http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55993
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |rejects-valid
Component|libstdc++ |c++
Summary|tuple_cat not a constant |[C++11] derived-to-base
|expression for result size |conversion fails in
|>= 3 |constant expression
Known to fail| |4.6.3, 4.7.3, 4.8.0
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-01-15
19:15:36 UTC ---
This seems to be a C++ front end bug, here's the code reduced to remove library
dependencies:
template<int N, typename T>
struct Head : T
{ };
template<int N, typename... T>
struct Tuple;
template<int N>
struct Tuple<N>
{ };
template<int N, typename T, typename... U>
struct Tuple<N, T, U...> : Tuple<N+1, U...>, Head<N, T>
{ };
template<typename T, typename U>
struct tuple : Tuple<0, T, U>
{ };
struct A { };
constexpr tuple<A, A> t{};
constexpr auto a = static_cast<const Head<0, A>&>(t);
tt.cc:22:52: error: accessing value of 't' through a 'const Head<0, A>' glvalue
in a constant expression
constexpr auto a = static_cast<const Head<0, A>&>(t);
^
