https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97246
Bug ID: 97246
Summary: [10.1 regression] mismatched argument pack lengths
Product: gcc
Version: 10.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: wjwray at gmail dot com
Target Milestone: ---
A deduced <typename... T> argument pack T... v now gives a
"mismatched argument pack lengths" error for T... and v...
i.e. static_assert( sizeof...(T) == sizeof...(v) ); // Fail !!
Here's a sample, working on 9.3, rejected since 10.1
https://godbolt.org/z/oM9ve5
template <int... Is, typename T>
T arg_T(decltype(Is)..., T, ...);
template <int I, int... Is>
inline constexpr auto get =
[]<typename... T>(decltype(Is)..., T... v, ...) {
static_assert( sizeof...(T) == sizeof...(v) );
if constexpr ( sizeof...(T) == 1 )
return (v,...);
else {
using V = decltype(arg_T<__integer_pack(I)...>(v...));
return get<I,__integer_pack(I)...>.template operator()<V>(v...);
}
};
static_assert( get<0>('\0', short{1}, 2, long{3}) == 0 );
(Will try to simplify & post a reduced sample in a later comment).
Note: the 'mismatched length' error shows when both T and v are used together
e.g. with forwarding references <typename... T> : (T&&... v) : ((T&&)v...)
