[gitmo/moose-website.git] / hosted-presentations / 2008 / nothingmuch-NPW / practical_moose.html

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<h1>YAPC::Asia::2008</h1>
<h2>Moose</h2>
</div>
<div class="topleft"></div>
<div class="topright"></div>
<div class="bottomleft"></div>
<div class="bottomright"></div>
</div>

<div class="presentation">

<div class="slide">
<h1>Moose</h1>
<h2></h2>
<h3>Yuval Kogman</h3>
<h4></h4>
</div>


<div class="slide">
<h1>Moose Is Not</h1>

<ul>
<li>Experimental</li>
<li>A toy</li>
<li>Just another accessor builder</li>
<li>A source filter</li>
<li>Perl black magic</li>
<li>Perl 6 in Perl 5</li>
</ul>

</div>

<div class="slide">
<h1>Moose Is</h1>

<ul>
<li>A complete modern object framework for Perl</li>
</ul>

</div>

<div class="slide">
<h1>Moose Is</h1>

<ul>
<li>Syntactic Sugar for <code>Class::MOP</code></li>
<li>Rich ancestry
<ul>
<li>CLOS (Common Lisp Object System)</li>
<li>Smalltalk</li>
<li>Alces latifrons</li>
<li>Perl 6</li>
<li>…</li>
</ul></li>
<li>Stable &amp; Production ready</li>
<li>Polite, incremental</li>
</ul>

</div>

<div class="slide">
<h1>A Simple Example</h1>

<pre><code>
package Person;

use strict;
use warnings;

sub new {
    my ( $class, @args ) = @_;

    @args = %{$args[0]} if @args == 1;

    return bless {
        @args,
    }, $class;
}

sub name {
    my ($self, @args) = @_;
    $self->{name} = $args[0] if @args;
    return $self->{name};
}

sub age {
    my ($self, @args) = @_;
    $self->{age} = $args[0] if @args;
    return $self->{age}; 
}

1;
</code></pre>

</div>

<div class="slide">
<h1>A Simple Moose Example</h1>

<pre><code>
package Person;
use Moose;

has name => (is => 'rw');
has age  => (is => 'rw');

1;
</code></pre>

</div>

<div class="slide">
<h1>A Simple Moose Example (cont.)</h1>

<ul>
<li><code>use Moose;</code> 
<ul>
<li>imports keywords</li>
<li><code>use strict; use warnings;</code></li>
<li><code>@ISA = qw(Moose::Object) unless @ISA</code></li>
</ul></li>
</ul>

</div>

<div class="slide">
<h1>A Simple Moose Example (cont.)</h1>

<ul>
<li><p><code>has</code> declares attributes</p>

<ul>
<li>generates accessors</li>
<li><code>is =&gt; 'rw'</code> → read/write accessor</li>
<li><code>is =&gt; 'ro'</code> → read only accessor</li>
<li><code>writer</code>, <code>reader</code></li>
</ul></li>
<li><p><code>new</code> inherited from <code>Moose::Object</code></p></li>
</ul>

<div class="notes">
<p>Now we&#8217;re going to discuss more features of the attributes</p>
</div>
</div>

<div class="slide">
<h1>Variations on a Moose Example</h1>

<pre><code>
package Manager;
use Moose;

has name => (
    is  => 'rw',
    isa => 'Str',
    default => 'Bob'
);

has staff => (
    is      => 'ro',
    isa     => 'ArrayRef',
    lazy    => 1,
    default => sub { [qw(Bob Alice Tim)] },
);
</code></pre>

<div class="notes">
<p>Adds default, isa</p>
</div>
</div>

<div class="slide">
<h1>Variations on a Moose Example (cont.)</h1>

<ul>
<li><p><code>default</code> is a</p>

<ul>
<li>code reference</li>
<li>or non-reference (numbers, strings)</li>
<li>used when no parameter is given to <code>new</code></li>
</ul></li>
<li><p><code>lazy</code> delays <code>default</code></p>

<ul>
<li>called on first usage of <code>$object-&gt;staff</code></li>
<li>not inside <code>new</code></li>
</ul></li>
</ul>

