https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67775
Bug ID: 67775
Summary: [concepts] bug when using variadic expansions in
compound requirements
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: ---
The below code prints 0, but it should print 1.
/////////////////////////////////////////////////////////////
#include <type_traits>
#include <utility>
#include <iostream>
template <class X>
concept bool cpt_RealScalar = std::is_floating_point<X>::value;
namespace detail {
template <class, class> constexpr bool k_evaluator_impl = false;
template <std::size_t... Indexes, class E>
requires requires(E e) {
{ e((Indexes, 0)...) } -> cpt_RealScalar;
// requires cpt_RealScalar<decltype(e((Indexes,0)...))>; // this version
works
}
constexpr bool k_evaluator_impl<std::index_sequence<Indexes...>, E> = true;
}
template <class X, std::size_t K> concept bool cpt_KEvaluator =
detail::k_evaluator_impl<std::make_index_sequence<K>, X>;
int main() {
auto f = [](int, int, int) -> double { return 3; };
std::cout << cpt_KEvaluator<decltype(f), 3> << '\n';
return 0;
}
/////////////////////////////////////////////////////////////
