1 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.0//EN" "http://www.w3.org/MarkUp/DTD/xhtml-rdfa-1.dtd">
3 <html xmlns="http://www.w3.org/1999/xhtml">
6 <title>Introduction to Moose</title>
7 <meta http-equiv="Content-Type" content="text/html;charset=utf-8" />
9 <meta name="generator" content="S5" />
10 <meta name="version" content="S5 1.2a2" />
11 <meta name="author" content="Eric A. Meyer" />
12 <meta name="company" content="Complex Spiral Consulting" />
13 <!-- configuration parameters -->
14 <meta name="defaultView" content="slideshow" />
15 <meta name="controlVis" content="hidden" />
16 <!-- style sheet links -->
17 <link rel="stylesheet" href="ui/default/slides.css" type="text/css" media="projection" id="slideProj" />
18 <link rel="stylesheet" href="ui/default/outline.css" type="text/css" media="screen" id="outlineStyle" />
19 <link rel="stylesheet" href="ui/default/print.css" type="text/css" media="print" id="slidePrint" />
20 <link rel="stylesheet" href="ui/default/opera.css" type="text/css" media="projection" id="operaFix" />
21 <!-- embedded styles -->
22 <style type="text/css" media="all">
23 .imgcon {width: 525px; margin: 0 auto; padding: 0; text-align: center;}
24 #anim {width: 270px; height: 320px; position: relative; margin-top: 0.5em;}
25 #anim img {position: absolute; top: 42px; left: 24px;}
26 img#me01 {top: 0; left: 0;}
27 img#me02 {left: 23px;}
29 img#me05 {top: 43px;left: 36px;}
32 <script src="ui/default/slides.js" type="text/javascript"></script>
33 <link rel="stylesheet" href="ui/custom.css" type="text/css" />
38 <div id="controls"><!-- DO NOT EDIT --></div>
39 <div id="currentSlide"><!-- DO NOT EDIT --></div>
40 <div id="header"></div>
43 <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>
44 <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>.
47 <h2>Introduction to Moose</h2>
51 <div class="presentation">
54 <h1>Introduction to Moose</h1>
59 <h1>Moose Summed Up</h1>
62 <li><strong>Declarative</strong> OO sugar</li>
63 <li>Introspectable</li>
64 <li>Extensible (MooseX::* on CPAN)</li>
69 <h1>Moose Background</h1>
72 <li>Created by Stevan Little, first released in 2006</li>
73 <li>Moose builds on Perl 5's native OO</li>
74 <li>Borrows ideas from other languages, notably Perl 6</li>
75 <li>Provides semantics for common operations</li>
79 <div class="slide fake-slide0">
80 <h1>Part 0: Moose Concepts</h1>
93 <li>Method modifiers</li>
94 <li>Constructor and destructor</li>
95 <li>One metaclass object</li>
98 <li>Classes do roles</li>
103 <h1>Class Example</h1>
105 <pre><code>package Person;
106 <span class="highlight">use Moose;</span></code></pre>
109 <li>Poof, a Moose-based class!</li>
117 <li>Aka property, slot, field, member variable</li>
118 <li>A piece of data owned by an object</li>
129 <li>Access-control (read-only vs read-write)</li>
130 <li>An optional type</li>
131 <li>Accessor methods</li>
132 <li>Delegation methods</li>
133 <li>Optional default value</li>
134 <li>Many more features</li>
137 <li>Stored in the object, but don't worry about that</li>
142 <h1>Attribute Example</h1>
144 <pre><code>package Person;
147 <span class="highlight">has first_name => ( is => 'rw' );</span></code></pre>
155 <li>Nothing fancy here, just Perl subroutines</li>
158 <pre><code>package Person;
161 <span class="highlight">sub greet { ... }</span></code></pre>
168 <li>Classes <strong>do</strong> (or consume) roles</li>
169 <li>Similar to mixins and Java interfaces</li>
177 <li>Like classes, can have attributes, methods, do roles</li>
178 <li>Roles can require methods</li>
179 <li>Roles are composed (flattened) into classes</li>
184 <h1>Role Example</h1>
186 <pre><code>package HasPermissions;
187 <span class="highlight">use Moose::Role;</span>
189 has is_admin => ( is => 'rw' );</code></pre>
193 <h1>Role Example</h1>
199 <pre><code>package Person;
202 <span class="highlight">with 'HasPermissions';</span></code></pre>
206 <h1>Method Modifiers</h1>
210 <li>"<strong>Before</strong> foo(), do this first"</li>
211 <li>"Do this <strong>after</strong> foo()</li>
212 <li>"Put this code <strong>around</strong> foo()"</li>
217 <h1>Before and After</h1>
219 <pre><code>before 'foo'
220 => sub { warn 'About to call foo()' };
223 => sub { warn 'Leaving foo()' };</code></pre>
230 <pre><code>around 'foo' => sub {
231 my $real_foo = shift;
234 warn 'Just before foo()';
236 $self->$real_foo( @_, bar => 42 );
238 return ( @return, 'modify return values' );
243 <h1>Type Constraints</h1>
246 <li>NOT A FULL-BLOWN TYPE SYSTEM!</li>
247 <li>But still darn useful</li>
248 <li>Constrain attribute values</li>
249 <li>Coerce from other types</li>
254 <h1>Type Constraint Example</h1>
256 <pre><code>package Person;
261 <span class="highlight">isa => 'Int'</span>,
265 Person->new( weight => 'fat' );</code></pre>
272 <li>Attributes can define delegations</li>
273 <li>Lets you hide some implementation details</li>
274 <li>Fewer objects to chase around</li>
281 <pre><code>package Person;
287 <span class="highlight">handles => { 'blog_hostname' => 'host' },</span>
290 <span class="highlight">$person->blog_hostname;</span>
291 # really calls $person->blog_uri->host</code></pre>
295 <h1>Constructors</h1>
298 <li>Moose creates <code>new()</code> for you</li>
299 <li>Provide an optional <code>BUILDARGS()</code> and <code>BUILD()</code></li>
307 <li>Provide an optional <code>DEMOLISH()</code></li>
312 <h1>Moose Meta-API</h1>
315 <li>Answers questions like ...
317 <li>What methods does this class have?</li>
318 <li>What are its parents?</li>
319 <li>What attributes does it have (including inherited attributes)?</li>
320 <li>What roles does it do?</li>
321 <li>Much, much, more</li>
328 <h1>Moose Meta-API</h1>
331 <li>Not just for introspection ...
