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+ <a rel="license" href="http://creativecommons.org/licenses/by-sa/3.0/us/"><img alt="Creative Commons License" style="border-width:0" src="http://i.creativecommons.org/l/by-sa/3.0/us/88x31.png" /></a>
+ <br /><span xmlns:dc="http://purl.org/dc/elements/1.1/" href="http://purl.org/dc/dcmitype/Text" property="dc:title" rel="dc:type">Introduction to Moose</span> by <span xmlns:cc="http://creativecommons.org/ns#" property="cc:attributionName">David Rolsky</span> is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by-sa/3.0/us/">Creative Commons Attribution-Share Alike 3.0 United States License</a>.
+ </div>
+
<h2>Introduction to Moose</h2>
</div>
</div>
<ul>
<li><strong>Declarative</strong> OO sugar</li>
<li>Introspectable</li>
- <li>Extensible</li>
+ <li>Extensible (MooseX::* on CPAN)</li>
</ul>
</div>
-<div class="slide fake-slide0">
- <h1>Part 0: Moose Concepts</h1>
-</div>
-
<div class="slide">
- <h1>Moose background</h1>
+ <h1>Moose Background</h1>
<ul>
+ <li>Created by Stevan Little, first released in 2006</li>
<li>Moose builds on Perl 5's native OO</li>
<li>Borrows ideas from other languages, notably Perl 6</li>
<li>Provides semantics for common operations</li>
</ul>
</div>
+<div class="slide fake-slide0">
+ <h1>Part 0: Moose Concepts</h1>
+</div>
+
<div class="slide">
<h1>Classes</h1>
<pre><code>package Person;
use Moose;
-<span class="highlight">has 'first_name' => ( is => 'rw' );</span></code></pre>
+<span class="highlight">has first_name => ( is => 'rw' );</span></code></pre>
</div>
<pre><code>package Person;
use Moose;
-has 'weight' => ( is => 'ro', <span class="highlight">isa => 'Int'</span> );
+has weight => (
+ is => 'ro',
+ <span class="highlight">isa => 'Int'</span>,
+);
# kaboom
Person->new( weight => 'fat' );</code></pre>
<pre><code>package Person;
use Moose;
-has 'blog_uri' => (
+has blog_uri => (
is => 'rw',
isa => 'URI',
<span class="highlight">handles => { 'blog_hostname' => 'host' },</span>
);
<span class="highlight">$person->blog_hostname;</span>
-# really calls $person->blog_uri->host
+# really calls $person->blog_uri->host</code></pre>
</div>
<div class="slide">
<div class="slide">
<h1>Typo?</h1>
- <code>$self->{last_na<span class="highlight">n</span>e}</code>
+ <code>$self->{last_na<span class="wrong">n</span>e}</code>
</div>
<div class="slide">
<pre><code>package EvilEmployee;
use Moose;
extends 'Person';
-extends 'Thief';</pre></code>
+extends 'Thief';</code></pre>
<h2 class="right">RIGHT</h2>
<pre><code>package EvilEmployee;
use Moose;
-extends 'Person', 'Thief';</pre></code>
+extends 'Person', 'Thief';</code></pre>
</div>
<div class="slide">
<pre><code>package My::LWP;
use Moose;
-extends 'LWP';</pre></code>
+extends 'LWP';</code></pre>
<ul>
<li>No <code>Moose::Object</code>, so ...
