https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67720
Bug ID: 67720
Summary: [concepts] bug with recursive constrained function
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 is valid but gives this error with gcc:
main.cpp: In instantiation of ‘auto f(const std::tuple<_El0, _El ...>&)
requires predicate((cpt_BooleanFalseConstant<decltype(p((get<0>)(f::t)))>)())
[with TFirst = std::integral_constant<int, 9>; TRest =
{std::integral_constant<int, 3>, std::integral_constant<int, 5>}]’:
main.cpp:34:11: required from ‘auto f(const std::tuple<_El0, _El ...>&)
requires predicate((cpt_BooleanFalseConstant<decltype(p((get<0>)(f::t)))>)())
[with TFirst = std::integral_constant<int, 6>; TRest =
{std::integral_constant<int, 9>, std::integral_constant<int, 3>,
std::integral_constant<int, 5>}]’
main.cpp:44:6: required from here
main.cpp:34:11: error: call of overloaded
‘f(std::tuple<std::integral_constant<int, 3>, std::integral_constant<int, 5>
>)’ is ambiguous
return f(std::tuple<TRest...>());
^
main.cpp:24:6: note: candidate: auto f(const std::tuple<_El0, _El ...>&)
requires predicate((cpt_BooleanTrueConstant<decltype(p((get<0>)(f::t)))>)())
[with TFirst = std::integral_constant<int, 3>; TRest =
{std::integral_constant<int, 5>}]
auto f(const std::tuple<TFirst, TRest...>& t)
^
main.cpp:31:6: note: candidate: auto f(const std::tuple<_El0, _El ...>&)
requires predicate((cpt_BooleanFalseConstant<decltype(p((get<0>)(f::t)))>)())
[with TFirst = std::integral_constant<int, 3>; TRest =
{std::integral_constant<int, 5>}]
auto f(const std::tuple<TFirst, TRest...>& t)
////////////////////////////////////////////////////////////
#include <type_traits>
#include <tuple>
template <class X>
requires requires {
X::value;
}
constexpr bool lift_boolean_constant_value = X::value;
template <class X> concept bool cpt_BooleanTrueConstant() {
return requires { requires lift_boolean_constant_value<X>; };
}
template <class X> concept bool cpt_BooleanFalseConstant() {
return requires { requires !lift_boolean_constant_value<X>; };
}
template<int X>
auto p(std::integral_constant<int, X>) {
return std::integral_constant<bool, (X < 5)>();
}
template<class TFirst, class... TRest>
auto f(const std::tuple<TFirst, TRest...>& t)
requires cpt_BooleanTrueConstant<decltype(p(std::get<0>(t)))>()
{
return 1;
}
template<class TFirst, class... TRest>
auto f(const std::tuple<TFirst, TRest...>& t)
requires cpt_BooleanFalseConstant<decltype(p(std::get<0>(t)))>()
{
return f(std::tuple<TRest...>());
}
int main() {
std::tuple<
std::integral_constant<int, 6>,
std::integral_constant<int, 9>,
std::integral_constant<int, 3>,
std::integral_constant<int, 5>
> t;
f(t);
return 0;
}
////////////////////////////////////////////////////////////
