Moose Design Patterns

Moose Design Patterns

Ynon [email protected]://ynonperek.com

Tuesday, February 28, 2012

mailto:[email protected]


http://ynonperek.com


Good Code Bad Code


OOP Use Cases

• Write code that other developers will use

• Write code that will survive in an ever changing environment


Meet The Moose


Moose

• Post Modern Object Oriented Perl

• Consistent OO Framework

• Stable


A First Class

package Person;use Moose;

has 'name', is => 'ro', isa => 'Str';has 'age', is => 'rw', isa => 'Int';

package main;use feature ':5.10';

my $p = Person->new(name => "James");say $p->name;

Class Def

Class Use

• A class is just a package

• A method is just a sub

• An attribute is ...We’ll get to that later


Object Methods

• A method takes the object (invocant) as its first argument

• That’s why we usemy $self = shift

package Car;use Moose;

has 'speed', is => 'ro';

sub go { my $self = shift; print "Vroom Vroom [speed: ", $self->speed, "]\n";}

package main;my $c = Car->new(speed => 10);$c->go;


Whats In The Box

• A new method

• use strict, use warnings

• Type Validation

• Organize Your Code


OO Design


OO Design Patterns

Tested, Proven development paradigms for speeding up

development process


Pattern Structure

• Name

• Problem

• Solution

• Consequences


Categories

Creational Behavioral Structural

Singleton

Factory

Builder

Observer

Template Method

Mixins

Composite

Flyweight


Creational Patterns

• Abstract instantiation process

• We must only create one log file instance for the entire system

• An XML tree is built gradually, node-by-node


Singleton Pattern

• Ensure a class only has one instance

• Manage Resource Sharing


Moose Singletonpackage Logger;use MooseX::Singleton;

sub debug { ... }sub warn { ... }

package main;

my $logger = Logger->instance;my $same = Logger->instance;

my $and_again = Logger->new;

$logger->debug("Hello World");


Factory

• Create a different object based on some conditional

• Treat the newly created objects the same way

• Practical: abstract away OS related code


Factory

• Use a Role to specify common behavior

package AppConfig;use Moose::Role;

requires 'debug_mode';requires 'native_separators';requires 'root_fs';


Factory

• All creation logic stays in the factory

package ConfigFactory;use Moose;

sub build_config { my $cfg; given ($^O) { $cfg = WinConfig->new when /MSWin32/; $cfg = UnixConfig->new; } return $cfg;}


Factory

• Users only need to know about the role, not the various implementations

package main;

my $cfg = ConfigFactory->build_config;

say $cfg->debug_mode;


Creational Patterns


Behavioral Patterns

• Assignment of responsibility between objects and classes

• Use either inheritance or composition


Template Methods


Template Method

• Separate the algorithm from the actual implementation

• Define the skeleton of an algorithm

• Example: Paint on a canvas or printer


Painter Example

Draw Pixel


Roles: Partials

• Template methods are implemented using roles

• Use requires to define a partial implementation

package Painter;use Moose::Role;

requires 'drawPixel';

sub draw_line { ... }sub draw_triangle { ... }sub draw_rectangle { ... }


Roles: Partialspackage ScreenPainter;use Moose;

with 'Painter';

sub draw_pixel { ... }

package main;my $painter = ScreenPainter->new;

$painter->draw_line(0, 0, 100, 100);


Behavioral Patterns


Structural

• Control structure of an object

• Is it composed of other objects ?

• How are these parts used ?

• Composition, Decorator, Adapter


Composition: What

Contact EmailSend Mail Send Mail

Phone

CallCall


Moose Composition

• Moose has a built-in support for delegation

• Use handles on an attribute to create an effective composition

• Prefer composition over inheritance


Delegation: Howpackage Contact;use Moose;

has 'email' => ( is => 'ro', handles => [ qw/send_mail/ ]);

• Can take regular expressions

• Can take hashref

• perldoc Moose::Manual::Delegation my $c = Contact->new;

$c->send_mail(subject => "Hello", text => "...");


Delegation

• Delegation is explicit

• Performed via attributes

• Highly recommended


OO DesignConsider design patterns

Use the power of perl

Clean Code is worth it


Ynon [email protected]://ynonperek.com

Thanks For Listening






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Moose Design Patterns

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