https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111358
Bug ID: 111358
Summary: libstdc++'s optional::and_then and optional::transform
are not ADL-proof
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Keywords: rejects-valid
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: de34 at live dot cn
Target Milestone: ---
The following program is incorrectly rejected when using libstdc++
(https://godbolt.org/z/eavTYjEdx):
```
#include <optional>
namespace fvs {
struct Foo {};
void operator*(std::optional<fvs::Foo>) = delete;
}
int main()
{
std::optional<fvs::Foo>{}.and_then(
[](auto&&){ return std::optional<char>{}; });
std::optional<fvs::Foo>{}.transform(
[](auto&&){ return 0; });
}
```
The reason of compilation error is that libstdc++ uses **this in and_then and
transform functions, which triggers ADL and finds unwanted operator*().
These monadic operations are currently specified in [optional.monadic] with
value(), so they should be ADL-proof.
