Rename Basics::Recipe3 to Basics::BinaryTree_AttributeFeatures

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

package Moose::Cookbook::Basics::Recipe4;

# ABSTRACT: Subtypes, and modeling a simple B<Company> class hierarchy

__END__


=pod

=begin testing-SETUP

use Test::Requires {
    'Locale::US'     => '0',
    'Regexp::Common' => '0',
};

=end testing-SETUP

=head1 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;
  };

=head1 DESCRIPTION

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

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

Finally, we introduce the C<required> attribute option.

In the C<Address> class we define two subtypes. The first uses the
L<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 C<USState> type
a subtype of Moose's builtin C<Str> type. This is done using the C<as>
sugar. The actual constraint is defined using C<where>. This function
accepts a single subroutine reference. That subroutine will be called
with the value to be checked in C<$_> (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 C<USState> type just like Moose's builtin types:

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

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

The next C<subtype>, C<USZipCode>, uses
L<Regexp::Common>. L<Regexp::Common> includes a regex for validating
US zip codes. We use this constraint for the C<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 C<MyApp::Type::USState> (just as you would do with class names).

These two subtypes allow us to define a simple C<Address> class.

Then we define our C<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 C<Company> class's
C<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, C<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
C<required> attribute can still be false or C<undef>, if its type
constraint allows that.

The next attribute, C<employees>, uses a I<parameterized> type
constraint:

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

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

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

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

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

To do that, we need to hook into object construction. Moose lets us do
this by writing a C<BUILD> method in our class. When your class
defines a C<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 C<BUILD> methods in your class hierarchy
will be called automatically; there is no need to (and you should not)
call the superclass C<BUILD> method.

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

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

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

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

To do this we can use an C<after> modifier:

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

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

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

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

The only new feature in the C<Employee> class is the C<override>
method modifier:

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

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

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

=head1 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 C<subtype> function, the C<required>
attribute, and the C<override> method modifier.

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

=head1 FOOTNOTES

=over 4

=item (1)

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

=item (2)

Note that C<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.

=back

=begin testing

{
    package Company;

    sub get_employee_count { scalar @{(shift)->employees} }
}

use Scalar::Util 'isweak';

my $ii;
is(
    exception {
        $ii = Company->new(
            {
                name    => 'Infinity Interactive',
                address => Address->new(
                    street   => '565 Plandome Rd., Suite 307',
                    city     => 'Manhasset',
                    state    => 'NY',
                    zip_code => '11030'
                ),
                employees => [
                    Employee->new(
                        first_name => 'Jeremy',
                        last_name  => 'Shao',
                        title      => 'President / Senior Consultant',
                        address    => Address->new(
                            city => 'Manhasset', state => 'NY'
                        )
                    ),
                    Employee->new(
                        first_name => 'Tommy',
                        last_name  => 'Lee',
                        title      => 'Vice President / Senior Developer',
                        address =>
                            Address->new( city => 'New York', state => 'NY' )
                    ),
                    Employee->new(
                        first_name     => 'Stevan',
                        middle_initial => 'C',
                        last_name      => 'Little',
                        title          => 'Senior Developer',
                        address =>
                            Address->new( city => 'Madison', state => 'CT' )
                    ),
                ]
            }
        );
    },
    undef,
    '... created the entire company successfully'
);

isa_ok( $ii, 'Company' );

is( $ii->name, 'Infinity Interactive',
    '... got the right name for the company' );

isa_ok( $ii->address, 'Address' );
is( $ii->address->street, '565 Plandome Rd., Suite 307',
    '... got the right street address' );
is( $ii->address->city,     'Manhasset', '... got the right city' );
is( $ii->address->state,    'NY',        '... got the right state' );
is( $ii->address->zip_code, 11030,       '... got the zip code' );

is( $ii->get_employee_count, 3, '... got the right employee count' );

# employee #1

isa_ok( $ii->employees->[0], 'Employee' );
isa_ok( $ii->employees->[0], 'Person' );

is( $ii->employees->[0]->first_name, 'Jeremy',
    '... got the right first name' );
is( $ii->employees->[0]->last_name, 'Shao', '... got the right last name' );
ok( !$ii->employees->[0]->has_middle_initial, '... no middle initial' );
is( $ii->employees->[0]->middle_initial, undef,
    '... got the right middle initial value' );
is( $ii->employees->[0]->full_name,
    'Jeremy Shao, President / Senior Consultant',
    '... got the right full name' );
is( $ii->employees->[0]->title, 'President / Senior Consultant',
    '... got the right title' );
is( $ii->employees->[0]->employer, $ii, '... got the right company' );
ok( isweak( $ii->employees->[0]->{employer} ),
    '... the company is a weak-ref' );

isa_ok( $ii->employees->[0]->address, 'Address' );
is( $ii->employees->[0]->address->city, 'Manhasset',
    '... got the right city' );
is( $ii->employees->[0]->address->state, 'NY', '... got the right state' );

