On Sun, 8 Sep 2019 at 18:12, Tom Honermann <tom_at_[hidden]> wrote:

> On 9/8/19 6:00 AM, Corentin via Lib wrote:
>
>
>
> On Sun, 8 Sep 2019 at 11:17, Corentin <corentin.jabot_at_[hidden]> wrote:
>
>>
>>
>> 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
>>
>
>
> To be clear, the difference of whether the EGC algorithm is required to be
> tailored or not is that tailoring for all intent and purposes requires
> icu or something with CLDR, which restrict the platforms on which this can
> be implemented
>
> Tailoring is not relevant to this discussion.
>
It is - see https://unicode.org/reports/tr29/ "ch" is 2 EGCS in most
locales but in Slovak it's 1. I don't make the rules :D

The locale dependency stems from the encoding itself being dependent on
> locale. Again, LANG=C vs LANG=C.UTF-8. If the specified behavior is
> encoding dependent (as it would have to be for field width to be a count of
> any of code points, scalar values, or EGCs), then it is also locale
> dependent (for char and wchar_t). Thus there is a trade off:
>
> 1. Either the behavior is locale dependent in which case, field widths
> could be specified such that they count code points, scalar values, or EGCs
> when the locale selects a Unicode encoding (and something else for
> non-Unicode encodings), or
> 2. The behavior is not locale dependent in which case, field widths
> can only be specified in terms of code units.
>
>
Agreed, but let me rephrase:

Either a string is text and therefore we need and to know its encoding, or
it is a sequence of bytes (in the case of char)
I have an opinion about what we are dealing with in this context :D


Recall that, unless there is a call to std::setlocale, all C and C++
> processes start with the locale set to "C"
>
Tom.
>
>
>
>
>>
>>
>>
>>
>>>
>>>
>>> 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.
>>>>> _______________________________________________
>>>>> Lib mailing list
>>>>> Lib_at_[hidden]
>>>>> Subscription: https://lists.isocpp.org/mailman/listinfo.cgi/lib
>>>>> <https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.isocpp.org%2Fmailman%2Flistinfo.cgi%2Flib&data=02%7C01%7Cbion%40microsoft.com%7C92b795de78e843d852bf08d73422ffe8%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637035197252874608&sdata=ieyJCXmZ0Bj3UfW4Lvi3hW1HlOq6oeEML86Xyry9uFI%3D&reserved=0>
>>>>> Link to this post: http://lists.isocpp.org/lib/2019/09/13440.php
>>>>> <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>
>>>>>
>>>>
>>>> _______________________________________________
>>>> Lib mailing list
>>>> Lib_at_[hidden]
>>>> Subscription: https://lists.isocpp.org/mailman/listinfo.cgi/lib
>>>> <https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.isocpp.org%2Fmailman%2Flistinfo.cgi%2Flib&data=02%7C01%7Cbion%40microsoft.com%7C92b795de78e843d852bf08d73422ffe8%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637035197252884602&sdata=B0%2BhF8pSkAy2MbEwWHk1r3uVjbIpvIoQ%2Fi%2BckyTQ94A%3D&reserved=0>
>>>> Link to this post: http://lists.isocpp.org/lib/2019/09/13446.php
>>>> <https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Flists.isocpp.org%2Flib%2F2019%2F09%2F13446.php&data=02%7C01%7Cbion%40microsoft.com%7C92b795de78e843d852bf08d73422ffe8%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637035197252894598&sdata=NVwyEiiPWSwvAApse%2FxktecxI6oAiGhUWKjyXw8yYMw%3D&reserved=0>
>>>>
>>>
> _______________________________________________
> Lib mailing listLib_at_[hidden]
> Subscription: https://lists.isocpp.org/mailman/listinfo.cgi/lib
> Link to this post: http://lists.isocpp.org/lib/2019/09/13453.php
>
>
>