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1 | |
2 | package # hide the package from PAUSE |
3 | InsideOutClass; |
4 | |
5 | use strict; |
6 | use warnings; |
7 | |
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8 | our $VERSION = '0.03'; |
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9 | |
10 | use Scalar::Util 'refaddr'; |
11 | |
12 | use base 'Class::MOP::Class'; |
13 | |
14 | sub construct_instance { |
15 | my ($class, %params) = @_; |
16 | # create a scalar ref to use as |
17 | # the inside-out instance |
18 | my $instance = \(my $var); |
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19 | foreach my $attr ($class->compute_all_applicable_attributes()) { |
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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 ... |
24 | my $val; |
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; |
31 | } |
32 | return $instance; |
33 | } |
34 | |
35 | package # hide the package from PAUSE |
36 | InsideOutClass::Attribute; |
37 | |
38 | use strict; |
39 | use warnings; |
40 | |
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41 | our $VERSION = '0.04'; |
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42 | |
43 | use Scalar::Util 'refaddr'; |
44 | |
45 | use base 'Class::MOP::Attribute'; |
46 | |
47 | sub generate_accessor_method { |
48 | my ($self, $attr_name) = @_; |
49 | $attr_name = ($self->associated_class->name . '::' . $attr_name); |
50 | eval 'sub { |
51 | $' . $attr_name . '{ refaddr($_[0]) } = $_[1] if scalar(@_) == 2; |
52 | $' . $attr_name . '{ refaddr($_[0]) }; |
53 | }'; |
54 | } |
55 | |
56 | sub generate_reader_method { |
57 | my ($self, $attr_name) = @_; |
58 | eval 'sub { |
59 | $' . ($self->associated_class->name . '::' . $attr_name) . '{ refaddr($_[0]) }; |
60 | }'; |
61 | } |
62 | |
63 | sub generate_writer_method { |
64 | my ($self, $attr_name) = @_; |
65 | eval 'sub { |
66 | $' . ($self->associated_class->name . '::' . $attr_name) . '{ refaddr($_[0]) } = $_[1]; |
67 | }'; |
68 | } |
69 | |
70 | sub generate_predicate_method { |
71 | my ($self, $attr_name) = @_; |
72 | eval 'sub { |
73 | defined($' . ($self->associated_class->name . '::' . $attr_name) . '{ refaddr($_[0]) }) ? 1 : 0; |
74 | }'; |
75 | } |
76 | |
77 | ## &remove_attribute is left as an exercise for the reader :) |
78 | |
79 | 1; |
80 | |
81 | __END__ |
82 | |
83 | =pod |
84 | |
85 | =head1 NAME |
86 | |
87 | InsideOutClass - A set of example metaclasses which implement the Inside-Out technique |
88 | |
89 | =head1 SYNOPSIS |
90 | |
91 | package Foo; |
92 | |
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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' |
98 | ); |
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99 | |
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100 | __PACKAGE__->meta->add_attribute('foo' => ( |
101 | reader => 'get_foo', |
102 | writer => 'set_foo' |
103 | )); |
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104 | |
105 | sub new { |
106 | my $class = shift; |
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107 | bless $class->meta->construct_instance(@_) => $class; |
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108 | } |
109 | |
110 | # now you can just use the class as normal |
111 | |
112 | =head1 DESCRIPTION |
113 | |
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. |
117 | |
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 |
123 | this difference. |
124 | |
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> |
130 | infastructure. |
131 | |
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. |
136 | |
137 | =head1 AUTHOR |
138 | |
139 | Stevan Little E<lt>stevan@iinteractive.comE<gt> |
140 | |
141 | =head1 COPYRIGHT AND LICENSE |
142 | |
143 | Copyright 2006 by Infinity Interactive, Inc. |
144 | |
145 | L<http://www.iinteractive.com> |
146 | |
147 | This library is free software; you can redistribute it and/or modify |
148 | it under the same terms as Perl itself. |
149 | |
150 | =cut |