Fails to build with Boost 1.70.0

[jbeich]

Regressed by boostorg/asio@59066d80b26e. Probably similar to zaphoyd/websocketpp#794. Dropping std::ref() appears to help.

wesnoth/src/server/server_base.cpp

Line 80 in 587d741

socket_ptr socket = std::make_shared<boost::asio::ip::tcp::socket>(std::ref(io_service_));

In file included from src/server/server_base.cpp:15:
In file included from src/server/server_base.hpp:26:
In file included from /usr/local/include/boost/asio.hpp:24:
In file included from /usr/local/include/boost/asio/basic_datagram_socket.hpp:20:
In file included from /usr/local/include/boost/asio/basic_socket.hpp:27:
In file included from /usr/local/include/boost/asio/executor.hpp:338:
/usr/local/include/boost/asio/impl/executor.hpp:179:22: error: no member named 'context' in
      'std::__1::reference_wrapper<boost::asio::io_context>'
    return executor_.context();
           ~~~~~~~~~ ^
/usr/local/include/boost/asio/impl/executor.hpp:142:3: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::context' requested here
  impl(const Executor& e, const Allocator& a) BOOST_ASIO_NOEXCEPT
  ^
/usr/local/include/boost/asio/impl/executor.hpp:137:30: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::impl' requested here
    impl* p = new (mem.ptr_) impl(e, a);
                             ^
/usr/local/include/boost/asio/impl/executor.hpp:333:50: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::create' requested here
  : impl_(impl<Executor, std::allocator<void> >::create(e))
                                                 ^
/usr/include/c++/v1/memory:2156:18: note: in instantiation of function template specialization
      'boost::asio::executor::executor<std::__1::reference_wrapper<boost::asio::io_context> >' requested here
      : __value_(_VSTD::forward<_Args>(_VSTD::get<_Indexes>(__args))...) {}
                 ^
/usr/include/c++/v1/__config:816:15: note: expanded from macro '_VSTD'
#define _VSTD std::_LIBCPP_ABI_NAMESPACE
              ^
/usr/include/c++/v1/memory:2259:9: note: in instantiation of function template specialization
      'std::__1::__compressed_pair_elem<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor>, 1,
      false>::__compressed_pair_elem<std::__1::reference_wrapper<boost::asio::io_context> &&, 0>' requested here
        _Base2(__pc, _VSTD::move(__second_args),
        ^
/usr/include/c++/v1/memory:3672:16: note: in instantiation of function template specialization
      'std::__1::__compressed_pair<std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> >, boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>
      >::__compressed_pair<std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> > &, std::__1::reference_wrapper<boost::asio::io_context> &&>' requested here
            :  __data_(piecewise_construct, _VSTD::forward_as_tuple(__a),
               ^
/usr/include/c++/v1/memory:4331:26: note: in instantiation of function template specialization
      'std::__1::__shared_ptr_emplace<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor>, std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> > >::__shared_ptr_emplace<std::__1::reference_wrapper<boost::asio::io_context> >'
      requested here
    ::new(__hold2.get()) _CntrlBlk(__a2, _VSTD::forward<_Args>(__args)...);
                         ^
/usr/include/c++/v1/memory:4710:29: note: in instantiation of function template specialization
      'std::__1::shared_ptr<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>
      >::make_shared<std::__1::reference_wrapper<boost::asio::io_context> >' requested here
    return shared_ptr<_Tp>::make_shared(_VSTD::forward<_Args>(__args)...);
                            ^
src/server/server_base.cpp:80:27: note: in instantiation of function template specialization
      'std::__1::make_shared<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>,
      std::__1::reference_wrapper<boost::asio::io_context> >' requested here
        socket_ptr socket = std::make_shared<boost::asio::ip::tcp::socket>(std::ref(io_service_));
                                 ^
In file included from src/server/server_base.cpp:15:
In file included from src/server/server_base.hpp:26:
In file included from /usr/local/include/boost/asio.hpp:24:
In file included from /usr/local/include/boost/asio/basic_datagram_socket.hpp:20:
