Thank you for your interest, Liang!

I replied privately regarding WG21 membership requirements and how to
submit a proposal. In this response, I'm just discussing the content of
the draft proposal.

std::fpos is a class template parameterized by a State type parameter
that equates to std::mbstate_t for std::fpos specializations provided by
the standard library. The proposed design omits formatting for the state
object notionally held by a std::fpos value and made accessible via the
state() member function. The proposal does not explicitly discuss why
this choice is made though an argument can be inferred based on the
description of how the ostream operators support formatting of these
types via (possibly non-conforming?) implicit conversion to
std::streamoff. The standard does not yet provide an input parsing
equivalent to std::format() (though a proposal does exist; see P1729
(Text Parsing) <https://wg21.link/p1729>). Should an input equivalent be
added, I would expect it to be possible to parse formatted output such
that an equivalent value is produced. It might therefore make sense for
the std::fpos formatter to at least support formatting of the state
value as well (either by default or perhaps via an option in the format
string). I would like to see the proposal updated to discuss/address
support for the associated state value. In general, discarding data
should be done explicitly, so an argument to do so implicitly should be
present and compelling.

Tom.

On 8/12/24 7:41 AM, 梁家铭 via SG16 wrote:
> Hi,
>
> I'm Liang Jiaming. Recently I've floated my idea in std-proposal
> mailing list for adding formatter for fpos (see ISOCPP std-proposals
> List: [std-proposals] Adding formatter for std::fpos
> <https://lists.isocpp.org/std-proposals/2024/07/10526.php>), the type
> typically returned by `tellg/p` of C++ streams. After multiple rounds
> of discussions with Authur O'Dwyer and Victor Zverorich, I've finished
> my proposal design and wording (see ISOCPP std-proposals List: Re:
> [std-proposals] P3070 and formatter<fpos>, was Re: Proposal draft for
> adding formatter for fpos
> <https://lists.isocpp.org/std-proposals/2024/08/10809.php>). The
> proposal draft is uploaded to PXXXXR0: Adding formatter for fpos
> (extra-creativity.github.io)
> <https://extra-creativity.github.io/public/cpp/proposals/add%20formatter%20for%20fpos.html>.
>
> This is the first time I draft a proposal, so I'm not quite familiar
> with the related procedures even after reading How To Submit a
> Proposal : Standard C++ (isocpp.org)
> <https://isocpp.org/std/submit-a-proposal>. It seems that before
> presenting the proposal to LEWG, I need to present it first to SG16
> and the paper needs to be assigned with an official proposal number.
> But I'm not quite sure what I should really do next, so I send a mail
> to SG16 mailing list. Any help would be appreciated :-)
>
> Thank you all in advance!
>
> Liang Jiaming
>
>
>