🚀 go-pugleaf

>>>
What is needed is the ability to use member functions as callbacks
without any constraint on the type of the object they are invoked on.
This is possible in C++ only by using various implementation-dependent
hacks to escape the type system, because the language does not provide
any way to express such a construct.
<<<

  The scheme presented by Richard Hickey in the C++ Report, Feb 95, 
achieved this in what seemed to me an implementation-independent way. 
Briefly; the creator of a functor would pass an object's and a function's 
address to a template factory function; this would cause the 
instantiation of various code, and return an object of a class Callback, 
which would internally hold the addresses, the object address being 
cast to void*.

 The Callback object had an operator() which would take the various 
parameters expected for the callback, and pass them to another function 
generated by the Factory specialisation. This function would cast the 
void pointer to the appropriate type for the object, and complete the 
call.

  No type information was shared between the caller and the called 
modules, other than the declaration of various Callback classes and 
associated functions. In fact, different Callback classes were required 
to deal with functions having different numbers of parameters.

                                     David



[ To submit articles: Try just posting with your newsreader.
		      If that fails, use mailto:std-c++@ncar.ucar.edu
  FAQ:    http://reality.sgi.com/employees/austern_mti/std-c++/faq.html
  Policy: http://reality.sgi.com/employees/austern_mti/std-c++/policy.html
  Comments? mailto:std-c++-request@ncar.ucar.edu
]