In file included from /usr/local/include/boost/asio/basic_socket.hpp:27:
In file included from /usr/local/include/boost/asio/executor.hpp:338:
/usr/local/include/boost/asio/impl/executor.hpp:169:15: error: no member named 'on_work_started' in
      'std::__1::reference_wrapper<boost::asio::io_context>'
    executor_.on_work_started();
    ~~~~~~~~~ ^
/usr/local/include/boost/asio/impl/executor.hpp:142:3: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::on_work_started' requested here
  impl(const Executor& e, const Allocator& a) BOOST_ASIO_NOEXCEPT
  ^
/usr/local/include/boost/asio/impl/executor.hpp:137:30: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::impl' requested here
    impl* p = new (mem.ptr_) impl(e, a);
                             ^
/usr/local/include/boost/asio/impl/executor.hpp:333:50: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::create' requested here
  : impl_(impl<Executor, std::allocator<void> >::create(e))
                                                 ^
/usr/include/c++/v1/memory:2156:18: note: in instantiation of function template specialization
      'boost::asio::executor::executor<std::__1::reference_wrapper<boost::asio::io_context> >' requested here
      : __value_(_VSTD::forward<_Args>(_VSTD::get<_Indexes>(__args))...) {}
                 ^
/usr/include/c++/v1/__config:816:15: note: expanded from macro '_VSTD'
#define _VSTD std::_LIBCPP_ABI_NAMESPACE
              ^
/usr/include/c++/v1/memory:2259:9: note: in instantiation of function template specialization
      'std::__1::__compressed_pair_elem<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor>, 1,
      false>::__compressed_pair_elem<std::__1::reference_wrapper<boost::asio::io_context> &&, 0>' requested here
        _Base2(__pc, _VSTD::move(__second_args),
        ^
/usr/include/c++/v1/memory:3672:16: note: in instantiation of function template specialization
      'std::__1::__compressed_pair<std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> >, boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>
      >::__compressed_pair<std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> > &, std::__1::reference_wrapper<boost::asio::io_context> &&>' requested here
            :  __data_(piecewise_construct, _VSTD::forward_as_tuple(__a),
               ^
/usr/include/c++/v1/memory:4331:26: note: in instantiation of function template specialization
      'std::__1::__shared_ptr_emplace<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor>, std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> > >::__shared_ptr_emplace<std::__1::reference_wrapper<boost::asio::io_context> >'
      requested here
    ::new(__hold2.get()) _CntrlBlk(__a2, _VSTD::forward<_Args>(__args)...);
                         ^
/usr/include/c++/v1/memory:4710:29: note: in instantiation of function template specialization
      'std::__1::shared_ptr<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>
      >::make_shared<std::__1::reference_wrapper<boost::asio::io_context> >' requested here
    return shared_ptr<_Tp>::make_shared(_VSTD::forward<_Args>(__args)...);
                            ^
src/server/server_base.cpp:80:27: note: in instantiation of function template specialization
      'std::__1::make_shared<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>,
      std::__1::reference_wrapper<boost::asio::io_context> >' requested here
        socket_ptr socket = std::make_shared<boost::asio::ip::tcp::socket>(std::ref(io_service_));
                                 ^
In file included from src/server/server_base.cpp:15:
In file included from src/server/server_base.hpp:26:
In file included from /usr/local/include/boost/asio.hpp:24:
In file included from /usr/local/include/boost/asio/basic_datagram_socket.hpp:20:
In file included from /usr/local/include/boost/asio/basic_socket.hpp:27:
In file included from /usr/local/include/boost/asio/executor.hpp:338:
/usr/local/include/boost/asio/impl/executor.hpp:174:15: error: no member named 'on_work_finished' in
      'std::__1::reference_wrapper<boost::asio::io_context>'
    executor_.on_work_finished();
    ~~~~~~~~~ ^
/usr/local/include/boost/asio/impl/executor.hpp:142:3: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::on_work_finished' requested here
  impl(const Executor& e, const Allocator& a) BOOST_ASIO_NOEXCEPT
