Hello Is this a known problem or am I just too stupid? Since we switched to c++20 in VS2022 with toolset v143, the timers no longer compile. We have tested it with VS 17.5.0 and 17.5.4. Test code: asio::io_service io; asio::steady_timer t(io, 1s); Compiler: 1>\boost\boost_1_81_0\include\boost/asio/detail/io_object_impl.hpp(59,16): error C2665: 'boost::asio::any_io_executor::any_io_executor': no overloaded function could convert all the argument types 1>\boost\boost_1_81_0\include\boost/asio/impl/any_io_executor.ipp(34,18): message : could be 'boost::asio::any_io_executor::any_io_executor(std::nullptr_t) noexcept' 1>\boost\boost_1_81_0\include\boost/asio/detail/io_object_impl.hpp(59,16): message : 'boost::asio::any_io_executor::any_io_executor(std::nullptr_t) noexcept': cannot convert argument 1 from 'boost::asio::io_context::executor_type' to 'std::nullptr_t' 1>\boost\boost_1_81_0\include\boost/asio/detail/io_object_impl.hpp(59,37): message : No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called 1>E:\DitecLibs\Packages\boost\boost_1_81_0\include\boost/asio/any_io_executor.hpp(189,3): message : or 'boost::asio::any_io_executor::any_io_executor(std::nothrow_t,Executor,constraint<std::conditional<!std::is_same<OtherAnyExecutor,boost::asio::any_io_executor>::value&&!std::is_base_of<boost::asio::execution::detail::any_executor_base,Executor>::value,boost::asio::execution::detail::is_valid_target_executor<Executor,boost::asio::any_io_executor::supportable_properties_type>,std::false_type>::type::value,int>::type) noexcept' 1>\boost\boost_1_81_0\include\boost/asio/detail/io_object_impl.hpp(59,16): message : 'boost::asio::any_io_executor::any_io_executor(std::nothrow_t,Executor,constraint<std::conditional<!std::is_same<OtherAnyExecutor,boost::asio::any_io_executor>::value&&!std::is_base_of<boost::asio::execution::detail::any_executor_base,Executor>::value,boost::asio::execution::detail::is_valid_target_executor<Executor,boost::asio::any_io_executor::supportable_properties_type>,std::false_type>::type::value,int>::type) noexcept': expects 3 arguments - 1 provided 1>\boost\boost_1_81_0\include\boost/asio/any_io_executor.hpp(167,3): message : or 'boost::asio::any_io_executor::any_io_executor(Executor,constraint<std::conditional<!std::is_same<OtherAnyExecutor,boost::asio::any_io_executor>::value&&!std::is_base_of<boost::asio::execution::detail::any_executor_base,Executor>::value,boost::asio::execution::detail::is_valid_target_executor<Executor,boost::asio::any_io_executor::supportable_properties_type>,std::false_type>::type::value,int>::type)' 1>\boost\boost_1_81_0\include\boost/asio/detail/io_object_impl.hpp(59,16): message : Failed to specialize function template 'boost::asio::any_io_executor::any_io_executor(Executor,constraint<std::conditional<!std::is_same<OtherAnyExecutor,boost::asio::any_io_executor>::value&&!std::is_base_of<boost::asio::execution::detail::any_executor_base,Executor>::value,boost::asio::execution::detail::is_valid_target_executor<Executor,boost::asio::any_io_executor::supportable_properties_type>,std::false_type>::type::value,int>::type)' 1>\boost\boost_1_81_0\include\boost/asio/detail/io_object_impl.hpp(59,16): message : With the following template arguments: 1>\boost\boost_1_81_0\include\boost/asio/detail/io_object_impl.hpp(59,16): message : 'Executor=boost::asio::io_context::executor_type' 1>\boost\boost_1_81_0\include\boost/asio/any_io_executor.hpp(134,3): message : or 'boost::asio::any_io_executor::any_io_executor(std::nothrow_t,OtherAnyExecutor,constraint<std::conditional<!std::is_same<OtherAnyExecutor,boost::asio::any_io_executor>::value&&std::is_base_of<boost::asio::execution::detail::any_executor_base,Executor>::value,boost::asio::execution::detail::supportable_properties<0,void (boost::asio::execution::context_as_t<boost::asio::execution_context &>,boost::asio::execution::detail::blocking::never_t<0>,boost::asio::execution::prefer_only<boost::asio::execution::detail::blocking::possibly_t<0>>,boost::asio::execution::prefer_only<boost::asio::execution::detail::outstanding_work::tracked_t<0>>,boost::asio::execution::prefer_only<boost::asio::execution::detail::outstanding_work::untracked_t<0>>,boost::asio::execution::prefer_only<boost::asio::execution::detail::relationship::fork_t<0>>,boost::asio::execution::prefer_only<boost::asio::execution::detail::relationship::continuation_t<0>>)>::is_valid_target<OtherAnyExecutor>,std::false_type>::type::value,int>::type) noexcept' 1>\boost\boost_1_81_0\include\boost/asio/detail/io_object_impl.hpp(59,16): message : 'boost::asio::any_io_executor::any_io_executor(std::nothrow_t,OtherAnyExecutor,constraint<std::conditional<!std::is_same<OtherAnyExecutor,boost::asio::any_io_executor>::value&&std::is_base_of<boost::asio::execution::detail::any_executor_base,Executor>::value,boost::asio::execution::detail::supportable_properties<0,void (boost::asio::execution::context_as_t<boost::asio::execution_context &>,boost::asio::execution::detail::blocking::never_t<0>,boost::asio::execution::prefer_only<boost::asio::execution::detail::blocking::possibly_t<0>>,boost::asio::execution::prefer_only<boost::asio::execution::detail::outstanding_work::tracked_t<0>>,boost::asio::execution::prefer_only<boost::asio::execution::detail::outstanding_work::untracked_t<0>>,boost::asio::execution::prefer_only<boost::asio::execution::detail::relationship::fork_t<0>>,boost::asio::execution::prefer_only<boost::asio::execution::detail::relationship::continuation_t<0>>)>::is_valid_target<OtherAnyExecutor>,std::false_type>::type::value,int>::type) noexcept': expects 3 arguments - 1 provided 1>\boost\boost_1_81_0\include\boost/asio/any_io_executor.hpp(110,3): message : or 'boost::asio::any_io_executor::any_io_executor(OtherAnyExecutor,constraint<std::conditional<!std::is_same<OtherAnyExecutor,boost::asio::any_io_executor>::value&&std::is_base_of<boost::asio::execution::detail::any_executor_base,Executor>::value,boost::asio::execution::detail::supportable_properties<0,void (boost::asio::execution::context_as_t<boost::asio::execution_context &>,boost::asio::execution::detail::blocking::never_t<0>,boost::asio::execution::prefer_only<boost::asio::execution::detail::blocking::possibly_t<0>>,boost::asio::execution::prefer_only<boost::asio::execution::detail::outstanding_work::tracked_t<0>>,boost::asio::execution::prefer_only<boost::asio::execution::detail::outstanding_work::untracked_t<0>>,boost::asio::execution::prefer_only<boost::asio::execution::detail::relationship::fork_t<0>>,boost::asio::execution::prefer_only<boost::asio::execution::detail::relationship::continuation_t<0>>)>::is_valid_target<OtherAnyExecutor>,std::false_type>::type::value,int>::type)' 1>\boost\boost_1_81_0\include\boost/asio/detail/io_object_impl.hpp(59,16): message : Failed to specialize function template 'boost::asio::any_io_executor::any_io_executor(OtherAnyExecutor,constraint<std::conditional<!std::is_same<OtherAnyExecutor,boost::asio::any_io_executor>::value&&std::is_base_of<boost::asio::execution::detail::any_executor_base,Executor>::value,boost::asio::execution::detail::supportable_properties<0,void (boost::asio::execution::context_as_t<boost::asio::execution_context &>,boost::asio::execution::detail::blocking::never_t<0>,boost::asio::execution::prefer_only<boost::asio::execution::detail::blocking::possibly_t<0>>,boost::asio::execution::prefer_only<boost::asio::execution::detail::outstanding_work::tracked_t<0>>,boost::asio::execution::prefer_only<boost::asio::execution::detail::outstanding_work::untracked_t<0>>,boost::asio::execution::prefer_only<boost::asio::execution::detail::relationship::fork_t<0>>,boost::asio::execution::prefer_only<boost::asio::execution::detail::relationship::continuation_t<0>>)>::is_valid_target<OtherAnyExecutor>,std::false_type>::type::value,int>::type)' 1>\boost\boost_1_81_0\include\boost/asio/detail/io_object_impl.hpp(59,16): message : With the following template arguments: 1>\boost\boost_1_81_0\include\boost/asio/detail/io_object_impl.hpp(59,16): message : 'OtherAnyExecutor=boost::asio::io_context::executor_type' 1>\boost\boost_1_81_0\include\boost/asio/detail/io_object_impl.hpp(59,16): message : while trying to match the argument list '(boost::asio::io_context::executor_type)' 1>\boost\boost_1_81_0\include\boost/asio/basic_waitable_timer.hpp(284,1): message : see reference to function template instantiation 'boost::asio::detail::io_object_impl<boost::asio::detail::deadline_timer_service<boost::asio::detail::chrono_time_traits<Clock,WaitTraits>>,boost::asio::any_io_executor>::io_object_impl<ExecutionContext>(int,int,ExecutionContext &)' being compiled 1> with 1> [ 1> Clock=std::chrono::steady_clock, 1> WaitTraits=boost::asio::wait_traits<std::chrono::steady_clock>, 1> ExecutionContext=boost::asio::io_service 1> ] 1>\boost\boost_1_81_0\include\boost/asio/basic_waitable_timer.hpp(283,12): message : see reference to function template instantiation 'boost::asio::detail::io_object_impl<boost::asio::detail::deadline_timer_service<boost::asio::detail::chrono_time_traits<Clock,WaitTraits>>,boost::asio::any_io_executor>::io_object_impl<ExecutionContext>(int,int,ExecutionContext &)' being compiled 1> with 1> [ 1> Clock=std::chrono::steady_clock, 1> WaitTraits=boost::asio::wait_traits<std::chrono::steady_clock>, 1> ExecutionContext=boost::asio::io_service 1> ] 1>main.cpp(27,29): message : see reference to function template instantiation 'boost::asio::basic_waitable_timer<std::chrono::steady_clock,boost::asio::wait_traits<Clock>,boost::asio::any_io_executor>::basic_waitable_timer<boost::asio::io_service>(ExecutionContext &,const std::chrono::duration<__int64,std::nano> &,int)' being compiled 1> with 1> [ 1> Clock=std::chrono::steady_clock, 1> ExecutionContext=boost::asio::io_service 1> ] 1>main.cpp(27,22): message : see reference to function template instantiation 'boost::asio::basic_waitable_timer<std::chrono::steady_clock,boost::asio::wait_traits<Clock>,boost::asio::any_io_executor>::basic_waitable_timer<boost::asio::io_service>(ExecutionContext &,const std::chrono::duration<__int64,std::nano> &,int)' being compiled 1> with 1> [ 1> Clock=std::chrono::steady_clock, 1> ExecutionContext=boost::asio::io_service 1> ] What could be the reason for this? Best regards Sören