https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67656
Bug ID: 67656
Summary: [concepts] matched variadics in expression constraint
report as unmatched
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: ryan.burn at gmail dot com
Target Milestone: ---
In this code
/////////////////////////////////
template<class... Xs>
void consume(Xs&&...) {}
template<class... Xs>
struct A {
template<class... Ys>
requires requires(Ys... ys) {
consume(Xs{ys}...);
}
A(Ys&&... ys) {
}
};
int main() {
A<int, long> a(55, 2);
return 0;
}
/////////////////////////////////
"consume(Xs{ys}...)" is a valid expression so the constructor should be called,
but gcc gives a mismatched pack lengths error.
######### Error ##########
t2.cpp: In instantiation of ‘struct A<int, long int>’:
t2.cpp:15:17: required from here
t2.cpp:8:14: error: mismatched argument pack lengths while expanding ‘Xs{ys}’
consume(Xs{ys}...);
^
t2.cpp: In function ‘int main()’:
t2.cpp:15:23: error: no matching function for call to ‘A<int, long int>::A(int,
int)’
A<int, long> a(55, 2);
^
t2.cpp:10:3: note: candidate: A<Xs>::A(Ys&& ...) [with Ys = {int, int}; Xs =
{int, long int}]
A(Ys&&... ys) {
^
t2.cpp:10:3: note: constraints not satisfied
t2.cpp:5:8: note: candidate: constexpr A<int, long int>::A(const A<int, long
int>&)
struct A {
^
t2.cpp:5:8: note: candidate expects 1 argument, 2 provided
t2.cpp:5:8: note: candidate: constexpr A<int, long int>::A(A<int, long int>&&)
t2.cpp:5:8: note: candidate expects 1 argument, 2 provided
