Moose

use Moose;Finding Object Oriented Enlightenment

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ShutterstockDeveloper Ethos

Get feedback as early as possible, and work together

Prefer encapsulated, loosely coupled systems for core functionality

Choose the smallest implementation that doesn’t suck provides a way forward

Make your code readable,understandable, maintainable

• Get feedback as early as possible, and work together• Prefer encapsulated, loosely coupled systems for core functionality• Choose the smallest implementation that provides a way forward• Make your code readable, understandable, and maintainable

...the object-oriented approach encourages the programmer to place data where it is not directly accessible by the rest of the program. Instead, the data is accessed by calling specially written functions, commonly called methods...http://en.wikipedia.org/wiki/Object-oriented_programming

A Person Walks and Talks

start_walking stop_walking Person speak($something)

Prefer encapsulated, loosely coupledsystems for core functionalityChoose the smallest implementation thatprovides a way forwardMake your code readable, understandable,and maintainable

Ash Nazg Durbatulûk! Ash Nazg Gimbatul! Ash Nazg Gimbatul! Ash Nazg Gimbatul!

"I will take the Ring to Mordor. Though — Ido not know the way." -- Frodo, LoTR

Moose and Perl

Moose is a postmodern objectsystem for Perl 5 that takes the tedium out of writing object-oriented Perl. Itborrows all the best features from Perl 6, CLOS (Lisp), Smalltalk, Java, BETA, OCaml, Ruby and more, while still keeping true to its Perl 5 roots. http://moose.iinteractive.com/

package Point;use Moose; has x => (isa => Int, is => rw, required => 1);has y => (isa => Int, is => rw, required => 1); sub clear { my $self = shift; $self->x(0); $self->y(0);}

Building Blocks• Inheritance• Roles• Delegation

Inheritance

package Point;use Moose; has x => (isa => Int, is => rw, required => 1);has y => (isa => Int, is => rw, required => 1); sub clear { my $self = shift; $self->x(0); $self->y(0);}package Point3D;use Moose; extends Point; has z => (isa => Int, is => rw, required => 1); after clear => sub { my $self = shift; $self->z(0);};

package Eq;use Moose::Role;requires equal;my $defensive_coderef = sub { ... }; sub no_equal { my ($self, $other) = @_; !$self->equal($other);} package Currency;use Moose;with Eq; sub equal { my ($self, $other) = @_; $self->as_float == $other->as_float;}

Delegation

package MyObject;use Moose;use MyLogger;has ‘logger’ => ( is => ‘bare’, lazy_build => 1, handles => [qw/err warn/],);sub _build_logger { MyLogger->new }sub something_worth_logging { my ($self) = @_; $self->err(“Hey, there’s a problem!!!”);}

package MyObject;use Moose;use MooseX::Types::LoadableClass LoadableClass;has logger_class => ( is => ro, default => MyLogger, isa => LoadableClass, coerce => 1);has logger_args => ( is=>’ro’, isa=>‘HashRef’, default=> sub { +{} });has ‘logger’ => ( is => ‘bare’, lazy_build => 1, handles => [qw/err warn/]);sub _build_logger { my $self = shift; $self->logger_class($self->logger_args) ->new}

package MyObject;use Moose; with MooseX::Role::BuildInstanceOf => { target => Logger};has ‘+logger’ => (handles => [qw/err warn/]);

Examples

Test::DBIx::Class• Automatically deploy temporary databases based on exist DBIx::Class schema• Pluggable database targets (Sqlite, MySQL, PostgreSQL)

Approach• Create a Base Class with default functionality• Use Roles to allow ‘plugging in’ various target temporary database types

DBIx::Class::Migration• Make it easy to create deploys and upgrades for database schemas• Be ﬂexible but have sane, community accepted standards

Approach• Create a Base class with lots of delegate placeholders.• Create defaults classes that provide required functionality

GeneralAssembly::Guestbook • A Test Application to Demonstrate Perl to inspired learners • Code is probably overkill for the actual problem

My Learnings• Delegation seems the most normally useful approach to creating easily testable building blocks.• Roles are great for enforcing contracts and for enhancing objects with cross cutting functionality.• (Combine the two)++

Summary• There is no necessary tension between writing the least code and writing good code• Good design lets you evolve over time without nasty hacks

Moose

by John Napiorkowski

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