation experience with
>> code points (this is what both the fmt library and Python do).
>>
>> I would definitely vote for EGCs over code points. I think code points
>> are probably the worst of the options since it makes the results dependent
>> on Unicode normalization form.
>>
>
> I disagree. Code Units is the worse option. For me anything involving code
> units is a big red flag. I agree that EGCS is the best option. That doesn't
> drag locale, might be a bit involved for implementers in 20.
> I don't think specify EGCS for Unicode text and codepoints otherwise
> wouldn't be too difficult - implementation might be a bit challenging on
> some platforms in the 20 time frame but they could fallback to codepoints
> in the meantime. Not perfect but I think we need a good long term solution
> rather than a bad short term one
>
> Tom.
>>
>>
>> Cheers,
>> Victor
>>
>> On Sat, Sep 7, 2019 at 5:13 PM Tom Honermann via Lib <
>> lib_at_[hidden]> wrote:
>>
>>> [format.string.std]p7
>>> <https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Feel.is%2Fc%2B%2Bdraft%2Fformat%23string.std-7&data=02%7C01%7Cbion%40microsoft.com%7C92b795de78e843d852bf08d73422ffe8%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637035197252854619&sdata=WsHw%2BM62uyiOBrr91P6W1GzwGe313EDe30bKN5i006Q%3D&reserved=0>
>>> states:
>>>
>>> The *positive-integer* in *width* is a decimal integer defining the
>>> minimum field width. If *width* is not specified, there is no minimum
>>> field width, and the field width is determined based on the content of the
>>> field.
>>>
>>> Is field width measured in code units, code points, or something else?
>>>
>>> Consider the following example assuming a UTF-8 locale:
>>>
>>> std::format("{}", "\xC3\x81"); // U+00C1 { LATIN CAPITAL
>>> LETTER A WITH ACUTE }
>>> std::format("{}", "\x41\xCC\x81"); // U+0041 U+0301 { LATIN CAPITAL
>>> LETTER A } { COMBINING ACUTE ACCENT }
>>>
>>> In both cases, the arguments encode the same user-perceived character
>>> (Á). The first uses two UTF-8 code units to encode a single code point
>>> that represents a single glyph using a composed Unicode normalization
>>> form. The second uses three code units to encode two code points that
>>> represent the same glyph using a decomposed Unicode normalization form.
>>>
>>> How is the field width determined? If measured in code units, the first
>>> has a width of 2 and the second of 3. If measured in code points, the
>>> first has a width of 1 and the second of 2. If measured in grapheme
>>> clusters, both have a width of 1. Is the determination locale dependent?
>>>
>>> *Proposed resolution:*
>>>
>>> Field widths are measured in code units and are not locale dependent.
>>> Modify [format.string.std]p7
>>> <https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Feel.is%2Fc%2B%2Bdraft%2Fformat%23string.std-7&data=02%7C01%7Cbion%40microsoft.com%7C92b795de78e843d852bf08d73422ffe8%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637035197252864612&sdata=36WpbP64Oqoi4Pne9kFrEu6nauHLNr2VunnfkvdWcPY%3D&reserved=0>
>>> as follows:
>>>
>>> The *positive-integer* in *width* is a decimal integer defining the
>>> minimum field width. If *width* is not specified, there is no minimum
>>> field width, and the field width is determined based on the content of the
>>> field. *Field width is measured in code units. Each byte of a
>>> multibyte character contributes to the field width.*
>>>
>>> (*code unit* is not formally defined in the standard. Most uses occur
>>> in UTF-8 and UTF-16 specific contexts, but [lex.ext]p5
>>> <https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Feel.is%2Fc%2B%2Bdraft%2Flex.ext%235&data=02%7C01%7Cbion%40microsoft.com%7C92b795de78e843d852bf08d73422ffe8%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637035197252864612&sdata=UyG%2Fr7BXuLAPAXP78ekpXS%2FWhqdeU2QCHTmTeBPjImQ%3D&reserved=0>
>>> uses it in an encoding agnostic context.)
>>>
>>> Tom.
>>> _______________________________________________
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>>> <https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Flists.isocpp.org%2Flib%2F2019%2F09%2F13440.php&data=02%7C01%7Cbion%40microsoft.com%7C92b795de78e843d852bf08d73422ffe8%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637035197252874608&sdata=l4UxwaFExnxKireder%2F%2BAnU2mszZXMYatHrd2zGSSWQ%3D&reserved=0>
>>>
>>
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>>
>