6 Moose::Cookbook::Snack::BUILD - Overriding the I<new()> method to customize
7 the behaivor of Moose object creation
14 has 'example_file' => ( is => 'rw', required => 1);
18 # create the object only if the file does exist
19 if ( -e $self->example_file ) {
23 die('ERROR: file _' . $self->example_file . '_ does not exist');
30 # '$0' is the name of this script, set automatically by Perl
32 my $first_test = Build::Demo->new( example_file => $0 );
33 # this should fail (unless there's a file named 'foo'
34 # in the current directory)
35 my $second_test = Build::Demo->new( example_file => 'foo' );
39 The C<BUILD()> method allows you to write your own custom constructors for
42 =head2 Creating new objects in Perl and Moose
44 By convention, most objects in Perl are created by calling a C<new()> method
45 that they have created:
47 package My::Perl::Class;
50 # object initialization code goes here...
54 my $object = My::Perl::Class->new();
56 Moose is no different in this respect. However, since Moose handles the
57 C<new()> method for you, how do you change the default behaivor of the
58 C<new()> method in Moose? This is what the C<BUILD()> method was designed
61 package My::Moose::Class;
64 # object initialization code goes here...
68 my $object = My::Moose::Class->new();
70 =head2 Why would you want a custom constructor?
72 If your object needs to verify some behaivor or internal state before it is
73 created, a good time to do that is when the object is being created. Why
74 waste resources (CPU, memory) on objects that won't work because of missing
77 =head2 What is 'BUILDALL'?
79 (Taken from L<Moose::Object>) The C<BUILDALL> method will call every BUILD
80 method in the inheritance hierarchy, and pass it a hash-ref of the the %params
87 =item L<Moose::Object> - The base object for Moose (BUILDALL)
89 =item L<Moose::Cookbook::FAQ> - Frequently asked questions about Moose (How do
90 I write custom constructors with Moose?)
92 =item L<Moose::Cookbook::Recipe4> - Subtypes, and modeling a simple Company
93 class heirarchy (Example usage of BUILD in action)
95 =item L<Moose::Cookbook::WTF> - For when things go wrong with Moose ('Roles'
96 Ń•ection describes BUILD/BUILDALL)
100 The L<Moose::Cookbook::WTF> section entitled B<Roles> for more info about how
101 the BUILD/BUILDALL methods work.
107 Brian Manning <elspicyjack at gmail dot com>
109 =head1 COPYRIGHT AND LICENSE
111 Copyright (c)2008 by Brian Manning
113 This documentation is free software; you can redistribute it and/or modify
114 it under the same terms as Perl itself.