https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80871
Bug ID: 80871
Summary: Template partial ordering considered non-ambiguous
with deduced and non-deduced parameter packs
Product: gcc
Version: 7.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: barry.revzin at gmail dot com
Target Milestone: ---
Consider this example:
#ifdef VARIADIC
template <class... Ts, class... Us>
constexpr int foo(Us... ) { return 1; }
template <class... Us>
constexpr int foo(Us... ) { return 2; }
#else
template <class... Ts, class U>
constexpr int foo(U ) { return 1; }
template <class U>
constexpr int foo(U ) { return 2; }
#endif
int main() {
static_assert(foo(1) == 1, "!");
}
Without -DVARIADIC, the call to foo(1) is considered ambiguous and the program
fails to compile. But with -DVARIADIC, the program compiles. The call should be
ambiguous, since Ts... does not participate in partial ordering.
