Hello, It seems that Accumulators and Signals2 have problems to coexist. For instance, look at the following simple C++ program: --- [c++] --- #include <boost/accumulators/accumulators.hpp> #include <boost/accumulators/statistics/stats.hpp> #include <boost/accumulators/statistics/mean.hpp> #include <boost/signals2.hpp> int main() { } --- [/c++] --- If I compile it with GCC 4.6.0 (under Fedora Linux 15 x86_64): $ g++ -Wall -Wextra -pedantic -ansi -I,/boost-trunk -o boost_signals2_accumulators boost_signals2_accumulators.cpp I get the following errors: --- [error] --- In file included from ./boost-trunk/boost/signals2.hpp:20:0, from boost_signals2_accumulators.cpp:4: ./boost-trunk/boost/signals2/signal_type.hpp:29:2: error: #error This header requires BOOST_PARAMETER_MAX_ARITY to be defined as 7 or greater prior to including Boost.Parameter headers In file included from ./boost-trunk/boost/signals2.hpp:20:0, from boost_signals2_accumulators.cpp:4: ./boost-trunk/boost/signals2/signal_type.hpp:78:9: error: wrong number of template arguments (6, should be 5) ./boost-trunk/boost/parameter/parameters.hpp:714:8: error: provided for ‘template<class PS0, class PS1, class PS2, class PS3, class PS4> struct boost::parameter::parameters’ ./boost-trunk/boost/signals2/signal_type.hpp:83:9: error: ‘parameter_spec’ is not a class or namespace ./boost-trunk/boost/signals2/signal_type.hpp:83:29: error: expected unqualified-id before ‘<’ token ./boost-trunk/boost/signals2/signal_type.hpp:99:11: error: ‘args’ was not declared in this scope ./boost-trunk/boost/signals2/signal_type.hpp:105:9: error: template argument 1 is invalid ./boost-trunk/boost/signals2/signal_type.hpp:108:31: error: ‘args’ was not declared in this scope ./boost-trunk/boost/signals2/signal_type.hpp:108:67: error: template argument 1 is invalid ./boost-trunk/boost/signals2/signal_type.hpp:111:31: error: ‘args’ was not declared in this scope ./boost-trunk/boost/signals2/signal_type.hpp:111:94: error: template argument 1 is invalid ./boost-trunk/boost/signals2/signal_type.hpp:115:31: error: ‘args’ was not declared in this scope ./boost-trunk/boost/signals2/signal_type.hpp:115:97: error: template argument 1 is invalid ./boost-trunk/boost/signals2/signal_type.hpp:121:13: error: ‘args’ was not declared in this scope ./boost-trunk/boost/signals2/signal_type.hpp:124:11: error: template argument 1 is invalid ./boost-trunk/boost/signals2/signal_type.hpp:128:31: error: ‘args’ was not declared in this scope ./boost-trunk/boost/signals2/signal_type.hpp:128:69: error: template argument 1 is invalid --- [/error] --- I've tried both with last Boost devel version and Boost 1.46.0. Note, I have no problem if one of the two libraries are not used (e.g. if I comment either the first 3 #includes or the last one). Any idea? Thank you very much!! Best, -- Marco