New Cubed Callbacks

From: Jesse Jones (jesjones_at_[hidden])
Date: 2000-11-23 02:57:09

I've uploaded a new version of my callbacks to the Callbacks2 directory. 
It includes the following changes:

1) A compile time error is emitted if too few arguments are used when 
calling the callback. I pretty much took the approach recommended by 
Gregor and added numbered base class objects.
2) The return type no longer has to be default constructable.
3) Renamed boost::details::unused unused_arg (in the hope that this would 
be slightly clearer to clients).
4) The method ctors no longer require raw pointers.
5) Sprinkled some typename keywords here and there as recommended by 
Gregor.
6) Replaced NULL with 0 (Gregor says NULL was causing problems with GCC). 
This change stinks. :-)

  -- Jesse