| // Testcase from P1814R0 |
| // { dg-do compile { target c++20 } } |
| |
| template <class T> struct identity { using type = T; }; |
| template <class T> using identity_t = typename identity<T>::type; |
| template <class T> concept Int = __is_same_as (T, int); |
| |
| template <class T, class U> struct C { |
| C(T, U); // #1 { dg-message "constraint" } |
| }; |
| template<class T, class U> |
| C(T, U) -> C<T, identity_t<U>>; // #2 { dg-message "constraint" } |
| |
| template<class V> |
| using A = C<V *, V *>; |
| |
| template<Int W> |
| using B = A<W>; |
| |
| int i{}; |
| double d{}; |
| A a1(&i, &i); // { dg-bogus "" "Deduces A<int>" } |
| A a2(i, i); // { dg-error "" "cannot deduce V * from i" } |
| A a3(&i, &d); // { dg-error "" } #1: Cannot deduce (V*, V*) from (int *, double *) |
| // #2: Cannot deduce A<V> from C<int *, double *> |
| B b1(&i, &i); // { dg-bogus "" "Deduces B<int>" } |
| B b2(&d, &d); // { dg-error "" "cannot deduce B<W> from C<double *, double *>" } |
