NAME

       Class::Virtual - Base class for virtual base classes.

SYNOPSIS

         package My::Virtual::Idaho;
         use base qw(Class::Virtual);

         __PACKAGE__->virtual_methods(qw(new foo bar this that));

         package My::Private::Idaho;
         use base qw(My::Virtual::Idaho);

         # Check to make sure My::Private::Idaho implemented everything
         my @missing = __PACKAGE__->missing_methods;
         die __PACKAGE__ . ' forgot to implement ' . join ', ', @missing
             if @missing;

         # If My::Private::Idaho forgot to implement new(), the program will
         # halt and yell about that.
         my $idaho = My::Private::Idaho->new;

         # See what methods we're obligated to implement.
         my @must_implement = __PACKAGE__->virtual_methods;

DESCRIPTION

       This is a base class for implementing virtual base classes (what some people call an
       abstract class).  Kinda kooky.  It allows you to explicitly declare what methods are
       virtual and that must be implemented by subclasses.  This might seem silly, since your
       program will halt and catch fire when an unimplemented virtual method is hit anyway, but
       there's some benefits.

       The error message is more informative.  Instead of the usual "Can't locate object method"
       error, you'll get one explaining that a virtual method was left unimplemented.

       Subclass authors can explicitly check to make sure they've implemented all the necessary
       virtual methods.  When used as part of a regression test, it will shield against the
       virtual method requirements changing out from under the subclass.

       Finally, subclass authors can get an explicit list of everything they're expected to
       implement.

       Doesn't hurt and it doesn't slow you down.

   Methods
       virtual_methods
             Virtual::Class->virtual_methods(@virtual_methods);
             my @must_implement = Sub::Class->virtual_methods;

           This is an accessor to the list of virtual_methods.  Virtual base classes will declare
           their list of virtual methods.  Subclasses will look at them.  Once the virtual
           methods are set they cannot be undone.

       missing_methods
             my @missing_methods = Sub::Class->missing_methods;

           Returns a list of methods Sub::Class has not yet implemented.

CAVEATS and BUGS

       Autoloaded methods are currently not recognized.  I have no idea how to solve this.

AUTHOR

       Michael G Schwern <schwern@pobox.com>

LEGAL

       Copyright 2000, 2001, 2003, 2004 Michael G Schwern

       This program is free software; you can redistribute it and/or modify it under the same
       terms as Perl itself.

       See <http://www.perl.com/perl/misc/Artistic.html>

SEE ALSO

       Class::Virtually::Abstract