Commit | Line | Data |
471c4f09 |
1 | |
2 | =pod |
3 | |
4 | =head1 NAME |
5 | |
3824830b |
6 | Moose::Cookbook::Recipe4 - Subtypes, and modeling a simple B<Company> class hierarchy |
471c4f09 |
7 | |
8 | =head1 SYNOPSIS |
9 | |
10 | package Address; |
471c4f09 |
11 | use Moose; |
05d9eaf6 |
12 | use Moose::Util::TypeConstraints; |
471c4f09 |
13 | |
14 | use Locale::US; |
15 | use Regexp::Common 'zip'; |
16 | |
17 | my $STATES = Locale::US->new; |
18 | |
19 | subtype USState |
20 | => as Str |
21 | => where { |
172e0738 |
22 | (exists $STATES->{code2state}{uc($_)} || |
23 | exists $STATES->{state2code}{uc($_)}) |
471c4f09 |
24 | }; |
25 | |
26 | subtype USZipCode |
27 | => as Value |
28 | => where { |
29 | /^$RE{zip}{US}{-extended => 'allow'}$/ |
30 | }; |
31 | |
32 | has 'street' => (is => 'rw', isa => 'Str'); |
33 | has 'city' => (is => 'rw', isa => 'Str'); |
34 | has 'state' => (is => 'rw', isa => 'USState'); |
35 | has 'zip_code' => (is => 'rw', isa => 'USZipCode'); |
36 | |
37 | package Company; |
471c4f09 |
38 | use Moose; |
05d9eaf6 |
39 | use Moose::Util::TypeConstraints; |
471c4f09 |
40 | |
7c6cacb4 |
41 | has 'name' => (is => 'rw', isa => 'Str', required => 1); |
471c4f09 |
42 | has 'address' => (is => 'rw', isa => 'Address'); |
43 | has 'employees' => (is => 'rw', isa => subtype ArrayRef => where { |
ad5ed80c |
44 | (blessed($_) && $_->isa('Employee') || return) for @$_; 1 |
471c4f09 |
45 | }); |
46 | |
47 | sub BUILD { |
48 | my ($self, $params) = @_; |
49 | if ($params->{employees}) { |
50 | foreach my $employee (@{$params->{employees}}) { |
51 | $employee->company($self); |
52 | } |
53 | } |
54 | } |
55 | |
ad5ed80c |
56 | after 'employees' => sub { |
57 | my ($self, $employees) = @_; |
58 | if (defined $employees) { |
59 | foreach my $employee (@{$employees}) { |
60 | $employee->company($self); |
61 | } |
62 | } |
63 | }; |
471c4f09 |
64 | |
65 | package Person; |
471c4f09 |
66 | use Moose; |
67 | |
7c6cacb4 |
68 | has 'first_name' => (is => 'rw', isa => 'Str', required => 1); |
69 | has 'last_name' => (is => 'rw', isa => 'Str', required => 1); |
172e0738 |
70 | has 'middle_initial' => (is => 'rw', isa => 'Str', |
71 | predicate => 'has_middle_initial'); |
471c4f09 |
72 | has 'address' => (is => 'rw', isa => 'Address'); |
73 | |
74 | sub full_name { |
75 | my $self = shift; |
76 | return $self->first_name . |
172e0738 |
77 | ($self->has_middle_initial ? |
78 | ' ' . $self->middle_initial . '. ' |
79 | : |
80 | ' ') . |
471c4f09 |
81 | $self->last_name; |
82 | } |
83 | |
84 | package Employee; |
471c4f09 |
85 | use Moose; |
86 | |
87 | extends 'Person'; |
88 | |
7c6cacb4 |
89 | has 'title' => (is => 'rw', isa => 'Str', required => 1); |
471c4f09 |
90 | has 'company' => (is => 'rw', isa => 'Company', weak_ref => 1); |
91 | |
92 | override 'full_name' => sub { |
93 | my $self = shift; |
94 | super() . ', ' . $self->title |
95 | }; |
2f04a0fc |
96 | |
471c4f09 |
97 | =head1 DESCRIPTION |
98 | |
172e0738 |
99 | In this recipe we introduce the C<subtype> keyword, and show |
2f04a0fc |
100 | how it can be useful for specifying type constraints |
101 | without building an entire class to represent them. We |
172e0738 |
102 | will also show how this feature can be used to leverage the |
2f04a0fc |
103 | usefulness of CPAN modules. In addition to this, we will |
e08c54f5 |
104 | introduce another attribute option. |
172e0738 |
105 | |
2f04a0fc |
106 | Let's first look at the C<subtype> feature. In the B<Address> class we have |
107 | defined two subtypes. The first C<subtype> uses the L<Locale::US> module, which |
108 | provides two hashes which can be used to perform existential checks for state |
109 | names and their two letter state codes. It is a very simple and very useful |
110 | module, and perfect for use in a C<subtype> constraint. |
172e0738 |
111 | |
112 | my $STATES = Locale::US->new; |
113 | subtype USState |
114 | => as Str |
115 | => where { |
116 | (exists $STATES->{code2state}{uc($_)} || |
117 | exists $STATES->{state2code}{uc($_)}) |
118 | }; |
119 | |
120 | Because we know that states will be passed to us as strings, we |
121 | can make C<USState> a subtype of the built-in type constraint |
2f04a0fc |
122 | C<Str>. This will ensure that anything which is a C<USState> will |
172e0738 |
