I know that signals can't be assigned or copied, and as far as I can tell I have made sure that never happens. However, I'm still getting the warning. We have no warning policy here. Code followed by compiler output, what do I need to do?: ------------------------------------------- #include #include struct rect {}; struct document { document() : changed_sig() {} virtual rect extents() const = 0; virtual ~document() {} boost::signals::connection attach(boost::function const& slot) { return changed_sig.connect(slot); } private: boost::signal changed_sig; document(document const&) {} document& operator=(document const&) { return *this;} protected: void changed(document & d) { changed_sig(d); } }; int main() { } ------------------------------------------------ 1>e:\boostvs2\include\boost\signals\trackable.hpp(163) : warning C4512: 'boost::signals::detail::bound_objects_visitor' : assignment operator could not be generated 1> e:\boostvs2\include\boost\signals\trackable.hpp(66) : see declaration of 'boost::signals::detail::bound_objects_visitor' 1>e:\boostvs2\include\boost\signals\signal_template.hpp(71) : warning C4512: 'boost::signals::detail::args1<T1>' : assignment operator could not be generated 1> with 1> [ 1> T1=document & 1> ] 1> e:\boostvs2\include\boost\signals\signal_template.hpp(344) : see reference to class template instantiation 'boost::signals::detail::args1<T1>' being compiled 1> with 1> [ 1> T1=document & 1> ] 1> e:\boostvs2\include\boost\signals\signal_template.hpp(335) : while compiling class template member function 'void boost::signal1::operator ()(T1)' 1> with 1> [ 1> R=void, 1> T1=document &, 1> Combiner=boost::last_value<void>, 1> Group=int, 1> GroupCompare=std::less<int>, 1> SlotFunction=boost::function 1> ] 1> e:\boostvs2\include\boost\signal.hpp(335) : see reference to class template instantiation 'boost::signal1' being compiled 1> with 1> [ 1> R=void, 1> T1=document &, 1> Combiner=boost::last_value<void>, 1> Group=int, 1> GroupCompare=std::less<int>, 1> SlotFunction=boost::function 1> ] 1> e:\dev_workspace\experimental\scratch\scratch\main.cpp(19) : see reference to class template instantiation 'boost::signal<Signature>' being compiled 1> with 1> [ 1> Signature=void (document &) 1> ] 1>Linking...