cleanup

[gitmo/Moose.git] / lib / Moose / Cookbook / Recipe4.pod

=pod

=head1 NAME

Moose::Cookbook::Recipe4

=head1 SYNOPSIS
  
  package Address;
  use strict;
  use warnings;
  use Moose;
  
  use Locale::US;
  use Regexp::Common 'zip';
  
  my $STATES = Locale::US->new;
  
  subtype USState 
      => as Str
      => where {
          (exists $STATES->{code2state}{uc($_)} || 
           exists $STATES->{state2code}{uc($_)})
      };
      
  subtype USZipCode 
      => as Value
      => where {
          /^$RE{zip}{US}{-extended => 'allow'}$/            
      };
  
  has 'street'   => (is => 'rw', isa => 'Str');
  has 'city'     => (is => 'rw', isa => 'Str');
  has 'state'    => (is => 'rw', isa => 'USState');
  has 'zip_code' => (is => 'rw', isa => 'USZipCode');   
  
  package Company;
  use strict;
  use warnings;
  use Moose;
  
  has 'name'      => (is => 'rw', isa => 'Str', required => 1);
  has 'address'   => (is => 'rw', isa => 'Address'); 
  has 'employees' => (is => 'rw', isa => subtype ArrayRef => where { 
      ($_->isa('Employee') || return) for @$_; 1 
  });    
  
  sub BUILD {
      my ($self, $params) = @_;
      if ($params->{employees}) {
          foreach my $employee (@{$params->{employees}}) {
              $employee->company($self);
          }
      }
  }
  
  sub get_employee_count { scalar @{(shift)->employees} }
  
  package Person;
  use strict;
  use warnings;
  use Moose;
  
  has 'first_name'     => (is => 'rw', isa => 'Str', required => 1);
  has 'last_name'      => (is => 'rw', isa => 'Str', required => 1);       
  has 'middle_initial' => (is => 'rw', isa => 'Str', 
                           predicate => 'has_middle_initial');  
  has 'address'        => (is => 'rw', isa => 'Address');
  
  sub full_name {
      my $self = shift;
      return $self->first_name . 
            ($self->has_middle_initial ? 
                ' ' . $self->middle_initial . '. ' 
                : 
                ' ') .
             $self->last_name;
  }
    
  package Employee;
  use strict;
  use warnings;
  use Moose;  
  
  extends 'Person';
  
  has 'title'   => (is => 'rw', isa => 'Str', required => 1);
  has 'company' => (is => 'rw', isa => 'Company', weak_ref => 1);  
  
  override 'full_name' => sub {
      my $self = shift;
      super() . ', ' . $self->title
  };
    
=head1 DESCRIPTION

In this recipe we introduce the C<subtype> keyword, and show 
how that can be useful for specifying specific type constraints 
without having to build an entire class to represent them. We 
will also show how this feature can be used to leverage the 
usefulness of CPAN modules. In addition to this, we will also 
introduce another attribute option as well.

Lets first get into the C<subtype> features. In the B<Address> 
class we have defined two subtypes. The first C<subtype> uses 
the L<Locale::US> module, which provides two hashes which can be 
used to do existence checks for state names and their two letter 
state codes. It is a very simple, and very useful module, and 
perfect to use in a C<subtype> constraint. 
  
  my $STATES = Locale::US->new;  
  subtype USState 
      => as Str
      => where {
          (exists $STATES->{code2state}{uc($_)} || 
           exists $STATES->{state2code}{uc($_)})
      };

Because we know that states will be passed to us as strings, we 
can make C<USState> a subtype of the built-in type constraint 
C<Str>. This will assure that anything which is a C<USState> will 
also pass as a C<Str>. Next, we create a constraint specializer 
using the C<where> keyword. The value being checked against in 
the C<where> clause can be found in the C<$_> variable (1). Our 
constraint specializer will then look to see if the string given 
is either a state name or a state code. If the string meets this 
criteria, then the constraint will pass, otherwise it will fail.
We can now use this as we would any built-in constraint, like so:

  has 'state' => (is => 'rw', isa => 'USState');

The C<state> accessor will now check all values against the 
C<USState> constraint, thereby only allowing valid state names or 
state codes to be stored in the C<state> slot. 

The next C<subtype>, does pretty much the same thing using the 
L<Regexp::Common> module, and constrainting the C<zip_code> slot.

  subtype USZipCode 
      => as Value
      => where {
          /^$RE{zip}{US}{-extended => 'allow'}$/            
      };

Using subtypes can save a lot of un-needed abstraction by not 
requiring you to create many small classes for these relatively 
simple values. It also allows you to define these constraints 
and share them among many different classes (avoiding unneeded 
duplication) because type constraints are stored by string in a 
global registry and always accessible to C<has>.

With these two subtypes and some attributes, we pretty much define 
as much as we need for a basic B<Address> class. Next we define 
a basic B<Company> class, which itself has an address. As we saw in 
earlier recipes, we can use the C<Address> type constraint that 
Moose automatically created for us.

  has 'address' => (is => 'rw', isa => 'Address');

A company also needs a name, so we define that too.

  has 'name' => (is => 'rw', isa => 'Str', required => 1);

Here we introduce another attribute option, the C<required> option. 
This option tells Moose that C<name> is a required parameter in 
the B<Company> constructor, and that the C<name> accessor cannot 
accept an undefined value for the slot. The result is that C<name> 
should always have a value. 

=head1 FOOTNOTES

=over 4

=item (1)

The value being checked is also passed as the first argument to 
the C<where> block as well, so it can also be accessed as C<$_[0]> 
as well.

=back

=head1 AUTHOR

Stevan Little E<lt>stevan@iinteractive.comE<gt>

=head1 COPYRIGHT AND LICENSE

Copyright 2006 by Infinity Interactive, Inc.

L<http://www.iinteractive.com>

This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.

=cut