Hi, I have some questions about signals. If I add a function to both Hello and World, from the "Hello World" example, called alternate() and set up signals like so: boost::signal<void (Hello*) > sig_h; boost::signal< void (World*) > sig_w; sig_h.connect(boost::mem_fn(&Hello::alternate)); sig_w.connect(boost::mem_fn(&World::alternate)); I have to define two different signals since the object type is part of the signal definition. Is there an easy way to get a single signal to call the alternate() function of both Hello and World? I recently found this signal slot solution. http://www.codeproject.com/cpp/ElmueSignalsandSlots.asp There is an extra level of indirection here, in that you define a slot that points to the function. I'd be interested to see what people on this forum think about this solution. If I understand things correctly, this solution doesn't seem to fit into the categories listed in the "Choice of Slot Definitions" docs. Also a general signal slot question. What are the main reasons why developers don't use an inherited pure interface for every callback type? A signal would be a template class with a list of pointers to the interface and some methods to operate on the list. Not flexible enough? Doesn't scale well to larger uses? Time spent calling virtual functions? I saw this in the boost signal docs that might apply - "the use of a large number of small adaptor classes containing virtual functions has been found to cause an unacceptable increase in the size of executables (polymorphic class types require more code than non-polymorphic types)". Thanks Frank