333 <li>Add methods, attributes, roles, etc</li>
334 <li>Extend and alter core features</li>
344 <li>A quick bit of propaganda ...</li>
351 <pre><code>package Person;
354 has last_name => (
361 <h1>Without Moose</h1>
363 <pre class="small"><code>package Person;
373 if (exists $args{last_name}) {
374 confess "Attribute (last_name) does not pass the type constraint because: "
375 . "Validation failed for 'Str' with value $args{last_name}"
376 if ref($args{last_name});
377 $self->{last_nane} = $args{last_name};
380 return bless $self, $class;
388 confess "Attribute (last_name) does not pass the type constraint because: "
389 . "Validation failed for 'Str' with value $value"
391 $self->{last_name} = $value;
394 return $self->{last_name};
400 <h1>Side by side</h1>
402 <table class="side-by-side">
405 <pre><code>package Person;
408 has last_name => (
414 <pre class="small"><code>package Person;
424 if (exists $args{last_name}) {
425 confess "Attribute (last_name) does not pass the type constraint because: "
426 . "Validation failed for 'Str' with value $args{last_name}"
427 if ref($args{last_name});
428 $self->{last_nane} = $args{last_name};
431 return bless $self, $class;
439 confess "Attribute (last_name) does not pass the type constraint because: "
440 . "Validation failed for 'Str' with value $value"
442 $self->{last_name} = $value;
445 return $self->{last_name};
454 <h1>Side by side</h1>
456 <table class="side-by-side">
459 <pre><code><span class="match-moose">package Person;</span>
462 has last_name => (
468 <pre class="small"><code><span class="match-unsweet">package Person;</span>
478 if (exists $args{last_name}) {
479 confess "Attribute (last_name) does not pass the type constraint because: "
480 . "Validation failed for 'Str' with value $args{last_name}"
481 if ref($args{last_name});
482 $self->{last_nane} = $args{last_name};
485 return bless $self, $class;
493 confess "Attribute (last_name) does not pass the type constraint because: "
494 . "Validation failed for 'Str' with value $value"
496 $self->{last_name} = $value;
499 return $self->{last_name};
507 <h1>Side by side</h1>
509 <table class="side-by-side">
512 <pre><code>package Person;
513 <span class="match-moose">use Moose;</span>
515 has last_name => (
521 <pre class="small"><code>package Person;
522 <span class="match-unsweet">use strict;
529 my $self = {};</span>
531 if (exists $args{last_name}) {
532 confess "Attribute (last_name) does not pass the type constraint because: "
533 . "Validation failed for 'Str' with value $args{last_name}"
534 if ref($args{last_name});
535 $self->{last_nane} = $args{last_name};
538 <span class="match-unsweet">return bless $self, $class;
546 confess "Attribute (last_name) does not pass the type constraint because: "
547 . "Validation failed for 'Str' with value $value"
549 $self->{last_name} = $value;
552 return $self->{last_name};
560 <h1>Side by side</h1>
562 <table class="side-by-side">
565 <pre><code>package Person;
568 <span class="match-moose">has last_name => (</span>
571 <span class="match-moose">);</span></code></pre>
574 <pre class="small"><code>package Person;
584 <span class="match-unsweet">if (exists $args{last_name}) {</span>
585 confess "Attribute (last_name) does not pass the type constraint because: "
586 . "Validation failed for 'Str' with value $args{last_name}"
587 if ref($args{last_name});
588 <span class="match-unsweet">$self->{last_nane} = $args{last_name};
591 return bless $self, $class;
599 confess "Attribute (last_name) does not pass the type constraint because: "
600 . "Validation failed for 'Str' with value $value"
602 $self->{last_name} = $value;
605 return $self->{last_name};
613 <h1>Side by side</h1>
615 <table class="side-by-side">
618 <pre><code>package Person;
621 has last_name => (
622 <span class="match-moose">is => 'rw',</span>
627 <pre class="small"><code>package Person;
637 if (exists $args{last_name}) {
638 confess "Attribute (last_name) does not pass the type constraint because: "
639 . "Validation failed for 'Str' with value $args{last_name}"
640 if ref($args{last_name});
641 $self->{last_nane} = $args{last_name};
644 return bless $self, $class;
647 <span class="match-unsweet">sub last_name {
651 my $value = shift;</span>
652 confess "Attribute (last_name) does not pass the type constraint because: "
653 . "Validation failed for 'Str' with value $value"
655 <span class="match-unsweet">$self->{last_name} = $value;
658 return $self->{last_name};
659 }</span></code></pre>
666 <h1>Side by side</h1>
668 <table class="side-by-side">
671 <pre><code>package Person;
674 has last_name => (
676 <span class="match-moose">isa => 'Str',</span>
680 <pre class="small"><code>package Person;
690 if (exists $args{last_name}) {
691 <span class="match-unsweet">confess "Attribute (last_name) does not pass the type constraint because: "
692 . "Validation failed for 'Str' with value $args{last_name}"
693 if ref($args{last_name});</span>
694 $self->{last_nane} = $args{last_name};
697 return bless $self, $class;
705 <span class="match-unsweet">confess "Attribute (last_name) does not pass the type constraint because: "
706 . "Validation failed for 'Str' with value $value"
707 if ref($value);</span>
708 $self->{last_name} = $value;
711 return $self->{last_name};
719 <h1>Side by side</h1>
721 <table class="side-by-side">
722 <tr class="incremental">
726 <tr class="incremental">
727 <td>92 characters</td>
728 <td>741 characters</td>
732 <pre><code>package Person;
735 has last_name => (
741 <pre class="small"><code>package Person;
751 if (exists $args{last_name}) {
752 confess "Attribute (last_name) does not pass the type constraint because: "
753 . "Validation failed for 'Str' with value $args{last_name}"
754 if ref($args{last_name});
755 $self->{last_nane} = $args{last_name};
758 return bless $self, $class;
766 confess "Attribute (last_name) does not pass the type constraint because: "
767 . "Validation failed for 'Str' with value $value"
769 $self->{last_name} = $value;
772 return $self->{last_name};
782 <pre class="small"><code>sub new {
787 if (exists $args{last_name}) {
788 confess "Attribute (last_name) does not pass the type constraint because: "
789 . "Validation failed for 'Str' with value $args{last_name}"
790 if ref($args{last_name});
791 $self->{last_nane} = $args{last_name};
794 return bless $self, $class;
801 <pre class="small"><code>if (exists $args{last_name}) {
802 confess "Attribute (last_name) does not pass the type constraint because: "
803 . "Validation failed for 'Str' with value $args{last_name}"
804 if ref($args{last_name});
805 $self->{last_nane} = $args{last_name};
812 <code>$self->{last_nane} = $args{last_name};</code>
817 <code>$self->{last_na<span class="wrong">n</span>e}</code>
823 <pre><code>package Person;
826 has last_name => (
832 <div class="slide fake-slide0">
833 <h1>Part 1: Moose Classes</h1>
837 <h1>Moose Classes</h1>
840 <li>Moose classes are Perl packages which <code>use Moose</code></li>
845 <h1>Moose.pm and Your Class</h1>
847 <pre><code>package Person;
848 use Moose;</code></pre>
851 <li><code>Moose.pm</code> provides declarative sugar</li>
852 <li>Turns on <code>strict</code> and <code>warnings</code></li>
853 <li>Creates metaclasses for your class: <code>Person->meta</code></li>
854 <li>Moose classes automatically inherit from <code>Moose::Object</code></li>
859 <h1>What <code>Moose::Object</code> Provides</h1>
862 <li>Constructor - <code>new()</code></li>
863 <li>Calls your <code>BUILDARGS()</code> and/or <code>BUILD()</code></li>
864 <li>Calls your <code>DEMOLISH</code> during object destruction</li>
872 <li>Takes <code>@_</code>, returns a hash reference of attribute names/value</li>
873 <li>Accepts a hash or hashref; throws otherwise</li>
874 <li>Provide your own for other cases</li>
875 <li><strong>Always</strong> call <code>$class->SUPER::BUILDARGS(@_)</code> as a fallback!</li>
880 <h1>BUILDARGS Example</h1>
882 <pre><code>package Person;
888 if ( @_ == 1 && ! ref $_[0] ) {
889 <span class="highlight">return { ssn => $_[0] };</span>
892 <span class="highlight">return $class->SUPER::BUILDARGS(@_)</span>;
895 <span class="highlight">Person->new('123-45-6789')</span></code></pre>
902 <li>Called after object is created, before <code>new</code> returns</li>
903 <li>Chance to do more complex validation, set complex attributes</li>
904 <li>Called in reverse inheritance order, parents to children</li>
905 <li>Return value is ignored</li>
910 <h1>BUILD Example</h1>
912 <pre><code>package Person;
918 if ( $self->country_of_residence
920 die 'All US residents'
921 . ' must have an SSN'
922 unless $self->has_ssn;
928 <h1>Object Construction a la Moose</h1>
930 <pre><code>Person->new(@_)</code></pre>
933 <li>Calls <code>Person->BUILDARGS(@_)</code> to turn <code>@_</code> into a hashref</li>
934 <li>Blesses a reference</li>
935 <li>Populates attributes based on the hashref from #1</li>
936 <li>Calls <code>$new_object->BUILDALL($constructor_args)</code>
937 <br />... which calls all <code>BUILD</code> methods</li>
938 <li>Returns the object</li>
943 <h1>The Object is Oqaque</h1>
946 <li>Technically it's a hash reference</li>
947 <li><span class="wrong">If you <em>ever</em> treat it as one <strong>you are doing it wrong!</strong></span></li>
955 <li>Like <code>DESTROY</code>, but Moose makes sure all <code>DEMOLISH</code> methods in a hierarchy are called</li>
956 <li>Called in normal inheritance order, children to parents</li>
964 <li><code>extends</code> is sugar for declaring parent classes</li>
967 <pre><code>package Employee;
969 <span class="highlight">extends 'Person';</span></code></pre>
976 <li>Each call to <code>extends</code> <strong>resets</strong> your parents</li>
979 <h2 class="wrong">Wrong</h2>
981 <pre><code>package EvilEmployee;
984 extends 'Thief';</code></pre>
986 <h2 class="right">Right</h2>
988 <pre><code>package EvilEmployee;
990 extends 'Person', 'Thief';</code></pre>
994 <h1>Extending un-Moose-y Parents</h1>
996 <pre><code>package My::LWP;
998 extends 'LWP';</code></pre>
1001 <li>No <code>Moose::Object</code>, so ...
