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