[Bug c++/95454] type-level nodiscard not applied to constructors

[steve+gcc at tecwec dot eu via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95454

Eric Estievenart  changed:

   What|Removed |Added

 CC||steve+gcc at tecwec dot eu

--- Comment #1 from Eric Estievenart  ---
Indeed, confirming with even simpler code ( https://godbolt.org/z/EPbsfxYcj ):

struct [[nodiscard]] Z {};

void f()
{
Z{}; // should warn but does not
}

Tested all versions: 11.2, trunk, with -Wall -Wextra -

This is really a need for modern code, even experienced developpers sometimes
forget the 'lock' in
Lock lock{&mutex};
and this has severe consequences ;-)

[Bug c++/95454] type-level nodiscard not applied to constructors

[kyrylo.bohdanenko at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95454

Kyrylo Bohdanenko  changed:

   What|Removed |Added

 CC||kyrylo.bohdanenko at gmail dot 
com

--- Comment #2 from Kyrylo Bohdanenko  ---
Still relevant as of the current trunk.

A workaround would be to declare the constructor(s) [[nodiscard]]:

struct Data {
[[nodiscard]] Data() {}
};

int main() {
Data{};
}

This actually issues a warning:

: In function 'int main()':
:6:11: warning: ignoring return value of 'Data::Data()', declared with
attribute 'nodiscard' [-Wunused-result]

Sandbox: https://godbolt.org/z/3Koj8rra7

[Bug c++/95454] type-level nodiscard not applied to constructors

[johelegp at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95454

--- Comment #3 from Johel Ernesto Guerrero Peña  ---
> A workaround would be to declare the constructor(s) [[nodiscard]]:

That's generally a [better
recommendation](https://github.com/mpusz/units/issues/136). Though I think
you'd have to `= default` SMFs to get the same effects as the  type-level
annotation.

[Bug c++/95454] type-level nodiscard not applied to constructors

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95454

Andrew Pinski  changed:

   What|Removed |Added

 Resolution|--- |DUPLICATE
 Status|UNCONFIRMED |RESOLVED

--- Comment #4 from Andrew Pinski  ---
Dup of bug 85973.

*** This bug has been marked as a duplicate of bug 85973 ***