<div class="notes">
<p>discusses default</p>

<p>non refs make accidental sharing hard</p>
</div>
</div>

<div class="slide">
<h1>Variations on a Moose Example (cont.)</h1>

<ul>
<li><code>isa</code> specifies a type
<ul>
<li><code>Moose::Util::TypeConstraints</code>
<ul>
<li><code>Any, Item, Bool, Undef, Defined, Value, Num, Int, Str, Ref, ScalarRef, ArrayRef, HashRef, CodeRef, RegexpRef, GlobRef, FileHandle, Object and Role</code></li>
</ul></li>
<li>Types don&#8217;t need to exist</li>
</ul></li>
</ul>

<pre><code>
            has 'date' => (isa => 'DateTime'); # DWIM
</code></pre>

<div class="notes">
<p>isa, type constraints</p>
</div>
</div>

<div class="slide">
<h1>Typical Family</h1>

<ul>
<li>Types have a hierarchy
<ul>
<li><code>Item</code> ⊃ <code>Defined</code> ⊃ <code>Ref</code> ⊃ <code>Object</code></li>
</ul></li>
</ul>

<pre><code>
        subtype 'Ref'
            => as 'Defined'
            => where {  ref($_) };

        subtype 'Object'
            => as 'Ref'
            => where { blessed($_) }
</code></pre>

<div class="notes">
<p>type hierarchy</p>
</div>
</div>

<div class="slide">
<h1>Conventional Delegates</h1>

<pre><code>
package Employee;
use Moose;
extends qw(Person);

has manager =>  (
    is  => 'ro',
    isa => 'Manager',
    handles => {
        manager_name => 'name',
        coworkers    => 'staff',
    }
);
</code></pre>

<ul>
<li>manager <code>handles</code> certain methods for <code>Employee</code>
<ul>
<li><code>$emp-&gt;coworkers</code> == <code>$emp-&gt;manager-&gt;staff</code></li>
</ul></li>
</ul>

</div>

<div class="slide">
<h1>Conventional Delegates (cont.)</h1>

<pre><code>
has phone => (
    ...
    handles => [qw(number extension)],
);
</code></pre>

</div>

<div class="slide">
<h1>Conventional Delegates (cont.)</h1>

<pre><code>
has phone => (
    ...
    isa     => "Phone",
    handles => qr/^[a-z]w+$/,
);
</code></pre>

</div>

<div class="slide">
<h1>Conventional Delegates (cont.)</h1>

<pre><code>
has phone => (
    ...
    handles => "Dialing", # a role
);
</code></pre>

</div>

<div class="slide">
<h1>UnConventional Delegates</h1>

<pre><code>
package Company;
use Moose;
use MooseX::AttributeHelpers;

has employees => (
    metaclass => 'Collection::Array',
    isa => 'ArrayRef[Employees]',
    is  => 'rw',
    provides => {
        push  => 'add_employee',
        pop   => 'remove_employee',
        count => 'number_of_employees',
        empty => 'any_employees',
    },
);
</code></pre>

</div>

<div class="slide">
<h1>Modified Methods</h1>

<pre><code>
before 'employees' => sub { warn 'calling employees' };

after 'employees' => sub { warn 'finished calling employees' };
</code></pre>

<ul>
<li>Pre/Post hooks
<ul>
<li>Get a copy of <code>@_</code></li>
<li>Return value is ignored</li>
</ul></li>
</ul>

</div>

<div class="slide">
<h1>Modified Methods (cont.)</h1>

<pre><code>
around 'employees' => sub { 
    my ($next, $self, @args) = @_;
    ...
    my @return = $self->$next(@args);
    ...
    return @return;
};
</code></pre>

</div>

<div class="slide">
<h1>Modified Methods (cont.)</h1>

<pre><code>
package Employee;
use Moose;

sub do_work {
    my $self = shift;

    $self->punch_in;

    inner(); # call subclass here

    $self->punch_out;
}
</code></pre>

</div>

<div class="slide">
<h1>Modified Methods (cont.)</h1>

<pre><code>
package Employee::Chef;
use Moose;

extends qw(Employee);

augment do_work => sub {
    my $self = shift;

    while ( @burgers ) {
        $self->flip_burger(shift @burgers);
    }
};