<pre><code>package Employee;
use Moose;
-<span class="incremental current">extends 'Person';</span>
+<span class="current">extends 'Person';</span>
<span class="incremental">overrides</span> work => sub {
my $self = shift;
die "Pay me first" unless $self->got_paid;
<span class="incremental">super();</span>
}<span class="incremental">;</span></code></pre>
+</div>
<div class="slide">
<h1>Caveat <code>super</code></h1>
<pre><code>package Person;
use Moose;
-has 'first_name' => ( <span class="highlight">is => 'rw'</span> );
+has first_name => ( <span class="highlight">is => 'rw'</span> );
my $person =
Person->new( first_name => 'Dave' );
<pre><code>package Person;
use Moose;
-has 'first_name' => ( <span class="highlight">is => 'ro'</span> );
+has first_name => ( <span class="highlight">is => 'ro'</span> );
my $person =
Person->new( first_name => 'Dave' );
</div>
<div class="slide">
+ <h1>Classes Summary</h1>
+
+ <ul>
+ <li><code>use Moose</code></li>
+ <li><code>Class->meta</code></li>
+ <li><code>Moose::Object</code> base class</li>
+ <li><code>extends</code>, <code>overrides</code>, and <code>super</code></li>
+ <li>Simple attributes: <code>has</code>, <code>is => 'ro'</code>, & <code>is => 'rw'</code></li>
+ <li><code>no Moose</code></li>
+ <li><code>__PACKAGE__->meta->make_immutable</code></li>
+ </ul>
+</div>
+
+<div class="slide">
<h1>Exercises</h1>
- <pre>$ cd exercises
+ <pre># cd exercises
$ perl bin/prove -lv t/00-prereq.t
Missing anything? Install it. (see tarballs/)
# perl bin/prove -lv t/01-classes.t
-Iterate til this passes all its tests
+Iterate til this passes all its tests</pre>
+</div>
+
+<div class="slide fake-slide0">
+ <h1>Part 2: Roles</h1>
+</div>
+
+<div class="slide">
+ <h1>Just What Is a Role?</h1>
+
+ <ul>
+ <li>Mixin? Interface? Trait?</li>
+ <li>Yes ... and more!</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Roles Can Have State <strong>and</strong> Behavior</h1>
+
+ <pre><code>package HasPermissions;
+use Moose::Role;
+
+<span class="current"># state
+has access_level => ( is => 'rw' );</span>
+
+<span class="incremental"># behavior
+sub can_access {
+ my $self = shift;
+ my $required = shift;
+
+ return $self->access_level >= $required;
+}</span></code></pre>
+
+</div>
+
+<div class="slide">
+ <h1>Roles Can Define Interfaces</h1>
+
+ <pre><code>package Printable;
+use Moose::Role;
+
+requires 'as_string';</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Roles Can Do All Three</h1>
+
+ <pre><code>package Printable;
+use Moose::Role;
+
+requires 'as_string';
+
+has has_been_printed => ( is => 'rw' );
+
+sub print {
+ my $self = shift;
+ print $self->as_string;
+ $self->has_been_printed(1);
+}</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Classes Consume Roles</h1>
+
+ <pre><code>package Person;
+use Moose;
+
+with 'HasPermissions';</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Classes Consume Roles</h1>
+
+<pre><code>my $person = Person->new(
+ first_name => 'Kenichi',
+ last_name => 'Asai',
+ access_level => 42,
+);
+
+print $person->full_name
+ . ' has '
+ . $person->can_access(42)
+ ? 'great power'
+ : 'little power';</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Roles in Practice</h1>
+
+ <ul>
+ <li>Consuming a role =~ inlining the role</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>In Other Words ...</h1>
+
+<pre><code>package Person;
+use Moose;
+
+<span class="highlight">with 'Printable';</span></code></pre>
+</div>
+
+<div class="slide">
+ <h1>In Other Words ...</h1>
+
+<pre><code>package Person;
+use Moose;
+
+<span class="delete">with 'Printable';</span>
+
+<span class="highlight">has has_been_printed => ( is => 'rw' );
+
+sub print {
+ my $self = shift;
+ print $self->as_string;
+ $self->has_been_printed(1);
+}</span></code></pre>
+</div>
+
+<div class="slide">
+ <h1>Except</h1>
+
+ <ul>
+ <li>Role consumption is introspectable</li>
+ </ul>
+
+ <pre><code>if ( Person->does('Printable') ) { ... }
+
+# or ...
