boost/thread/detail/move.hpp causes compilation failures

[apolukhin]

Test for boost::variant https://github.com/boostorg/variant/blob/46d8b92f73db38651a212521ff2d7c049dbcc21b/test/issue53.cpp#L15 fails on msvc-14.1 https://ci.appveyor.com/project/apolukhin/variant-ykfti/branch/develop/job/mtd52h6mhphj3dv9#L4402

C:\boost-local\boost/thread/detail/move.hpp(52): error C2528: '->': pointer to reference is illegal
C:\boost-local\boost/type_traits/is_convertible.hpp(490): note: see reference to class template instantiation 'boost::detail::thread_move_t<T>' being compiled
        with
        [
            T=T0 &
        ]
C:\boost-local\boost/core/enable_if.hpp(41): note: see reference to class template instantiation 'boost::is_convertible<T &,boost::detail::thread_move_t<spanac&>>' being compiled
        with
        [
            T=T0
        ]
C:\boost-local\boost/variant/variant.hpp(1020): note: see reference to class template instantiation 'boost::enable_if<boost::is_convertible<T &,boost::detail::thread_move_t<spanac&>>,boost::detail::thread_move_t<spanac&>>' being compiled
        with
        [
            T=T0
        ]
C:\boost-local\boost/variant/detail/visitation_impl.hpp(112): note: see reference to function template instantiation 'bool boost::detail::variant::invoke_visitor<Visitor,true>::internal_visit<T&>(spanac&,int)' being compiled
        with
        [
            Visitor=visitor_t,
            T=T0
        ]

Possible fixes:

• move the function into a separate namespace boost::thread::detail
• change the triat for move from is_convertible to something else... for example

  typename enable_if_c<T::use_thread_move, boost::detail::thread_move_t<T> >::type move(T& t)
  {
      return boost::detail::thread_move_t<T>(t);
  }

[viboes]

IIRC boost::move was there since the versions from Anthony Williams of Boost.Thread. We added the BOOST_THREAD_USES_MOVE to make it possible to use the better move sematic emulation from Boost.Move.

Unfortunately BOOST_THREAD_USES_MOVE is not defined by default. You need to define a higher version of Boost.Thread.

define BOOST_THREAD_VERSION 3

https://godbolt.org/z/3eayCt

If you have a non breaking change PR I will be open to analyze it.