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1 | =pod |
2 | |
3 | =head1 NAME |
4 | |
5 | Moose::Unsweetened - Moose idioms in plain old Perl 5 without the sugar |
6 | |
7 | =head1 DESCRIPTION |
8 | |
9 | If you're trying to figure out just what the heck Moose does, and how |
10 | it saves you time, you might find it helpful to see what Moose is |
11 | I<really> doing for you. This document shows you the translation from |
12 | Moose sugar back to plain old Perl 5. |
13 | |
14 | =head1 CLASSES AND ATTRIBUTES |
15 | |
16 | First, we define two very small classes the Moose way. |
17 | |
18 | package Person; |
19 | |
20 | use DateTime; |
21 | use DateTime::Format::Natural; |
22 | use Moose; |
23 | use Moose::Util::TypeConstraints; |
24 | |
25 | has name => ( |
26 | is => 'rw', |
27 | isa => 'Str', |
28 | required => 1, |
29 | ); |
30 | |
31 | # Moose doesn't know about non-Moose-based classes. |
32 | class_type 'DateTime'; |
33 | |
34 | my $en_parser = DateTime::Format::Natural->new( |
35 | lang => 'en', |
36 | time_zone => 'UTC', |
37 | ); |
38 | |
39 | coerce 'DateTime' |
40 | => from 'Str' |
41 | => via { $en_parser->parse_datetime($_) }; |
42 | |
43 | has birth_date => ( |
44 | is => 'rw', |
45 | isa => 'DateTime', |
46 | ); |
47 | |
48 | subtype 'ShirtSize' |
49 | => as 'Str' |
50 | => where { /^(?:s|m|l|xl|xxl)$/i } |
51 | => message { "$_ is not a valid shirt size (s, m, l, xl, xxl)" }; |
52 | |
53 | has shirt_size => ( |
54 | is => 'rw', |
55 | isa => 'ShirtSize', |
56 | default => 'l', |
57 | ); |
58 | |
59 | This is a fairly simple class with three attributes. We also define a |
60 | type to validate t-shirt sizes because we don't want to end up with |
61 | something like "blue" for the shirt size! |
62 | |
63 | package User; |
64 | |
65 | use Email::Valid; |
66 | use Moose; |
67 | use Moose::Util::TypeConstraints; |
68 | |
69 | extends 'Person'; |
70 | |
71 | subtype 'Email' |
72 | => as 'Str' |
73 | => where { Email::Valid->address($_) } |
74 | => message { "$_ is not a valid email address" }; |
75 | |
76 | has email_address => ( |
77 | is => 'rw', |
78 | isa => 'Email', |
79 | required => 1, |
80 | ); |
81 | |
82 | This class subclasses Person to add a single attribute, email address. |
83 | |
84 | Now we will show what these classes would look like in plain old Perl |
85 | 5. For the sake of argument, we won't use any base classes or any |
86 | helpers like C<Class::Accessor>. |
87 | |
88 | package Person; |
89 | |
90 | use strict; |
91 | use warnings; |
92 | |
93 | use Carp qw( confess ); |
94 | use DateTime; |
95 | use DateTime::Format::Natural; |
96 | |
97 | |
98 | sub new { |
99 | my $class = shift; |
100 | my %p = ref $_[0] ? %{ $_[0] } : @_; |
101 | |
102 | exists $p{name} |
103 | or confess 'name is a required attribute'; |
104 | $class->_validate_name( $p{name} ); |
105 | |
106 | exists $p{birth_date} |
107 | or confess 'birth_date is a required attribute'; |
108 | |
109 | my $date = $p{birth_date}; |
110 | $class->_coerce_birth_date( \$date ); |
111 | $class->_validate_birth_date( $date ); |
112 | |
113 | $p{shirt_size} = 'l' |
114 | unless exists $p{shirt_size}: |
115 | |
116 | $class->_validate_shirt_size( $p{shirt_size} ); |
117 | |
118 | my $self = map { $_ => $p{$_} } qw( name shirt_size ); |
119 | $self->{birth_date} = $date; |
120 | |
121 | return bless $self, $class; |
122 | } |
123 | |
124 | sub _validate_name { |
125 | shift; |
126 | my $name = shift; |
127 | |
128 | local $Carp::CarpLevel = $Carp::CarpLevel + 1; |
129 | |
130 | defined $name |
131 | or confess 'name must be a string'; |
132 | } |
133 | |
134 | { |
135 | my $en_parser = DateTime::Format::Natural->new( |
136 | lang => 'en', |
137 | time_zone => 'UTC', |
138 | ); |
139 | |
140 | sub _coerce_birth_date { |
141 | shift; |
142 | my $date = shift; |
143 | |
144 | return unless defined $date && ! ref $date; |
145 | |
146 | my $dt = $en_parser->parse_datetime($date); |
147 | |
148 | return $dt ? $dt : undef; |
149 | } |
150 | } |
151 | |
152 | sub _validate_birth_date { |
153 | shift; |
154 | my $birth_date = shift; |
155 | |
156 | local $Carp::CarpLevel = $Carp::CarpLevel + 1; |
157 | |
158 | $birth_date->isa('DateTime') ) |
159 | or confess 'birth_date must be a DateTime object'; |
160 | } |
161 | |
162 | sub _validate_shirt_size { |
163 | shift; |
164 | my $shirt_size = shift; |
165 | |
166 | local $Carp::CarpLevel = $Carp::CarpLevel + 1; |
167 | |
168 | defined $shirt_size |
169 | or confess 'shirt_size cannot be undef'; |
170 | |
171 | $shirt_size =~ /^(?:s|m|l|xl|xxl)$/ |
172 | or confess "$shirt_size is not a valid shirt size (s, m, l, xl, xxl)"; |
173 | } |
174 | |
175 | sub name { |
176 | my $self = shift; |
177 | |
178 | if (@_) { |
179 | $self->_validate_name( $_[0] ); |
180 | $self->{name} = $_[0]; |
