SG16 will hold a meeting today, Wednesday, March 26th, at 19:30 UTC (timezone conversion).

Once again, my apologies for sending the agenda so late.

If you need a .ics file to import into your calendar, you can download it here.

The agenda follows.

• P3491R2: define_static_{string,object,array}.
• P3391R0: constexpr std::format.
  

The features proposed in P3491R2 were previously discussed in SG16 in the context of P2996R5 (Reflection for C++26) during the 2024-08-14 meeting. As P2996 progressed, these features were split to the new paper. The guidance we provided in that meeting was to remove define_static_string() in favor of adding define_static_array() as a means to avoid questions about null terminators for strings. The new paper proposes both define_static_string() and define_static_array() (as well as define_static_object()), but addresses the null termination question by statically determining if the range passed to define_static_string() corresponds to a string literal; if it does, then the null terminator presumed to be present in the range is ignored. A possible implementation of define_static_string() is described in section 3.3, "Possible Implementation". The ability to check if a pointer points to a (portion of a) string literal during constant evaluation is also exposed via a suite of is_string_literal() overloads. We'll discuss this new design and, if all goes well, poll forwarding the paper. Note that LEWG has already forwarded this paper for C++26 and any concerns we identify that would require design changes will presumably have to be addressed as LWG issues.

P3391R0 seeks to make std::format() available during constant evaluation with appropriate limitations. The proposal omits support for std::chrono types which saves us the effort of having to decide how to handle the locale dependent conversion specifiers from [time.format]. The proposal does not add constexpr to the std::format() overloads that have a std::locale parameter, but it is currently silent regarding handling of the L option for the standard format specifiers in [format.string.std]. We'll discuss and provide guidance regarding handling of that option. Possibilities include excluding calls that specify this option during constant evaluation or specifying the behavior as-if for the "C" locale. Note that none of std::locale::classic(), std::locale::global(), the std::locale constructors, or the std::locale facets are currently declared constexpr.

Tom.