1003 <li>No attribute-handling <code>new()</code></li>
1004 <li>No <code>BUILDARGS()</code> or <code>BUILD()</code></li>
1005 <li>No <code>DEMOLISH()</code></li>
1008 <li>But see <code>MooseX::NonMoose</code> for a workaround</li>
1013 <h1><code>override</code> and <code>super</code></h1>
1016 <li><code>override</code> is another method modifier</li>
1017 <li>An alternative to Perl's <code>SUPER::</code></li>
1022 <h1><code>override</code> and <code>super</code></h1>
1024 <pre><code>package Employee;
1027 <span class="current incremental">extends 'Person';</span>
1029 <span class="incremental">override</span> work => sub {
1032 die "Pay me first" unless $self->got_paid;
1033 <span class="incremental">super();</span>
1034 }<span class="incremental">;</span></code></pre>
1038 <h1>Caveat <code>super</code></h1>
1041 <li>Mostly like <code>$self->SUPER::work(@_)</code></li>
1042 <li><strong>But</strong> cannot change <code>@_</code>!</li>
1043 <li>Binds the parent's method at compile time</li>
1048 <h1>Minimal Attributes</h1>
1051 <li><code>has 'foo'</code></li>
1052 <li>Use <code>is => 'ro'</code> or <code>is => 'rw'</code></li>
1053 <li>Attributes without "is" have no accessors</li>
1058 <h1>Read-write attributes</h1>
1060 <pre><code>package Person;
1063 has first_name => ( <span class="highlight">is => 'rw'</span> );
1066 Person->new( first_name => 'Dave' );
1068 $person->first_name('Stevan');
1069 print $person->first_name; # Stevan</code></pre>
1074 <h1>Read-only attributes</h1>
1076 <pre><code>package Person;
1079 has first_name => ( <span class="highlight">is => 'ro'</span> );
1082 Person->new( first_name => 'Dave' );
1084 $person->first_name('Stevan');
1085 print $person->first_name; # Dave</code></pre>
1090 <h1>There is More to Come</h1>
1093 <li>Attributes have a <em>lot</em> of features</li>
1098 <h1>Cleaning Up Moose Droppings</h1>
1100 <pre><code>package Person;
1104 Person->can('extends');</code></pre>
1107 <li>Not very hygienic</li>
1112 <h1>Cleaning Up Moose Droppings</h1>
1114 <pre><code>package Person;
1122 Person->can('extends');</code></pre>
1129 <li><code>no Moose</code> at the end of a package is a best practice</li>
1135 <h1>Immutability</h1>
1138 <li><span style="font-family: URW Chancery L; font-size: 140%">Stevan's Incantation of Fleet-Footedness</span></li>
1141 <pre><code>package Person;
1144 <span class="highlight">__PACKAGE__->meta->make_immutable;</span></code></pre>
1148 <h1>What <code>make_immutable</code> does</h1>
1152 <li>Uses <code>eval</code> to "inline" a constructor</li>
1153 <li>Memoizes a lot of meta-information</li>
1154 <li>Makes loading your class slower</li>
1155 <li>Makes object creation <em>much</em> faster</li>
1160 <h1>When to Immutabilize?</h1>
1163 <li><em>Almost</em> always</li>
1164 <li>Startup time vs execution time</li>
1169 <h1>Classes Summary</h1>
1172 <li><code>use Moose</code></li>
1173 <li><code>Class->meta</code></li>
1174 <li><code>Moose::Object</code> base class</li>
1175 <li><code>extends</code>, <code>override</code>, and <code>super</code></li>
1176 <li>Simple attributes: <code>has</code>, <code>is => 'ro'</code>, & <code>is => 'rw'</code></li>
1177 <li><code>no Moose</code></li>
1178 <li><code>__PACKAGE__->meta->make_immutable</code></li>
1191 # perl bin/prove -lv t/00-prereq.t
1193 # perl install-moose (if needed)
1195 # perl bin/prove -lv t/01-classes.t
1197 Iterate til this passes all its tests</pre>
1200 <div class="slide fake-slide0">
1201 <h1>Part 2: Roles</h1>
1205 <h1>Just What Is a Role?</h1>
1208 <li>Mixin? Interface? Trait?</li>
1209 <li>Yes ... and more!</li>
1214 <h1>Roles Can Have State <strong>and</strong> Behavior</h1>
1216 <pre><code>package HasPermissions;
1219 <span class="current incremental"># state
1220 has access_level => ( is => 'rw' );</span>
1222 <span class="incremental"># behavior
1225 my $required = shift;
1227 return $self->access_level >= $required;
1228 }</span></code></pre>
1233 <h1>Roles Can Define Interfaces</h1>
1235 <pre><code>package Printable;
1238 requires 'as_string';</code></pre>
1242 <h1>Roles Can Do All Three</h1>
1244 <pre><code>package Printable;
1247 requires 'as_string';
1249 has has_been_printed => ( is => 'rw' );
1253 print $self->as_string;
1254 $self->has_been_printed(1);
1259 <h1>Classes Consume Roles</h1>
1261 <pre><code>package Person;
1264 with 'HasPermissions';</code></pre>
1268 <h1>Classes Consume Roles</h1>
1270 <pre><code>my $person = Person->new(
1271 first_name => 'Kenichi',
1272 last_name => 'Asai',
1273 access_level => 42,
1276 print $person->full_name
1278 . $person->can_access(42)
1280 : 'little power';</code></pre>
1284 <h1>Roles in Practice</h1>
1287 <li>Consuming a role =~ inlining the role</li>
1292 <h1>In Other Words ...</h1>
1294 <pre><code>package Person;
1297 <span class="highlight">with 'Printable';</span></code></pre>
1301 <h1>In Other Words ...</h1>
1303 <pre><code>package Person;
1306 <span class="delete">with 'Printable';</span>
1308 <span class="highlight">has has_been_printed => ( is => 'rw' );
1312 print $self->as_string;
1313 $self->has_been_printed(1);
1314 }</span></code></pre>
1321 <li>Role consumption is introspectable</li>
1324 <pre><code>if ( Person->does('Printable') ) { ... }
1328 if ( Person->meta->does('Printable') ) { ... }</code></pre>
1333 <h1>These Names Are the Same</h1>
1336 <li>What if a role and class define the same method?</li>
1337 <li>A class's <em>local</em> methods win over the role's</li>
1338 <li>The role's methods win over the class's <em>inherited</em> methods</li>
1343 <h1>Conflicts Between Roles</h1>
1346 <li>Two roles with a method of the same name</li>
1347 <li>Generates a compile-time error when consumed by a class</li>
1352 <h1>Conflict Example</h1>
1354 <pre><code>package IsFragile;
1359 package CanBreakdance;
1362 sub break { ... }</code></pre>
1366 <h1>Conflict Example</h1>
1368 <pre><code>package FragileDancer;
1371 <span class="highlight">with 'IsFragile', 'CanBreakdance';</span></code></pre>
1374 <li>Only one <code>with</code>!</li>
1379 <h1>Conflict Resolution</h1>
1382 <li>The consuming class must resolve the conflict by implementing the method</li>
1383 <li>Can use some combination of method exclusion and aliasing</li>
1388 <h1>Method Aliasing</h1>
1390 <pre><code>package FragileDancer;
1393 <span class="highlight">with 'IsFragile' =>
1395 { break => 'break_bone' } },
1398 { break => 'break_it_down' } };</span></code></pre>
1401 <li>Renames the roles' methods</li>
1402 <li>Still conflicts, need to <code>exclude</code> as well</li>
1407 <h1>Method Exclusion</h1>
1409 <pre><code>package FragileDancer;
1412 <span class="highlight">with 'IsFragile' =>
1414 { break => 'break_bone' },
1415 exclude => 'break' },
1418 { break => 'break_dance' },
