Is it true, that structured bindings in clang (I use recently builded clang version 4.0.0 (trunk 282683)) are implemented using some stuff from <tuple>, like braces-init lists may use stuff from <initializer_list>?
I wrote simple code just to play with some of latest features implemented:
struct S { int a; char b; double c; };
auto [a, b, c] = S{1, '2', 3.0};
using A = decltype(a);
using A = int;
using B = decltype(b);
using B = char;
using C = decltype(c);
using C = double;
So far so good, but when I add const qualifier before auto:
struct S { int a; char b; double c; };
const auto [a, b, c] = S{1, '2', 3.0};
using A = decltype(a);
using A = int const;
using B = decltype(b);
using B = char const;
using C = decltype(c);
using C = double const;
I get a strange error description:
In file included from /home/user/test/main.cpp:1:
In file included from /home/user/test/./test.hpp:4:
In file included from /usr/local/bin/../include/c++/v1/utility:193:
/usr/local/bin/../include/c++/v1/__tuple:29:14: fatal error: implicit instantiation of undefined template 'std::__1::tuple_size<S>'
: public tuple_size<_Tp> {};
^
/home/user/test/main.cpp:110:16: note: in instantiation of template class 'std::__1::tuple_size<const S>' requested here
const auto [a, b, c] = S{1, '2', 3.0};
^
/usr/local/bin/../include/c++/v1/__tuple:25:50: note: template is declared here
template <class _Tp> class _LIBCPP_TYPE_VIS_ONLY tuple_size;
^
I.e. there is interaction with accidentally included <tuple>.
I know that structured bindings are partially implemented in clang, but either way it is interesting how <tuple> may be related to them?
Should I include <tuple> to use structured bindings?
Additional:
auto, auto & and auto && works, but auto const and auto const & not.