6 Moose::Cookbook::Roles::Recipe1 - The Moose::Role example
16 my ( $self, $other ) = @_;
17 not $self->equal_to($other);
28 my ( $self, $other ) = @_;
29 $self->compare($other) == 0;
33 my ( $self, $other ) = @_;
34 $self->compare($other) == 1;
38 my ( $self, $other ) = @_;
39 $self->compare($other) == -1;
42 sub greater_than_or_equal_to {
43 my ( $self, $other ) = @_;
44 $self->greater_than($other) || $self->equal_to($other);
47 sub less_than_or_equal_to {
48 my ( $self, $other ) = @_;
49 $self->less_than($other) || $self->equal_to($other);
60 with 'Comparable', 'Printable';
62 has 'amount' => ( is => 'rw', isa => 'Num', default => 0 );
65 my ( $self, $other ) = @_;
66 $self->amount <=> $other->amount;
71 sprintf '$%0.2f USD' => $self->amount;
76 Roles have two primary purposes: as interfaces, and as a means of code
77 reuse. This recipe demonstrates the latter, with roles that define
78 comparison and display code for objects.
80 Let's start with CB<Eq>. First, note that we've replaced C<use Moose>
81 with C<use Moose::Role>. We also have a new sugar function, C<required>:
85 This says that any class which consumes this role must provide an
86 C<equal_to> method. It can provide this method directly, or by
87 consuming some other role.
89 The C<Eq> role defines its C<not_equal_to> method in terms of the
90 required C<equal_to> method. This lets us minimize the methods that
91 consuming classes must provide.
93 The next role, C<Comparable>, builds on the C<Eq> role. We include
94 C<Eq> in C<Comparable> using C<with>, another new sugar function:
98 The C<with> function takes a list of roles to consume. In our example,
99 the C<Comparable> role provides the C<equal_to> method required by
100 C<Eq>. However, it could opt not to, in which case a class that
101 consumed C<Comparable> would have to provide its own C<equal_to>. In
102 other words, a role can consume another role I<without> providing any
105 The C<Comparable> role requires a method, C<compare>:
109 The C<Comparable> role also provides a number of other methods, all of
110 which ultimately rely on C<compare>.
113 my ( $self, $other ) = @_;
114 $self->compare($other) == 0;
118 my ( $self, $other ) = @_;
119 $self->compare($other) == 1;
123 my ( $self, $other ) = @_;
124 $self->compare($other) == -1;
127 sub greater_than_or_equal_to {
128 my ( $self, $other ) = @_;
129 $self->greater_than($other) || $self->equal_to($other);
132 sub less_than_or_equal_to {
133 my ( $self, $other ) = @_;
134 $self->less_than($other) || $self->equal_to($other);
137 Finally, we the C<Printable> role. This role exists solely to provide
138 an interface. It has no methods, just a list of required methods. In
139 this case, it just requires a C<to_string> method.
141 An interface role is useful because it defines both a method and a
142 I<name>. We know that any class which does this role has a
143 C<to_string> method, but we can also assume that this method has the
144 semantics we want. Presumably, in real code we would define those
145 semantics in the documentation for the C<Printable> role. (1)
147 Finally, we have the C<US::Currency> class which consumes both the
148 C<Comparable> and C<Printable> roles.
150 with 'Comparable', 'Printable';
152 It also defines a regular Moose attribute, C<amount>:
154 has 'amount' => ( is => 'rw', isa => 'Num', default => 0 );
156 Finally we see the implementation of the methods required by our
157 roles. We have a C<compare> method:
160 my ( $self, $other ) = @_;
161 $self->amount <=> $other->amount;
164 By consuming the C<Comparable> role and defining this method, we gain
165 the following methods for free: C<equal_to>, C<greater_than>,
166 C<less_than>, C<greater_than_or_equal_to> and
167 C<less_than_or_equal_to>.
169 Then we have our C<to_string> method:
173 sprintf '$%0.2f USD' => $self->amount;
178 Roles can very powerful. They are a great way of encapsulating
179 reusable behavior, as well as communicating (semantic and interface)
180 information about the methods our classes provide.
188 Consider two classes, C<Runner> and C<Process>, both of which define a
189 C<run> method. If we just require that an object implements a C<run>
190 method, we still aren't saying anything about what that method
191 I<actually does>. If we require an object that implements the
192 C<Executable> role, we're saying something about semantics.
198 Stevan Little E<lt>stevan@iinteractive.comE<gt>
200 Dave Rolsky E<lt>autarch@urth.orgE<gt>
202 =head1 COPYRIGHT AND LICENSE
204 Copyright 2006-2009 by Infinity Interactive, Inc.
206 L<http://www.iinteractive.com>
208 This library is free software; you can redistribute it and/or modify
209 it under the same terms as Perl itself.