Shipping multiple feature-test macros for the same feature is trivially
simple for implementors. Requiring users to check multiple feature-test
macros to detect a single feature - the detection needs to work both in old
and new implementations - seems hostile.

On Mon, Nov 25, 2019, 13:21 Ville Voutilainen via Lib <lib_at_[hidden]>
wrote:

> On Mon, 25 Nov 2019 at 23:11, Billy O'Neal (VC LIBS) via Lib
> <lib_at_[hidden]> wrote:
> >
> > This was explicitly brought up for review in LWG and if I recall
> correctly the result was that we were OK with this inconsistency since that
> feature test macro had already been shipping in implementation(s).
>
> Vague recollections are not worth much to me. This is at
> http://wiki.edg.com/bin/view/Wg21belfast/LWGThursdayAfternoon
>
> "Discussion about inconsistency of __cpp_lib_array_constexpr vs
> __cpp_lib_constexpr_*header*
> Consistency is nice, but not necessary. No consensus to change. "
>
> Granted, those notes aren't worth much to me either. :) They do seem
> to indicate that LWG discussed this
> very matter. I still don't see a very convincing reason to deviate
> from the policy, considering Richard's correct
> remark that the existing feature-testing macro can continue to ship.
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