| // { dg-do compile { target c++20 } } |
| |
| // Here, normal overload resolution would consider B::operator bool when |
| // evaluating A(b), leading to a hard error instantiating Error<int>, but we |
| // avoid considering it by noticing that converting bool (a scalar) to A (a |
| // class) would require a user-defined conversion, which is not allowed when |
| // we're already dealing with the user-defined conversion to A. |
| |
| // This seems to be allowed by [temp.inst]/9: "If the function selected by |
| // overload resolution (12.4) can be determined without instantiating a class |
| // template definition, it is unspecified whether that instantiation actually |
| // takes place." |
| |
| template <class T> |
| struct Error { static constexpr auto value = T::value; }; |
| |
| struct A { A(const A&); }; |
| |
| template <class T> |
| struct B { operator bool() requires Error<T>::value; }; |
| |
| template <class T> |
| concept C = requires (B<T> b) { A(b); }; |
| |
| static_assert(!C<int>); |
