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 { $en_parser->parse_datetime($_) };
50 => where { /^(?:s|m|l|xl|xxl)$/i }
51 => message { "$_ is not a valid shirt size (s, m, l, xl, xxl)" };
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!
67 use Moose::Util::TypeConstraints;
73 => where { Email::Valid->address($_) }
74 => message { "$_ is not a valid email address" };
76 has email_address => (
82 This class subclasses Person to add a single attribute, email address.
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>.
93 use Carp qw( confess );
95 use DateTime::Format::Natural;
100 my %p = ref $_[0] ? %{ $_[0] } : @_;
103 or confess 'name is a required attribute';
104 $class->_validate_name( $p{name} );
106 exists $p{birth_date}
107 or confess 'birth_date is a required attribute';
109 my $date = $p{birth_date};
110 $class->_coerce_birth_date( \$date );
111 $class->_validate_birth_date( $date );
114 unless exists $p{shirt_size}:
116 $class->_validate_shirt_size( $p{shirt_size} );
118 my $self = map { $_ => $p{$_} } qw( name shirt_size );
119 $self->{birth_date} = $date;
121 return bless $self, $class;
128 local $Carp::CarpLevel = $Carp::CarpLevel + 1;
131 or confess 'name must be a string';
135 my $en_parser = DateTime::Format::Natural->new(
140 sub _coerce_birth_date {
144 return unless defined $date && ! ref $date;
146 my $dt = $en_parser->parse_datetime($date);
148 return $dt ? $dt : undef;
152 sub _validate_birth_date {
154 my $birth_date = shift;
156 local $Carp::CarpLevel = $Carp::CarpLevel + 1;
158 $birth_date->isa('DateTime') )
159 or confess 'birth_date must be a DateTime object';
162 sub _validate_shirt_size {
164 my $shirt_size = shift;
166 local $Carp::CarpLevel = $Carp::CarpLevel + 1;
169 or confess 'shirt_size cannot be undef';
171 $shirt_size =~ /^(?:s|m|l|xl|xxl)$/
172 or confess "$shirt_size is not a valid shirt size (s, m, l, xl, xxl)";
179 $self->_validate_name( $_[0] );
180 $self->{name} = $_[0];
183 return $self->{name};
192 $self->_coerce_birth_date( $date );
193 $self->_validate_birth_date( $date );
194 $self->{birth_date} = $date;
197 return $self->{birth_date};
204 $self->_validate_shirt_size( $_[0] );
205 $self->{shirt_size} = $_[0];
208 return $self->{shirt_size};
211 Wow, that was a mouthful! One thing to note is just how much space the
212 data validation code consumes. As a result, it's pretty common for
213 Perl 5 programmers to just not bother, which results in much more
216 Did you spot the bug?
218 It's in the C<_validate_birth_date()> method. We should check that
219 that value in C<$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.
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.
229 Also note that if we add a superclass to Person we'll have to change
230 the constructor to account for that.
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!)
243 use Carp qw( confess );
245 use Scalar::Util qw( blessed );
252 my %p = ref $_[0] ? %{ $_[0] } : @_;
254 exists $p{email_address}
255 or confess 'email_address is a required attribute';
256 $class->_validate_email_address( $p{email_address} );
258 my $self = $class->SUPER::new(%p);
260 $self->{email_address} = $p{email_address};
265 sub _validate_email_address {
267 my $email_address = shift;
269 local $Carp::CarpLevel = $Carp::CarpLevel + 1;
271 defined $email_address
272 or confess 'email_address must be a string';
274 Email::Valid->address($email_address)
275 or confess "$email_address is not a valid email address";
282 $self->_validate_email_address( $_[0] );
283 $self->{email_address} = $_[0];
286 return $self->{email_address};
289 That one was shorter, but it only has one attribute.
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:
300 validate => sub { defined $_ },
304 validate => sub { blessed $_ && $_->isa('DateTime') },
308 validate => sub { defined $_ && $_ =~ /^(?:s|m|l|xl|xxl)$/i },
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!
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
323 Dave Rolsky E<lt>autarch@urth.orgE<gt>
325 =head1 COPYRIGHT AND LICENSE
327 Copyright 2008 by Infinity Interactive, Inc.
329 L<http://www.iinteractive.com>
331 This library is free software; you can redistribute it and/or modify
332 it under the same terms as Perl itself.