+
+if ( Person->meta->does('Printable') ) { ... }</code></pre>
+
+</div>
+
+<div class="slide">
+ <h1>These Names Are the Same</h1>
+
+ <ul>
+ <li>What if a role and class define the same method?</li>
+ <li>A class's <em>local</em> methods win over the role's</li>
+ <li>The role's methods win over the class's <em>inherited</em> methods</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Conflicts Between Roles</h1>
+
+ <ul>
+ <li>Two roles with a method of the same name</li>
+ <li>Generates a compile-time error when consumed by a class</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Conflict Example</h1>
+
+ <pre><code>package IsFragile;
+use Moose::Role;
+
+sub break { ... }
+
+package CanBreakdance;
+use Moose::Role;
+
+sub break { ... }</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Conflict Example</h1>
+
+ <pre><code>package FragileDancer;
+use Moose;
+
+<span class="highlight">with 'IsFragile', 'CanBreakdance';</span></code></pre>
+
+ <ul>
+ <li>Only one <code>with</code>!</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Conflict Resolution</h1>
+
+ <ul>
+ <li>The consuming class must resolve the conflict by implementing th emethod</li>
+ <li>Can use some combination of method exclusion and aliasing</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Method Aliasing</h1>
+
+ <pre><code>package FragileDancer;
+use Moose;
+
+<span class="highlight">with 'IsFragile' =>
+ { alias =>
+ { break => 'break_bone' } },
+ 'CanBreakdance' =>
+ { alias =>
+ { break => 'break_it_down' } };</span></code></pre>
+
+ <ul>
+ <li>Renames the roles' methods</li>
+ <li>Still conflicts, need to <code>exclude</code> as well</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Method Exclusion</h1>
+
+ <pre><code>package FragileDancer;
+use Moose;
+
+<span class="highlight">with 'IsFragile' =>
+ { alias =>
+ { break => 'break_bone' },
+ exclude => 'break' },
+ 'CanBreakdance' =>
+ { alias =>
+ { break => 'break_dance' },
+ exclude => 'break' };</span></code></pre>
+</div>
+
+<div class="slide">
+ <h1>And then ...</h1>
+
+ <pre><code>package FragileDancer;
+use Moose;
+
+sub break {
+ my $self = shift;
+
+ $self->break_dance;
+ if ( rand(1) < 0.5 ) {
+ $self->break_bone;
+ }
+}</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Still Full of Fail</h1>
+
+ <ul>
+ <li>Roles are also about semantics!</li>
+ <li>We've fulfilled the letter and lost the spirit</li>
+ <li>Roles have a <em>meaning</em></li>
+ <li>Think twice before blindly aliasing and excluding methods!</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Hot Role-on-Role Action</h1>
+
+ <pre><code>package Comparable;
+use Moose::Role;
+
+requires 'compare';</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Hot Role-on-Role Action</h1>
+
+ <pre><code>package TestsEquality;
+use Moose::Role;
+
+with 'Comparable';
+
+sub is_equal {
+ my $self = shift;
+ return $self->compare(@_) == 0;
+}</code></pre>
+</div>
+
+<div class="slide">
+ <h1>And then ...</h1>
+
+ <pre><code>package Integer;
+use Moose;
+
+with 'TestsEquality';
+
+# Satisfies the Comparable role
+sub compare { ... }
+
+Integer->does('TestsEquality'); # true
+Integer->does('Comparable'); # also true!</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Name Conflicts Between Roles</h1>
+
+ <pre><code>package HasSubProcess;
+use Moose::Role;
+
+<span class="highlight">sub execute { ... }</span>
+
+package Killer;
+use Moose::Role;
+
+with 'HasSubProcess';
+
+<span class="highlight">sub execute { ... }</span></code></pre>
+</div>
+
+<div class="slide">
+ <h1>Delayed Conflict</h1>
+
+ <pre><code>package StateOfTexas;
+with 'Killer';</code></pre>
+
+ <ul>
+ <li><code>StateOfTexas</code> must implement its own <code>execute</code></li>
+ <li>But loading the <code>Killer</code> role by itself does not cause an error</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Roles as Interfaces</h1>
+
+ <ul>
+ <li>Roles can <code>require</code> methods of their consumers</li>
+ <li>Compile-time checks</li>
+ <li>Method must exist when the role is consumed</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>The Attribute Gotcha</h1>
+
+<pre><code>package HasSize;
+use Moose::Role;
+
+<span class="current">requires 'size';</span>
+
+package Shirt;
+use Moose;
+
+<span class="incremental">with 'HasSize';
+
+has size => ( is => 'ro' );</span></code></pre>
+</div>
+
+<div class="slide">
+ <h1>The Attribute Gotcha Workaround</h1>
+
+ <pre><code>package HasSize;
+use Moose::Role;
+
+requires 'size';
+
+package Shirt;
+use Moose;
+
+has size => ( is => 'ro' );
+
+with 'HasSize';</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Compile-time Is a Lie</h1>
+
+ <ul>
+ <li>Really, it's <em>package load</em> time</li>
+ <li>That's run-time, but before the "real" run-time</li>
+ <li>Moose does not rewire Perl, it's just sugar!</li>
+ <li>(but <code>MooseX::Declare</code> <em>does</em> rewire Perl)</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Enforcing Roles</h1>
+
+ <pre><code>package Comparison;
+use Moose;
+
+has [ 'left', 'right' ] => (
+ is => 'ro',
+ <span class="highlight">does => 'Comparable',</span>
+);
+</code></pre>
+
+ <ul>
+ <li>A sneak peek at type constraints</li>
+ </ul>
+</div>
+
+
+<div class="slide">
+ <h1>Roles Can Be Applied to Objects</h1>
+
+ <pre><code>use Moose::Util qw( apply_all_roles );
+
+my $fragile_person = Person->new( ... );
+apply_all_roles( $fragile_person, 'IsFragile' );</code></pre>
+
+ <ul>
+ <li>Does not change the <code>Person</code> class</li>
+ <li>Works with non-Moose classes, great for monkey-patching!</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Roles Are Dirty Too</h1>
+
+ <ul>
+ <li>Once again, clean up those Moose droppings</li>
+ </ul>
+
+ <pre><code>package Comparable;
+use Moose::Role;
+
+requires 'compare';
+
+<span class="highlight">no Moose::Role;</span></code></pre>
+
+ <ul>
+ <li>But roles cannot be made immutable</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>The Zen of Roles</h1>
+
+ <ul>
+ <li>Roles represent discrete units of ...