$chef->do_work; # punch in, flip burgers, punch out
</code></pre>

</div>

<div class="slide">
<h1>Some Type of Coercion</h1>

<pre><code>
package Employee;
use Moose;
use Moose::Util::TypeConstraints;
extends qw(Person);

class_type 'Manager';

coerce 'Manager' => (
    from 'Str' => via { Manager->new( name => $_ ) },
);

has manager => (
    is => 'ro',
    isa => 'Manager',
    required => 1, 
    coerce => 1,
);
</code></pre>

</div>

<div class="slide">
<h1>Some Type of Coercion (cont.)</h1>

<pre><code>
# import type constraint keywords
use Moose::Util::TypeConstraints;


# define Manager, a subtype of Object
class_type "Manager";


# define the conversion
... via { Manager->new( name => $_ ) }


# enable it per attribute
has manager => (
    ...
    coerce => 1,
);
</code></pre>

<div class="notes">
<p>breakdown of the example</p>

<p>class types are automatically created for all Moose classes</p>
</div>
</div>

<div class="slide">
<h1>Some Type of Digression</h1>

<pre><code>
has employees => (
    is => 'rw',
    isa => 'ArrayRef[Employee]',
);

has shopping_carts => (
    is => 'rw',
    isa => 'ArrayRef[ArrayRef[ShinyBead]]'
);
</code></pre>

<div class="notes">
<p>Going to go into features of the type system for a bit</p>

<p>Parametrized types</p>
</div>
</div>

<div class="slide">
<h1>Some Type of Digression (cont.)</h1>

<pre><code>
has language => (
    is => 'rw',
    isa => 'English | Welsh | Scots | Gaelic',
);  

has member => (
    is => 'rw',
    isa => 'Employee | ArrayRef[ Employee | Group ]',
);
</code></pre>

<div class="notes">
<p>Union types</p>
</div>
</div>

<div class="slide">
<h1>Some Type of Digression (cont.)</h1>

<pre><code>
package Foo;
use Moose;
use Moose::Util::TypeConstraints;

use Test::Deep qw(eq_deeply ...);

type 'SomethingTricky' => where {
    eq_deeply( $_, ... );
};

has 'bar' => (
    is  => 'rw',
    isa => 'SomethingTricky',
);
</code></pre>

<div class="notes">
<p>Test::Deep custom validator</p>

<p>Can use any validation from the CPAN</p>
</div>
</div>

<div class="slide">
<h1>Some Parametrized Type of Coercion</h1>

<pre><code>
use Moose::Util::TypeConstraints;

subtype 'ArrayRef[Employee]' => as 'ArrayRef';

coerce 'ArrayRef[Employee]' => (
    from 'ArrayRef[Str]' via {
        [ map { Employee->new( name => $_ ) } @$_ ]
    },
);

has staff => (
    isa    => 'ArrayRef[Employee]',
    coerce => 1,
);
</code></pre>

<div class="notes">
<p>coerce parametrized ArrayRef[Employee] from ArrayRef[Str]</p>
</div>
</div>

<div class="slide">
<h1>Role of the Moose </h1>

<ul>
<li>A role is like a…
<ul>
<li>Java Interface: safe</li>
<li>mixin: useful</li>
</ul></li>
<li>A role is for small reusable behaviors
<ul>
<li>better than using a multiple inheritence</li>
</ul></li>
</ul>

</div>

<div class="slide">
<h1>Role of the Moose (cont.)</h1>

<ul>
<li>Roles on the CPAN:
<ul>
<li><code>MooseX::Clone</code> - Flexible <code>clone</code> method</li>
<li><code>MooseX::Storage</code> - Flexible serialization</li>
<li><code>MooseX::Getopt</code> - <code>@ARGV</code> aware constructor</li>
<li><code>MooseX::LogDispatch</code> - <code>$self-&gt;logger-&gt;info("something happenned")</code></li>
<li><code>MooseX::Param</code> - <code>param</code> method like <code>CGI.pm</code>&#8217;s,</li>
</ul></li>
</ul>

<div class="notes">
<p>Some examples of small reusable behaviors</p>

<p>Param is good for interacting with e.g. CGI::Expand or similar modules</p>
</div>
</div>

<div class="slide">
<h1>Role of the Moose (cont.)</h1>

<pre><code>
package Minion;
use Moose;

extends qw(Employee);

with qw(Salaried::Hourly);


package Boss;
use Moose;

extends qw(Employee);

with qw(Salaried::Monthly);