  ^
/usr/local/include/boost/asio/impl/executor.hpp:137:30: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::impl' requested here
    impl* p = new (mem.ptr_) impl(e, a);
                             ^
/usr/local/include/boost/asio/impl/executor.hpp:333:50: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::create' requested here
  : impl_(impl<Executor, std::allocator<void> >::create(e))
                                                 ^
/usr/include/c++/v1/memory:2156:18: note: in instantiation of function template specialization
      'boost::asio::executor::executor<std::__1::reference_wrapper<boost::asio::io_context> >' requested here
      : __value_(_VSTD::forward<_Args>(_VSTD::get<_Indexes>(__args))...) {}
                 ^
/usr/include/c++/v1/__config:816:15: note: expanded from macro '_VSTD'
#define _VSTD std::_LIBCPP_ABI_NAMESPACE
              ^
/usr/include/c++/v1/memory:2259:9: note: in instantiation of function template specialization
      'std::__1::__compressed_pair_elem<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor>, 1,
      false>::__compressed_pair_elem<std::__1::reference_wrapper<boost::asio::io_context> &&, 0>' requested here
        _Base2(__pc, _VSTD::move(__second_args),
        ^
/usr/include/c++/v1/memory:3672:16: note: in instantiation of function template specialization
      'std::__1::__compressed_pair<std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> >, boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>
      >::__compressed_pair<std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> > &, std::__1::reference_wrapper<boost::asio::io_context> &&>' requested here
            :  __data_(piecewise_construct, _VSTD::forward_as_tuple(__a),
               ^
/usr/include/c++/v1/memory:4331:26: note: in instantiation of function template specialization
      'std::__1::__shared_ptr_emplace<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor>, std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> > >::__shared_ptr_emplace<std::__1::reference_wrapper<boost::asio::io_context> >'
      requested here
    ::new(__hold2.get()) _CntrlBlk(__a2, _VSTD::forward<_Args>(__args)...);
                         ^
/usr/include/c++/v1/memory:4710:29: note: in instantiation of function template specialization
      'std::__1::shared_ptr<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>
      >::make_shared<std::__1::reference_wrapper<boost::asio::io_context> >' requested here
    return shared_ptr<_Tp>::make_shared(_VSTD::forward<_Args>(__args)...);
                            ^
src/server/server_base.cpp:80:27: note: in instantiation of function template specialization
      'std::__1::make_shared<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>,
      std::__1::reference_wrapper<boost::asio::io_context> >' requested here
        socket_ptr socket = std::make_shared<boost::asio::ip::tcp::socket>(std::ref(io_service_));
                                 ^
In file included from src/server/server_base.cpp:15:
In file included from src/server/server_base.hpp:26:
In file included from /usr/local/include/boost/asio.hpp:24:
In file included from /usr/local/include/boost/asio/basic_datagram_socket.hpp:20:
In file included from /usr/local/include/boost/asio/basic_socket.hpp:27:
In file included from /usr/local/include/boost/asio/executor.hpp:338:
/usr/local/include/boost/asio/impl/executor.hpp:184:15: error: no member named 'dispatch' in
      'std::__1::reference_wrapper<boost::asio::io_context>'
    executor_.dispatch(BOOST_ASIO_MOVE_CAST(function)(f), allocator_);
    ~~~~~~~~~ ^
/usr/local/include/boost/asio/impl/executor.hpp:142:3: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::dispatch' requested here
  impl(const Executor& e, const Allocator& a) BOOST_ASIO_NOEXCEPT
  ^
/usr/local/include/boost/asio/impl/executor.hpp:137:30: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::impl' requested here
    impl* p = new (mem.ptr_) impl(e, a);
                             ^
/usr/local/include/boost/asio/impl/executor.hpp:333:50: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::create' requested here
  : impl_(impl<Executor, std::allocator<void> >::create(e))
                                                 ^
/usr/include/c++/v1/memory:2156:18: note: in instantiation of function template specialization