+ <ul>
+ <li>state</li>
+ <li>behavior</li>
+ <li>interface</li>
+ </ul>
+ </li>
+ <li>Roles are shareable between unrelated classes</li>
+ <li>Roles are what a class <em>does</em>, not what it <em>is</em></li>
+ <li>Roles <em>add</em> functionality, inheritance <em>specializes</em></li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Abstract Examples</h1>
+
+ <ul>
+ <li>Human <em>@ISA</em> Animal</li>
+ <li>Human <em>does</em> Toolmaker (as <em>does</em> Chimpanzee)</li>
+ <li>Car <em>@ISA</em> Vehicle</li>
+ <li>Car <em>does</em> HasEngine</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Real Examples</h1>
+
+ <ul>
+ <li>Objects representing SQL database components and queries
+ <ul>
+ <li>Schema, Table, Column, ColumnAlias</li>
+ <li>Select, Insert, Update, Delete</li>
+ </ul>
+ </li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Real Examples</h1>
+
+ <ul>
+ <li>Column and ColumnAlias both <em>do</em> ColumnLike</li>
+ <li>ColumnLike things can be used in certain parts of queries</li>
+ <li>All queries <em>do</em> HasWhereClause</li>
+ <li>Select <em>does</em> Comparable and Selectable (for subselects)</li>
+ <li>A where clause requires its components to <em>do</em> Comparable</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Exercises</h1>
+
+ <pre># cd exercises
+# perl bin/prove -lv t/02-roles.t
+
+Iterate til this passes all its tests</pre>
+</div>
+
+<div class="slide fake-slide0">
+ <h1>Part 3: Basic Attributes</h1>
+</div>
+
+<div class="slide">
+ <h1>Attributes Are Huge</h1>
+
+ <ul>
+ <li>Moose's biggest feature</li>
+ <li>The target of <em>many</em> MooseX modules</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Quick Review</h1>
+
+ <ul>
+ <li>Declared with <code>has</code></li>
+ <li>Read-only or read-write</li>
+ </ul>
+
+ <pre><code>package Shirt;
+use Moose;
+
+has 'color' => ( is => 'ro' );
+has 'is_ripped' => ( is => 'rw' );</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Required-ness</h1>
+
+ <ul>
+ <li>Required means "must be passed to the constructor"</li>
+ <li>But can be <code>undef</code></li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Required-ness</h1>
+
+ <pre><code>package Person;
+use Moose;
+
+has first_name => (
+ is => 'ro',
+ <span class="current">required => 1,</span>
+);
+
+<span class="incremental">Person->new( first_name => undef ); # ok
+Person->new(); # kaboom</span></code></pre>
+</div>
+
+<div class="slide">
+ <h1>Default and Builder</h1>
+
+ <ul>
+ <li>Attributes can have defaults</li>
+ <li>Simple non-referecne scalars (number, string)</li>
+ <li>Subroutine reference</li>
+ <li>A builder method</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Default</h1>
+
+ <ul>
+ <li>Can be a non-reference scalar (including <code>undef</code>)</li>
+ </ul>
+
+ <pre><code>package Person;
+use Moose;
+
+has bank => (
+ is => 'rw',
+ default => 'Spire FCU',
+);</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Default</h1>
+
+ <ul>
+ <li>Can be a subroutine reference</li>
+ </ul>
+
+ <pre><code>package Person;
+use Moose;
+
+has bank => (
+ is => 'rw',
+ default =>
+ sub { Bank->new(
+ name => 'Spire FCU' ) },
+);</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Default as a Subroutine Reference</h1>
+
+ <ul>
+ <li>Called as a method on the object</li>
+ <li>Called anew for each object</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Why No Other Reference Types?</h1>
+
+ <pre><code>package Person;
+use Moose;
+
+has bank => (
+ is => 'rw',
+ <span class="wrong">default => Bank->new(
+ name => 'Spire FCU' ),</span>
+);</code></pre>
+
+ <ul>
+ <li>Now <strong>every</strong> person shares the <strong>same</strong> Bank object!</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Defaulting to an Empty Reference</h1>
+
+ <pre><code>package Person;
+use Moose;
+
+has packages => (
+ is => 'rw',
+ default => <span class="highlight">sub { [] }</span>,
+);</code></pre>
+</div>
