Class::Virtual(3pm)					User Contributed Perl Documentation				       Class::Virtual(3pm)

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

perl v5.10.1							    2007-10-23						       Class::Virtual(3pm)