We haven't had a __cpp_concepts since the TS specified its value as 201507 - which GCC defines. I've been making up values since then for various compilers which cmcstl2 supports to various degrees: 

* clang-concepts defines __cpp_concepts to 201707L - the date of the Toronto merge - to indicate support for concepts as merged.

* MSVC uses 201811L - the date of the P1084 merge - to indicate that it supports the above plus P1084's changes to return-type-requirements. (Unfortunately MSVC does not yet support the changes in P1141 which were merged at the same meeting.)

I'd appreciate a bump for the changes in Cologne. P1452 seems significant enough to me, but regardless it would be nice to have a way to discriminate between what MSVC will support in 16.3 and C++20 concepts' final form.

On Mon, Sep 16, 2019 at 8:26 AM John Spicer <jhs@edg.com> wrote:

Yes, I think we should have one.

John.

On Sep 14, 2019, at 4:07 PM, Barry Revzin <barry.revzin@gmail.com> wrote:

On Sat, Sep 14, 2019, 2:38 PM Jason Merrill via Core <core@lists.isocpp.org> wrote:

This doesn't seem to have been addressed at Cologne.  I don't think
any of the changes at Cologne (conditionally trivial, unconstrained
TTP, dropping return-type requirements) require a version bump, does
anyone else?

So I'd stick with the 201811 value.

Jason

Wait, do we even have a __cpp_concepts? We have a __cpp_lib_concepts (... that def needs to be bumped to 201907), but not one for the language. We should add one...

Barry

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