That's a warning, not an error, and it's emitted when a class has a reference data member or a const data member, which inhibits the implicit definition of a copy assignment operator: C:\Temp>type hiss.cpp struct Foo { explicit Foo(int& i) : r(i) { } int& r; }; struct Bar { explicit Bar(int i) : c(i) { } const int c; }; C:\Temp>cl /EHsc /nologo /W4 /c hiss.cpp hiss.cpp hiss.cpp(5) : warning C4512: 'Foo' : assignment operator could not be generated hiss.cpp(1) : see declaration of 'Foo' hiss.cpp(11) : warning C4512: 'Bar' : assignment operator could not be generated hiss.cpp(7) : see declaration of 'Bar' Assuming that the reference/const data member is intentional, this warning is pure noise and should be suppressed by push/disable/pop (i.e. in Boost's headers). Stephan T. Lavavej Visual C++ Libraries Developer -----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of Edward Diener Sent: Wednesday, May 11, 2011 7:07 PM To: boost@lists.boost.org Subject: [boost] [signals2] trunk - vc++ 10 warning about assignment operator An attempt to instantiate a signals2 signal of the form: template <class T> class notification_boost_signal2 { public: boost::signals2::signal<void (const i_some_interface<T> &,boost::optional<T>,T)> sig; }; for notification_boost_signal2<char>, gives the error message in vc++ of: "C:\Programming\VersionControl\boost\boost/signals2/detail/signal_template.hpp(367) : warning C4512: 'boost::signals2::detail::signal3_impl<R,T1,T2,T3,Combiner,Group,GroupCompare,SlotFunction,ExtendedSlotFunction,Mutex>::slot_invoker' : assignment operator could not be generated" There is a huge template trace leading up to this final warning, but before giving it I wonder if anyone knows what it is about ? Perhaps Frank Mori Hess or Douglas Gregor is out there and can tell me what is happening. _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost