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1 | |
2 | package # hide the package from PAUSE |
3 | ClassEncapsulatedAttributes; |
4 | |
5 | use strict; |
6 | use warnings; |
7 | |
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8 | our $VERSION = '0.04'; |
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9 | |
10 | use base 'Class::MOP::Class'; |
11 | |
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12 | sub initialize { |
13 | (shift)->SUPER::initialize(@_, |
14 | # use the custom attribute metaclass here |
15 | ':attribute_metaclass' => 'ClassEncapsulatedAttributes::Attribute' |
16 | ); |
17 | } |
18 | |
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19 | sub construct_instance { |
20 | my ($class, %params) = @_; |
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21 | my $instance = {}; |
22 | foreach my $current_class ($class->class_precedence_list()) { |
23 | $instance->{$current_class} = {} |
24 | unless exists $instance->{$current_class}; |
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25 | my $meta = $current_class->meta; |
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26 | foreach my $attr_name ($meta->get_attribute_list()) { |
27 | my $attr = $meta->get_attribute($attr_name); |
28 | # if the attr has an init_arg, use that, otherwise, |
29 | # use the attributes name itself as the init_arg |
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30 | my $init_arg = $attr->init_arg(); |
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31 | # try to fetch the init arg from the %params ... |
32 | my $val; |
33 | $val = $params{$current_class}->{$init_arg} |
34 | if exists $params{$current_class} && |
35 | exists ${$params{$current_class}}{$init_arg}; |
36 | # if nothing was in the %params, we can use the |
37 | # attribute's default value (if it has one) |
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38 | if (!defined $val && $attr->has_default) { |
39 | $val = $attr->default($instance); |
40 | } |
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41 | # now add this to the instance structure |
42 | $instance->{$current_class}->{$attr_name} = $val; |
43 | } |
44 | } |
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45 | return $instance; |
46 | } |
47 | |
48 | package # hide the package from PAUSE |
49 | ClassEncapsulatedAttributes::Attribute; |
50 | |
51 | use strict; |
52 | use warnings; |
53 | |
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54 | our $VERSION = '0.02'; |
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55 | |
56 | use base 'Class::MOP::Attribute'; |
57 | |
58 | sub generate_accessor_method { |
59 | my ($self, $attr_name) = @_; |
60 | my $class_name = $self->associated_class->name; |
61 | eval qq{sub { |
62 | \$_[0]->{'$class_name'}->{'$attr_name'} = \$_[1] if scalar(\@_) == 2; |
63 | \$_[0]->{'$class_name'}->{'$attr_name'}; |
64 | }}; |
65 | } |
66 | |
67 | sub generate_reader_method { |
68 | my ($self, $attr_name) = @_; |
69 | my $class_name = $self->associated_class->name; |
70 | eval qq{sub { |
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71 | Carp::confess "Cannot assign a value to a read-only accessor" if \@_ > 1; |
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72 | \$_[0]->{'$class_name'}->{'$attr_name'}; |
73 | }}; |
74 | } |
75 | |
76 | sub generate_writer_method { |
77 | my ($self, $attr_name) = @_; |
78 | my $class_name = $self->associated_class->name; |
79 | eval qq{sub { |
80 | \$_[0]->{'$class_name'}->{'$attr_name'} = \$_[1]; |
81 | }}; |
82 | } |
83 | |
84 | sub generate_predicate_method { |
85 | my ($self, $attr_name) = @_; |
86 | my $class_name = $self->associated_class->name; |
87 | eval qq{sub { |
88 | defined \$_[0]->{'$class_name'}->{'$attr_name'} ? 1 : 0; |
89 | }}; |
90 | } |
91 | |
92 | ## &remove_attribute is left as an exercise for the reader :) |
93 | |
94 | 1; |
95 | |
96 | __END__ |
97 | |
98 | =pod |
99 | |
100 | =head1 NAME |
101 | |
102 | ClassEncapsulatedAttributes - A set of example metaclasses with class encapsulated attributes |
103 | |
104 | =head1 SYNOPSIS |
105 | |
106 | package Foo; |
107 | |
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108 | use metaclass 'ClassEncapsulatedAttributes'; |
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109 | |
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110 | Foo->meta->add_attribute('foo' => ( |
111 | accessor => 'Foo_foo', |
112 | default => 'init in FOO' |
113 | )); |
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114 | |
115 | sub new { |
116 | my $class = shift; |
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117 | $class->meta->new_object(@_); |
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118 | } |
119 | |
120 | package Bar; |
121 | our @ISA = ('Foo'); |
122 | |
123 | # duplicate the attribute name here |
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124 | Bar->meta->add_attribute('foo' => ( |
125 | accessor => 'Bar_foo', |
126 | default => 'init in BAR' |
127 | )); |
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128 | |
129 | # ... later in other code ... |
130 | |
131 | my $bar = Bar->new(); |
132 | prints $bar->Bar_foo(); # init in BAR |
133 | prints $bar->Foo_foo(); # init in FOO |
134 | |
135 | # and ... |
136 | |
137 | my $bar = Bar->new( |
138 | 'Foo' => { 'foo' => 'Foo::foo' }, |
139 | 'Bar' => { 'foo' => 'Bar::foo' } |
140 | ); |
141 | |
142 | prints $bar->Bar_foo(); # Foo::foo |
143 | prints $bar->Foo_foo(); # Bar::foo |
144 | |
145 | =head1 DESCRIPTION |
146 | |
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147 | This is an example metaclass which encapsulates a class's |
148 | attributes on a per-class basis. This means that there is no |
149 | possibility of name clashes with inherited attributes. This |
150 | is similar to how C++ handles its data members. |
151 | |
152 | =head1 ACKNOWLEDGEMENTS |
153 | |
154 | Thanks to Yuval "nothingmuch" Kogman for the idea for this example. |
155 | |
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156 | =head1 AUTHOR |
157 | |
158 | Stevan Little E<lt>stevan@iinteractive.comE<gt> |
159 | |
160 | =head1 COPYRIGHT AND LICENSE |
161 | |
162 | Copyright 2006 by Infinity Interactive, Inc. |
163 | |
164 | L<http://www.iinteractive.com> |
165 | |
166 | This library is free software; you can redistribute it and/or modify |
167 | it under the same terms as Perl itself. |
168 | |
169 | =cut |