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Subject: Re: WG14 N2688: Sterile characters
From: Tom Honermann (tom_at_[hidden])
Date: 2021-04-06 16:47:38


On 4/6/21 4:49 PM, Corentin Jabot wrote:
>
>
> On Tue, Apr 6, 2021 at 10:17 PM Jens Maurer via SG16
> <sg16_at_[hidden] <mailto:sg16_at_[hidden]>> wrote:
>
> On 06/04/2021 05.33, Tom Honermann via SG16 wrote:
> > FYI, WG14 will be considering N2688
> <http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2688.pdf>, a
> paper proposing to clarify how characters in character and string
> literals are handled when the execution character set (literal
> encoding) does not support representation for the source character
> (/basic-c-char/ or /universal-character-name/ in C++) or escape
> sequence (presumably just /simple-escape-sequence/ in C++, but the
> paper doesn't explicitly exclude numeric escape sequences).
>
> In C++, we say implementation-defined for character literals
> and, for string literals:
>
> If the string-literal’s encoding-prefix is absent or L, then
> the string-literal is conditionally-supported
> and an implementation-defined code unit sequence is encoded.
> Otherwise, the string-literal is ill-formed.
>
> So, C++ allows to pick a fresh random character every time
> the situation occurs, except that UTF-x string literals
> are ill-formed if they contain a non-encodable character
> (can those even exist?)
>
> Should SG16 offer a C++ perspective to WG14, e.g. via SG22?
>
CCing Aaron.

I'd rather not spend SG16 telecon time on this, but If WG14 elects to
make a change, then I think SG22 can handle propagating the change to
WG21 or otherwise resolving any incompatibility, consulting SG16 as
Aaron feels necessary.

>
> We might want to postpone that discussion - Peter and I will bring an
> updated revision of wg21.link/P1854 which makes that ill-formed in C++.
> I will note that "non-encodable character" is certainly a better term
> than "sterile character" (better yet: non representable abstract
> character)

And that would be good information to share with SG22.

Tom.

>
>
> Jens
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