Hi, I don't know if this is a regression on Boost.TypeTraits or if I'm using incorrectly the is_function trait. John, could you confirm there is a bug in is_function? Best, Vicente Test output: Sandia-darwin-4.4 - thread - async__async_p / darwin-4.4 Rev 81191 / Mon, 5 Nov 2012 06:30:00 +0000 *Report Time: *Mon, 5 Nov 2012 14:19:58 +0000 Compile [2012-11-05 07:50:44 UTC]: fail "/opt/local/bin/g++-mp-4.4" -ftemplate-depth-128 -O0 -fno-inline -Wall -pedantic -g -dynamic -gdwarf-2 -fexceptions -fPIC -Wextra -Wno-long-long -fpermissive -pedantic -DBOOST_ALL_NO_LIB=1 -DBOOST_CHRONO_DYN_LINK=1 -DBOOST_SYSTEM_DYN_LINK=1 -DBOOST_SYSTEM_NO_DEPRECATED -DBOOST_THREAD_BUILD_DLL=1 -DBOOST_THREAD_POSIX -DBOOST_THREAD_THROW_IF_PRECONDITION_NOT_SATISFIED -DBOOST_THREAD_USE_DLL=1 -I".." -c -o "/Volumes/scratch/kbelco/boost/results/boost/bin.v2/libs/thread/test/async__async_p.test/darwin-4.4/debug/threading-multi/sync/futures/async/async_pass.o" "../libs/thread/test/sync/futures/async/async_pass.cpp" In file included from ../boost/type_traits/is_convertible.hpp:28, from ../boost/thread/detail/move.hpp:13, from ../boost/thread/future.hpp:20, from ../libs/thread/test/sync/futures/async/async_pass.cpp:28: ../boost/type_traits/is_function.hpp: In instantiation of 'boost::detail::is_function_chooser<false>::result_<boost::rv<boost::rv<boost::packaged_task<int()> > >&>': ../boost/type_traits/is_function.hpp:60: instantiated from 'boost::detail::is_function_impl<boost::rv<boost::rv<boost::packaged_task<int()> > >&>' ../boost/type_traits/is_function.hpp:102: instantiated from 'boost::is_function<boost::rv<boost::rv<boost::packaged_task<int()> > >&>' ../boost/type_traits/is_convertible.hpp:354: instantiated from 'const bool boost::detail::is_convertible_impl<boost::rv<boost::packaged_task<int()> >&, boost::rv<boost::rv<boost::packaged_task<int()> > >&>::value' ../boost/type_traits/is_convertible.hpp:480: instantiated from 'boost::is_convertible<boost::rv<boost::packaged_task<int()> >&, boost::rv<boost::rv<boost::packaged_task<int()> > >&>' ../boost/thread/future.hpp:2717: instantiated from 'boost::future<T> boost::async(boost::launch, R (*)()) [with R = int]' ../libs/thread/test/sync/futures/async/async_pass.cpp:117: instantiated from here ../boost/type_traits/is_function.hpp:52: error: forming pointer to reference type 'boost::rv<boost::rv<boost::packaged_task<int()> > >&'