1Class::Virtual(3)     User Contributed Perl Documentation    Class::Virtual(3)
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3
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NAME

6       Class::Virtual - Base class for virtual base classes.
7

SYNOPSIS

9         package My::Virtual::Idaho;
10         use base qw(Class::Virtual);
11
12         __PACKAGE__->virtual_methods(qw(new foo bar this that));
13
14
15         package My::Private::Idaho;
16         use base qw(My::Virtual::Idaho);
17
18         # Check to make sure My::Private::Idaho implemented everything
19         my @missing = __PACKAGE__->missing_methods;
20         die __PACKAGE__ . ' forgot to implement ' . join ', ', @missing
21             if @missing;
22
23         # If My::Private::Idaho forgot to implement new(), the program will
24         # halt and yell about that.
25         my $idaho = My::Private::Idaho->new;
26
27         # See what methods we're obligated to implement.
28         my @must_implement = __PACKAGE__->virtual_methods;
29

DESCRIPTION

31       THIS MODULE IS DISCOURAGED! Avoid using it for new code.  There's
32       nothing wrong with it, but there are better ways to accomplish the same
33       thing.  Look into the Moose ecosystem.
34
35       This is a base class for implementing virtual base classes (what some
36       people call an abstract class).  Kinda kooky.  It allows you to
37       explicitly declare what methods are virtual and that must be
38       implemented by subclasses.  This might seem silly, since your program
39       will halt and catch fire when an unimplemented virtual method is hit
40       anyway, but there's some benefits.
41
42       The error message is more informative.  Instead of the usual "Can't
43       locate object method" error, you'll get one explaining that a virtual
44       method was left unimplemented.
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46       Subclass authors can explicitly check to make sure they've implemented
47       all the necessary virtual methods.  When used as part of a regression
48       test, it will shield against the virtual method requirements changing
49       out from under the subclass.
50
51       Finally, subclass authors can get an explicit list of everything
52       they're expected to implement.
53
54       Doesn't hurt and it doesn't slow you down.
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56   Methods
57       virtual_methods
58             Virtual::Class->virtual_methods(@virtual_methods);
59             my @must_implement = Sub::Class->virtual_methods;
60
61           This is an accessor to the list of virtual_methods.  Virtual base
62           classes will declare their list of virtual methods.  Subclasses
63           will look at them.  Once the virtual methods are set they cannot be
64           undone.
65
66       missing_methods
67             my @missing_methods = Sub::Class->missing_methods;
68
69           Returns a list of methods Sub::Class has not yet implemented.
70

CAVEATS and BUGS

72       Autoloaded methods are currently not recognized.  I have no idea how to
73       solve this.
74

AUTHOR

76       Michael G Schwern <schwern@pobox.com>
77

79       Copyright 2000-2015 Michael G Schwern
80
81       This program is free software; you can redistribute it and/or modify it
82       under the same terms as Perl itself.
83
84       See <http://dev.perl.org/licenses/>
85

SEE ALSO

87       Class::Virtually::Abstract
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91perl v5.30.0                      2019-07-26                 Class::Virtual(3)
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