From Code to Community: Sponsoring The Perl and Raku Conference 2025 Learn more

RSHERER / Class-Data-Inheritable-0.10 / lib / Class / Data / Inheritable.pm 

            

              
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
—
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148

              
package Class::Data::Inheritable;
use strict qw(vars subs);
our $VERSION = '0.10';
sub mk_classdata {
    my ($declaredclass, $attribute, $data) = @_;
    if( ref $declaredclass ) {
        require Carp;
        Carp::croak("mk_classdata() is a class method, not an object method");
    }
    my $accessor = sub {
        my $wantclass = ref($_[0]) || $_[0];
        return $wantclass->mk_classdata($attribute)->(@_)
          if @_>1 && $wantclass ne $declaredclass;
        $data = $_[1] if @_>1;
        return $data;
    };
    my $alias = "_${attribute}_accessor";
    *{$declaredclass.'::'.$attribute} = $accessor;
    *{$declaredclass.'::'.$alias}     = $accessor;
}
1;
__END__
=head1 NAME
Class::Data::Inheritable - Inheritable, overridable class data
=head1 SYNOPSIS
  package Stuff;
  use base qw(Class::Data::Inheritable);
  # Set up DataFile as inheritable class data.
  Stuff->mk_classdata('DataFile');
  # Declare the location of the data file for this class.
  Stuff->DataFile('/etc/stuff/data');
  # Or, all in one shot:
  Stuff->mk_classdata(DataFile => '/etc/stuff/data');
=head1 DESCRIPTION
Class::Data::Inheritable is for creating accessor/mutators to class
data.  That is, if you want to store something about your class as a
whole (instead of about a single object).  This data is then inherited
by your subclasses and can be overridden.
For example:
  Pere::Ubu->mk_classdata('Suitcase');
will generate the method Suitcase() in the class Pere::Ubu.
This new method can be used to get and set a piece of class data.
  Pere::Ubu->Suitcase('Red');
  $suitcase = Pere::Ubu->Suitcase;
The interesting part happens when a class inherits from Pere::Ubu:
  package Raygun;
  use base qw(Pere::Ubu);
   
  # Raygun's suitcase is Red.
  $suitcase = Raygun->Suitcase;
Raygun inherits its Suitcase class data from Pere::Ubu.
Inheritance of class data works analogous to method inheritance.  As
long as Raygun does not "override" its inherited class data (by using
Suitcase() to set a new value) it will continue to use whatever is set
in Pere::Ubu and inherit further changes:
  # Both Raygun's and Pere::Ubu's suitcases are now Blue
  Pere::Ubu->Suitcase('Blue');
However, should Raygun decide to set its own Suitcase() it has now
"overridden" Pere::Ubu and is on its own, just like if it had
overridden a method:
  # Raygun has an orange suitcase, Pere::Ubu's is still Blue.
  Raygun->Suitcase('Orange');
Now that Raygun has overridden Pere::Ubu further changes by Pere::Ubu
no longer effect Raygun.
  # Raygun still has an orange suitcase, but Pere::Ubu is using Samsonite.
  Pere::Ubu->Suitcase('Samsonite');
=head1 Methods
=head2 mk_classdata
  Class->mk_classdata($data_accessor_name);
  Class->mk_classdata($data_accessor_name => $value);
This is a class method used to declare new class data accessors.
A new accessor will be created in the Class using the name from
$data_accessor_name, and optionally initially setting it to the given
value.
To facilitate overriding, mk_classdata creates an alias to the
accessor, _field_accessor().  So Suitcase() would have an alias
_Suitcase_accessor() that does the exact same thing as Suitcase().
This is useful if you want to alter the behavior of a single accessor
yet still get the benefits of inheritable class data.  For example.
  sub Suitcase {
      my($self) = shift;
      warn "Fashion tragedy" if @_ and $_[0] eq 'Plaid';
      $self->_Suitcase_accessor(@_);
  }
=head1 AUTHOR
Original code by Damian Conway.
Maintained by Michael G Schwern until September 2005.
Now maintained by Tony Bowden.
=head1 BUGS and QUERIES
Please direct all correspondence regarding this module to:
  bug-Class-Data-Inheritable@rt.cpan.org
=head1 COPYRIGHT and LICENSE
Copyright (c) 2000-2005, Damian Conway and Michael G Schwern. 
All Rights Reserved.  
This module is free software. It may be used, redistributed and/or
modified under the same terms as Perl itself.
=head1 SEE ALSO
L<perltooc> has a very elaborate discussion of class data in Perl.