1419 exclude => 'break' };</span></code></pre>
1423 <h1>And then ...</h1>
1425 <pre><code>package FragileDancer;
1432 if ( rand(1) < 0.5 ) {
1439 <h1>Still Full of Fail</h1>
1442 <li>Roles are also about semantics!</li>
1443 <li>We've fulfilled the letter and lost the spirit</li>
1444 <li>Roles have a <em>meaning</em></li>
1445 <li>Think twice before blindly aliasing and excluding methods!</li>
1450 <h1>Hot Role-on-Role Action</h1>
1452 <pre><code>package Comparable;
1455 requires 'compare';</code></pre>
1459 <h1>Hot Role-on-Role Action</h1>
1461 <pre><code>package TestsEquality;
1468 return $self->compare(@_) == 0;
1473 <h1>And then ...</h1>
1475 <pre><code>package Integer;
1478 with 'TestsEquality';
1480 # Satisfies the Comparable role
1483 Integer->does('TestsEquality'); # true
1484 Integer->does('Comparable'); # also true!</code></pre>
1488 <h1>Name Conflicts Between Roles</h1>
1490 <pre><code>package HasSubProcess;
1493 <span class="highlight">sub execute { ... }</span>
1498 with 'HasSubProcess';
1500 <span class="highlight">sub execute { ... }</span></code></pre>
1504 <h1>Delayed Conflict</h1>
1506 <pre><code>package StateOfTexas;
1507 with 'Killer';</code></pre>
1510 <li><code>StateOfTexas</code> must implement its own <code>execute</code></li>
1511 <li>But loading the <code>Killer</code> role by itself does not cause an error</li>
1516 <h1>Roles as Interfaces</h1>
1519 <li>Roles can <code>require</code> methods of their consumers</li>
1520 <li>Compile-time checks</li>
1521 <li>Method must exist when the role is consumed</li>
1526 <h1>The Attribute Gotcha</h1>
1528 <pre><code>package HasSize;
1531 <span class="current incremental">requires 'size';</span>
1536 <span class="incremental">with 'HasSize';
1538 has size => ( is => 'ro' );</span></code></pre>
1542 <h1>The Attribute Gotcha Workaround</h1>
1544 <pre><code>package HasSize;
1552 has size => ( is => 'ro' );
1554 with 'HasSize';</code></pre>
1558 <h1>Compile-time Is a Lie</h1>
1561 <li>Really, it's <em>package load</em> time</li>
1562 <li>That's run-time, but before the "real" run-time</li>
1563 <li>Moose does not rewire Perl, it's just sugar!</li>
1564 <li>(but <code>MooseX::Declare</code> <em>does</em> rewire Perl)</li>
1569 <h1>Enforcing Roles</h1>
1571 <pre><code>package Comparison;
1574 has [ 'left', 'right' ] => (
1576 <span class="highlight">does => 'Comparable',</span>
1581 <li>A sneak peek at type constraints</li>
1587 <h1>Roles Can Be Applied to Objects</h1>
1589 <pre><code>use Moose::Util qw( apply_all_roles );
1591 my $fragile_person = Person->new( ... );
1592 apply_all_roles( $fragile_person, 'IsFragile' );</code></pre>
1595 <li>Does not change the <code>Person</code> class</li>
1596 <li>Works with non-Moose classes, great for monkey-patching!</li>
1601 <h1>Roles Are Dirty Too</h1>
1604 <li>Once again, clean up those Moose droppings</li>
1607 <pre><code>package Comparable;
1612 <span class="highlight">no Moose::Role;</span></code></pre>
1615 <li>But roles cannot be made immutable</li>
1620 <h1>The Zen of Roles</h1>
1623 <li>Roles represent discrete units of ...
1630 <li>Roles are shareable between unrelated classes</li>
1631 <li>Roles are what a class <em>does</em>, not what it <em>is</em></li>
1632 <li>Roles <em>add</em> functionality, inheritance <em>specializes</em></li>
1637 <h1>Abstract Examples</h1>
1640 <li>Human <em>@ISA</em> Animal</li>
1641 <li>Human <em>does</em> Toolmaker (as <em>does</em> Chimpanzee)</li>
1642 <li>Car <em>@ISA</em> Vehicle</li>
1643 <li>Car <em>does</em> HasEngine</li>
1648 <h1>Real Examples</h1>
1651 <li>Objects representing SQL database components and queries
1653 <li>Schema, Table, Column, ColumnAlias</li>
1654 <li>Select, Insert, Update, Delete</li>
1661 <h1>Real Examples</h1>
1664 <li>Column and ColumnAlias both <em>do</em> ColumnLike</li>
1665 <li>ColumnLike things can be used in certain parts of queries</li>
1666 <li>All queries <em>do</em> HasWhereClause</li>
1667 <li>Select <em>does</em> Comparable and Selectable (for subselects)</li>
1668 <li>A where clause requires its components to <em>do</em> Comparable</li>
1673 <h1>Roles Summary</h1>
1676 <li>Roles can define an interface with <code>requires</code></li>
1677 <li>Roles can have state (attributes) and behavior (methods)</li>
1678 <li>Roles can mix interface, state, & behavior</li>
1679 <li>Roles are composed (flattened) into classes</li>
1680 <li>Roles can do other roles</li>
1681 <li>Roles can be used as a type in APIs (must do Comparable)</li>
1693 # perl bin/prove -lv t/02-roles.t
1695 Iterate til this passes all its tests</pre>
1698 <div class="slide fake-slide0">
1699 <h1>Part 3: Basic Attributes</h1>
1703 <h1>Attributes Are Huge</h1>
1706 <li>Moose's biggest feature</li>
1707 <li>The target of <em>many</em> MooseX modules</li>
1712 <h1>Quick Review</h1>
1715 <li>Declared with <code>has</code></li>
1716 <li>Read-only or read-write</li>
1719 <pre><code>package Shirt;
1722 has 'color' => ( is => 'ro' );
1723 has 'is_ripped' => ( is => 'rw' );</code></pre>
1727 <h1>Required-ness</h1>
1730 <li>Required means "must be passed to the constructor"</li>
1731 <li>But can be <code>undef</code></li>
1736 <h1>Required-ness</h1>
1738 <pre><code>package Person;
1741 has first_name => (
1743 <span class="current incremental">required => 1,</span>
1746 <span class="incremental">Person->new( first_name => undef ); # ok
1747 Person->new(); # kaboom</span></code></pre>
1751 <h1>Default and Builder</h1>
1754 <li>Attributes can have defaults</li>
1755 <li>Simple non-referecne scalars (number, string)</li>
1756 <li>Subroutine reference</li>
1757 <li>A builder method</li>
1765 <li>Can be a non-reference scalar (including <code>undef</code>)</li>
1768 <pre><code>package Person;
1773 default => 'Spire FCU',
1781 <li>Can be a subroutine reference</li>
1784 <pre><code>package Person;
1791 name => 'Spire FCU' ) },
1796 <h1>Default as a Subroutine Reference</h1>
1799 <li>Called as a method on the object</li>
1800 <li>Called anew for each object</li>
1805 <h1>Why No Other Reference Types?</h1>
1807 <pre><code>package Person;
1812 <span class="wrong">default => Bank->new(
1813 name => 'Spire FCU' ),</span>
1817 <li>Now <strong>every</strong> person shares the <strong>same</strong> Bank object!</li>
1822 <h1>Defaulting to an Empty Reference</h1>
1824 <pre><code>package Person;
1827 has packages => (
1829 default => <span class="highlight">sub { [] }</span>,
1834 <h1>What if I Want to Share?</h1>
1836 <pre><code>package Person;
1839 my $highlander_bank =
1840 Bank->new( name => 'Spire FCU' );
1844 default => sub { $highlander_bank },
1852 <li>A method <em>name</em> which returns the default</li>
1859 <pre><code>package Person;
1864 builder => '_build_bank',
