On 20/05/2026 01:16, Thiago Macieira via Std-Proposals wrote:
> On Tuesday, 19 May 2026 12:58:24 Pacific Daylight Time Ville Voutilainen via
> Std-Proposals wrote:
>> In case this idea had actual convincing motivation, there's no reason
>> *whatsoever* to do it with an attribute.
>
> Actually, an attribute might be appropriate here and simply let the compiler
> warn if the function is actually called in code, instead of making it a hard
> error. It would not be the end of the world if helper functions that are
> usually used to compute a type more easily than a sequence of
> std::conditional_t got actually called.
>
> Most of the time, such functions are private in some form or another, so only
> the author of the code in question is even going to call them. The author can
> already do a static_assert on a type-dependent false like std::declval does,
> but will they bother to write that code?
>
>

gcc has attributes [[gnu::error("This function must not be called")]]
and [[gnu::warning("Calling this gives a warning")]]. The warning or
error messages are not emitted if the call is eliminated (via dead-code
elimination, only using it in unevaluated contexts, etc.).

These should be reasonable candidates for standardisation?

Then the OP can have:

 #define unevaluated error("Unevaluated contexts only")

or whatever suits his preferences.