A mutable class will throw errors from inside CMOP, and that's expected
[gitmo/Moose.git] / examples / InsideOutClass.pod
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2package # hide the package from PAUSE
3 InsideOutClass::Attribute;
4
5use strict;
6use warnings;
7
8our $VERSION = '0.02';
9
10use Carp 'confess';
11use Scalar::Util 'refaddr';
12
13use base 'Class::MOP::Attribute';
14
15sub initialize_instance_slot {
16 my ($self, $meta_instance, $instance, $params) = @_;
17 my $init_arg = $self->init_arg;
18 # try to fetch the init arg from the %params ...
19 my $val;
20 $val = $params->{$init_arg} if exists $params->{$init_arg};
21 # if nothing was in the %params, we can use the
22 # attribute's default value (if it has one)
23 if (!defined $val && defined $self->default) {
24 $val = $self->default($instance);
25 }
26 my $_meta_instance = $self->associated_class->get_meta_instance;
27 $_meta_instance->initialize_slot($instance, $self->name);
28 $_meta_instance->set_slot_value($instance, $self->name, $val);
29}
30
31sub accessor_metaclass { 'InsideOutClass::Method::Accessor' }
32
33package # hide the package from PAUSE
34 InsideOutClass::Method::Accessor;
35
36use strict;
37use warnings;
38
39our $VERSION = '0.01';
40
41use Carp 'confess';
42use Scalar::Util 'refaddr';
43
44use base 'Class::MOP::Method::Accessor';
45
46## Method generation helpers
47
48sub _generate_accessor_method {
49 my $attr = (shift)->associated_attribute;
50 my $meta_class = $attr->associated_class;
51 my $attr_name = $attr->name;
52 return sub {
53 my $meta_instance = $meta_class->get_meta_instance;
54 $meta_instance->set_slot_value($_[0], $attr_name, $_[1]) if scalar(@_) == 2;
55 $meta_instance->get_slot_value($_[0], $attr_name);
56 };
57}
58
59sub _generate_reader_method {
60 my $attr = (shift)->associated_attribute;
61 my $meta_class = $attr->associated_class;
62 my $attr_name = $attr->name;
63 return sub {
64 confess "Cannot assign a value to a read-only accessor" if @_ > 1;
65 $meta_class->get_meta_instance
66 ->get_slot_value($_[0], $attr_name);
67 };
68}
69
70sub _generate_writer_method {
71 my $attr = (shift)->associated_attribute;
72 my $meta_class = $attr->associated_class;
73 my $attr_name = $attr->name;
74 return sub {
75 $meta_class->get_meta_instance
76 ->set_slot_value($_[0], $attr_name, $_[1]);
77 };
78}
79
80sub _generate_predicate_method {
81 my $attr = (shift)->associated_attribute;
82 my $meta_class = $attr->associated_class;
83 my $attr_name = $attr->name;
84 return sub {
85 defined $meta_class->get_meta_instance
86 ->get_slot_value($_[0], $attr_name) ? 1 : 0;
87 };
88}
89
90package # hide the package from PAUSE
91 InsideOutClass::Instance;
92
93use strict;
94use warnings;
95
96our $VERSION = '0.01';
97
98use Carp 'confess';
99use Scalar::Util 'refaddr';
100
101use base 'Class::MOP::Instance';
102
103sub create_instance {
104 my ($self, $class) = @_;
105 bless \(my $instance), $self->_class_name;
106}
107
108sub get_slot_value {
109 my ($self, $instance, $slot_name) = @_;
110 $self->associated_metaclass->get_package_symbol('%' . $slot_name)->{refaddr $instance};
111}
112
113sub set_slot_value {
114 my ($self, $instance, $slot_name, $value) = @_;
115 $self->associated_metaclass->get_package_symbol('%' . $slot_name)->{refaddr $instance} = $value;
116}
117
118sub initialize_slot {
119 my ($self, $instance, $slot_name) = @_;
120 $self->associated_metaclass->add_package_symbol(('%' . $slot_name) => {})
121 unless $self->associated_metaclass->has_package_symbol('%' . $slot_name);
122 $self->associated_metaclass->get_package_symbol('%' . $slot_name)->{refaddr $instance} = undef;
123}
124
125sub is_slot_initialized {
126 my ($self, $instance, $slot_name) = @_;
127 return 0 unless $self->associated_metaclass->has_package_symbol('%' . $slot_name);
128 return exists $self->associated_metaclass->get_package_symbol('%' . $slot_name)->{refaddr $instance} ? 1 : 0;
129}
130
1311;
132
133__END__
134
135=pod
136
137=head1 NAME
138
139InsideOutClass - A set of example metaclasses which implement the Inside-Out technique
140
141=head1 SYNOPSIS
142
143 package Foo;
144
145 use metaclass (
146 ':attribute_metaclass' => 'InsideOutClass::Attribute',
147 ':instance_metaclass' => 'InsideOutClass::Instance'
148 );
149
150 __PACKAGE__->meta->add_attribute('foo' => (
151 reader => 'get_foo',
152 writer => 'set_foo'
153 ));
154
155 sub new {
156 my $class = shift;
157 $class->meta->new_object(@_);
158 }
159
160 # now you can just use the class as normal
161
162=head1 DESCRIPTION
163
164This is a set of example metaclasses which implement the Inside-Out
165class technique. What follows is a brief explaination of the code
166found in this module.
167
168We must create a subclass of B<Class::MOP::Instance> and override
169the slot operations. This requires
170overloading C<get_slot_value>, C<set_slot_value>, C<slot_initialized>, and
171C<initialize_slot>, as well as their inline counterparts. Additionally we
172overload C<add_slot> in order to initialize the global hash containing the
173actual slot values.
174
175And that is pretty much all. Of course I am ignoring need for
176inside-out objects to be C<DESTROY>-ed, and some other details as
177well (threading, etc), but this is an example. A real implementation is left as
178an exercise to the reader.
179
180=head1 AUTHORS
181
182Stevan Little E<lt>stevan@iinteractive.comE<gt>
183
184Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
185
186=head1 COPYRIGHT AND LICENSE
187
188Copyright 2006-2008 by Infinity Interactive, Inc.
189
190L<http://www.iinteractive.com>
191
192This library is free software; you can redistribute it and/or modify
193it under the same terms as Perl itself.
194
195=cut