5 Moose::Unsweetened - Moose idioms in plain old Perl 5 without the sugar
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.
14 =head1 CLASSES AND ATTRIBUTES
16 First, we define two very small classes the Moose way.
21 use DateTime::Format::Natural;
23 use Moose::Util::TypeConstraints;
31 # Moose doesn't know about non-Moose-based classes.
32 class_type 'DateTime';
34 my $en_parser = DateTime::Format::Natural->new(
41 => via { $en_parser->parse_datetime($_) };
47 handles => { birth_year => 'year' },
52 => where { /^(?:s|m|l|xl|xxl)$/i }
53 => message { "$_ is not a valid shirt size (s, m, l, xl, xxl)" };
61 This is a fairly simple class with three attributes. We also define a
62 type to validate t-shirt sizes because we don't want to end up with
63 something like "blue" for the shirt size!
69 use Moose::Util::TypeConstraints;
75 => where { Email::Valid->address($_) }
76 => message { "$_ is not a valid email address" };
78 has email_address => (
84 This class subclasses Person to add a single attribute, email address.
86 Now we will show what these classes would look like in plain old Perl
87 5. For the sake of argument, we won't use any base classes or any
88 helpers like C<Class::Accessor>.
95 use Carp qw( confess );
97 use DateTime::Format::Natural;
102 my %p = ref $_[0] ? %{ $_[0] } : @_;
105 or confess 'name is a required attribute';
106 $class->_validate_name( $p{name} );
108 exists $p{birth_date}
109 or confess 'birth_date is a required attribute';
111 $p{birth_date} = $class->_coerce_birth_date( $p{birth_date} );
112 $class->_validate_birth_date( $p{birth_date} );
115 unless exists $p{shirt_size}:
117 $class->_validate_shirt_size( $p{shirt_size} );
119 return bless \%p, $class;
126 local $Carp::CarpLevel = $Carp::CarpLevel + 1;
129 or confess 'name must be a string';
133 my $en_parser = DateTime::Format::Natural->new(
138 sub _coerce_birth_date {
142 return $date unless defined $date && ! ref $date;
144 my $dt = $en_parser->parse_datetime($date);
146 return $dt ? $dt : undef;
150 sub _validate_birth_date {
152 my $birth_date = shift;
154 local $Carp::CarpLevel = $Carp::CarpLevel + 1;
156 $birth_date->isa('DateTime') )
157 or confess 'birth_date must be a DateTime object';
160 sub _validate_shirt_size {
162 my $shirt_size = shift;
164 local $Carp::CarpLevel = $Carp::CarpLevel + 1;
167 or confess 'shirt_size cannot be undef';
169 $shirt_size =~ /^(?:s|m|l|xl|xxl)$/
170 or confess "$shirt_size is not a valid shirt size (s, m, l, xl, xxl)";
177 $self->_validate_name( $_[0] );
178 $self->{name} = $_[0];
181 return $self->{name};
188 my $date = $self->_coerce_birth_date( $_[0] );
189 $self->_validate_birth_date( $date );
191 $self->{birth_date} = $date;
194 return $self->{birth_date};
200 return $self->birth_date->year;
207 $self->_validate_shirt_size( $_[0] );
208 $self->{shirt_size} = $_[0];
211 return $self->{shirt_size};
214 Wow, that was a mouthful! One thing to note is just how much space the
215 data validation code consumes. As a result, it's pretty common for
216 Perl 5 programmers to just not bother, which results in much more
219 Did you spot the (intentional) bug?
221 It's in the C<_validate_birth_date()> method. We should check that
222 that value in C<$birth_date> is actually defined and object before we
223 go and call C<isa()> on it! Leaving out those checks means our data
224 validation code could actually cause our program to die. Oops.
226 Also note that if we add a superclass to Person we'll have to change
227 the constructor to account for that.
229 (As an aside, getting all the little details of what Moose does for
230 you just right in this code was not easy, which just emphasizes the
231 point, that Moose saves you a lot of work!)
240 use Carp qw( confess );
242 use Scalar::Util qw( blessed );
249 my %p = ref $_[0] ? %{ $_[0] } : @_;
251 exists $p{email_address}
252 or confess 'email_address is a required attribute';
253 $class->_validate_email_address( $p{email_address} );
255 my $self = $class->SUPER::new(%p);
257 $self->{email_address} = $p{email_address};
262 sub _validate_email_address {
264 my $email_address = shift;
266 local $Carp::CarpLevel = $Carp::CarpLevel + 1;
268 defined $email_address
269 or confess 'email_address must be a string';
271 Email::Valid->address($email_address)
272 or confess "$email_address is not a valid email address";
279 $self->_validate_email_address( $_[0] );
280 $self->{email_address} = $_[0];
283 return $self->{email_address};
286 That one was shorter, but it only has one attribute.
288 Between the two classes, we have a whole lot of code that doesn't do
289 much. We could probably simplify this by defining some sort of
290 "attribute and validation" hash, like this:
297 validate => sub { defined $_ },
301 validate => sub { blessed $_ && $_->isa('DateTime') },
305 validate => sub { defined $_ && $_ =~ /^(?:s|m|l|xl|xxl)$/i },
309 Then we could define a base class that would accept such a definition,
310 and do the right thing. Keep that sort of thing up and we're well on
311 our way to writing a half-assed version of Moose!
313 Of course, there are CPAN modules that do some of what Moose does,
314 like C<Class::Accessor>, C<Class::Meta>, and so on. But none of them
315 put together all of Moose's features along with a layer of declarative
316 sugar, nor are these other modules designed for extensibility in the
317 same way as Moose. With Moose, it's easy to write a MooseX module to
318 replace or extend a piece of built-in functionality.
322 Dave Rolsky E<lt>autarch@urth.orgE<gt>
324 =head1 COPYRIGHT AND LICENSE
326 Copyright 2008 by Infinity Interactive, Inc.
328 L<http://www.iinteractive.com>
330 This library is free software; you can redistribute it and/or modify
331 it under the same terms as Perl itself.