</code></pre>

<ul>
<li><code>with</code> adds roles into your class
<ul>
<li><code>Salaried::Hourly</code> was added to <code>Minion</code></li>
</ul></li>
</ul>

</div>

<div class="slide">
<h1>Role of the Moose (cont.)</h1>

<pre><code>
package Salaried;
use Moose::Role;

requires 'paycheck_amount';
</code></pre>

<ul>
<li>Just an interface</li>
</ul>

</div>

<div class="slide">
<h1>Role of the Moose (cont.)</h1>

<pre><code>
package Salaried::Hourly;
use Moose::Role;

with qw(Salaried);

has hourly_rate => (
    isa => "Num",
    is  => "rw",
    required => 1,
);

has logged_hours => (
    isa => "Num",
    is  => "rw",
    default => 0,
);

# satisfy the Salaried interface:
sub paycheck_amount {
    my $self = shift;
    $self->logged_hours * $self->hourly_rate;
}

</code></pre>

<ul>
<li>More than an interface</li>
</ul>

</div>

<div class="slide">
<h1>Role of the Moose (cont.)</h1>

<ul>
<li>More than Java Interfaces
<ul>
<li>Interfaces are behavior &#8220;contracts&#8221;</li>
<li>Roles can also have code</li>
</ul></li>
</ul>

<div class="notes">
<p>roles can have attributes and methods
roles provide behavior, not just interface</p>
</div>
</div>

<div class="slide">
<h1>Role of the Moose (cont.)</h1>

<ul>
<li>Role Composition
<ul>
<li>Not inheritence</li>
<li>Symmetric</li>
<li>Unordered</li>
</ul></li>
</ul>

</div>

<div class="slide">
<h1>Role of the Moose (cont.)</h1>

<ul>
<li>Role Composition
<ul>
<li>Less ambiguity</li>
<li>Compile time errors</li>
<li>…And ways to fix them</li>
</ul></li>
</ul>

<div class="notes">
<p>symmetric composition means no precedence - if two roles try to define the same thing you get a compile time error that needs to be resolved
multiple inheritence silently assumes you want the first class</p>

<p>roles cause errors at compile time, unlike multiple inheritence</p>

<p>roles also provide easy ways to fix the errors</p>
</div>
</div>

<div class="slide">
<h1>Role of the Moose (cont.)</h1>

<pre><code>
package Ballet;
use Moose::Role;

sub dance {
    pirouette();
}

package Punk;
use Moose::Role

sub dance {
    MOSH!!!11one();
}

package Foo;
use Moose;

# KABOOM:
with qw(
    Punk
    Ballet
);
</code></pre>

<div class="notes">
<p>conflicts</p>
</div>
</div>

<div class="slide">
<h1>Role of the Moose (cont.)</h1>

<pre><code>
package Ent::Puppy;
use Moose;

with (
    Tree => {
        alias => {
            bark => "tree_bark",
        },
    },
    Dog => {
        alias => {
            bark => "bark_sound",
        }
    },
);

sub bark {
    my $self = shift;

    if ( $condition ) {
        $self->tree_bark;
    } else {
        $self->bark_sound;
    }
}
</code></pre>

<ul>
<li>Not that common in practice</li>
</ul>

<div class="notes">
<p>Composition parameters
Easier conflict resolution
Finer grained control</p>
</div>
</div>

<div class="slide">
<h1>MOPs Mean Cleanliness</h1>

<ul>
<li>Moose is based on <code>Class::MOP</code>
<ul>
<li>Metaobject Protocol for Perl 5</li>
<li>&#8220;makes an object for everything&#8221;</li>
</ul></li>
</ul>

<pre><code>
my $class = $obj->meta;       # $obj's metaclass
my $meta  = MyApp->meta;      # MyApp's metaclass
my $emo   = $obj->meta->meta; # even more meta!

warn  $obj->meta->name;
</code></pre>

</div>

<div class="slide">
<h1>Looking in From the Inside</h1>

<pre><code>
my $metaclass = $self->meta; 

$metaclass->superclasses;

$metaclass->linearized_isa;

$metaclass->has_method("foo");

$metaclass->compute_all_applicable_attributes;