123 | also pass as a C<Str>. Next, we create a constraint specializer |
124 | using the C<where> keyword. The value being checked against in |
125 | the C<where> clause can be found in the C<$_> variable (1). Our |
2f04a0fc |
126 | constraint specializer will then check whether the given string |
172e0738 |
127 | is either a state name or a state code. If the string meets this |
128 | criteria, then the constraint will pass, otherwise it will fail. |
129 | We can now use this as we would any built-in constraint, like so: |
130 | |
131 | has 'state' => (is => 'rw', isa => 'USState'); |
132 | |
133 | The C<state> accessor will now check all values against the |
134 | C<USState> constraint, thereby only allowing valid state names or |
135 | state codes to be stored in the C<state> slot. |
136 | |
2f04a0fc |
137 | The next C<subtype> does pretty much the same thing using the L<Regexp::Common> |
138 | module, and is used as the constraint for the C<zip_code> slot. |
172e0738 |
139 | |
140 | subtype USZipCode |
141 | => as Value |
142 | => where { |
143 | /^$RE{zip}{US}{-extended => 'allow'}$/ |
144 | }; |
145 | |
2f04a0fc |
146 | Using subtypes can save a lot of unnecessary abstraction by not requiring you to |
147 | create many small classes for these relatively simple values. They also allow |
148 | you to reuse the same constraints in a number of classes (thereby avoiding |
149 | duplication), since all type constraints are stored in a global registry and |
150 | always accessible to C<has>. |
172e0738 |
151 | |
e08c54f5 |
152 | With these two subtypes and some attributes, we have defined |
2f04a0fc |
153 | as much as we need for a basic B<Address> class. Next, we define |
172e0738 |
154 | a basic B<Company> class, which itself has an address. As we saw in |
155 | earlier recipes, we can use the C<Address> type constraint that |
2f04a0fc |
156 | Moose automatically created for us: |
172e0738 |
157 | |
158 | has 'address' => (is => 'rw', isa => 'Address'); |
159 | |
2f04a0fc |
160 | A company also needs a name, so we define that as well: |
172e0738 |
161 | |
162 | has 'name' => (is => 'rw', isa => 'Str', required => 1); |
163 | |
164 | Here we introduce another attribute option, the C<required> option. |
165 | This option tells Moose that C<name> is a required parameter in |
166 | the B<Company> constructor, and that the C<name> accessor cannot |
167 | accept an undefined value for the slot. The result is that C<name> |
2f04a0fc |
168 | will always have a value. |
172e0738 |
169 | |
e08c54f5 |
170 | The next attribute option is not actually new, but a new variant |
2f04a0fc |
171 | of options we have already introduced: |
ad5ed80c |
172 | |
173 | has 'employees' => (is => 'rw', isa => subtype ArrayRef => where { |
174 | (blessed($_) && $_->isa('Employee') || return) for @$_; 1 |
175 | }); |
e08c54f5 |
176 | |
ad5ed80c |
177 | Here, instead of passing a string to the C<isa> option, we are passing |
4711f5f7 |
178 | an anonymous subtype of the C<ArrayRef> type constraint. This subtype |
2f04a0fc |
179 | basically checks that all the values in the ARRAY ref are instances of |
ad5ed80c |
180 | the B<Employee> class. |
181 | |
2f04a0fc |
182 | This will ensure that our employees will all be of the correct type. However, |
183 | the B<Employee> object (which we will see in a moment) also maintains a |
184 | reference to its associated B<Company>. In order to maintain this relationship |
185 | (and preserve the referential integrity of our objects), we need to perform some |
186 | processing of the employees over and above that of the type constraint check. |
187 | This is accomplished in two places. First we need to be sure that any employees |
188 | array passed to the constructor is properly initialized. For this we can use the |
189 | C<BUILD> method (2): |
ad5ed80c |
190 | |
191 | sub BUILD { |
192 | my ($self, $params) = @_; |
193 | if ($params->{employees}) { |
194 | foreach my $employee (@{$params->{employees}}) { |
195 | $employee->company($self); |
196 | } |
197 | } |
198 | } |
199 | |
2f04a0fc |
200 | The C<BUILD> method will be executed after the initial type constraint |
201 | check, so we can simply perform a basic existential check on the C<employees> |
ad5ed80c |
202 | param here, and assume that if it does exist, it is both an ARRAY ref |
2f04a0fc |