+
+<div class="slide">
+ <h1>What if I Want to Share?</h1>
+
+ <pre><code>package Person;
+use Moose;
+
+my $highlander_bank =
+ Bank->new( name => 'Spire FCU' );
+
+has bank => (
+ is => 'rw',
+ default => sub { $highlander_bank },
+);</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Builder</h1>
+
+ <ul>
+ <li>A method <em>name</em> which returns the default</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Builder</h1>
+
+ <pre><code>package Person;
+use Moose;
+
+has bank => (
+ is => 'rw',
+ builder => '_build_bank',
+);
+
+sub _build_bank {
+ my $self = shift;
+ return Bank->new( name => 'Spire FCU' );
+}</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Default vs Builder</h1>
+
+ <ul>
+ <li>Use default for simple scalars</li>
+ <li>Use default to return empty references</li>
+ <li>Use default for <em>very</em> trivial subroutine references</li>
+ <li>Use builder for everything else</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Builder Bonuses</h1>
+
+ <ul>
+ <li>Can be overridden and method modified, because it's called by <em>name</em></li>
+ <li>Roles can require a builder</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Role Requires Builder</h1>
+
+ <pre><code>package HasBank;
+use Moose::Role;
+
+requires '_build_bank';
+
+has bank => (
+ is => 'ro',
+ builder => '_build_bank',
+);</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Lazy, Good for Nothing Attributes</h1>
+
+ <ul>
+ <li>Normally, defaults are generated during object construction</li>
+ <li>This can be expensive</li>
+ <li>We want to default to <code>$self->size * 2</code>, but attribute initialization order is unpredictable</li>
+ <li>Use lazy attributes!</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>The Power of Dynamic Defaults</h1>
+
+ <pre><code>package Person;
+use Moose;
+
+has shoe_size => (
+ is => 'ro',
+);</code></pre>
+</div>
+
+<div class="slide">
+ <h1>The Power of Dynamic Defaults</h1>
+
+ <pre><code>has shoes => (
+ is => 'ro',
+ <span class="highlight">lazy => 1,</span>
+ builder => '_build_shoes',
+);
+
+sub _build_shoes {
+ my $self = shift;
+
+ return Shoes->new(
+ size => <span class="highlight">$_[0]->shoe_size</span> );
+}</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Lazy is Good</h1>
+
+ <ul>
+ <li>Lazy defaults are executed when the attribute is read</li>
+ <li>Can see other object attributes</li>
+ <li>Still need to watch out for circular laziness</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Clearer and Predicate</h1>
+
+ <ul>
+ <li>Attributes can have a value, including <code>undef</code>, or not</li>
+ <li>Can clear the value with a clearer method</li>
+ <li>Can check for the existence of a value with a predicate method</li>
+ <li>By default, these methods are not created</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Clearer and Predicate</h1>
+
+ <pre><code>package Person;
+use Moose;
+
+has account => (
+ is => 'ro',
+ lazy => 1,
+ builder => '_build_account',
+ <span class="highlight">clearer => '_clear_account',
+ predicate => 'has_account',</span>
+);</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Clearer and Lazy Defaults</h1>
+
+ <ul>
+ <li>Lazy defaults are good for computed attributes</li>
+ <li>Clear the attribute when the source data changes</li>
+ <li>Recalculated at next access</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Renaming constructor arguments</h1>
+
+ <ul>
+ <li>By default, constructor names = attribute names</li>
+ <li>Use <code>init_arg</code> to change this</li>
+ <li>Set <code>init_arg => undef</code> to make it unconstructable</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Some <code>init_arg</code> examples</h1>
+
+ <pre><code>package Person;
+use Moose;
+
+has shoe_size => (
+ is => 'ro',
+ <span class="highlight">init_arg => 'foot_size',</span>
+);
+
+Person->new( <span class="wrong">shoe_size => 13</span> );
+
+my $person =