      'boost::asio::executor::executor<std::__1::reference_wrapper<boost::asio::io_context> >' requested here
      : __value_(_VSTD::forward<_Args>(_VSTD::get<_Indexes>(__args))...) {}
                 ^
/usr/include/c++/v1/__config:816:15: note: expanded from macro '_VSTD'
#define _VSTD std::_LIBCPP_ABI_NAMESPACE
              ^
/usr/include/c++/v1/memory:2259:9: note: in instantiation of function template specialization
      'std::__1::__compressed_pair_elem<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor>, 1,
      false>::__compressed_pair_elem<std::__1::reference_wrapper<boost::asio::io_context> &&, 0>' requested here
        _Base2(__pc, _VSTD::move(__second_args),
        ^
/usr/include/c++/v1/memory:3672:16: note: in instantiation of function template specialization
      'std::__1::__compressed_pair<std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> >, boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>
      >::__compressed_pair<std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> > &, std::__1::reference_wrapper<boost::asio::io_context> &&>' requested here
            :  __data_(piecewise_construct, _VSTD::forward_as_tuple(__a),
               ^
/usr/include/c++/v1/memory:4331:26: note: in instantiation of function template specialization
      'std::__1::__shared_ptr_emplace<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor>, std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> > >::__shared_ptr_emplace<std::__1::reference_wrapper<boost::asio::io_context> >'
      requested here
    ::new(__hold2.get()) _CntrlBlk(__a2, _VSTD::forward<_Args>(__args)...);
                         ^
/usr/include/c++/v1/memory:4710:29: note: in instantiation of function template specialization
      'std::__1::shared_ptr<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>
      >::make_shared<std::__1::reference_wrapper<boost::asio::io_context> >' requested here
    return shared_ptr<_Tp>::make_shared(_VSTD::forward<_Args>(__args)...);
                            ^
src/server/server_base.cpp:80:27: note: in instantiation of function template specialization
      'std::__1::make_shared<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>,
      std::__1::reference_wrapper<boost::asio::io_context> >' requested here
        socket_ptr socket = std::make_shared<boost::asio::ip::tcp::socket>(std::ref(io_service_));
                                 ^
In file included from src/server/server_base.cpp:15:
In file included from src/server/server_base.hpp:26:
In file included from /usr/local/include/boost/asio.hpp:24:
In file included from /usr/local/include/boost/asio/basic_datagram_socket.hpp:20:
In file included from /usr/local/include/boost/asio/basic_socket.hpp:27:
In file included from /usr/local/include/boost/asio/executor.hpp:338:
/usr/local/include/boost/asio/impl/executor.hpp:189:15: error: no member named 'post' in
      'std::__1::reference_wrapper<boost::asio::io_context>'
    executor_.post(BOOST_ASIO_MOVE_CAST(function)(f), allocator_);
    ~~~~~~~~~ ^
/usr/local/include/boost/asio/impl/executor.hpp:142:3: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::post' requested here
  impl(const Executor& e, const Allocator& a) BOOST_ASIO_NOEXCEPT
  ^
/usr/local/include/boost/asio/impl/executor.hpp:137:30: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::impl' requested here
    impl* p = new (mem.ptr_) impl(e, a);
                             ^
/usr/local/include/boost/asio/impl/executor.hpp:333:50: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::create' requested here
  : impl_(impl<Executor, std::allocator<void> >::create(e))
                                                 ^
/usr/include/c++/v1/memory:2156:18: note: in instantiation of function template specialization
      'boost::asio::executor::executor<std::__1::reference_wrapper<boost::asio::io_context> >' requested here
      : __value_(_VSTD::forward<_Args>(_VSTD::get<_Indexes>(__args))...) {}
                 ^
/usr/include/c++/v1/__config:816:15: note: expanded from macro '_VSTD'
#define _VSTD std::_LIBCPP_ABI_NAMESPACE
              ^
/usr/include/c++/v1/memory:2259:9: note: in instantiation of function template specialization
      'std::__1::__compressed_pair_elem<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor>, 1,
