On Thu, 29 Aug 2019 at 04:05, Barry Revzin <barry.revzin_at_[hidden]> wrote:

> Hey all,
>
> I updated the SD-6 document on isocpp.org: https://wg21.link/sd6. I'm
> still having some CSS woes, but otherwise I updated the original document
> with the feature-test macros that have been adopted since it was first
> written, and organized the table by macro so that it's easy to see the
> history of values (e.g. for CTAD:
> https://isocpp.org/std/standing-documents/sd-6-sg10-feature-test-recommendations#__cpp_deduction_guides).
> Please let me know if anything is wrong there, or missing, or generally
> could be improved.
>
> Also, I went through the Straw Polls pages to see if we missed any macros
> and made the following list. I tried to be as liberal as possible in
> determining whether people would attempt to write code in both the old and
> new way, so as to prefer to produce a list with some things we could reject
> rather than miss more things... so I expect several of these may not
> actually need a macro. Several of them didn't (like "down with typename" -
> presumably you would just... write typename).
>
> Let me know what you think. What belongs, what doesn't belong, any
> opinions would be very helpful. I'm intending to write a paper for Belfast
> with whatever we all decide is actually missing:
>
> Toronto 2017 (201707)
> - Designated Initializers (P0329R4)
> - Familiar syntax for generic lambdas (P0428R2)
> - make_shared for arrays (P0674R1)
>
> Albuquerque 2017 (201711)
> - Range-for with initializer (P0614R1, bump __cpp_range_based_for?)
> - ADL and function templates (P0846R0)
> - Default constructible and assignable lambdas (P0624R2)
> - Lambdas in unevaluated contexts (P0315R4)
> - remove_cvref (P0550R2)
>

In theory remove_cvref_t<T> *could* be slightly more efficient (fewer
template instantiations) than remove_cv_t<remove_reference_t<T>> but I'm
not sure it's worth adding a macro for.



> - syncbuf (P0053R7)
> - to_address (P0653R2)
> - constexpr for complex (P0415R1)
> - atomic shared_ptr (P0718R2)
> - floating point atomic (P0020R6)
> - starts_with/ends_with (P0457R2)
>
> Jacksonville 2018 (201803)
> - Pack expansion in lambda init-capture (P0780R2)
> - Symmetry for <=> (P0905R1, should bump __cpp_impl_three_way_comparison?)
> - Comparing unordered containers (P0809R0)
> - <chrono> for calendars and timezones (P0355R7)
>

I was going to suggest bumping __cpp_lib_chrono, but that's had other
updates, and calendars probably deserve their own macro.


> - Manipulators for synchronized buffered ostream (P0753R2, should bump
> whatever syncbuf adds)
> - span (P0122R7)
>
> Rapperswil 2018 (201806)
> - Virtual calls in constexpr (P1064R0)
> - contains (P0458R2)
>

Does this need a macro? If it's not supported the fallback is to use
c.find(key) != c.end(), so if you have to write that anyway, you might as
well not bother using contains.


> - constexpr array comparison? (P1023R0)
>

I think there's an LWG issue (in Tentatively Ready state) about this.



> - shift algorithms (P0769R2)
> - identity (P0887R1)
> - is_nothrow_convertible (P0758R1)
> - integral power of 2 functions (P0556R3)
>
> San Diego 2018 (201811)
> - things that bump constexpr (try/catch P1002R1, dynamic_cast, polymorphic
> typeid P1327R1, and change active member of union P1330R0)
> - immediate functions (P1073R3)
> - optional/variant propogate triviality (P0602R4)
>

I'm undecided whether this needs to be exposed via feature test macros.


> - visit<R> (P0655R1)
> - constexpr pointer_traits (P1006R1, possibly with __cpp_lib_constexpr)
> - unwrap_ref_decay / unwrap_reference (P0318R1)
> - sane variant converting ctor (P0608R3)
>

This is a breaking change, but I'm not sure whether there's anything you
can do differently if the feature is implemented or not, so no need for a
macro?

- assume_aligned (P1007R3)
> - smart pointer with default init (P1020R1)
> - should span be regular (P1085R2, just bump from the other span paper)
>

I agree with a value bump not a new macro.


>
> Kona 2019 (201902)
> - extending structured bindings (P1091R3, P1381R1)
> - <=> != == (should bump both the class nttp macro, and the 3-way
> comparison macro)
> - polymorphic_allocator (P0339R6)
> - std:ssize (P1227R2)
> - more span things (P1024R3)
>

Bump __cpp_lib_span again.


>
> Cologne 2019 (201907
> - mothership library paper introduces a new macro for no reason (P1614R2),
> should have just bumped __cpp_lib_three_way_comparison
> - efficient stringbuf (P0408R7)
>