1869 return Bank->new( name => 'Spire FCU' );
1874 <h1>Default vs Builder</h1>
1877 <li>Use default for simple scalars</li>
1878 <li>Use default to return empty references</li>
1879 <li>Use default for <em>very</em> trivial subroutine references</li>
1880 <li>Use builder for everything else</li>
1885 <h1>Builder Bonuses</h1>
1888 <li>Can be overridden and method modified, because it's called by <em>name</em></li>
1889 <li>Roles can require a builder</li>
1894 <h1>Role Requires Builder</h1>
1896 <pre><code>package HasBank;
1899 requires '_build_bank';
1903 builder => '_build_bank',
1908 <h1>Lazy, Good for Nothing Attributes</h1>
1911 <li>Normally, defaults are generated during object construction</li>
1912 <li>This can be expensive</li>
1913 <li>We want to default to <code>$self->size * 2</code>, but attribute initialization order is unpredictable</li>
1914 <li>Use lazy attributes!</li>
1919 <h1>The Power of Dynamic Defaults</h1>
1921 <pre><code>package Person;
1924 has shoe_size => (
1930 <h1>The Power of Dynamic Defaults</h1>
1932 <pre><code>has shoes => (
1934 <span class="highlight">lazy => 1,</span>
1935 builder => '_build_shoes',
1941 return Shoes->new(
1942 size => <span class="highlight">$self->shoe_size</span> );
1947 <h1>Lazy is Good</h1>
1950 <li>Lazy defaults are executed when the attribute is read</li>
1951 <li>Can see other object attributes</li>
1952 <li>Still need to watch out for circular laziness</li>
1957 <h1>Clearer and Predicate</h1>
1960 <li>Attributes can have a value, including <code>undef</code>, or not</li>
1961 <li>Can clear the value with a clearer method</li>
1962 <li>Can check for the existence of a value with a predicate method</li>
1963 <li>By default, these methods are not created</li>
1968 <h1>Clearer and Predicate</h1>
1970 <pre><code>package Person;
1976 builder => '_build_account',
1977 <span class="highlight">clearer => '_clear_account',
1978 predicate => 'has_account',</span>
1983 <h1>Clearer and Lazy Defaults</h1>
1986 <li>Lazy defaults are good for computed attributes</li>
1987 <li>Clear the attribute when the source data changes</li>
1988 <li>Recalculated at next access</li>
1993 <h1>Renaming constructor arguments</h1>
1996 <li>By default, constructor names = attribute names</li>
1997 <li>Use <code>init_arg</code> to change this</li>
1998 <li>Set <code>init_arg => undef</code> to make it unconstructable</li>
2003 <h1>Some <code>init_arg</code> examples</h1>
2005 <pre><code>package Person;
2010 <span class="highlight">init_arg => 'foot_size',</span>
2013 Person->new( <span class="wrong">shoe_size => 13</span> );
2016 Person->new( <span class="right">foot_size => 13</span> );
2017 print $person->shoe_size;</code></pre>
2021 <h1>Some <code>init_arg</code> examples</h1>
2023 <pre><code>package Person;
2028 <span class="highlight">init_arg => undef,</span>
2031 Person->new( <span class="wrong">shoes => Shoes->new</span> );</code></pre>
2035 <h1>Why Set <code>init_arg => undef</code>?</h1>
2038 <li>Use this with a lazy default for attributes-as-cache</li>
2039 <li>Compute the value as needed</li>
2040 <li>Ensure that it is always generated correctly (not set by constructor)</li>
2041 <li>Use triggers or method modifiers (coming soon) to clear the value</li>
2046 <h1>Attribute Inheritance</h1>
2049 <li>By default, subclasses inherit attribute as-is</li>
2050 <li>Can change some attribute parameters in subclasses
2056 <li>others we've not yet covered</li>
2063 <h1>Attribute Inheritance Example</h1>
2065 <pre><code>package Employee;
2070 has '<span class="highlight">+first_name</span>' => (
2071 default => 'Joe',
2076 <h1>Attribute Inheritance Warning</h1>
2079 <li>An attribute is a contract about a class's API</li>
2080 <li>Don't break that contract in a subclass</li>
2081 <li>Especially important in the context of types</li>
2086 <h1>Changing Accessor Names</h1>
2088 <pre><code>package Person;
2091 has first_name => (
2092 <span class="highlight">accessor</span> => 'first_name',
2096 <li>The long-hand version of <code>is => 'rw'</code></li>
2101 <h1>Changing Accessor Names</h1>
2103 <pre><code>package Person;
2106 has first_name => (
2107 <span class="highlight">reader</span> => 'first_name',
2108 <span class="highlight">writer</span> => undef,
2112 <li>The long-hand version of <code>is => 'ro'</code></li>
2118 <h1>Changing Accessor Names</h1>
2120 <pre><code>package Person;
2123 has first_name => (
2124 <span class="highlight">reader</span> => 'get_first_name',
2125 <span class="highlight">writer</span> => 'set_first_name',
2130 <h1>Changing Accessor Names</h1>
2132 <pre><code>package Person;
2135 has first_name => (
2136 <span class="highlight">is</span> => 'rw',
2137 <span class="highlight">writer</span> => '_first_name',
2141 <li>Can also mix-and-match <code>is</code> and explicit names</li>
2146 <h1>ETOOMUCHTYPING</h1>
2149 <li><code>MooseX::FollowPBP</code><br /><code>get_foo</code> and <code>set_foo</code></li>
2150 <li><code>MooseX::SemiAffordanceAccessor</code><br /><code>foo</code> and <code>set_foo</code></li>
2155 <h1>ETOOMUCHTYPING</h1>
2157 <pre><code>package Person;
2159 <span class="highlight">use MooseX::SemiAffordanceAccessor;</span>
2161 has first_name => (
2166 <li>Creates <code>first_name</code> and <code>set_first_name</code></li>
2171 <h1>Basic Attributes Summary</h1>
2174 <li>Attributes can be <code>required</code></li>
2175 <li>Attributes can have a <code>default</code> or <code>builder</code></li>
2176 <li>Attributes with a default or builder can be <code>lazy</code></li>
2177 <li>Attributes can have a <code>clearer</code> and/or <code>predicate</code></li>
2178 <li>An attribute's constructor name can be changed with <code>init_arg</code></li>
2179 <li>A subclass can alter its parents' attributes</li>
2180 <li>Attribute accessor names can be changed</li>
2192 # perl bin/prove -lv t/03-basic-attributes.t
2194 Iterate til this passes all its tests</pre>
2197 <div class="slide fake-slide0">
2198 <h1>Part 4: Method Modifiers</h1>
2202 <h1>What is a Method Modifier</h1>
2205 <li>Apply to an existing method</li>
2206 <li>... from a parent class, the current class, or a role</li>
2207 <li>Roles can provide modifiers that are applied at composition time</li>
2212 <h1>What is a Method Modifier</h1>
2215 <li>"Inject" behavior</li>
2216 <li>Add behavior to generated methods (accessors, delegations)</li>
2217 <li>Provide roles which modify existing behavior</li>
2222 <h1>Before and After</h1>
2225 <li>Simplest modifiers - <code>before</code> and <code>after</code></li>
2226 <li>Guess when they run!</li>
2231 <h1>Uses for <code>before</code></h1>
2234 <li>As a pre-call check</li>
2237 <pre><code>package Person;
2240 before work => sub {
2242 die 'I have no job!'