      false>::__compressed_pair_elem<std::__1::reference_wrapper<boost::asio::io_context> &&, 0>' requested here
        _Base2(__pc, _VSTD::move(__second_args),
        ^
/usr/include/c++/v1/memory:3672:16: note: in instantiation of function template specialization
      'std::__1::__compressed_pair<std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> >, boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>
      >::__compressed_pair<std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> > &, std::__1::reference_wrapper<boost::asio::io_context> &&>' requested here
            :  __data_(piecewise_construct, _VSTD::forward_as_tuple(__a),
               ^
/usr/include/c++/v1/memory:4331:26: note: in instantiation of function template specialization
      'std::__1::__shared_ptr_emplace<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor>, std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> > >::__shared_ptr_emplace<std::__1::reference_wrapper<boost::asio::io_context> >'
      requested here
    ::new(__hold2.get()) _CntrlBlk(__a2, _VSTD::forward<_Args>(__args)...);
                         ^
/usr/include/c++/v1/memory:4710:29: note: in instantiation of function template specialization
      'std::__1::shared_ptr<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>
      >::make_shared<std::__1::reference_wrapper<boost::asio::io_context> >' requested here
    return shared_ptr<_Tp>::make_shared(_VSTD::forward<_Args>(__args)...);
                            ^
src/server/server_base.cpp:80:27: note: in instantiation of function template specialization
      'std::__1::make_shared<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>,
      std::__1::reference_wrapper<boost::asio::io_context> >' requested here
        socket_ptr socket = std::make_shared<boost::asio::ip::tcp::socket>(std::ref(io_service_));
                                 ^
In file included from src/server/server_base.cpp:15:
In file included from src/server/server_base.hpp:26:
In file included from /usr/local/include/boost/asio.hpp:24:
In file included from /usr/local/include/boost/asio/basic_datagram_socket.hpp:20:
In file included from /usr/local/include/boost/asio/basic_socket.hpp:27:
In file included from /usr/local/include/boost/asio/executor.hpp:338:
/usr/local/include/boost/asio/impl/executor.hpp:194:15: error: no member named 'defer' in
      'std::__1::reference_wrapper<boost::asio::io_context>'
    executor_.defer(BOOST_ASIO_MOVE_CAST(function)(f), allocator_);
    ~~~~~~~~~ ^
/usr/local/include/boost/asio/impl/executor.hpp:142:3: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::defer' requested here
  impl(const Executor& e, const Allocator& a) BOOST_ASIO_NOEXCEPT
  ^
/usr/local/include/boost/asio/impl/executor.hpp:137:30: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::impl' requested here
    impl* p = new (mem.ptr_) impl(e, a);
                             ^
/usr/local/include/boost/asio/impl/executor.hpp:333:50: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::create' requested here
  : impl_(impl<Executor, std::allocator<void> >::create(e))
                                                 ^
/usr/include/c++/v1/memory:2156:18: note: in instantiation of function template specialization
      'boost::asio::executor::executor<std::__1::reference_wrapper<boost::asio::io_context> >' requested here
      : __value_(_VSTD::forward<_Args>(_VSTD::get<_Indexes>(__args))...) {}
                 ^
/usr/include/c++/v1/__config:816:15: note: expanded from macro '_VSTD'
#define _VSTD std::_LIBCPP_ABI_NAMESPACE
              ^
/usr/include/c++/v1/memory:2259:9: note: in instantiation of function template specialization
      'std::__1::__compressed_pair_elem<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor>, 1,
      false>::__compressed_pair_elem<std::__1::reference_wrapper<boost::asio::io_context> &&, 0>' requested here
        _Base2(__pc, _VSTD::move(__second_args),
        ^
/usr/include/c++/v1/memory:3672:16: note: in instantiation of function template specialization
      'std::__1::__compressed_pair<std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> >, boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>
      >::__compressed_pair<std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> > &, std::__1::reference_wrapper<boost::asio::io_context> &&>' requested here