+ Person->new( <span class="right">foot_size => 13</span> );
+print $person->shoe_size;</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Some <code>init_arg</code> examples</h1>
+
+<pre><code>package Person;
+use Moose;
+
+has shoes => (
+ is => 'ro',
+ <span class="highlight">init_arg => undef,</span>
+);
+
+Person->new( <span class="wrong">shoes => Shoes->new</span> );</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Why Set <code>init_arg => undef</code>?</h1>
+
+ <ul>
+ <li>Use this with a lazy default for attributes-as-cache</li>
+ <li>Compute the value as needed</li>
+ <li>Ensure that it is always generated correctly (not set by constructor)</li>
+ <li>Use triggers or method modifiers (coming soon) to clear the value</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Attribute Inheritance</h1>
+
+ <ul>
+ <li>By default, subclasses inherit attribute as-is</li>
+ <li>Can change some attribute parameters in subclasses
+ <ul>
+ <li>default</li>
+ <li>builder</li>
+ <li>required</li>
+ <li>lazy</li>
+ <li>others we've not yet covered</li>
+ </ul>
+ </li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Attribute Inheritance Example</h1>
+
+ <pre><code>package Employee;
+use Moose;
+
+extends 'Person';
+
+has '<span class="highlight">+first_name</span>' => (
+ default => 'Joe',
+);</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Attribute Inheritance Warning</h1>
+
+ <ul>
+ <li>An attribute is a contract about a class's API</li>
+ <li>Don't break that contract in a subclass</li>
+ <li>Especially important in the context of types</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Changing Accessor Names</h1>
+
+ <pre><code>package Person;
+use Moose;
+
+has first_name => (
+ <span class="highlight">reader</span> => 'first_name',
+ <span class="highlight">writer</span> => 'first_name',
+);</code></pre>
+
+ <ul>
+ <li>The long-hand version of <code>is => 'rw'</code></li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Changing Accessor Names</h1>
+
+ <pre><code>package Person;
+use Moose;
+
+has first_name => (
+ <span class="highlight">reader</span> => 'first_name',
+ <span class="highlight">writer</span> => undef,
+);</code></pre>
+
+ <ul>
+ <li>The long-hand version of <code>is => 'ro'</code></li>
+ </ul>
+</div>
+
+
+<div class="slide">
+ <h1>Changing Accessor Names</h1>
+
+ <pre><code>package Person;
+use Moose;
+
+has first_name => (
+ <span class="highlight">reader</span> => 'get_first_name',
+ <span class="highlight">writer</span> => 'set_first_name,
+);</code></pre>
+</div>
+
+<div class="slide">
+ <h1>Changing Accessor Names</h1>
+
+ <pre><code>package Person;
+use Moose;
+
+has first_name => (
+ <span class="highlight">is</span> => 'rw',
+ <span class="highlight">writer</span> => '_first_name',
+);</code></pre>
+
+ <ul>
+ <li>Can also mix-and-match</li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>ETOOMUCHTYPING</h1>
+
+ <ul>
+ <li><code>MooseX::FollowPBP</code><br /><code>get_foo</code> and <code>set_foo</code></li>
+ <li><code>MooseX::SemiAffordanceAccessor</code><br /><code>foo</code> and <code>set_foo</code></li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>ETOOMUCHTYPING</h1>
+
+ <pre><code>package Person;
+use Moose;
+<span class="highlight">use MooseX::SemiAffordanceAccessor;</span>
+
+has first_name => (
+ is => 'rw',
+);</code></pre>
+
+ <ul>
+ <li>Creates <code>first_name</code> and <code>set_first_name</code></li>
+ </ul>
+</div>
+
+<div class="slide">
+ <h1>Exercises</h1>
+
+ <pre># cd exercises
+# perl bin/prove -lv t/03-basic-attributes.t
+
+Iterate til this passes all its tests</pre>
+</div>
+
+</div>
+</body>
+</html>
+
+<!--
+
+Copyright 2009 David Rolsky. All Rights Reserved.
+
+This work is licensed under a Creative Commons Attribution-Share Alike
+3.0 United States License See
+http://creativecommons.org/licenses/by-sa/3.0/us/ for details.
+
+-->
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