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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 $VERSION = '0.03'; |
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9 | |
10 | use base 'Class::MOP::Class'; |
11 | |
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12 | sub initialize { |
13 | (shift)->SUPER::initialize(@_, |
14 | # use the custom attribute metaclass here |
15 | ':attribute_metaclass' => 'ClassEncapsulatedAttributes::Attribute' |
16 | ); |
17 | } |
18 | |
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19 | sub construct_instance { |
20 | my ($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) |
38 | $val ||= $attr->default($instance) if $attr->has_default(); |
39 | # now add this to the instance structure |
40 | $instance->{$current_class}->{$attr_name} = $val; |
41 | } |
42 | } |
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43 | return $instance; |
44 | } |
45 | |
46 | package # hide the package from PAUSE |
47 | ClassEncapsulatedAttributes::Attribute; |
48 | |
49 | use strict; |
50 | use warnings; |
51 | |
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52 | our $VERSION = '0.02'; |
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53 | |
54 | use base 'Class::MOP::Attribute'; |
55 | |
56 | sub generate_accessor_method { |
57 | my ($self, $attr_name) = @_; |
58 | my $class_name = $self->associated_class->name; |
59 | eval qq{sub { |
60 | \$_[0]->{'$class_name'}->{'$attr_name'} = \$_[1] if scalar(\@_) == 2; |
61 | \$_[0]->{'$class_name'}->{'$attr_name'}; |
62 | }}; |
63 | } |
64 | |
65 | sub generate_reader_method { |
66 | my ($self, $attr_name) = @_; |
67 | my $class_name = $self->associated_class->name; |
68 | eval qq{sub { |
69 | \$_[0]->{'$class_name'}->{'$attr_name'}; |
70 | }}; |
71 | } |
72 | |
73 | sub generate_writer_method { |
74 | my ($self, $attr_name) = @_; |
75 | my $class_name = $self->associated_class->name; |
76 | eval qq{sub { |
77 | \$_[0]->{'$class_name'}->{'$attr_name'} = \$_[1]; |
78 | }}; |
79 | } |
80 | |
81 | sub generate_predicate_method { |
82 | my ($self, $attr_name) = @_; |
83 | my $class_name = $self->associated_class->name; |
84 | eval qq{sub { |
85 | defined \$_[0]->{'$class_name'}->{'$attr_name'} ? 1 : 0; |
86 | }}; |
87 | } |
88 | |
89 | ## &remove_attribute is left as an exercise for the reader :) |
90 | |
91 | 1; |
92 | |
93 | __END__ |
94 | |
95 | =pod |
96 | |
97 | =head1 NAME |
98 | |
99 | ClassEncapsulatedAttributes - A set of example metaclasses with class encapsulated attributes |
100 | |
101 | =head1 SYNOPSIS |
102 | |
103 | package Foo; |
104 | |
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105 | use metaclass 'ClassEncapsulatedAttributes'; |
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106 | |
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107 | Foo->meta->add_attribute('foo' => ( |
108 | accessor => 'Foo_foo', |
109 | default => 'init in FOO' |
110 | )); |
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111 | |
112 | sub new { |
113 | my $class = shift; |
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114 | $class->meta->new_object(@_); |
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115 | } |
116 | |
117 | package Bar; |
118 | our @ISA = ('Foo'); |
119 | |
120 | # duplicate the attribute name here |
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121 | Bar->meta->add_attribute('foo' => ( |
122 | accessor => 'Bar_foo', |
123 | default => 'init in BAR' |
124 | )); |
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125 | |
126 | # ... later in other code ... |
127 | |
128 | my $bar = Bar->new(); |
129 | prints $bar->Bar_foo(); # init in BAR |
130 | prints $bar->Foo_foo(); # init in FOO |
131 | |
132 | # and ... |
133 | |
134 | my $bar = Bar->new( |
135 | 'Foo' => { 'foo' => 'Foo::foo' }, |
136 | 'Bar' => { 'foo' => 'Bar::foo' } |
137 | ); |
138 | |
139 | prints $bar->Bar_foo(); # Foo::foo |
140 | prints $bar->Foo_foo(); # Bar::foo |
141 | |
142 | =head1 DESCRIPTION |
143 | |
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144 | This is an example metaclass which encapsulates a class's |
145 | attributes on a per-class basis. This means that there is no |
146 | possibility of name clashes with inherited attributes. This |
147 | is similar to how C++ handles its data members. |
148 | |
149 | =head1 ACKNOWLEDGEMENTS |
150 | |
151 | Thanks to Yuval "nothingmuch" Kogman for the idea for this example. |
152 | |
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153 | =head1 AUTHOR |
154 | |
155 | Stevan Little E<lt>stevan@iinteractive.comE<gt> |
156 | |
157 | =head1 COPYRIGHT AND LICENSE |
158 | |
159 | Copyright 2006 by Infinity Interactive, Inc. |
160 | |
161 | L<http://www.iinteractive.com> |
162 | |
163 | This library is free software; you can redistribute it and/or modify |
164 | it under the same terms as Perl itself. |
165 | |
166 | =cut |