            :  __data_(piecewise_construct, _VSTD::forward_as_tuple(__a),
               ^
/usr/include/c++/v1/memory:4331:26: note: in instantiation of function template specialization
      'std::__1::__shared_ptr_emplace<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor>, std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> > >::__shared_ptr_emplace<std::__1::reference_wrapper<boost::asio::io_context> >'
      requested here
    ::new(__hold2.get()) _CntrlBlk(__a2, _VSTD::forward<_Args>(__args)...);
                         ^
/usr/include/c++/v1/memory:4710:29: note: in instantiation of function template specialization
      'std::__1::shared_ptr<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>
      >::make_shared<std::__1::reference_wrapper<boost::asio::io_context> >' requested here
    return shared_ptr<_Tp>::make_shared(_VSTD::forward<_Args>(__args)...);
                            ^
src/server/server_base.cpp:80:27: note: in instantiation of function template specialization
      'std::__1::make_shared<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>,
      std::__1::reference_wrapper<boost::asio::io_context> >' requested here
        socket_ptr socket = std::make_shared<boost::asio::ip::tcp::socket>(std::ref(io_service_));
                                 ^
In file included from src/server/server_base.cpp:15:
In file included from src/server/server_base.hpp:26:
In file included from /usr/local/include/boost/asio.hpp:24:
In file included from /usr/local/include/boost/asio/basic_datagram_socket.hpp:20:
In file included from /usr/local/include/boost/asio/basic_socket.hpp:27:
In file included from /usr/local/include/boost/asio/executor.hpp:338:
/usr/local/include/boost/asio/impl/executor.hpp:218:22: error: invalid operands to binary expression ('const
      std::__1::reference_wrapper<boost::asio::io_context>' and 'const
      std::__1::reference_wrapper<boost::asio::io_context>')
    return executor_ == *static_cast<const Executor*>(e->target());
           ~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/include/boost/asio/impl/executor.hpp:142:3: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::equals' requested here
  impl(const Executor& e, const Allocator& a) BOOST_ASIO_NOEXCEPT
  ^
/usr/local/include/boost/asio/impl/executor.hpp:137:30: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::impl' requested here
    impl* p = new (mem.ptr_) impl(e, a);
                             ^
/usr/local/include/boost/asio/impl/executor.hpp:333:50: note: in instantiation of member function
      'boost::asio::executor::impl<std::__1::reference_wrapper<boost::asio::io_context>, std::__1::allocator<void>
      >::create' requested here
  : impl_(impl<Executor, std::allocator<void> >::create(e))
                                                 ^
/usr/include/c++/v1/memory:2156:18: note: in instantiation of function template specialization
      'boost::asio::executor::executor<std::__1::reference_wrapper<boost::asio::io_context> >' requested here
      : __value_(_VSTD::forward<_Args>(_VSTD::get<_Indexes>(__args))...) {}
                 ^
/usr/include/c++/v1/__config:816:15: note: expanded from macro '_VSTD'
#define _VSTD std::_LIBCPP_ABI_NAMESPACE
              ^
/usr/include/c++/v1/memory:2259:9: note: in instantiation of function template specialization
      'std::__1::__compressed_pair_elem<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor>, 1,
      false>::__compressed_pair_elem<std::__1::reference_wrapper<boost::asio::io_context> &&, 0>' requested here
        _Base2(__pc, _VSTD::move(__second_args),
        ^
/usr/include/c++/v1/memory:3672:16: note: in instantiation of function template specialization
      'std::__1::__compressed_pair<std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> >, boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>
      >::__compressed_pair<std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> > &, std::__1::reference_wrapper<boost::asio::io_context> &&>' requested here
            :  __data_(piecewise_construct, _VSTD::forward_as_tuple(__a),
               ^
/usr/include/c++/v1/memory:4331:26: note: in instantiation of function template specialization
