Mailing list review Summary:

• No implementation concerns for libstdc++, should be possible for libc++ too
• Please put the wording in code font
• Use __cpp_lib_constexpr_charconv as feature macro

No further comment that would indicate interest

Direction: Update the wording and send to a LEWG telecon

P2291R1 Add Constexpr Modifiers to Functions to_chars and from_chars for Integral Types in <charconv> Header (Daniil Goncharov, Karaev Alexander)

The paper will be scheduled for the next LEWG electronic polling period.

This paper has been advanced from mailing list review to electronic polls; 12 people endorsed the motion as of the time of this comment.

P2291R2 Add Constexpr Modifiers to Functions to_chars and from_chars for Integral Types in <charconv> Header (Daniil Goncharov, Karaev Alexander)

2021 September Library Evolution Polls

P2451: 2021 September Library Evolution Poll Outcomes

Poll 5: Send P2291R2 (Add constexpr Modifiers To Functions to_chars And from_chars For Integral Types In <charconv> Header) to Library Working Group for C++23, classified as an improvement of an existing feature (P0592R4 bucket 2 item).

Outcome: Strong consensus in favor.

Selected Comments

Having finally specified these most basic operations in a way that is appropriate for the language, it only makes sense that they would be made available for compile time programming. The lack of floating-point support is an obviously necessary concession to practicality which can hopefully be eventually addressed.

— Strongly Favor

According to implementers this is not hard to provide and would allow constexpr format in the future, which is an useful feature to have. It would certainly help some constexpr libraries like CTRE, etc.

— Strongly Favor

This is a step in the right direction, we should make functionality available in constexpr context unless there is a good reason not to.

— Strongly Favor

This seems straightforward, and it has been tested, and it's the kind of thing you would expect to be able to do at compile time.

— Weakly Favor

I know that this change will be a welcome one for implementers of libraries like CTRE. However, I'm concerned that this will require implementation heroics to prevent large compile time costs for all files that only include <charconv> for use at runtime. Although there are obvious approaches that could be used to mitigate this, the paper doesn't discuss the additional compile time overhead of moving integral to_chars/from_chars into the header nor possible mitigations.

— Neutral

P2291R3 Add Constexpr Modifiers to Functions to_chars and from_chars for Integral Types in Header (Daniil Goncharov, Karaev Alexander)

LWG reviewed an approved by unanimous consent for c++23 on 2022-05-06

This has been applied.