2 package # hide the package from PAUSE
10 use Scalar::Util 'refaddr';
12 use base 'Class::MOP::Class';
14 sub construct_instance {
15 my ($class, %params) = @_;
16 # create a scalar ref to use as
17 # the inside-out instance
18 my $instance = \(my $var);
19 foreach my $attr ($class->compute_all_applicable_attributes()) {
20 # if the attr has an init_arg, use that, otherwise,
21 # use the attributes name itself as the init_arg
22 my $init_arg = $attr->has_init_arg() ? $attr->init_arg() : $attr->name;
23 # try to fetch the init arg from the %params ...
25 $val = $params{$init_arg} if exists $params{$init_arg};
26 # if nothing was in the %params, we can use the
27 # attribute's default value (if it has one)
28 $val ||= $attr->default($instance) if $attr->has_default();
29 # now add this to the instance structure
30 $class->get_package_variable('%' . $attr->name)->{ refaddr($instance) } = $val;
35 package # hide the package from PAUSE
36 InsideOutClass::Attribute;
41 our $VERSION = '0.04';
43 use Scalar::Util 'refaddr';
45 use base 'Class::MOP::Attribute';
47 sub generate_accessor_method {
48 my ($self, $attr_name) = @_;
49 $attr_name = ($self->associated_class->name . '::' . $attr_name);
51 $' . $attr_name . '{ refaddr($_[0]) } = $_[1] if scalar(@_) == 2;
52 $' . $attr_name . '{ refaddr($_[0]) };
56 sub generate_reader_method {
57 my ($self, $attr_name) = @_;
59 $' . ($self->associated_class->name . '::' . $attr_name) . '{ refaddr($_[0]) };
63 sub generate_writer_method {
64 my ($self, $attr_name) = @_;
66 $' . ($self->associated_class->name . '::' . $attr_name) . '{ refaddr($_[0]) } = $_[1];
70 sub generate_predicate_method {
71 my ($self, $attr_name) = @_;
73 defined($' . ($self->associated_class->name . '::' . $attr_name) . '{ refaddr($_[0]) }) ? 1 : 0;
77 ## &remove_attribute is left as an exercise for the reader :)
87 InsideOutClass - A set of example metaclasses which implement the Inside-Out technique
93 use metaclass 'InsideOutClass' => (
94 # tell our metaclass to use the
95 # InsideOut attribute metclass
96 # to construct all it's attributes
97 ':attribute_metaclass' => 'InsideOutClass::Attribute'
100 __PACKAGE__->meta->add_attribute('foo' => (
107 bless $class->meta->construct_instance(@_) => $class;
110 # now you can just use the class as normal
114 This is a set of example metaclasses which implement the Inside-Out
115 class technique. What follows is a brief explaination of the code
116 found in this module.
118 First step is to subclass B<Class::MOP::Class> and override the
119 C<construct_instance> method. The default C<construct_instance>
120 will create a HASH reference using the parameters and attribute
121 default values. Since inside-out objects don't use HASH refs, and
122 use package variables instead, we need to write code to handle
125 The next step is to create the subclass of B<Class::MOP::Attribute>
126 and override the method generation code. This requires overloading
127 C<generate_accessor_method>, C<generate_reader_method>,
128 C<generate_writer_method> and C<generate_predicate_method>. All
129 other aspects are taken care of with the existing B<Class::MOP::Attribute>
132 And that is pretty much all. Of course I am ignoring need for
133 inside-out objects to be C<DESTROY>-ed, and some other details as
134 well, but this is an example. A real implementation is left as an
135 exercise to the reader.
139 Stevan Little E<lt>stevan@iinteractive.comE<gt>
141 =head1 COPYRIGHT AND LICENSE
143 Copyright 2006 by Infinity Interactive, Inc.
145 L<http://www.iinteractive.com>
147 This library is free software; you can redistribute it and/or modify
148 it under the same terms as Perl itself.