Commit | Line | Data |
4300f56a |
1 | |
2 | package LazyClass; |
3 | |
4 | use strict; |
5 | use warnings; |
6 | |
7 | use Class::MOP 'meta'; |
8 | |
9 | our $VERSION = '0.01'; |
10 | |
11 | use base 'Class::MOP::Class'; |
12 | |
13 | sub construct_instance { |
14 | my ($class, %params) = @_; |
15 | my $instance = {}; |
16 | foreach my $attr (map { $_->{attribute} } $class->compute_all_applicable_attributes()) { |
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 = $attr->has_init_arg() ? $attr->init_arg() : $attr->name; |
20 | # try to fetch the init arg from the %params ... |
21 | my $val; |
22 | $val = $params{$init_arg} if exists $params{$init_arg}; |
23 | # now add this to the instance structure |
24 | # only if we have found a value at all |
25 | $instance->{$attr->name} = $val if defined $val; |
26 | } |
27 | return $instance; |
28 | } |
29 | |
30 | package LazyClass::Attribute; |
31 | |
32 | use strict; |
33 | use warnings; |
34 | |
35 | use Class::MOP 'meta'; |
36 | |
37 | our $VERSION = '0.01'; |
38 | |
39 | use base 'Class::MOP::Attribute'; |
40 | |
41 | sub generate_accessor_method { |
42 | my ($self, $attr_name) = @_; |
43 | sub { |
44 | if (scalar(@_) == 2) { |
45 | $_[0]->{$attr_name} = $_[1]; |
46 | } |
47 | else { |
48 | if (!exists $_[0]->{$attr_name}) { |
49 | my $attr = $self->associated_class->get_attribute($attr_name); |
50 | $_[0]->{$attr_name} = $attr->has_default ? $attr->default($_[0]) : undef; |
51 | } |
52 | $_[0]->{$attr_name}; |
53 | } |
54 | }; |
55 | } |
56 | |
57 | sub generate_reader_method { |
58 | my ($self, $attr_name) = @_; |
59 | sub { |
60 | if (!exists $_[0]->{$attr_name}) { |
61 | my $attr = $self->associated_class->get_attribute($attr_name); |
62 | $_[0]->{$attr_name} = $attr->has_default ? $attr->default($_[0]) : undef; |
63 | } |
64 | $_[0]->{$attr_name}; |
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 | |
82 | sub meta { |
83 | LazyClass->initialize($_[0] => ( |
84 | ':attribute_metaclass' => 'LazyClass::Attribute' |
85 | )); |
86 | } |
87 | |
88 | BinaryTree->meta->add_attribute('$:node' => ( |
89 | accessor => 'node', |
90 | init_arg => ':node' |
91 | )); |
92 | |
93 | BinaryTree->meta->add_attribute('$:left' => ( |
94 | reader => 'left', |
95 | default => sub { BinaryTree->new() } |
96 | )); |
97 | |
98 | BinaryTree->meta->add_attribute('$:right' => ( |
99 | reader => 'right', |
100 | default => sub { BinaryTree->new() } |
101 | )); |
102 | |
103 | sub new { |
104 | my $class = shift; |
105 | bless $class->meta->construct_instance(@_) => $class; |
106 | } |
107 | |
108 | # ... later in code |
109 | |
110 | my $btree = BinaryTree->new(); |
111 | # ... $btree is an empty hash, no keys are initialized yet |
112 | |
113 | =head1 DESCRIPTION |
114 | |
115 | This is an example metclass in which all attributes are created |
116 | lazily. This means that no entries are made in the instance HASH |
117 | until the last possible moment. |
118 | |
119 | The example above of a binary tree is a good use for such a |
120 | metaclass because it allows the class to be space efficient |
121 | without complicating the programing of it. This would also be |
122 | ideal for a class which has a large amount of attributes, |
123 | several of which are optional. |
124 | |
125 | =head1 AUTHOR |
126 | |
127 | Stevan Little E<lt>stevan@iinteractive.comE<gt> |
128 | |
129 | =head1 COPYRIGHT AND LICENSE |
130 | |
131 | Copyright 2006 by Infinity Interactive, Inc. |
132 | |
133 | L<http://www.iinteractive.com> |
134 | |
135 | This library is free software; you can redistribute it and/or modify |
136 | it under the same terms as Perl itself. |
137 | |
138 | =cut |