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1 | |
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2 | package # hide the package from PAUSE |
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3 | LazyClass::Attribute; |
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4 | |
5 | use strict; |
6 | use warnings; |
7 | |
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8 | use Carp 'confess'; |
9 | |
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10 | our $VERSION = '0.04'; |
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11 | |
12 | use base 'Class::MOP::Attribute'; |
13 | |
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14 | sub initialize_instance_slot { |
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15 | my ($self, $instance, $params) = @_; |
16 | |
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17 | # if the attr has an init_arg, use that, otherwise, |
18 | # use the attributes name itself as the init_arg |
19 | my $init_arg = $self->init_arg(); |
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20 | |
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21 | if ( exists $params->{$init_arg} ) { |
22 | my $val = $params->{$init_arg}; |
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23 | $self->associated_class |
24 | ->get_meta_instance |
25 | ->set_slot_value($instance, $self->name, $val); |
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26 | } |
27 | } |
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28 | |
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29 | sub generate_accessor_method { |
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30 | my $attr = shift; |
31 | |
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32 | my $attr_name = $attr->name; |
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33 | my $meta_instance = $attr->associated_class->get_meta_instance; |
34 | |
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35 | sub { |
36 | if (scalar(@_) == 2) { |
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37 | $meta_instance->set_slot_value($_[0], $attr_name, $_[1]); |
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38 | } |
39 | else { |
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40 | unless ( $meta_instance->is_slot_initialized($_[0], $attr_name) ) { |
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41 | my $value = $attr->has_default ? $attr->default($_[0]) : undef; |
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42 | $meta_instance->set_slot_value($_[0], $attr_name, $value); |
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43 | } |
44 | |
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45 | $meta_instance->get_slot_value($_[0], $attr_name); |
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46 | } |
47 | }; |
48 | } |
49 | |
50 | sub generate_reader_method { |
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51 | my $attr = shift; |
52 | |
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53 | my $attr_name = $attr->name; |
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54 | my $meta_instance = $attr->associated_class->get_meta_instance; |
55 | |
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56 | sub { |
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57 | confess "Cannot assign a value to a read-only accessor" if @_ > 1; |
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58 | |
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59 | unless ( $meta_instance->is_slot_initialized($_[0], $attr_name) ) { |
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60 | my $value = $attr->has_default ? $attr->default($_[0]) : undef; |
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61 | $meta_instance->set_slot_value($_[0], $attr_name, $value); |
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62 | } |
63 | |
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64 | $meta_instance->get_slot_value($_[0], $attr_name); |
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65 | }; |
66 | } |
67 | |
68 | 1; |
69 | |
70 | __END__ |
71 | |
72 | =pod |
73 | |
74 | =head1 NAME |
75 | |
76 | LazyClass - An example metaclass with lazy initialization |
77 | |
78 | =head1 SYNOPSIS |
79 | |
80 | package BinaryTree; |
81 | |
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82 | use metaclass 'Class::MOP::Class' => ( |
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83 | ':attribute_metaclass' => 'LazyClass::Attribute' |
84 | ); |
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85 | |
86 | BinaryTree->meta->add_attribute('$:node' => ( |
87 | accessor => 'node', |
88 | init_arg => ':node' |
89 | )); |
90 | |
91 | BinaryTree->meta->add_attribute('$:left' => ( |
92 | reader => 'left', |
93 | default => sub { BinaryTree->new() } |
94 | )); |
95 | |
96 | BinaryTree->meta->add_attribute('$:right' => ( |
97 | reader => 'right', |
98 | default => sub { BinaryTree->new() } |
99 | )); |
100 | |
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101 | sub new { |
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102 | my $class = shift; |
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103 | $class->meta->new_object(@_); |
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104 | } |
105 | |
106 | # ... later in code |
107 | |
108 | my $btree = BinaryTree->new(); |
109 | # ... $btree is an empty hash, no keys are initialized yet |
110 | |
111 | =head1 DESCRIPTION |
112 | |
113 | This is an example metclass in which all attributes are created |
114 | lazily. This means that no entries are made in the instance HASH |
115 | until the last possible moment. |
116 | |
117 | The example above of a binary tree is a good use for such a |
118 | metaclass because it allows the class to be space efficient |
119 | without complicating the programing of it. This would also be |
120 | ideal for a class which has a large amount of attributes, |
121 | several of which are optional. |
122 | |
123 | =head1 AUTHOR |
124 | |
125 | Stevan Little E<lt>stevan@iinteractive.comE<gt> |
126 | |
127 | =head1 COPYRIGHT AND LICENSE |
128 | |
129 | Copyright 2006 by Infinity Interactive, Inc. |
130 | |
131 | L<http://www.iinteractive.com> |
132 | |
133 | This library is free software; you can redistribute it and/or modify |
134 | it under the same terms as Perl itself. |
135 | |
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136 | =cut |