> Could you give an indication of the respective use-case?

Here is an example for subscript and multiplication sign:

static_assert(unit_symbol(mag_ratio<1, 18000> * metre / second) == "[1/18 ×
10⁻³ m]/s");
static_assert(unit_symbol<usf{.encoding = portable}>(mag_ratio<1, 18000> *
metre / second) == "[1/18 x 10^-3 m]/s");

> Could you give a sample std::format invocation where this would happen?
> In particular, I'm opposed to throwing an exception if the value of a
> format argument (not the format string) happens to be a little off.

Formatting of a dot (⋅) can be found at
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p3045r3.html#unit-formatting
.
The exception is thrown because of a problem in a format string. Someone
requested portable output and a dot as a separator.

> So maybe
>
> inline constexpr auto \u03c0 = pi; // U+03C0 GREEK SMALL LETTER PI
>
> or, actually showing the glyph:
>
> inline constexpr auto π /* U+03C0 GREEK SMALL LETTER PI */ = pi;

Thanks. I think the second option is a better option, as a user can
directly copy-paste glyphs into the code. Do we agree that it is how it
should appear in the wording?

Best

Mat

śr., 23 paź 2024 o 23:21 Jens Maurer <jens.maurer_at_[hidden]> napisał(a):

>
>
> On 23/10/2024 21.59, Mateusz Pusz via SG16 wrote:
> > Hi SG16 :-)
> >
> > At the last meeting about units, I said that we do not have to decide on
> any specific Unicode symbols for now, as the systems of units are the
> subject of the next papers. It turns out I was wrong :-(
> >
> > We need a few Unicode characters for the first proposal. Those are:
>
> Could you give an indication of the respective use-case?
>
> > Name Symbol C++ code Portable alternative
> > Superscript Zero ⁰ u8"\u2070" "0"
> > Superscript One ¹ u8"\u00b9" "1"
> > Superscript Two ² u8"\u00b2" "2"
> > Superscript Three ³ u8"\u00b3" "3"
> > Superscript Four ⁴ u8"\u2074" "4"
> > Superscript Five ⁵ u8"\u2075" "5"
> > Superscript Six ⁶ u8"\u2076" "6"
> > Superscript Seven ⁷ u8"\u2077" "7"
> > Superscript Eight ⁸ u8"\u2078" "8"
> > Superscript Nine ⁹ u8"\u2079" "9"
> > Superscript Minus ⁻ u8"\u207b" "-"
> > Multiplication Sign × u8"\u00d7" "x"
> > Mathematical Italic Small Pi 𝜋 u8"\U0001D70B" "pi"
> > Per Mille Sign ‰ u8"\u2030" "%o"
> > Dot Operator ⋅ u8"\u22C5" <none>*
> >
> >
> > * This option is valid only for UTF-8 encoding. Otherwise, we propose to
> throw an exception during format string processing.
>
> Could you give a sample std::format invocation where this would happen?
> In particular, I'm opposed to throwing an exception if the value of a
> format argument (not the format string) happens to be a little off.
>
> > 2. Is the C++ spelling correct? Should we spell them in the spec with
> '\u', '\U', or maybe some other way?
>
> That depends on where they appear. If they appear in strings, something
> like "\uXXXX"
> (with quotation marks, with optional encoding-prefix) seems appropriate.
>
> If they appear in source code, see below.
>
> > 3. Are the portable alternatives fine (especially "%o" might be
> controversial above)?
>
> What would be an alternative if we didn't like "%o"? I'm not seeing one.
>
> > 4. Is there a better way to spell `inline constexpr auto 𝜋 = pi;` to be
> explicit about the specific Unicode symbol used for the identifier?
>
> So, this is an identifier, not a string literal. I think we shouldn't rely
> on glyphs for anything outside of ASCII for unique character
> identification;
> we shouldn't require consumers of the standard to be able to read non-Latin
> scripts (even if we're talking about math symbols).
> So maybe
>
> inline constexpr auto \u03c0 = pi; // U+03C0 GREEK SMALL LETTER PI
>
> or, actually showing the glyph:
>
> inline constexpr auto π /* U+03C0 GREEK SMALL LETTER PI */ = pi;
>
> Jens
>