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1 | |
2 | =pod |
3 | |
4 | =head1 NAME |
5 | |
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6 | Moose::Cookbook::Extending::Recipe3 - Providing an alternate base object class |
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7 | |
8 | =head1 SYNOPSIS |
9 | |
10 | package MyApp::Base; |
11 | use Moose; |
12 | |
13 | extends 'Moose::Object'; |
14 | |
15 | before 'new' => sub { warn "Making a new " . $_[0] }; |
16 | |
17 | no Moose; |
18 | |
19 | package MyApp::UseMyBase; |
20 | use Moose (); |
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21 | use Moose::Exporter; |
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22 | |
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23 | Moose::Exporter->setup_import_methods( also => 'Moose' ); |
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24 | |
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25 | sub init_meta { |
26 | shift; |
27 | Moose->init_meta( @_, base_class => 'MyApp::Object' ); |
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28 | } |
29 | |
30 | =head1 DESCRIPTION |
31 | |
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32 | A common extension is to provide an alternate base class. One way to |
33 | do that is to make a C<MyApp::base> and add C<S<extends |
34 | 'MyApp::Base'>> to every class in your application. That's pretty |
35 | tedious. Instead, you can create a Moose-alike module that sets the |
36 | base object class to C<MyApp::Base> for you. |
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37 | |
38 | Then, instead of writing C<S<use Moose>> you can write C<S<use |
39 | MyApp::UseMyBase>>. |
40 | |
41 | In this particular example, our base class issues some debugging |
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42 | output every time a new object is created, but you can think of some |
43 | more interesting things to do with your own base class. |
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44 | |
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45 | This uses the magic of L<Moose::Exporter>. When we call S<C<< |
46 | Moose::Exporter->setup_import_methods( also => 'Moose' ) >>> it builds |
47 | C<import> and C<unimport> methods for you. The S<C<< also => 'Moose' |
48 | >>> bit says that we want to export everything that Moose does. |
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49 | |
50 | The C<import> method that gets created will call our C<init_meta> |
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51 | method, passing it S<C<< for_caller => $caller >>> as its |
52 | arguments. The C<$caller> is set to the class that actually imported |
53 | us in the first place. |
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54 | |
55 | See the L<Moose::Exporter> docs for more details on its API. |
56 | |
57 | =head1 USING MyApp::UseMyBase |
58 | |
59 | To actually use our new base class, we simply use C<MyApp::UseMyBase> |
60 | I<instead> of C<Moose>. We get all the Moose sugar plus our new base |
61 | class. |
62 | |
63 | package Foo; |
64 | |
65 | use MyApp::UseMyBase; |
66 | |
67 | has 'size' => ( is => 'rw' ); |
68 | |
69 | no MyApp::UseMyBase; |
70 | |
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71 | =head1 CONCLUSION |
72 | |
73 | This is an awful lot of magic for a simple base class. You will often |
74 | want to combine a metaclass trait with a base class extension, and |
75 | that's when this technique is useful. |
76 | |
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77 | =head1 AUTHOR |
78 | |
79 | Dave Rolsky E<lt>autarch@urth.orgE<gt> |
80 | |
81 | =head1 COPYRIGHT AND LICENSE |
82 | |
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83 | Copyright 2006-2009 by Infinity Interactive, Inc. |
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84 | |
85 | L<http://www.iinteractive.com> |
86 | |
87 | This library is free software; you can redistribute it and/or modify |
88 | it under the same terms as Perl itself. |
89 | |
90 | =cut |