# … lots more
</code></pre>

<div class="notes">
<p>simple introspection</p>
</div>
</div>

<div class="slide">
<h1>Looking in From the Inside (cont.)</h1>

<pre><code>
Moose::Meta::Class->create( Bar =>
      version      => '0.01',
      superclasses => [ 'Foo' ],
      attributes => [
          Moose::Meta::Attribute->new( bar => ... ),
          Moose::Meta::Attribute->new( baz => ... ),
      ],
      methods => {
          calculate_bar => sub { ... },
          construct_baz => sub { ... }
      },
);

my $anon_meta = Moose::Meta::Class->create_anon_class( ... );
</code></pre>

<div class="notes">
<p>Classes can be created programmatically</p>
</div>
</div>

<div class="slide">
<h1>Looking in From the Inside (cont.)</h1>

<pre><code>
has foo => ( is => "rw" );

__PACKAGE__->meta->add_attribute(
    "foo",  
    is => "rw",
);
</code></pre>

<ul>
<li>Moose is just sugar
<ul>
<li>The MOP does the hard work</li>
</ul></li>
</ul>

</div>

<div class="slide">
<h1>The Metaclass Tango</h1>

<ul>
<li>Metaclassses control class behavior</li>
</ul>

<pre><code>
has employees => (
    metaclass => 'Collection::Array',
    ...
);
</code></pre>

<ul>
<li>custom attribute metaclasses
<ul>
<li>change how attributes work</li>
</ul></li>
<li>Many customizable parts
<ul>
<li><code>Moose::Meta::Class</code>, <code>Moose::Meta::Attribute,</code><code>Moose::Meta::Method</code>, <code>Moose::Meta::Method::Accessor</code> <code>Moose::Meta::Instance</code>, <code>Moose::Meta::Role</code>, <code>Moose::Meta::TypeConstraint</code>, …,</li>
</ul></li>
</ul>

</div>

<div class="slide">
<h1>Working in the Meta Frame</h1>

<ul>
<li><code>$work</code> project:</li>
<li>CMS for a flash website</li>
<li>Content is in XML</li>
</ul>

</div>

<div class="slide">
<h1>Working in the Meta Frame (cont.)</h1>

<ul>
<li>Step 1. use Moose</li>
<li>Step 2. ???</li>
<li>Step 3. Profit!</li>
</ul>

</div>

<div class="slide">
<h1>Working in the Meta Frame (cont.)</h1>

<ul>
<li>Step 2.1. Client&#8217;s XML schemas → Moose classes
<ul>
<li>Automatic class definitions</li>
<li>High level objects in runtime</li>
<li>XML storage backed
<ul>
<li>SAX → Moose</li>
<li>Moose → SAX</li>
</ul></li>
</ul></li>
</ul>

</div>

<div class="slide">
<h1>Working in the Meta Frame (cont.)</h1>

<ul>
<li>Step 2.2. Meta descriptions
<ul>
<li>Extend the metaclasses</li>
<li>Embed additional information
<ul>
<li>field types</li>
<li>access control</li>
</ul></li>
</ul></li>
</ul>

</div>

<div class="slide">
<h1>Working in the Meta Frame (cont.)</h1>

<ul>
<li>Step 2.3 Introspection goodness
<ul>
<li>Generic web frontend</li>
<li>Object introspection based
<ul>
<li>HTML view</li>
<li>Editing widgets</li>
</ul></li>
<li>Clean, extensible</li>
</ul></li>
</ul>

</div>

<div class="slide">
<h1>Drawbacks of Moose</h1>

<ul>
<li>Load time
<ul>
<li><code>MooseX::Compile</code> is in the works</li>
</ul></li>
<li>Some features are slow
<ul>
<li>but you only pay for what you use</li>
</ul></li>
<li>Extending non-Hash based classes is tricky.
<ul>
<li>but possible: <code>MooseX::GlobRef::Object</code></li>
</ul></li>
</ul>

</div>

<div class="slide">
<h1>Benefits of Moose</h1>

<ul>
<li>Less boilerplate
<ul>
<li>attribute storage/access</li>
<li>construction</li>
<li>destruction</li>
<li>verification</li>
<li>…</li>
</ul></li>
</ul>

