Not that I agree with the proposal, but the scenario I'm hearing:
1) A cpp file includes a header with an [[unimplemented]] function
(say the modf example above)
2) That cpp file then includes a header with the same function, but
this time without the [[unimplemented]] attribute
3) The cpp file then calls that function.

If one was to use =delete instead, #2 would be a compiler error as
that would be redeclaring the same function. And if #2 doesn't exist,
then the compilation could emit a diagnostic (before it got to the
link stage). Though I'm not yet sold that simply not declaring the
function at all isn't the better option anyway.

On Wed, Mar 19, 2025 at 7:39 AM Thiago Macieira via Std-Proposals
<std-proposals_at_[hidden]> wrote:
>
> On Wednesday, 19 March 2025 02:17:41 Pacific Daylight Time Hans Åberg via Std-
> Proposals wrote:
> > Assume that GCC has the declaration:
> > namespace std{
> > [[unimplemented]] std::float128_t modf(std::float128_t, std::float128_t*);
> > }
>
> This means no one can call this function. It being implemented later by
> someone else does not change the fact it cannot be called. So why would anyone
> implement it?
>
> I ask again: in what way is this different from =delete("unimplemented")?
>
> --
> Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
> Principal Engineer - Intel DCAI Platform & System Engineering
>
>
>
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