# Class::Virtual - phpMan

## 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 MODULE IS DISCOURAGED! Avoid using it for new code. There's nothing
    wrong with it, but there are better ways to accomplish the same thing.
    Look into the Moose ecosystem.

    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 2000-2015 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://dev.perl.org/licenses/>>

## SEE ALSO
    [Class::Virtually::Abstract]