2243 unless $self->has_title;
2248 <h1>Uses for <code>before</code></h1>
2251 <li>Logging/Debugging</li>
2254 <pre><code>package Person;
2257 before work => sub {
2259 return unless $DEBUG;
2261 warn "Called work on ", $self->full_name,
2262 "with the arguments: [@_]\n";
2267 <h1>Uses for <code>after</code></h1>
2270 <li>Also works for logging/debugging</li>
2271 <li>Post-X side-effects (recording audit info)</li>
2274 <pre><code>package Person;
2277 after work => sub {
2279 $self->work_count(
2280 $self->work_count + 1 );
2288 <li>Modifiers are useful for adding behavior to generated methods</li>
2293 <h1>Other Uses Example</h1>
2295 <pre><code>has password => (
2297 clearer => 'clear_password',
2300 has hashed_password => (
2302 builder => '_build_hashed_password',
2303 clearer => '_clear_hashed_password',
2306 after clear_password => sub {
2308 $self->_clear_hashed_password;
2313 <h1><code>before</code> and <code>after</code> Limitations</h1>
2316 <li>Cannot alter method parameters</li>
2317 <li>Cannot alter return value</li>
2318 <li>But <strong>can</strong> throw an exception</li>
2323 <h1>The <code>around</code> Modifier</h1>
2326 <li>The big gun</li>
2327 <li>Can alter parameters <strong>and/or</strong> return values</li>
2328 <li>Can skip calling the wrapped method entirely</li>
2333 <h1>The power of <code>around</code></h1>
2335 <pre><code>around insert => sub {
2339 $self->_validate_insert(@_);
2343 $self->_munge_insert(@_) );
2345 $new_user->_assign_uri;
2352 <h1>Modifier Order</h1>
2355 <li>Before runs order from last to first</li>
2356 <li>After runs in order from first to last</li>
2357 <li>Around runs in order from last to first</li>
2362 <h1>Modifier Order Illustrated</h1>
2365 <span class="current incremental">before 2
2367 <span class="incremental">around 2
2369 <span class="incremental">wrapped method</span>
2370 <span class="incremental">around 1
2372 <span class="incremental">after 1
2378 <h1>Modifiers in Roles</h1>
2381 <li>Roles can use these modifiers</li>
2382 <li>Very powerful!</li>
2387 <h1>Modifiers in Roles</h1>
2389 <pre><code>package IsUnreliable;
2392 <span class="highlight">requires 'run';
2394 around run</span> => sub {
2398 return if rand(1) < 0.5;
2400 return $self->$orig(@_);
2405 <h1>Augment and Inner</h1>
2408 <li>Inverted <code>super</code></li>
2409 <li>From least- to most-specific</li>
2410 <li>Grandparent to parent to child</li>
2411 <li>Not allowed in roles</li>
2416 <h1>Augment and Inner</h1>
2418 <pre><code>package Document;
2420 sub xml { '<doc>' . <span class="highlight">inner()</span> . '</doc>' }
2425 <span class="highlight">augment xml</span> =>
2426 sub { title() . <span class="highlight">inner()</span> . summary() };
2431 <span class="highlight">augment xml</span> =>
2432 sub { tps_xml() . <span class="highlight">inner()</span> };</code></pre>
2436 <h1>Augment and Inner</h1>
2439 <li>When we call <code>$tps->xml</code> ...
2441 <li><code>Document->xml</code></li>
2442 <li><code>Report->xml</code></li>
2443 <li><code>TPSReport->xml</code></li>
2450 <h1>Augment and Inner Usage</h1>
2453 <li>Call <code>inner()</code> to "fill in the blank"</li>
2454 <li>Requires designing for subclassing</li>
2455 <li>Call <code>inner()</code> in the terminal class, just in case</li>
2460 <h1>Method Modifiers Summary</h1>
2463 <li>Use <code>before</code> and <code>after</code> for ...
2466 <li>pre- or post-validation</li>
2467 <li>to add behavior to generated methods</li>
2470 <li>These two modifiers cannot change parameters or return values</li>
2475 <h1>Method Modifiers Summary</h1>
2478 <li>Use <code>around</code> to ...
2480 <li>alter parameters passed to the original method</li>
2481 <li>alter the return value of the original method</li>
2482 <li>not call the original method at all (or call a <em>different</em> method)</li>
2489 <h1>Method Modifiers Summary</h1>
2492 <li>When using modifiers in a role, require the modified method</li>
2493 <li>Use <code>augment</code> and <code>inner</code> to invert the normal subclassing flow ...
2495 <li>Least- to most-specific (parents to children)</li>
2496 <li>Build in "insertability" (stick more stuff in the "middle")</li>
2499 <li>Always call <code>inner</code> in the most specific subclass to allow for future extension</li>
2511 # perl bin/prove -lv t/04-method-modifiers.t
2513 Iterate til this passes all its tests</pre>
2516 <div class="slide fake-slide0">
2517 <h1>Part 5: Types</h1>
2521 <h1>A Type System for Perl</h1>
2524 <li>Sort of ...</li>
2525 <li><em>Variables</em> are not typed</li>
2526 <li>Attributes can have types</li>
2527 <li>MooseX modules let you define method signatures</li>
2532 <h1>Components of a Moose Type</h1>
2535 <li>A type is a name and a constraint</li>
2536 <li>Types have a hierarchy</li>
2537 <li>Constraints are cumulative from parents</li>
2538 <li>Types can have associated coercions</li>
2543 <h1>Built-in Type Hierarchy</h1>
2562 <h1>Built-in Type Hierarchy</h1>
2595 <li>Like Perl's <code>if ($foo)</code></li>
2600 <h1>Value (and subtypes)</h1>
2603 <li><code>Value</code> is true when <code>! ref $thing</code></li>
2604 <li><code>Value</code> and <code>Str</code> are effectively the same, but <code>Str</code> is more expressive</li>
2605 <li>An overloaded object which numifies does not pass the <code>Num</code> constraint!</li>
2606 <li>Perl 5's overloading is hopelessly broken</li>
2611 <h1>ClassName and RoleName</h1>
2614 <li>A string with a package name</li>
2615 <li>The package <strong>must already be loaded</strong></li>
2620 <h1>Parameterizable Types</h1>
2623 <li>What does <code>ArrayRef[`a]</code> mean?</li>
2624 <li><code>s/`a/Int/</code> (or <code>Str</code> or ...)</li>
2625 <li>When you use it you can write ...
