Hi Marcin,

On 2026-02-10T10:56:23+0100, Marcin Jaczewski via Std-Proposals wrote:
> niedz., 8 lut 2026 o 19:34 Arthur O'Dwyer via Std-Proposals
> <std-proposals_at_[hidden]> napisał(a):
[...]
> >> How does this use of an attribute fit the idea that attributes
> >> have optional semantics, given that the program will be ill-formed
> >> without the attribute present?
> >
> >
> > It doesn't. Nobody likes the "ignorable attribute rule." See for example
>
> False, I like how they are handled :P
> Only problem is people try sove in things that they should not.

How do you feel about this?

 alx_at_devuan:~/tmp$ cat nodiscard.c++
 [[nodiscard]] int f(void);

 int
 main(void)
 {
  typeof(int (void) ) *fp1;
  typeof(int (void)[[nodiscard]]) *fp2;

  fp1 = &f; // I would expect a diagnostic here.
  fp1();

  fp2 = &f;
  fp2();
 }
 alx_at_devuan:~/tmp$ g++ -S -Wall -Wextra nodiscard.c++
 nodiscard.c++: In function ‘int main()’:
 nodiscard.c++:7:38: warning: ‘nodiscard’ attribute can only be applied to functions or to class or enumeration types [-Wattributes]
     7 | typeof(int (void)[[nodiscard]]) *fp2;
       | ^


>
> First of all, non-ignorable attributes should be explicit and ilformed
> even if the compiler does not know them even in C++11.

Agree.

> I suggested adding the prefix `!!` for one like this, this could be
> any symbol that makes C++11 reject this code and make this feature
> backward and forward compatible.

We already have non-ignorable attributes: scoped ones. This means that
[[::attr]] is already the syntax for non-ignorable attributes. It only
needs to be specified in the standard that the empty prefix is for the
standard.

> This will make a clear distinction between these two versions.


Have a lovely day!
Alex

-- 
<https://www.alejandro-colomar.es>