Report from the St. Louis 2024 ISO C++ Committee meeting¶
We made significant progress in the standardization of this library during the ISO C++ Committee meeting in St. Louis.
P30942R3: std::basic_fixed_string¶
First, the fixed_string was unanimously forwarded from the SG18 LEWG Incubator to the Library
Evolution Working Group (LEWG). The group suggested a few minor changes to the paper, which
resulted in the R3 version of the proposal.
The paper is in excellent shape, and the entire wording is ready as well. Hopefully it will progress quickly through the remaining groups in the Committee.
P3045R1: Quantities and units library¶
In the SG6 (Numerics), we had a really efficient discussion about the recently raised usability issues with temperatures and the Minimal Viable Product (MVP) scope.
The following polls were taken:
POLL: If WG21 adds anything to the standard to provide units or quantities, then such a solution must at least include the necessary abstractions for units, dimensions, and quantity kinds. (It does not have to provide system definitions, e.g. ISQ/SI definitions.)
| Strongly in Favor | In favor | Neutral | Against | Strongly Against |
|---|---|---|---|---|
| 7 | 4 | 7 | 0 | 0 |
POLL: If WG21 adds anything to the standard to provide units or quantities, then such a solution must at least include the necessary abstractions for units, dimensions, quantity kinds, and quantities of the same kind. (It does not have to provide system definitions, e.g. ISQ/SI definitions.)
| Strongly in Favor | In favor | Neutral | Against | Strongly Against |
|---|---|---|---|---|
| 5 | 2 | 5 | 2 | 0 |
POLL: If WG21 adds anything to the standard to provide units or quantities, then such a solution must at least include the necessary abstractions for units, dimensions, quantity kinds, and affine spaces. (It does not have to provide system definitions, e.g. ISQ/SI definitions.)
| Strongly in Favor | In favor | Neutral | Against | Strongly Against |
|---|---|---|---|---|
| 5 | 0 | 8 | 1 | 0 |
As we can see, there are no controversies about the first poll that states that the MVP should include at least:
- units,
- dimensions,
- quantity kinds (e.g., frequency vs activity, plane angle vs solid angle, fuel_consumption vs area).
The next polls add either:
- quantities of the same kind (e.g., length vs width vs wavelength, potential energy vs kinetic energy),
- the affine space abstractions (i.e., point origins and
quantity_point).
SG6 considered those less important, but no one was strongly against including those in the MVP. We were asked to return with better motivation and usage examples for those features.
If you are depending on quantities of the same kind or quantity points in your project and you
would like to see them in the std library, please let us know about your use cases.
Besides SG6, we spent six hours in the SG18 LEWG Incubator discussing the details of the library design. The proposal was very well received, and we got a few valuable comments and suggestions that we will apply to the next version of the paper.