https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98569
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2021-01-07
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Reduced:
#include <concepts>
struct U
{
U(U&&) = delete;
};
struct V
{
using value_type = U;
};
template<typename Coll, typename T>
requires std::convertible_to<T, typename Coll::value_type>
void add(Coll& coll, const T& val)
{
}
int main()
{
V v;
U u;
add(v, u);
}
Compiled with -std=gnu++2a gives:
prog.cc: In function 'int main()':
prog.cc:22:7: error: no matching function for call to 'U::U()'
22 | U u;
| ^
prog.cc:5:5: note: candidate: 'U::U(U&&)' (deleted)
5 | U(U&&) = delete;
| ^
prog.cc:5:5: note: candidate expects 1 argument, 0 provided
prog.cc:3:8: note: candidate: 'constexpr U::U(const U&)' (deleted)
3 | struct U
| ^
prog.cc:3:8: note: candidate expects 1 argument, 0 provided
prog.cc:23:13: error: no matching function for call to 'add(V&, U&)'
23 | add(v, u);
| ^
prog.cc:15:6: note: candidate: 'template<class Coll, class T> requires
convertible_to<T, typename Coll::value_type> void add(Coll&, const T&)'
15 | void add(Coll& coll, const T& val)
| ^~~
prog.cc:15:6: note: template argument deduction/substitution failed:
prog.cc:15:6: note: constraints not satisfied
In file included from prog.cc:1:
/opt/wandbox/gcc-head/include/c++/11.0.0/concepts: In substitution of
'template<class Coll, class T> requires convertible_to<T, typename
Coll::value_type> void add(Coll&, const T&) [with Coll = V; T = U]':
prog.cc:23:13: required from here
/opt/wandbox/gcc-head/include/c++/11.0.0/concepts:72:13: required for the
satisfaction of 'convertible_to<T, typename Coll::value_type>' [with T = U;
Coll = V]
/opt/wandbox/gcc-head/include/c++/11.0.0/concepts:72:30: note: the expression
'is_convertible_v<_From, _To> [with _From = U; _To = U]' evaluated to 'false'
72 | concept convertible_to = is_convertible_v<_From, _To>
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
