Can any one please explain to me why the former fails while the latter compilesThe definition: // usage in a ctor initialisation list ..., where m_button_monitor is of type ButtonMonitor, , m_button_monitor(boost::bind(boost::mem_fn(&CView::OnRun), this, ID_TOOLBUTTON_AUTO)) //definition 1 of ButtonMonitor that fails // the error message by MS VC9SP1: // error C2664: 'programmer_board::ButtonMonitor::ButtonMonitor(boost::function<Signatur e> &)' : //cannot convert parameter 1 from 'boost::_bi::bind_t' to 'boost::function<Signature> &' // class ButtonMonitor { public: ButtonMonitor(boost::function& f) : m_f(f) { } void UpdateStatus(BUTTON_STATUS status) { m_f(); }; private: boost::function& m_f; }; //definition 2 of ButtonMonitor that works class ButtonMonitor { public: ButtonMonitor(const boost::function& f) : m_f(f) { } void UpdateStatus(BUTTON_STATUS status) { m_f(); }; private: const boost::function& m_f; }; Thanks,