On 26/02/2025 02:48, F. v.S. via Std-Discussion wrote:
> It's possibly intended that P1494R5 "Partial program correctness"
> doesn't add any feature-test macro. I'm convinced by Jens Maurer that
> there shouldn't be a core FTM. But given there's already
> __cpp_lib_unreachable, shouldn't there be __cpp_lib_observable?
>

Yes, I would agree that there should be one.

Note that there's currently a draft (P3641R0) that proposes to rename
std::observable() to std::observable_checkpoint(); if that paper gets
accepted, the FTM should likely become __cpp_lib_observable_checkpoint.
(P3641 isn't proposing the FTM, though.)

My 2 c,
--
Giuseppe D'Angelo