# employee #2

isa_ok( $ii->employees->[1], 'Employee' );
isa_ok( $ii->employees->[1], 'Person' );

is( $ii->employees->[1]->first_name, 'Tommy',
    '... got the right first name' );
is( $ii->employees->[1]->last_name, 'Lee', '... got the right last name' );
ok( !$ii->employees->[1]->has_middle_initial, '... no middle initial' );
is( $ii->employees->[1]->middle_initial, undef,
    '... got the right middle initial value' );
is( $ii->employees->[1]->full_name,
    'Tommy Lee, Vice President / Senior Developer',
    '... got the right full name' );
is( $ii->employees->[1]->title, 'Vice President / Senior Developer',
    '... got the right title' );
is( $ii->employees->[1]->employer, $ii, '... got the right company' );
ok( isweak( $ii->employees->[1]->{employer} ),
    '... the company is a weak-ref' );

isa_ok( $ii->employees->[1]->address, 'Address' );
is( $ii->employees->[1]->address->city, 'New York',
    '... got the right city' );
is( $ii->employees->[1]->address->state, 'NY', '... got the right state' );

# employee #3

isa_ok( $ii->employees->[2], 'Employee' );
isa_ok( $ii->employees->[2], 'Person' );

is( $ii->employees->[2]->first_name, 'Stevan',
    '... got the right first name' );
is( $ii->employees->[2]->last_name, 'Little', '... got the right last name' );
ok( $ii->employees->[2]->has_middle_initial, '... got middle initial' );
is( $ii->employees->[2]->middle_initial, 'C',
    '... got the right middle initial value' );
is( $ii->employees->[2]->full_name, 'Stevan C. Little, Senior Developer',
    '... got the right full name' );
is( $ii->employees->[2]->title, 'Senior Developer',
    '... got the right title' );
is( $ii->employees->[2]->employer, $ii, '... got the right company' );
ok( isweak( $ii->employees->[2]->{employer} ),
    '... the company is a weak-ref' );

isa_ok( $ii->employees->[2]->address, 'Address' );
is( $ii->employees->[2]->address->city, 'Madison', '... got the right city' );
is( $ii->employees->[2]->address->state, 'CT', '... got the right state' );

# create new company

my $new_company
    = Company->new( name => 'Infinity Interactive International' );
isa_ok( $new_company, 'Company' );

my $ii_employees = $ii->employees;
foreach my $employee (@$ii_employees) {
    is( $employee->employer, $ii, '... has the ii company' );
}

$new_company->employees($ii_employees);

foreach my $employee ( @{ $new_company->employees } ) {
    is( $employee->employer, $new_company,
        '... has the different company now' );
}

## check some error conditions for the subtypes

isnt(
    exception {
        Address->new( street => {} ),;
    },
    undef,
    '... we die correctly with bad args'
);

isnt(
    exception {
        Address->new( city => {} ),;
    },
    undef,
    '... we die correctly with bad args'
);

isnt(
    exception {
        Address->new( state => 'British Columbia' ),;
    },
    undef,
    '... we die correctly with bad args'
);

is(
    exception {
        Address->new( state => 'Connecticut' ),;
    },
    undef,
    '... we live correctly with good args'
);

isnt(
    exception {
        Address->new( zip_code => 'AF5J6$' ),;
    },
    undef,
    '... we die correctly with bad args'
);

is(
    exception {
        Address->new( zip_code => '06443' ),;
    },
    undef,
    '... we live correctly with good args'
);

isnt(
    exception {
        Company->new(),;
    },
    undef,
    '... we die correctly without good args'
);

is(
    exception {
        Company->new( name => 'Foo' ),;
    },
    undef,
    '... we live correctly without good args'
);

isnt(
    exception {
        Company->new( name => 'Foo', employees => [ Person->new ] ),;
    },
    undef,
    '... we die correctly with good args'
);

is(
    exception {
        Company->new( name => 'Foo', employees => [] ),;
    },
    undef,
    '... we live correctly with good args'
);

=end testing

=cut