[Boost-bugs] [Boost C++ Libraries] #13404: boost::container::container_detail::forward_as_tuple conflicts with std::forward_as_tuple

Subject: [Boost-bugs] [Boost C++ Libraries] #13404: boost::container::container_detail::forward_as_tuple conflicts with std::forward_as_tuple
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2018-01-17 17:06:13

#13404: boost::container::container_detail::forward_as_tuple conflicts with
std::forward_as_tuple
--------------------------------------------+---------------------------
 Reporter:  Mikhail Kremniov <mkremniov@…>  |      Owner:  Ion Gaztañaga
     Type:  Bugs                            |     Status:  new
Milestone:  To Be Determined                |  Component:  container
  Version:  Boost 1.66.0                    |   Severity:  Problem
 Keywords:                                  |
--------------------------------------------+---------------------------
 Internals of libc++ make unqualified calls to forward_as_tuple; this may
 result in the "call ... is ambiguous" error if
 boost::container::container_detail is one of the associated namespaces for
 the call.

 E.g. test.cpp:
 {{{
 #include <boost/container/set.hpp>
 #include <tuple>

 int main()
 {
     boost::container::set<int> set;

     std::tuple_cat(std::make_tuple(set));
 }
 }}}

 The terminal:
 {{{
 $ clang++-5.0 ~/tmp/test.cpp -std=c++14 -o test -stdlib=libc++ -isystem
 ./boost_1_66_0
 In file included from /home/brd/tmp/test.cpp:1:
 In file included from ./boost_1_66_0/boost/container/set.hpp:28:
 In file included from ./boost_1_66_0/boost/container/detail/tree.hpp:36:
 In file included from
 ./boost_1_66_0/boost/container/detail/node_alloc_holder.hpp:30:
 In file included from
 ./boost_1_66_0/boost/container/detail/allocator_version_traits.hpp:26:
 In file included from
 ./boost_1_66_0/boost/container/throw_exception.hpp:27:
 In file included from /home/brd/soft/clang+llvm-5.0.0-linux-
 x86_64-ubuntu14.04/bin/../include/c++/v1/string:470:
 In file included from /home/brd/soft/clang+llvm-5.0.0-linux-
 x86_64-ubuntu14.04/bin/../include/c++/v1/string_view:169:
 In file included from /home/brd/soft/clang+llvm-5.0.0-linux-
 x86_64-ubuntu14.04/bin/../include/c++/v1/__string:56:
 In file included from /home/brd/soft/clang+llvm-5.0.0-linux-
 x86_64-ubuntu14.04/bin/../include/c++/v1/algorithm:643:
 In file included from /home/brd/soft/clang+llvm-5.0.0-linux-
 x86_64-ubuntu14.04/bin/../include/c++/v1/memory:653:
 /home/brd/soft/clang+llvm-5.0.0-linux-
 x86_64-ubuntu14.04/bin/../include/c++/v1/tuple:1318:16: error: call to
 'forward_as_tuple' is ambiguous
         return
 forward_as_tuple(_VSTD::forward<_Types>(_VSTD::get<_I0>(__t))...,
                ^~~~~~~~~~~~~~~~
 /home/brd/soft/clang+llvm-5.0.0-linux-
 x86_64-ubuntu14.04/bin/../include/c++/v1/tuple:1348:12: note: in
 instantiation of function template specialization
 'std::__1::__tuple_cat<std::__1::tuple<>, std::__1::__tuple_indices<>,
       std::__1::__tuple_indices<0>
 >::operator()<std::__1::tuple<boost::container::set<int,
 std::__1::less<int>, boost::container::new_allocator<int>,
 boost::container::tree_opt<boost::container::tree_type_enum::red_black_tree,
 true> > >
       >' requested here
     return __tuple_cat<tuple<>, __tuple_indices<>,
            ^
 /home/brd/tmp/test.cpp:8:10: note: in instantiation of function template
 specialization
 'std::__1::tuple_cat<std::__1::tuple<boost::container::set<int,
 std::__1::less<int>, boost::container::new_allocator<int>,
 boost::container::tree_opt<boost::container::tree_type_enum::red_black_tree,
 true> > >>' requested here
     std::tuple_cat(std::make_tuple(set));
          ^
 ./boost_1_66_0/boost/container/detail/variadic_templates_tools.hpp:81:20:
 note: candidate function [with Values = <boost::container::set<int,
 std::__1::less<int>, boost::container::new_allocator<int>,
 boost::container::tree_opt<boost::container::tree_type_enum::red_black_tree,
 true> >>]
 tuple<Values&&...> forward_as_tuple(Values&&... values)
                    ^
 /home/brd/soft/clang+llvm-5.0.0-linux-
 x86_64-ubuntu14.04/bin/../include/c++/v1/tuple:1114:1: note: candidate
 function [with _Tp = <boost::container::set<int, std::__1::less<int>,
 boost::container::new_allocator<int>,
 boost::container::tree_opt<boost::container::tree_type_enum::red_black_tree,
 true> >>]
 forward_as_tuple(_Tp&&... __t) _NOEXCEPT
 ^
 1 error generated.
 }}}

 P.S. I wonder, why is boost::container::container_detail::forward_as_tuple
 needed at all, since it doesn't seem to be used outside of tests. Can it
 be removed?

-- 
Ticket URL: <https://svn.boost.org/trac10/boost/ticket/13404>
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