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Moose::Cookbook::BasicUseroContribMoose::Cookbook::Basics::Company_Subtypes(3)

NAME
       Moose::Cookbook::Basics::Company_Subtypes - Demonstrates the use of
       subtypes and how to model classes related to companies, people,
       employees, etc.

VERSION
       version 2.1005

SYNOPSIS
	 package Address;
	 use Moose;
	 use Moose::Util::TypeConstraints;

	 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 Moose;
	 use Moose::Util::TypeConstraints;

	 has 'name' => ( is => 'rw', isa => 'Str', required => 1 );
	 has 'address'	 => ( is => 'rw', isa => 'Address' );
	 has 'employees' => (
	     is	     => 'rw',
	     isa     => 'ArrayRef[Employee]',
	     default => sub { [] },
	 );

	 sub BUILD {
	     my ( $self, $params ) = @_;
	     foreach my $employee ( @{ $self->employees } ) {
		 $employee->employer($self);
	     }
	 }

	 after 'employees' => sub {
	     my ( $self, $employees ) = @_;
	     return unless $employees;
	     foreach my $employee ( @$employees ) {
		 $employee->employer($self);
	     }
	 };

	 package Person;
	 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 Moose;

	 extends 'Person';

	 has 'title'	=> ( is => 'rw', isa => 'Str',	   required => 1 );
	 has 'employer' => ( is => 'rw', isa => 'Company', weak_ref => 1 );

	 override 'full_name' => sub {
	     my $self = shift;
	     super() . ', ' . $self->title;
	 };

DESCRIPTION
       This recipe introduces the "subtype" sugar function from
       Moose::Util::TypeConstraints. The "subtype" function lets you
       declaratively create type constraints without building an entire class.

       In the recipe we also make use of Locale::US and Regexp::Common to
       build constraints, showing how constraints can make use of existing
       CPAN tools for data validation.

       Finally, we introduce the "required" attribute option.

       In the "Address" class we define two subtypes. The first uses the
       Locale::US module to check the validity of a state. It accepts either a
       state abbreviation of full name.

       A state will be passed in as a string, so we make our "USState" type a
       subtype of Moose's builtin "Str" type. This is done using the "as"
       sugar. The actual constraint is defined using "where". This function
       accepts a single subroutine reference. That subroutine will be called
       with the value to be checked in $_ (1). It is expected to return a true
       or false value indicating whether the value is valid for the type.

       We can now use the "USState" type just like Moose's builtin types:

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

       When the "state" attribute is set, the value is checked against the
       "USState" constraint. If the value is not valid, an exception will be
       thrown.

       The next "subtype", "USZipCode", uses Regexp::Common. Regexp::Common
       includes a regex for validating US zip codes. We use this constraint
       for the "zip_code" attribute.

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

       Using a subtype instead of requiring a class for each type greatly
       simplifies the code. We don't really need a class for these types, as
       they're just strings, but we do want to ensure that they're valid.

       The type constraints we created are reusable. Type constraints are
       stored by name in a global registry, which means that we can refer to
       them in other classes. Because the registry is global, we do recommend
       that you use some sort of namespacing in real applications, like
       "MyApp::Type::USState" (just as you would do with class names).

       These two subtypes allow us to define a simple "Address" class.

       Then we define our "Company" class, which has an address. As we saw in
       earlier recipes, Moose automatically creates a type constraint for each
       our classes, so we can use that for the "Company" class's "address"
       attribute:

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

       A company also needs a name:

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

       This introduces a new attribute option, "required". If an attribute is
       required, then it must be passed to the class's constructor, or an
       exception will be thrown. It's important to understand that a
       "required" attribute can still be false or "undef", if its type
       constraint allows that.

       The next attribute, "employees", uses a parameterized type constraint:

	 has 'employees' => (
	     is	     => 'rw',
	     isa     => 'ArrayRef[Employee]'
	     default => sub { [] },
	 );

       This constraint says that "employees" must be an array reference where
       each element of the array is an "Employee" object. It's worth noting
       that an empty array reference also satisfies this constraint, such as
       the value given as the default here.

