Moose:A Postmodern Object System

for Perl

Stuart Skelton

2

What is OOP?

“Traditional” programming is procedural Subroutines work on variables my $distance = distance($point1,$point2); Variables are dumb Just stores for data

3

What is OOP?

Object Oriented programming inverts this Variables are objects Objects can carry out certain processes

Called methods my $distance = $point1->distance($point2);

Objects are intelligent Objects know what methods they can carry

out

4

Some Concepts

A Class is a type of intelligent variable (blueprint of an object) e.g. Dog

An Object is an instance of a class e.g. Amber

An Attribute is a piece of data in an object e.g. KennelClubName

A Method is an action that an object does e.g. Bark

5

Methods

Methods can be either class methods or object methods

Class methods are called on a class my $amber = Dog->new;

Object methods are called on an object $amber->bark;

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Constructors

All classes need a constructor method Creates a new object of that class Usually a class method Often called new my $amber = Dog->new; my $hunter = new Dog;

7

Accessors & Mutators

Access object attributes with an accessor method

say “The kennel club name of Amber is “,$amber->get_kennel_club_name;

Change an attribute with a mutator method $amber->set_age( $amber->get_age + 1);

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Accessor & Mutators

Accessors and mutators are often the same method

say “The kennel club name of Amber is “, $amber->kennel_club_name;

$amber->age($amber->age + 1);

Checks number of parameters Reacts appropriately

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Traditional Perl OOP

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Basic Anatomy

Package Classname;

atribute1

attribute2

method1

method2

1;

package PointTP;

sub new{ my $class = shift; my $self = { x => shift, y => shift, }; bless $self, $class; return $self;}

sub set_x { my ( $self, $x ) = @_; $self->{x} = $x if defined($x);}sub get_x { my( $self ) = @_; return $self->{x};}sub set_y { my ( $self, $y ) = @_; $self->{y} = $y if defined($y);}sub get_y { my( $self ) = @_; return $self->{y};}

#!/usr/bin/perl

use Modern::Perl ;

use PointTP ;

my $point1 = Point->new(1,2) ;

say $point1->get_x() ; # prints 1

#change the x-coord

$point1->set_x(-10);

say $point1->get_x() ; # prints -10

sub set_x {

my ( $self, $x ) = @_;

$self->{x} = $x if defined($x);

}

sub get_x {

my( $self ) = @_;

return $self->{x};

} sub x { my ($self, $new_x) = @_;

if (defined $new_x) { $self->{x} = $new_x; }

return $self->{x};}

#!/usr/bin/perl

use Modern::Perl ;

use Point ;

my $point1 = Point->new(1,2) ;

say $point1->x() ; # prints 1

#change the x-coord

$point1->x(-10);

say $point1->x() ; # prints -10

Moose

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Moose

Moose is a Modern Object System for Perl 5 Based on Perl 6 object system More powerful More flexible Easier

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Simple Moose Classpackage Point;use Moose;

has x => ( is => 'rw', isa => 'Num', required => 1);has y => ( is => 'rw', isa => 'Num', required => 1);

no Moose;__PACKAGE__->meta->make_immutable;

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What's Going On?

use Moose; Loads Moose environment Makes our class a subclass of Moose::Object Turns on use strict and use warnings

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Declarative Attributes

has x => ( is => 'rw', isa => 'Num', required => 1); Creates an attribute called 'x' Makes it read/write Must be a number Is required

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Housekeeping

Moose classes carry a lot of baggage We can (and should) turn some of it off no Moose;

Remove Moose exports from your namespace See also namespace::autoclean

__PACKAGE__->meta->make_immutable;

No more changes to class definition Performance improvements

Required Attributes

By default Moose attributes are optional Make them mandatory with required has x => (

... required => 1,); my $point1 = Point->new;

“Attribute (x) is required at constructor Point::new”

Attribute Defaults

Set a default for missing attributes has accuracy => ( default => 0.5,);

Or a subroutine reference has accuracy => ( default => sub { rand },);

Attribute Builder

Define a builder method instead of a default subroutine

has accuracy => ( builder => '_build_accuracy',);

sub _build_accuracy { return rand;}

Easier to subclass

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Read/Write Attributes

Moose creates methods to access/alter attributes

$point1->x(-1);say $point1->x;

The 'is' property controls how they work 'rw' : read and write 'ro' : read only

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Read/Write Attributes

But PBP says use get_* and set_*

has x => ( .... , reader => get_x, Writer => set_x,);

use MooseX::FollowPBP;

Rule of Thumb, pick a style and stick with it

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Other Methods

Not all methods are constructors or accessors/mutators

Write other methods as usual First parameter is object reference

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Other Methods

package Point;

...

sub distance

{

my $self = shift ;

my $newpoint = shift ;

return unless $newpoint->isa('Point') ;

return sqrt(

($self->x - $newpoint->x)**2

+

($self->y - $newpoint->y)**2

) ;

}

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Using the Point

#!/usr/bin/perl

use Modern::Perl ;

use Point ;

my $point1 = Point->new(x=>-7,y=>-4) ;

my $point2 = Point->new(x=>17,y=>6) ;

say join ' ' , 'The Distance between point 1',

$point1->toString ,

'and point 2',

$point2->toString,

'is' , $point1->distance($point2) ;

# prints 'The Distance between point 1 (-7,-4) and point 2 (17,6) is 26'

Sub Classing

A subclass is a specialisation of a superclass More specific behaviour New attributes New methods Overriding superclass methods and attributes

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package Point3D;use Moose;extends 'Point' ;

has z => ( is => 'rw', isa => 'Num', required => 1 );

override distance => sub { my $self = shift; my $newpoint = shift; return unless $newpoint->isa('Point3D') ; my $distance2d = super(); return sqrt( $distance2d**2 + ($self->z - $newpoint->z)**2 ) ;};

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use Modern::Perl ;use Point3D ;

my $point1 = Point3D->new(x=>-7,y=>-4,z=>3);my $point2 = Point3D->new(x=>17,y=>6,z=>2.5);

say join ' ' , 'The Distance between point 1', $point1->toString , 'and point 2', $point2->toString, 'is' , $point1->distance($point2) ;# prints 'The Distance between point 1 (-7,-4,3) and point 2 (17,6,2.5) is 26.0048072478917'

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Other Atrribute types

any Item Bool Maybe[`a] Undef Defined Value Str Num Int ClassName RoleName

Ref ScalarRef[`a] ArrayRef[`a] HashRef[`a] CodeRef RegexpRef GlobRef FileHandle Object

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package Farm; use Moose;

has 'animals' => ( traits => ['Array'], is => 'ro', isa => 'ArrayRef[Animal]', default => sub { [] }, handles => { all_animals => 'elements', add_animal => 'push', find_animal => 'first', get_animal => 'get', count_animals => 'count', has_animals => 'count', has_no_animals => 'is_empty', sorted_animals => 'sort', }, );

no Moose; 1;

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package Galaxy; use Moose;

has 'planets' => ( traits => ['Hash'], is => 'ro', isa => 'HashRef[Planets]', default => sub { {} }, handles => { set_planets => 'set', get_planets => 'get', has_no_planets => 'is_empty', num_planets => 'count', delete_planets => 'delete', }, );

no Moose; 1;

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Further Information

Moose does a lot more We have only scratched the surface Good documentation

CPAN Moose::Manual::* Moose::Cookbook::*

No good book yet