What is the point?
If the function is not implemented, you can't use it.

[[unimplemented]] void foo();

void main()
{
 foo();
}

It will always result in an invalid program. You can't call foo, ever, so why even define foo in the first place?
What is the point of defining a "language feature" when all of its use cases result in an invalid application? i.e. all use cases are invalid.


-----Original Message-----
From: Std-Proposals <std-proposals-bounces_at_lists.isocpp.org> On Behalf Of Hans Åberg via Std-Proposals
Sent: Tuesday, March 18, 2025 8:45 PM
To: marcinjaczewski86_at_[hidden]
Cc: Hans Åberg <haberg_1_at_icloud.com>; std-proposals_at_lists.isocpp.org
Subject: Re: [std-proposals] unimplemented attribute


> On 18 Mar 2025, at 20:23, Marcin Jaczewski <marcinjaczewski86_at_gmail.com> wrote:
>
> wt., 18 mar 2025 o 20:18 Hans Åberg <haberg_1_at_icloud.com> napisał(a):
>>
>>> On 18 Mar 2025, at 20:10, Marcin Jaczewski <marcinjaczewski86_at_gmail.com> wrote:
>>>
>>> Should this code compile or not? when exactly should it compiler and
>>> when it should not?
>>
>> If it is a warning, it compiles with a diagnostic. But if you think it is safe, an error may be required.
>
> But this means this will not link, what point for warning as the whole
> compilation fails?
> If we have definitions when this warning is pointless as linking will
> succeed and program will run.
> Or do I miss something here? Because what you say is behavior of `[[obsolete]]`.

If you only get a linker error, it may be tricker to find out what exactly is missing; a warning would tell that.

With an error, one must handle the case when the definition is in a source file and the unimplemented directive in a header file, which must be overridden somehow if used in another source file. With a warning one gets a correct compile.


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