</div>

<div class="slide">
<h1>Benefits of Moose (cont.)</h1>

<ul>
<li>Shorter
<ul>
<li>less reading</li>
<li>less writing</li>
<li>less code means fewer bugs</li>
</ul></li>
</ul>

</div>

<div class="slide">
<h1>Benefits of Moose (cont.)</h1>

<ul>
<li>Less testing
<ul>
<li>Moose is very well tested
<ul>
<li>no need to check accessor behavior, etc</li>
</ul></li>
<li>focus on your code&#8217;s purpose
<ul>
<li>not that it is &#8220;assembled&#8221; correctly</li>
<li>http://c2.com/cgi/wiki?IntentionNotAlgorithm</li>
</ul></li>
</ul></li>
</ul>

</div>

<div class="slide">
<h1>Benefits of Moose (cont.)</h1>

<ul>
<li>More readable
<ul>
<li>declarative style is self documenting</li>
<li>good signal to noise ratio</li>
</ul></li>
</ul>

</div>

<div class="slide">
<h1>Benefits of Moose (cont.)</h1>

<ul>
<li>Meta object protocol
<ul>
<li>Cleans up Perl&#8217;s OO</li>
<li>Provides introspection</li>
<li>Enables powerful abstractions</li>
</ul></li>
</ul>

</div>

<div class="slide">
<h1>Benefits of Moose (cont.)</h1>

<ul>
<li>It&#8217;s the new black
<ul>
<li>All the cool kids hang out on #moose</li>
<li>Smart sounding buzzwords</li>
<li>Chicks dig antlers</li>
<li>Ruby is so 2007</li>
</ul></li>
</ul>

</div>

<div class="slide">
<h1>Bonus Material</h1>

</div>

<div class="slide">
<h1>Autobox</h1>

<pre><code>
package Units::Bytes;
use Moose::Role;
use Moose::Autobox;

sub bytes     { $_[0]                   }
sub kilobytes { $_[0] * 1024            }
sub megabytes { $_[0] * 1024->kilobytes }
sub gigabytes { $_[0] * 1024->megabytes }
sub terabytes { $_[0] * 1024->gigabytes }

Moose::Autobox->mixin_additional_role(
    SCALAR => 'Units::Bytes',
);
</code></pre>

</div>

<div class="slide">
<h1>Autobox (cont.)</h1>

<pre><code>
use Units::Bytes;
use Moose::Autobox; # autoboxing is lexical

is(5->bytes,     5,             '... got 5 bytes');
is(5->kilobytes, 5120,          '... got 5 kilobytes');
is(2->megabytes, 2097152,       '... got 2 megabytes');
is(1->gigabytes, 1073741824,    '... got 1 gigabyte');
is(2->terabytes, 2199023255552, '... got 2 terabytes');
</code></pre>

</div>

<div class="slide">
<h1>perl -Moose</h1>

<ul>
<li>Moose One Liners with <code>oose.pm</code></li>
</ul>

<pre><code>
perl -Moose -e 'has foo => ( is=> "rw" ); Class->new( foo => 1 )'
</code></pre>

<ul>
<li>Useful for testing if something works</li>
<li>Helpful on IRC</li>
<li><code>Devel::REPL</code> is cooler though ;-)</li>
</ul>

</div>

<div class="slide">
<h1>MooseX::POE</h1>

<pre><code>
package Counter;
use MooseX::POE;
use MooseX::AttributeHelpers;

has count => (
    traits => [qw(Counter)],
    provides => { inc => "increment_count" },
);

sub START {
    shift->yield('increment');
}

event increment => sub {
    my $self = shift;

    warn "Count is now " . $self->count;

    $self->increment_count;
    $self->yield('increment') unless $self->count > 3;
};

Counter->new( count => 0 );
POE::Kernel->run();
</code></pre>

<ul>
<li>PoCos made easy</li>
<li>Every object has a <code>POE::Session</code></li>
<li><code>event</code> declares POE object states</li>
</ul>

</div>

<div class="slide">
<h1>Fin</h1>

<ul>
<li><p>Slides written by:</p>

<ul>
<li>Chris Prather</li>
<li>Stevan Little</li>
<li>Robert Boone</li>
</ul></li>
<li><p>Slides deleted by:</p>

<ul>
<li>Yuval Kogman</li>
</ul></li>
</ul>

</div>


</div>

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