       Parameterizable type constraints (or "container types"), such as
       "ArrayRef[`a]", can be made more specific with a type parameter. In
       fact, we can arbitrarily nest these types, producing something like
       "HashRef[ArrayRef[Int]]". However, you can also just use the type by
       itself, so "ArrayRef" is legal. (2)

       If you jump down to the definition of the "Employee" class, you will
       see that it has an "employer" attribute.

       When we set the "employees" for a "Company" we want to make sure that
       each of these employee objects refers back to the right "Company" in
       its "employer" attribute.

       To do that, we need to hook into object construction. Moose lets us do
       this by writing a "BUILD" method in our class. When your class defines
       a "BUILD" method, it will be called by the constructor immediately
       after object construction, but before the object is returned to the
       caller. Note that all "BUILD" methods in your class hierarchy will be
       called automatically; there is no need to (and you should not) call the
       superclass "BUILD" method.

       The "Company" class uses the "BUILD" method to ensure that each
       employee of a company has the proper "Company" object in its "employer"
       attribute:

	 sub BUILD {
	     my ( $self, $params ) = @_;
	     foreach my $employee ( @{ $self->employees } ) {
		 $employee->employer($self);
	     }
	 }

       The "BUILD" method is executed after type constraints are checked, so
       it is safe to assume that if "$self->employees" has a value, it will be
       an array reference, and that the elements of that array reference will
       be "Employee" objects.

       We also want to make sure that whenever the "employees" attribute for a
       "Company" is changed, we also update the "employer" for each employee.

       To do this we can use an "after" modifier:

	 after 'employees' => sub {
	     my ( $self, $employees ) = @_;
	     return unless $employees;
	     foreach my $employee ( @$employees ) {
		 $employee->employer($self);
	     }
	 };

       Again, as with the "BUILD" method, we know that the type constraint
       check has already happened, so we know that if $employees is defined it
       will contain an array reference of "Employee" objects.

       Note that "employees" is a read/write accessor, so we must return early
       if it's called as a reader.

       The Person class does not really demonstrate anything new. It has
       several "required" attributes. It also has a "predicate" method, which
       we first used in Moose::Cookbook::Basics::BinaryTree_AttributeFeatures.

       The only new feature in the "Employee" class is the "override" method
       modifier:

	 override 'full_name' => sub {
	     my $self = shift;
	     super() . ', ' . $self->title;
	 };

       This is just a sugary alternative to Perl's built in "SUPER::" feature.
       However, there is one difference. You cannot pass any arguments to
       "super". Instead, Moose simply passes the same parameters that were
       passed to the method.

       A more detailed example of usage can be found in
       t/recipes/moose_cookbook_basics_recipe4.t.

CONCLUSION
       This recipe was intentionally longer and more complex. It illustrates
       how Moose classes can be used together with type constraints, as well
       as the density of information that you can get out of a small amount of
       typing when using Moose.

       This recipe also introduced the "subtype" function, the "required"
       attribute, and the "override" method modifier.

       We will revisit type constraints in future recipes, and cover type
       coercion as well.

FOOTNOTES
       (1) The value being checked is also passed as the first argument to the
	   "where" block, so it can be accessed as $_[0].

       (2) Note that "ArrayRef[]" will not work. Moose will not parse this as
	   a container type, and instead you will have a new type named
	   "ArrayRef[]", which doesn't make any sense.

AUTHOR
       Moose is maintained by the Moose Cabal, along with the help of many
       contributors. See "CABAL" in Moose and "CONTRIBUTORS" in Moose for
       details.

COPYRIGHT AND LICENSE
       This software is copyright (c) 2013 by Infinity Interactive, Inc..

       This is free software; you can redistribute it and/or modify it under
       the same terms as the Perl 5 programming language system itself.

perl v5.18.1			  Moose::Cookbook::Basics::Company_Subtypes(3)
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