      'std::__1::__shared_ptr_emplace<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor>, std::__1::allocator<boost::asio::basic_stream_socket<boost::asio::ip::tcp,
      boost::asio::executor> > >::__shared_ptr_emplace<std::__1::reference_wrapper<boost::asio::io_context> >'
      requested here
    ::new(__hold2.get()) _CntrlBlk(__a2, _VSTD::forward<_Args>(__args)...);
                         ^
/usr/include/c++/v1/memory:4710:29: note: in instantiation of function template specialization
      'std::__1::shared_ptr<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>
      >::make_shared<std::__1::reference_wrapper<boost::asio::io_context> >' requested here
    return shared_ptr<_Tp>::make_shared(_VSTD::forward<_Args>(__args)...);
                            ^
src/server/server_base.cpp:80:27: note: in instantiation of function template specialization
      'std::__1::make_shared<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::executor>,
      std::__1::reference_wrapper<boost::asio::io_context> >' requested here
        socket_ptr socket = std::make_shared<boost::asio::ip::tcp::socket>(std::ref(io_service_));
                                 ^
/usr/include/c++/v1/system_error:391:1: note: candidate function not viable: no known conversion from 'const
      std::__1::reference_wrapper<boost::asio::io_context>' to 'const std::__1::error_code' for 1st argument
operator==(const error_code& __x, const error_code& __y) _NOEXCEPT
^
/usr/include/c++/v1/system_error:398:1: note: candidate function not viable: no known conversion from 'const
      std::__1::reference_wrapper<boost::asio::io_context>' to 'const std::__1::error_code' for 1st argument
operator==(const error_code& __x, const error_condition& __y) _NOEXCEPT
^
/usr/include/c++/v1/system_error:406:1: note: candidate function not viable: no known conversion from 'const
      std::__1::reference_wrapper<boost::asio::io_context>' to 'const std::__1::error_condition' for 1st argument
operator==(const error_condition& __x, const error_code& __y) _NOEXCEPT
^
/usr/include/c++/v1/system_error:413:1: note: candidate function not viable: no known conversion from 'const
      std::__1::reference_wrapper<boost::asio::io_context>' to 'const std::__1::error_condition' for 1st argument
operator==(const error_condition& __x, const error_condition& __y) _NOEXCEPT
^
/usr/include/c++/v1/utility:580:1: note: candidate template ignored: could not match 'pair' against
      'reference_wrapper'
operator==(const pair<_T1,_T2>& __x, const pair<_T1,_T2>& __y)
^
/usr/include/c++/v1/iterator:712:1: note: candidate template ignored: could not match 'reverse_iterator' against
      'reference_wrapper'
operator==(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
^
/usr/include/c++/v1/iterator:941:1: note: candidate template ignored: could not match 'istream_iterator' against
      'reference_wrapper'
operator==(const istream_iterator<_Tp, _CharT, _Traits, _Distance>& __x,
^
/usr/include/c++/v1/iterator:1045:6: note: candidate template ignored: could not match 'istreambuf_iterator'
      against 'reference_wrapper'
bool operator==(const istreambuf_iterator<_CharT,_Traits>& __a,
     ^
/usr/include/c++/v1/iterator:1153:1: note: candidate template ignored: could not match 'move_iterator' against
      'reference_wrapper'
operator==(const move_iterator<_Iter1>& __x, const move_iterator<_Iter2>& __y)
^
/usr/include/c++/v1/iterator:1525:1: note: candidate template ignored: could not match '__wrap_iter' against
      'reference_wrapper'
operator==(const __wrap_iter<_Iter1>& __x, const __wrap_iter<_Iter2>& __y) _NOEXCEPT_DEBUG
^
/usr/include/c++/v1/tuple:1122:1: note: candidate template ignored: could not match 'tuple' against
      'reference_wrapper'
operator==(const tuple<_Tp...>& __x, const tuple<_Up...>& __y)
^
/usr/include/c++/v1/memory:1987:6: note: candidate template ignored: could not match 'allocator' against
      'reference_wrapper'
bool operator==(const allocator<_Tp>&, const allocator<_Up>&) _NOEXCEPT {return true;}
     ^
/usr/include/c++/v1/memory:2964:1: note: candidate template ignored: could not match 'unique_ptr' against
      'reference_wrapper'
operator==(const unique_ptr<_T1, _D1>& __x, const unique_ptr<_T2, _D2>& __y) {return __x.get() == __y.get();}
^
/usr/include/c++/v1/memory:3000:1: note: candidate template ignored: could not match 'unique_ptr' against
      'reference_wrapper'