2627 <li><code>ArrayRef</code> (== <code>ArrayRef[Item]</code>)</li>
2628 <li><code>ArrayRef[Str]</code></li>
2629 <li><code>ArrayRef[MyTypeName]</code></li>
2630 <li><code>ArrayRef[HashRef[Maybe[Int]]]</code></li>
2640 <li>Maybe means either the named type or <code>undef</code></li>
2641 <li><code>Maybe[Int]</code> accepts integers or <code>undef</code></li>
2649 <li>This or that (or that or ...)</li>
2650 <li><code>Int | ArrayRef[Int]</code></li>
2651 <li>But use a coercion instead when possible</li>
2652 <li>Or use a <code>role_type</code>, <code>duck_type</code>, or anything not a union</li>
2653 <li>A union is often a code smell</li>
2658 <h1>Making Your Own Types</h1>
2660 <pre><code>use Moose::Util::TypeConstraints;
2662 <span class="incremental current">subtype 'PositiveInt',</span>
2663 <span class="incremental">as 'Int',</span>
2664 <span class="incremental">where { $_ > 0 },</span>
2665 <span class="incremental">message { "The value you provided ($_)"
2666 . " was not a positive number." };</span>
2670 <span class="incremental">isa => 'PositiveInt',</span>
2675 <h1>Automatic Types</h1>
2678 <li>Moose creates a type for every Moose class and role</li>
2679 <li>Unknown names are assumed to be classes</li>
2684 <h1>Automatic Types</h1>
2686 <pre><code>package Employee;
2691 <span class="highlight">isa => 'Employee',</span>
2694 has start_date => (
2696 <span class="highlight">isa => 'DateTime',</span>
2701 <h1>Subtype Shortcuts - <code>class_type</code></h1>
2703 <pre><code>use Moose::Util::TypeConstraints;
2704 class_type 'DateTime';
2708 where { $_->isa('DateTime') },
2709 message { ... };</code></pre>
2713 <h1>Subtype Shortcuts - <code>role_type</code></h1>
2715 <pre><code>use Moose::Util::TypeConstraints;
2716 role_type 'Printable';
2718 subtype 'Printable',
2721 { Moose::Util::does_role(
2722 $_, 'Printable' ) },
2723 message { ... };</code></pre>
2727 <h1>Subtype Shortcuts - <code>duck_type</code></h1>
2729 <pre><code>use Moose::Util::TypeConstraints;
2730 duck_type Car => qw( run break_down );
2734 where { all { $_->can($_) }
2735 qw( run break_down ) },
2736 message { ... };</code></pre>
2740 <h1>Subtype Shortcuts - <code>enum</code></h1>
2742 <pre><code>use Moose::Util::TypeConstraints;
2743 enum Color => qw( red blue green ) );
2745 my %ok = map { $_ => 1 } qw( red blue green );
2749 message { ... };</code></pre>
2753 <h1>Anonymous Subtypes</h1>
2755 <pre><code>package Person;
2757 <span class="highlight">my $posint =
2758 subtype as 'Int', where { $_ > 0 };</span>
2762 <span class="highlight">isa => $posint,</span>
2766 <li>Shortcuts have anonymous forms as well</li>
2773 <pre><code>use Moose::Util::TypeConstraints;
2777 where { ! /[a-z]/ };
2779 <span class="incremental current">coerce 'UCStr',</span>
2780 <span class="incremental">from 'Str',</span>
2781 <span class="incremental">via { uc };</span>
2783 has shouty_name => (
2786 <span class="incremental">coerce => 1,</span>
2791 <h1>Coercion Examples</h1>
2793 <pre><code>subtype 'My::DateTime',
2794 as class_type 'DateTime';
2796 coerce 'My::DateTime',
2798 via { DateTime->new( %{$_} ) };
2800 coerce 'My::DateTime',
2802 via { DateTime->from_epoch(
2803 epoch => $_ ) };</code></pre>
2806 <li>Use coercion to inflate a value</li>
2811 <h1>Coercion Examples</h1>
2813 <pre><code>coerce 'ArrayRef[Int]',
2815 via { [ $_ ] };</code></pre>
2818 <li>Coerce instead of a union like <code style="white-space: nowrap">Int | ArrayRef[Int]</code></li>
2824 <h1>Using Types with Attributes</h1>
2826 <pre><code>package Person;
2828 use Moose::Util::TypeConstraints;
2832 <span class="highlight">isa => 'Num',</span>
2835 has favorite_numbers => (
2837 <span class="highlight">isa => 'ArrayRef[Int]',
2838 coerce => 1,</span>
2843 <h1>Typed Methods (Low-tech)</h1>
2845 <pre class="medium"><code>package Person;
2846 <span class="highlight">use MooseX::Params::Validate qw( validated_list );</span>
2850 <span class="highlight">my ( $tasks, $can_rest ) =
2854 { isa => 'ArrayRef[Task]',
2866 <h1>Typed Methods (High-tech)</h1>
2868 <pre class="medium"><code>package Person;
2870 <span class="highlight">use MooseX::Method::Signatures;</span>
2872 <span class="highlight">method work ( ArrayRef[Task] :$tasks,
2873 Bool :$can_rest = 0 )</span> {
2881 <h1>Digression: The Type Registry</h1>
2884 <li>Types are actually <code>Moose::Meta::TypeConstraint</code> <em>objects</em></li>
2885 <li>Stored in an interpreter-global registry mapping names to objects</li>
2893 <li>Coercions are attached to type objects</li>
2894 <li>Therefore also global</li>
2895 <li>Name conflicts between modules!</li>
2896 <li>Coercion conflicts between modules!</li>
2901 <h1>Namespace Fix</h1>
2904 <li>Use some sort of pseudo-namespacing scheme</li>
2905 <li>Never coerce directly to a class name, or <em>to</em> built-in types</li>
2910 <h1>Namespace Fix</h1>
2912 <pre><code>use Moose::Util::TypeConstraints;
2914 subtype <span class="highlight">'MyApp::Type::DateTime',</span>
2917 <span class="highlight">coerce 'MyApp::Type::DateTime',</span>
2919 via { DateTime->new( %{$_} ) }
2921 has creation_date => (
2923 <span class="highlight">isa => 'MyApp::Type::DateTime',</span>
2929 <h1>Namespace Fix</h1>
2931 <pre><code>subtype 'MyApp::Type::ArrayOfInt',
2934 coerce 'MyApp::Type::ArrayOfInt',
2936 via { [ $_ ] };</code></pre>
2940 <h1>Namespace Fix Pros and Cons</h1>
2943 <li><span class="right">Relatively simple</span></li>
2944 <li><span class="right">Already built into Moose</span></li>
2945 <li><span class="wrong">Conflates type and module namespaces</span></li>
2946 <li><span class="wrong">Type names are strings, so typos are easy to make and may be hard to find</span></li>
2951 <h1>MooseX::Types</h1>
2953 <pre><code>package MyApp::Types;
2956 <span class="highlight">-declare => [ qw( ArrayOfInt ) ]</span>;
2957 use MooseX::Types::Moose
2960 subtype <span class="highlight">ArrayOfInt</span>,
2963 coerce <span class="highlight">ArrayOfInt</span>
2965 via { [ $_ ] };</code></pre>
2969 <h1>MooseX::Types</h1>
2971 <pre><code>package MyApp::Account;
2973 use MyApp::Types qw( ArrayOfInt );
2975 has transaction_history => (
2982 <h1>MooseX::Types</h1>
2985 <li>Type names are exported functions, catches typos early</li>
2986 <li>Types must be pre-declared</li>
2987 <li>Types are stored with namespaces internally, but externally are short</li>
2988 <li>Import existing Moose types as functions from <code>MooseX::Types::Moose</code></li>
2989 <li>Still need string names for things like <code>ArrayRef['Email::Address']</code></li>
2994 <h1>MooseX::Types Pros and Cons</h1>
2997 <li><span class="right">Catches typos at compile time</span></li>
2998 <li><span class="right">Automatic namespacing</span></li>
2999 <li><span class="wrong">One more thing to install and learn</span></li>
3000 <li><span class="wrong">Every name gets types twice (declared and then defined)</span></li>
3001 <li><span class="wrong">Still stuck with strings when referring to class or role names</span></li>
3002 <li><span class="wrong">Coercion gotcha from earlier still applies to types exported from <code>MooseX::Types::Moose</code></span></li>
3007 <h1>Recommendation</h1>
3010 <li>Use <code>MooseX::Types</code></li>
3011 <li>Compile time error catching and automatic namespacing are huge wins</li>
3012 <li>Docs from <code>Moose::Util::TypeConstraints</code> are 98% compatible with <code>MooseX::Types</code> anyway</li>
3013 <li>A function exported by a type library works wherever a type name would</li>
3025 # perl bin/prove -lv t/05-types.t
3027 Iterate til this passes all its tests</pre>
3030 <div class="slide fake-slide0">
3031 <h1>Part 6: Advanced Attributes</h1>
3035 <h1>Weak References</h1>
3038 <li>A weak reference lets you avoid circular references</li>
3039 <li>Weak references do not increase the reference count</li>
3044 <h1>Circular Reference Illustrated</h1>
3046 <pre><code>my $foo = {};
3047 my $bar = { foo => $foo };
3048 $foo->{bar} = $bar;</code></pre>
3051 <li>Neither <code>$foo</code> nor <code>$bar</code> go out of scope<br />
3052 (until the program exits)</li>
3057 <h1>Weakening Circular References</h1>
3059 <pre><code>use Scalar::Util qw( weaken );
3062 my $bar = { foo => $foo };
3063 $foo->{bar} = $bar;
3064 weaken $foo->{bar}</code></pre>
3067 <li>When <code>$bar</code> goes out of scope, <code>$foo->{bar}</code> becomes <code>undef</code></li>
3072 <h1>Circular References in Attributes</h1>
3074 <pre><code>package Person;
3077 has name => ( is => 'ro' );
3078 has friend => ( is => 'rw' );
3080 my $alice = Person->new( name => 'Alice' );
3081 my $bob = Person->new( name => 'Bob' );
3082 $bob->friend($alice);
3083 $alice->friend($bob);</code></pre>
3089 <pre><code>package Person;
3092 has name => ( is => 'ro' );
3093 has friend => ( is => 'rw', <span class="highlight">weak_ref => 1</span> );
3095 my $alice = Person->new( name => 'Alice' );
3096 my $bob = Person->new( name => 'Bob' );
3097 $bob->friend($alice);
3098 $alice->friend($bob);</code></pre>
3102 <h1>Under the Hood</h1>
3105 <li>A <code>weak_ref</code> attribute calls <code>weaken</code> ...
