https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68388
Bug ID: 68388
Summary: incomplete type bug when using decltype
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 compiles fine with clang
(http://melpon.org/wandbox/permlink/Rm6dpbmC0N3eMJJa) and earlier versions of
gcc-6, but was recently broken. Gcc gives this error when compiling:
bug.cpp: In instantiation of ‘auto map_impl(std::index_sequence<Indexes ...>,
Functor, T1, T2) [with int ...Indexes = {0}; Functor = Less; T1 = Tuple<int>;
T2 = Tuple<int>]’:
bug.cpp:27:11: required from ‘auto map_impl(Functor, T1, T2) [with Functor =
Less; T1 = Tuple<int>; T2 = Tuple<int>]’
bug.cpp:40:26: required from here
bug.cpp:22:3: error: invalid use of incomplete type ‘class Tuple<decltype
(apply_impl<Indexes>(f, t1, t2))...>’
Tuple<decltype(apply_impl<Indexes>(f, t1, t2))...>();
^~~~~
bug.cpp:8:27: note: declaration of ‘class Tuple<decltype
(apply_impl<Indexes>(f, t1, t2))...>’
template <class...> class Tuple {};
///////////////////////////////////////////////////////////
typedef int size_t;
template <std::size_t... Indexes>
struct index_sequence {};
}
template <class...> class Tuple {};
template <std::size_t I, class TFirst>
auto get(Tuple<TFirst>) {
return TFirst();
}
template <std::size_t I, class Functor, class T1, class T2>
auto apply_impl(Functor f, T1 t1, T2 t2) {
return f(get<I>(t1), get<I>(t2));
}
template <std::size_t... Indexes, class Functor, class T1, class T2>
auto map_impl(std::index_sequence<Indexes...>, Functor f, T1 t1, T2 t2) {
Tuple<decltype(apply_impl<Indexes>(f, t1, t2))...>();
}
template <class Functor, class T1, class T2>
auto map_impl(Functor f, T1 t1, T2 t2) {
map_impl(std::index_sequence<0>(), f, t1, t2);
}
struct Less {
template <class Lhs, class Rhs>
auto operator()(Lhs lhs, Rhs rhs) -> decltype(lhs < rhs) {
return lhs < rhs;
}
};
int main() {
auto t1 = Tuple<int>();
auto t2 = Tuple<int>();
map_impl(Less(), t1, t2);
}
///////////////////////////////////////////////////////////