181 | } |
182 | |
183 | return $self->{name}; |
184 | } |
185 | |
186 | sub birth_date { |
187 | my $self = shift; |
188 | |
189 | if (@_) { |
190 | my $date = shift; |
191 | |
192 | $self->_coerce_birth_date( $date ); |
193 | $self->_validate_birth_date( $date ); |
194 | $self->{birth_date} = $date; |
195 | } |
196 | |
197 | return $self->{birth_date}; |
198 | } |
199 | |
200 | sub shirt_size { |
201 | my $self = shift; |
202 | |
203 | if (@_) { |
204 | $self->_validate_shirt_size( $_[0] ); |
205 | $self->{shirt_size} = $_[0]; |
206 | } |
207 | |
208 | return $self->{shirt_size}; |
209 | } |
210 | |
211 | Wow, that was a mouthful! One thing to note is just how much space the |
212 | data validation code consumes. As a result, it's pretty common for |
213 | Perl 5 programmers to just not bother, which results in much more |
214 | fragile code. |
215 | |
216 | Did you spot the bug? |
217 | |
218 | It's in the C<_validate_birth_date()> method. We should check that |
219 | that value in C<$birth_date> is actually defined and object before we |
220 | go and call C<isa()> on it! Leaving out those checks means our data |
221 | validation code could actually cause our program to die. Oops. |
222 | |
223 | There's one bit of code in there worth explaining, which is the |
224 | handling of the birth date for coercion. In both the constructor and |
225 | accessor, we first take a copy of the birth date before passing it to |
226 | the coercion routine. This is to avoid changing the value as it was |
227 | passed to those methods, which could cause problems for the caller. |
228 | |
229 | Also note that if we add a superclass to Person we'll have to change |
230 | the constructor to account for that. |
231 | |
232 | (As an aside, getting all the little details of what Moose does for |
233 | you just right in this code was not easy, which just emphasizes the |
234 | point, that Moose saves you a lot of work!) |
235 | |
236 | Now let's see User: |
237 | |
238 | package User; |
239 | |
240 | use strict; |
241 | use warnings; |
242 | |
243 | use Carp qw( confess ); |
244 | use Email::Valid; |
245 | use Scalar::Util qw( blessed ); |
246 | |
247 | use base 'Person'; |
248 | |
249 | |
250 | sub new { |
251 | my $class = shift; |
252 | my %p = ref $_[0] ? %{ $_[0] } : @_; |
253 | |
254 | exists $p{email_address} |
255 | or confess 'email_address is a required attribute'; |
256 | $class->_validate_email_address( $p{email_address} ); |
257 | |
258 | my $self = $class->SUPER::new(%p); |
259 | |
260 | $self->{email_address} = $p{email_address}; |
261 | |
262 | return $self; |
263 | } |
264 | |
265 | sub _validate_email_address { |
266 | shift; |
267 | my $email_address = shift; |
268 | |
269 | local $Carp::CarpLevel = $Carp::CarpLevel + 1; |
270 | |
271 | defined $email_address |
272 | or confess 'email_address must be a string'; |
273 | |
274 | Email::Valid->address($email_address) |
275 | or confess "$email_address is not a valid email address"; |
276 | } |
277 | |
278 | sub email_address { |
279 | my $self = shift; |
280 | |
281 | if (@_) { |
282 | $self->_validate_email_address( $_[0] ); |
283 | $self->{email_address} = $_[0]; |
284 | } |
285 | |
286 | return $self->{email_address}; |
287 | } |
288 | |
289 | That one was shorter, but it only has one attribute. |
290 | |
291 | Between the two classes, we have a whole lot of code that doesn't do |
292 | much. We could probably simplify this by defining some sort of |
293 | "attribute and validation" hash, like this: |
294 | |
295 | package Person; |
296 | |
297 | my %Attr = ( |
298 | name => { |
299 | required => 1, |
300 | validate => sub { defined $_ }, |
301 | }, |
302 | birth_date => { |
303 | required => 1, |
304 | validate => sub { blessed $_ && $_->isa('DateTime') }, |
305 | }, |
306 | shirt_size => { |
307 | required => 1, |
308 | validate => sub { defined $_ && $_ =~ /^(?:s|m|l|xl|xxl)$/i }, |
309 | } |
310 | ); |
311 | |
312 | Then we could define a base class that would accept such a definition, |
313 | and do the right thing. Keep that sort of thing up and you're well on |
314 | your way to writing a half-assed version of Moose! |
315 | |
316 | Of course, there are CPAN modules that do some of what Moose does, |
317 | like C<Class::Accessor>, C<Class::Meta>, and so on. But none of them |
318 | put together all of Moose's features along with a layer of declarative |
319 | sugar. |
320 | |
321 | =head1 AUTHOR |
322 | |
323 | Dave Rolsky E<lt>autarch@urth.orgE<gt> |
324 | |
325 | =head1 COPYRIGHT AND LICENSE |
326 | |
327 | Copyright 2008 by Infinity Interactive, Inc. |
328 | |
329 | L<http://www.iinteractive.com> |
330 | |
331 | This library is free software; you can redistribute it and/or modify |
332 | it under the same terms as Perl itself. |
333 | |
334 | =cut |