1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
|
# PODNAME: Moose::Cookbook::Legacy::Debugging_BaseClassReplacement
# ABSTRACT: Providing an alternate base object class
__END__
=pod
=encoding UTF-8
=head1 NAME
Moose::Cookbook::Legacy::Debugging_BaseClassReplacement - Providing an alternate base object class
=head1 VERSION
version 2.4000
=head1 SYNOPSIS
package MyApp::Base;
use Moose;
extends 'Moose::Object';
before 'new' => sub { warn "Making a new " . $_[0] };
no Moose;
package MyApp::UseMyBase;
use Moose ();
use Moose::Exporter;
Moose::Exporter->setup_import_methods( also => 'Moose' );
sub init_meta {
shift;
return Moose->init_meta( @_, base_class => 'MyApp::Base' );
}
=head1 DESCRIPTION
B<WARNING: Replacing the base class entirely, as opposed to applying roles to
the base class, is strongly discouraged. This recipe is provided solely for
reference when encountering older code that does this.>
A common extension is to provide an alternate base class. One way to
do that is to make a C<MyApp::Base> and add C<S<extends
'MyApp::Base'>> to every class in your application. That's pretty
tedious. Instead, you can create a Moose-alike module that sets the
base object class to C<MyApp::Base> for you.
Then, instead of writing C<S<use Moose>> you can write C<S<use
MyApp::UseMyBase>>.
In this particular example, our base class issues some debugging
output every time a new object is created, but you can think of some
more interesting things to do with your own base class.
This uses the magic of L<Moose::Exporter>. When we call C<<
Moose::Exporter->setup_import_methods( also => 'Moose' ) >> it builds
C<import> and C<unimport> methods for you. The C<< also => 'Moose' >>
bit says that we want to export everything that Moose does.
The C<import> method that gets created will call our C<init_meta>
method, passing it C<< for_caller => $caller >> as its
arguments. The C<$caller> is set to the class that actually imported
us in the first place.
See the L<Moose::Exporter> docs for more details on its API.
=for testing-SETUP use Test::Needs 'Test::Output';
use Test::Output;
=head1 USING MyApp::UseMyBase
To actually use our new base class, we simply use C<MyApp::UseMyBase>
I<instead> of C<Moose>. We get all the Moose sugar plus our new base
class.
package Foo;
use MyApp::UseMyBase;
has 'size' => ( is => 'rw' );
no MyApp::UseMyBase;
=head1 CONCLUSION
This is an awful lot of magic for a simple base class. You will often
want to combine a metaclass trait with a base class extension, and
that's when this technique is useful.
=begin testing
{
package Foo;
MyApp::UseMyBase->import;
has( 'size' => ( is => 'rw' ) );
}
ok( Foo->isa('MyApp::Base'), 'Foo isa MyApp::Base' );
ok( Foo->can('size'), 'Foo has a size method' );
my $foo;
stderr_like(
sub { $foo = Foo->new( size => 2 ) },
qr/^Making a new Foo/,
'got expected warning when calling Foo->new'
);
is( $foo->size(), 2, '$foo->size is 2' );
=end testing
=head1 AUTHORS
=over 4
=item *
Stevan Little <stevan@cpan.org>
=item *
Dave Rolsky <autarch@urth.org>
=item *
Jesse Luehrs <doy@cpan.org>
=item *
Shawn M Moore <sartak@cpan.org>
=item *
יובל קוג'מן (Yuval Kogman) <nothingmuch@woobling.org>
=item *
Karen Etheridge <ether@cpan.org>
=item *
Florian Ragwitz <rafl@debian.org>
=item *
Hans Dieter Pearcey <hdp@cpan.org>
=item *
Chris Prather <chris@prather.org>
=item *
Matt S Trout <mstrout@cpan.org>
=back
=head1 COPYRIGHT AND LICENSE
This software is copyright (c) 2006 by Infinity Interactive, Inc.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
=cut
|