operator==(const unique_ptr<_T1, _D1>& __x, nullptr_t) _NOEXCEPT
^
/usr/include/c++/v1/memory:3008:1: note: candidate template ignored: could not match 'unique_ptr' against
      'reference_wrapper'
operator==(nullptr_t, const unique_ptr<_T1, _D1>& __x) _NOEXCEPT
^
/usr/include/c++/v1/memory:4796:1: note: candidate template ignored: could not match 'shared_ptr' against
      'reference_wrapper'
operator==(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT
^
/usr/include/c++/v1/memory:4850:1: note: candidate template ignored: could not match 'shared_ptr' against
      'reference_wrapper'
operator==(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT
^
/usr/include/c++/v1/memory:4858:1: note: candidate template ignored: could not match 'shared_ptr' against
      'reference_wrapper'
operator==(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT
^
/usr/include/c++/v1/functional:2380:1: note: candidate template ignored: could not match 'function' against
      'reference_wrapper'
operator==(const function<_Rp(_ArgTypes...)>& __f, nullptr_t) _NOEXCEPT {return !__f;}
^
/usr/include/c++/v1/functional:2385:1: note: candidate template ignored: could not match 'function' against
      'reference_wrapper'
operator==(nullptr_t, const function<_Rp(_ArgTypes...)>& __f) _NOEXCEPT {return !__f;}
^
/usr/include/c++/v1/string_view:614:6: note: candidate template ignored: could not match 'basic_string_view'
      against 'reference_wrapper'
bool operator==(basic_string_view<_CharT, _Traits> __lhs,
     ^
/usr/include/c++/v1/string_view:623:6: note: candidate template ignored: could not match 'basic_string_view'
      against 'reference_wrapper'
bool operator==(basic_string_view<_CharT, _Traits> __lhs,
     ^
/usr/include/c++/v1/string_view:632:6: note: candidate template ignored: could not match 'basic_string_view'
      against 'reference_wrapper'
bool operator==(typename common_type<basic_string_view<_CharT, _Traits> >::type __lhs,
     ^
/usr/include/c++/v1/string:564:6: note: candidate template ignored: could not match 'fpos' against
      'reference_wrapper'
bool operator==(const fpos<_StateT>& __x, const fpos<_StateT>& __y)
     ^
/usr/include/c++/v1/string:3845:1: note: candidate template ignored: could not match 'basic_string' against
      'reference_wrapper'
operator==(const basic_string<_CharT, _Traits, _Allocator>& __lhs,
^
/usr/include/c++/v1/string:3857:1: note: candidate template ignored: could not match 'basic_string' against
      'reference_wrapper'
operator==(const basic_string<char, char_traits<char>, _Allocator>& __lhs,
^
/usr/include/c++/v1/string:3876:1: note: candidate template ignored: could not match 'const _CharT *' against
      'std::__1::reference_wrapper<boost::asio::io_context>'
operator==(const _CharT* __lhs,
^
/usr/include/c++/v1/string:3889:1: note: candidate template ignored: could not match 'basic_string' against
      'reference_wrapper'
operator==(const basic_string<_CharT,_Traits,_Allocator>& __lhs,
^
/usr/include/c++/v1/map:1563:1: note: candidate template ignored: could not match 'map' against
      'reference_wrapper'
operator==(const map<_Key, _Tp, _Compare, _Allocator>& __x,
^
/usr/include/c++/v1/map:2108:1: note: candidate template ignored: could not match 'multimap' against
      'reference_wrapper'
operator==(const multimap<_Key, _Tp, _Compare, _Allocator>& __x,
^
/usr/include/c++/v1/vector:3361:1: note: candidate template ignored: could not match 'vector' against
      'reference_wrapper'
operator==(const vector<_Tp, _Allocator>& __x, const vector<_Tp, _Allocator>& __y)
^
/usr/include/c++/v1/array:372:1: note: candidate template ignored: could not match 'array' against
      'reference_wrapper'
operator==(const array<_Tp, _Size>& __x, const array<_Tp, _Size>& __y)
^
/usr/include/c++/v1/set:859:1: note: candidate template ignored: could not match 'set' against 'reference_wrapper'
operator==(const set<_Key, _Compare, _Allocator>& __x,
^
/usr/include/c++/v1/set:1347:1: note: candidate template ignored: could not match 'multiset' against
      'reference_wrapper'
operator==(const multiset<_Key, _Compare, _Allocator>& __x,
^
7 errors generated.

[jyrkive]

Git blame tells that this std::ref has been there (originally as boost::ref) ever since @loonycyborg's initial server implementation based on Boost.Asio: e9ded20