Intro To Moose

Introduction to Object Oriented Programming in Perl with Moose.

Introduction to Object
Oriented Programming
with Moose

What is an Object?

• Holds information about it’s self
• Does stuff (functions)
• deﬁned by a class (not an object)

OO in Perl?

• DateTime
• WWW::Mechanize
• DBI
• IO::Handle

Often created with
new

• my $mech = WWW::Mechanize->new
• my $dt = DateTime->new(year => 2000,
month => ...);

But not always

• my $dt = DateTime->now(time_zone =>
‘America/Chicago’);

Holds information

• my $mech = WWW::Mechanize->new
• $mech->get($url)
• my $content = $mech->content()

Not an object.

• use Cwd;
• my $dir = getcwd();

Some times globals point the need for an
object
#!/usr/bin/env perl
use strict;
use warnings;
use WWW::Mechanize;

my $base = ‘http://www.google.com/search?q=’;
my $mech = $mech->new;

print query(“perl”)
print query(“moose”)

sub query {
my $query = shift;
$mech->get($url . $query);
return $mech->content;
}

Becomes....
package SearchEngine;
use Moose;
use WWW::Mechanize;

has ‘url_base’ => (isa => Str, is => ‘rw’,
default => ‘http://www.google.com/search?q=’);
has ‘mech’ => (isa => Object, is => ‘ro’,
default => sub {WWW::Mechanize->new});

sub query {
my $self = shift;
my $query = shift;

$self->mech->get($self->url_base . $query);
return $self->mech->content;
}
1;

Now I can query away

use SearchEngine;

my $google = SearchEngine->new;
my $alta = SearchEngine->new(url_base =>
‘http://www.altavista.com/web/results?q=’);

print $google->query(‘perl’);
print $alta->query(‘perl’);

print $google->query(‘Moose’);
print $alta->query(‘Moose’);

Change engines after new

use SearchEngine;

my $search = SearchEngine->new; # defaults to google
$search->url_base(‘http://www.altavista.com/web/results?q=’);

print $search->query(‘perl’);

Moose out of the box

• Type constraints ( )
http://tinyurl.com/moose-types

• use strict;
• use warnings
• don’t have to deﬁne new
• Delegation

Delegation
use Moose;
use WWW::Mechanize;

default => sub {WWW::Mechanize->new},
handles => { ‘content’ => ‘content’ }
handles => { ‘get’ => ‘get’ } );

sub query {
my $self = shift;
my $query = shift;

#$self->mech->get($self->url_base . $query);
$self->get($self->url_base . $query);

#return $self->mech->content;
return $self->content;
}
1;

Why Moose?

• See slide 25 - Intro to Moose

Why Moose
• Moose means less code

• (less code == less bugs)

• Less tests

• (why test what moose already does)

• over 6000 unit tests

• 0.24 seconds load time

• ~ 3mb for perl+moose

No Moose

•no Moose at the end of a package is a
best practice
• Just do it

Immutability

Stevan's Incantation of Fleet-
Footedness
package Person;
use Moose;

__PACKAGE__->meta->make_immutable;

What make_immutable does

Magic
• Uses eval to "inline" a constructor
• Memoizes a lot of meta-information
• Makes loading your class slower
• Makes object creation much faster

no immutable Moose;
use Moose;
use WWW::Mechanize;

default => sub {WWW::Mechanize->new},
handles => { ‘content’ => ‘content’ }
handles => { ‘get’ => ‘get’ } );

sub query {
my $self = shift;
my $query = shift;

#$self->mech->get($self->url_base . $query);
$self->get($self->url_base . $query);

#return $self->mech->content;
return $self->content;
}
__PACKAGE__->meta->make_immutable
no Moose;
1;

Moose is cool for tests!
# no_net.t

package pseudomech;
sub new{return bless {}}
sub get{
my $self = shift;
$self->{query} = shift;
}
sub content {
return shift->{query} . “ response”;
}

package main;
use Test::More tests => 2;
use SearchEngine;

my $google = SearchEngine->new(mech => pseudomech->new);

is($google->query(‘perl’), ‘perl response’);
is($google->query(‘Moose’), ‘Moose response’);

exit;

Roles

• Usually what you want when you try to do
inheritance
• lets 1 class take on the features of multiple
packages.

More Reading
• Moose Cookbook (heavy on the
inheritance)
• http://search.cpan.org/dist/Moose/lib/
Moose/Cookbook.pod
• Moose Website
• http://moose.perl.org

Intro To Moose

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