203 | and contains I<only> instances of B<Employee>. |
ad5ed80c |
204 | |
2f04a0fc |
205 | The next aspect we need to address is the C<employees> read/write |
ad5ed80c |
206 | accessor (see the C<employees> attribute declaration above). This |
2f04a0fc |
207 | accessor will correctly check the type constraint, but we need to extend it |
208 | with some additional processing. For this we use an C<after> method modifier, |
ad5ed80c |
209 | like so: |
210 | |
211 | after 'employees' => sub { |
212 | my ($self, $employees) = @_; |
213 | if (defined $employees) { |
214 | foreach my $employee (@{$employees}) { |
215 | $employee->company($self); |
216 | } |
217 | } |
218 | }; |
219 | |
220 | Again, as with the C<BUILD> method, we know that the type constraint |
221 | check has already happened, so we can just check for defined-ness on the |
222 | C<$employees> argument. |
223 | |
224 | At this point, our B<Company> class is complete. Next comes our B<Person> |
2f04a0fc |
225 | class and its subclass, the previously mentioned B<Employee> class. |
ad5ed80c |
226 | |
227 | The B<Person> class should be obvious to you at this point. It has a few |
4711f5f7 |
228 | C<required> attributes, and the C<middle_initial> slot has an additional |
ad5ed80c |
229 | C<predicate> method (which we saw in the previous recipe with the |
230 | B<BinaryTree> class). |
231 | |
2f04a0fc |
232 | Next, the B<Employee> class, which should also be pretty obvious at this |
4711f5f7 |
233 | point. It requires a C<title>, and maintains a weakened reference to a |
ad5ed80c |
234 | B<Company> instance. The only new item, which we have seen before in |
235 | examples, but never in the recipe itself, is the C<override> method |
2f04a0fc |
236 | modifier: |
e08c54f5 |
237 | |
ad5ed80c |
238 | override 'full_name' => sub { |
239 | my $self = shift; |
240 | super() . ', ' . $self->title |
241 | }; |
242 | |
e08c54f5 |
243 | This just tells Moose that I am intentionally overriding the superclass |
ad5ed80c |
244 | C<full_name> method here, and adding the value of the C<title> slot at |
245 | the end of the employee's full name. |
246 | |
e08c54f5 |
247 | And that's about it. |
ad5ed80c |
248 | |
249 | Once again, as with all the other recipes, you can go about using |
250 | these classes like any other Perl 5 class. A more detailed example of |
db1ab48d |
251 | usage can be found in F<t/004_recipe.t>. |
ad5ed80c |
252 | |
253 | =head1 CONCLUSION |
254 | |
255 | This recipe was intentionally longer and more complex to illustrate both |
256 | how easily Moose classes can interact (using class type constraints, etc.) |
2f04a0fc |
257 | and the sheer density of information and behaviors which Moose can pack |
ad5ed80c |
258 | into a relatively small amount of typing. Ponder for a moment how much |
259 | more code a non-Moose plain old Perl 5 version of this recipe would have |
2f04a0fc |
260 | been (including all the type constraint checks, weak references, and so on). |
ad5ed80c |
261 | |
262 | And of course, this recipe also introduced the C<subtype> keyword, and |
e08c54f5 |
263 | its usefulness within the Moose toolkit. In the next recipe we will |
ad5ed80c |
264 | focus more on subtypes, and introduce the idea of type coercion as well. |
e08c54f5 |
265 | |
172e0738 |
266 | =head1 FOOTNOTES |
267 | |
268 | =over 4 |
269 | |
270 | =item (1) |
271 | |
272 | The value being checked is also passed as the first argument to |
273 | the C<where> block as well, so it can also be accessed as C<$_[0]> |
274 | as well. |
275 | |
ad5ed80c |
276 | =item (2) |
277 | |
278 | The C<BUILD> method is called by C<Moose::Object::BUILDALL>, which is |
279 | called by C<Moose::Object::new>. C<BUILDALL> will climb the object |
4711f5f7 |
280 | inheritance graph and call the appropriate C<BUILD> methods in the |
ad5ed80c |
281 | correct order. |
282 | |
172e0738 |
283 | =back |
284 | |
471c4f09 |
285 | =head1 AUTHOR |
286 | |
287 | Stevan Little E<lt>stevan@iinteractive.comE<gt> |
288 | |
289 | =head1 COPYRIGHT AND LICENSE |
290 | |
b77fdbed |
291 | Copyright 2006, 2007 by Infinity Interactive, Inc. |
471c4f09 |
292 | |
293 | L<http://www.iinteractive.com> |
294 | |
295 | This library is free software; you can redistribute it and/or modify |
296 | it under the same terms as Perl itself. |
297 | |
e08c54f5 |
298 | =cut |