2 package # hide the package from PAUSE
10 use base 'Class::MOP::Class';
12 sub construct_instance {
13 my ($class, %params) = @_;
15 foreach my $attr ($class->compute_all_applicable_attributes()) {
16 # if the attr has an init_arg, use that, otherwise,
17 # use the attributes name itself as the init_arg
18 my $init_arg = $attr->init_arg();
19 # try to fetch the init arg from the %params ...
21 $val = $params{$init_arg} if exists $params{$init_arg};
22 # now add this to the instance structure
23 # only if we have found a value at all
24 $instance->{$attr->name} = $val if defined $val;
29 package # hide the package from PAUSE
37 our $VERSION = '0.02';
39 use base 'Class::MOP::Attribute';
41 sub generate_accessor_method {
42 my ($self, $attr_name) = @_;
44 if (scalar(@_) == 2) {
45 $_[0]->{$attr_name} = $_[1];
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;
57 sub generate_reader_method {
58 my ($self, $attr_name) = @_;
60 confess "Cannot assign a value to a read-only accessor" if @_ > 1;
61 if (!exists $_[0]->{$attr_name}) {
62 my $attr = $self->associated_class->get_attribute($attr_name);
63 $_[0]->{$attr_name} = $attr->has_default ? $attr->default($_[0]) : undef;
77 LazyClass - An example metaclass with lazy initialization
83 use metaclass 'LazyClass' => (
84 ':attribute_metaclass' => 'LazyClass::Attribute'
87 BinaryTree->meta->add_attribute('$:node' => (
92 BinaryTree->meta->add_attribute('$:left' => (
94 default => sub { BinaryTree->new() }
97 BinaryTree->meta->add_attribute('$:right' => (
99 default => sub { BinaryTree->new() }
104 $class->meta->new_object(@_);
109 my $btree = BinaryTree->new();
110 # ... $btree is an empty hash, no keys are initialized yet
114 This is an example metclass in which all attributes are created
115 lazily. This means that no entries are made in the instance HASH
116 until the last possible moment.
118 The example above of a binary tree is a good use for such a
119 metaclass because it allows the class to be space efficient
120 without complicating the programing of it. This would also be
121 ideal for a class which has a large amount of attributes,
122 several of which are optional.
126 Stevan Little E<lt>stevan@iinteractive.comE<gt>
128 =head1 COPYRIGHT AND LICENSE
130 Copyright 2006 by Infinity Interactive, Inc.
132 L<http://www.iinteractive.com>
134 This library is free software; you can redistribute it and/or modify
135 it under the same terms as Perl itself.