3107 <li>during object construction</li>
3108 <li>when the attribute is set via a writer</li>
3118 <li>A code reference run after an attribute is <em>set</em></li>
3119 <li>Like an <code>after</code> modifier, but makes intentions clearer</li>
3122 <h2 class="wrong">Gross</h2>
3124 <pre><code>after salary_level => {
3127 $self->clear_salary;
3132 <h1>Use a Trigger Instead</h1>
3134 <h2 class="right">Cleaner</h2>
3136 <pre><code>has salary_level => (
3138 trigger => sub { $_[0]->clear_salary },
3146 <li>Attributes can be objects</li>
3147 <li>Delegation transparently calls methods on those objects</li>
3152 <h1>Delegation Examples</h1>
3154 <pre><code>package Person;
3159 <span class="highlight">handles => [ 'inhale', 'exhale' ],</span>
3163 <li>Creates <code>$person->inhale</code> and <code>->exhale</code> methods</li>
3164 <li>Internally calls <code>$person->lungs->inhale</code></li>
3169 <h1>Why Delegation?</h1>
3172 <li>Reduce the number of classes exposed</li>
3173 <li>Re-arrange class internals -<br />
3174 turn a method into an attribute with delegation</li>
3175 <li>Provide convenenience methods</li>
3180 <h1>Moose's <code>handles</code> Parameter</h1>
3183 <li>Accepts many arguments ...
3185 <li>Array reference - list of methods to delegate as-is</li>
3186 <li>Hash reference - map of method names</li>
3187 <li>Regex - delegates all matching methods</li>
3188 <li>Role name - delegates all methods in the role</li>
3189 <li>Sub reference - does something complicated ;)</li>
3196 <h1>Array Reference</h1>
3199 <li>Takes each method name and creates a simple delegation from the delegating class to the delegatee attribute</li>
3204 <h1>Hash Reference</h1>
3207 <li>Mapping of names in the delegating class to the delegatee class</li>
3210 <pre><code>package Person;
3215 isa => 'BankAccount',
3216 <span class="highlight">handles => {
3217 receive_money => 'deposit',
3218 give_money => 'withdraw',
3224 <h1>Hash Reference Detailed</h1>
3226 <pre><code> handles => {
3227 receive_money => 'deposit',
3228 give_money => 'withdraw',
3232 <li><code>$person->receive_money</code> = <code>$person->account->deposit</code></li>
3233 <li><code>$person->give_money</code> = <code>$person->account->withdraw</code></li>
3240 <pre><code>package Person;
3246 handles => qr/.*/,
3250 <li>Creates a delegation for every method in the Name class</li>
3251 <li>Excludes <code>meta</code> and methods inherited from <code>Moose::Object</code></li>
3258 <pre><code>package Auditor;
3261 sub record_change { ... }
3262 sub change_history { ... }
3269 does => 'Auditor',
3270 <span class="highlight">handles => 'Auditor',</span>
3275 <h1>Role Name Detailed</h1>
3278 <li>Account gets delegate methods for each method in the <code>Auditor</code> role
3280 <li>record_history</li>
3281 <li>change_history</li>
3288 <h1>Traits and Metaclasses</h1>
3291 <li>The ultimate in customization</li>
3292 <li>Per attribute metaclasses</li>
3293 <li>Per attribute roles applied to the attribute metaclass</li>
3294 <li>Change the meta-level behavior</li>
3299 <h1>Traits and Metaclasses</h1>
3302 <li>The default metaclass is <code>Moose::Meta::Attribute</code></li>
3303 <li>Controls accessor generation, defaults, delegation, etc.</li>
3304 <li>Adding a role to this metaclass (or replacing it) allows for infinite customization</li>
3309 <h1>Traits and Metaclasses</h1>
3312 <li>Can add/alter/remove attribute parameter (from <code>has</code>)</li>
3313 <li>Can change behavior of created attribute</li>
3318 <h1>Simple Trait Example</h1>
3320 <pre><code>package Person;
3322 use MooseX::LabeledAttributes;
3325 <span class="highlight">traits => [ 'Labeled' ],</span>
3328 <span class="highlight">label => 'Social Security Number',</span>
3331 print <span class="highlight">Person->meta
3332 ->get_attribute('ssn')->label;</span></code></pre>
3336 <h1>Simple Metaclass Example</h1>
3338 <pre><code>package Person;
3340 use MooseX::LabeledAttributes;
3343 <span class="highlight">metaclass =>
3344 'MooseX::Meta::Attribute::Labeled',</span>
3347 <span class="highlight">label => 'Social Security Number',</span>
3350 print <span class="highlight">Person->meta
3351 ->get_attribute('ssn')->label;</span></code></pre>
3355 <h1>Traits vs Metaclass</h1>
3358 <li>Can apply any mix of traits to an attribute</li>
3359 <li>But just one metaclass</li>
3360 <li>Traits (aka roles) can cooperate</li>
3361 <li>Metaclasses require you to pick just one</li>
3366 <h1>Advanced Attributes Summary</h1>
3369 <li>Use <code>weak_ref</code> to avoid circular references</li>
3370 <li>Use trigger to do an action post-attribute write</li>
3371 <li>Use delegations to hide "internal" objects</li>
3372 <li>Traits and metaclasses let you extend Moose's core attribute features</li>
3384 # perl bin/prove -lv t/06-advanced-attributes.t
3386 Iterate til this passes all its tests</pre>
3389 <div class="slide fake-slide0">
3390 <h1>Part 7: Introspection</h1>
3393 <div class="slide fake-slide0">
3394 <h1>Part 8: A Tour of MooseX</h1>
3397 <div class="slide fake-slide0">
3398 <h1>Part 9: Writing Moose Extensions</h1>
3401 <div class="slide fake-slide0">
3406 <h1>More Information</h1>
3409 <li><a href="http://moose.perl.org/">http://moose.perl.org/</a></li>
3410 <li><a href="http://search.cpan.org/dist/Moose/lib/Moose/Manual.pod">Moose::Manual</a> and <a href="http://search.cpan.org/dist/Moose/lib/Moose/Cookbook.pod">Moose::Cookbook</a></li>
3411 <li><a href="irc://irc.perl.org/#moose">irc://irc.perl.org/#moose</a></li>
3412 <li>mailing list - <a href="mailto:moose@perl.org">moose@perl.org</a></li>
3413 <li>Slides and exercises are in Moose's git repo:
3415 <span style="white-space: nowrap">git://jules.scsys.co.uk/gitmo/moose-presentations</span></li>
3425 Copyright 2009 David Rolsky. All Rights Reserved.
3427 This work is licensed under a Creative Commons Attribution-Share Alike
3428 3.0 United States License See
3429 http://creativecommons.org/licenses/by-sa/3.0/us/ for details.