NAME
Moose::Cookbook::Basics::Company_Subtypes - Demonstrates the use of subtypes and how to model classes related to companies, people, employees, etc.
VERSION
version 2.2207
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 or 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() . ', ' . $self->title;
};
This is just a sugary alternative to Perl's built in SUPER::
feature. However, there is one difference. You cannot pass any arguments to super
. Instead, Moose simply passes the same parameters that were passed to the method.
A more detailed example of usage can be found in t/recipes/basics_company_subtypes.t.
CONCLUSION
This recipe was intentionally longer and more complex. It illustrates how Moose classes can be used together with type constraints, as well as the density of information that you can get out of a small amount of typing when using Moose.
This recipe also introduced the subtype
function, the required
attribute, and the override
method modifier.
We will revisit type constraints in future recipes, and cover type coercion as well.
FOOTNOTES
- (1)
-
The value being checked is also passed as the first argument to the
where
block, so it can be accessed as$_[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.
AUTHORS
Stevan Little <stevan@cpan.org>
Dave Rolsky <autarch@urth.org>
Jesse Luehrs <doy@cpan.org>
Shawn M Moore <sartak@cpan.org>
יובל קוג'מן (Yuval Kogman) <nothingmuch@woobling.org>
Karen Etheridge <ether@cpan.org>
Florian Ragwitz <rafl@debian.org>
Hans Dieter Pearcey <hdp@cpan.org>
Chris Prather <chris@prather.org>
Matt S Trout <mstrout@cpan.org>
COPYRIGHT AND LICENSE
This software is copyright (c) 2006 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.