Re: [boost] Callback library implementation

From: Douglas Gregor (gregod_at_[hidden])
Date: 2000-11-18 21:26:58

I've posted an implementation prototype at http://www.egroups.com/files/boost/Callback/ which I believe meets all of the prior requirements, including compilation on MSVC++ 6.0 (sp4).

Usage:
        - The "callback" class is the only class visible to the user. Callbacks are defined as such:
          callback<return_type, arg1_type, arg2_type, ...> my_callback;
          where some number of arguments (0 up to some predefined limit) may be specified.
        - Any functor taking appropriate argument types (arg1_type, arg2_type, etc must be convertible to the argument
          types taken by the functor) and returning an appropriate type (convertible to return_type) may be used as the
          callback target. Functors are assigned directly to the callback, e.g.,
          my_callback = my_functor();
        - Callbacks are functors, so the function call operator is overloaded with the given argument/return types.
        - Callbacks are convertible to bool. True indicates that there is a callback target, false otherwise. The empty()
          member returns true if there is no callback target, false otherwise.

The cost of a callback is equal to the cost of a virtual call plus a call to the functor itself. The size of a
callback is that of the virtual function table for one function plus the size of the target functor. Copying a callback is
reasonably quick (the cost of copying a shared_ptr).

Platforms tested (success):
        - Microsoft Visual C++ version 6 (service pack 4) on Windows 98
        - g++-2.95.2 (-ansi -pedantic -W -Wall) on x86 Linux

Platforms tested (failure):
        - SGI MIPSpro 7.3 (error in smart_ptr.h - did not look further)
        - egcs-2.7.2.3 (namespaces broken, compiler crashes)

        Doug Gregor