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>
56 <h2><a href="git://git.moose.perl.org/moose-presentations.git"><tt>git://git.moose.perl.org/moose-presentations.git</tt></a></h2>
60 <h1>Moose Summed Up</h1>
63 <li><strong>Declarative</strong> OO sugar</li>
64 <li>Introspectable</li>
65 <li>Extensible (MooseX::* on CPAN)</li>
70 <h1>Moose Background</h1>
73 <li>Created by Stevan Little, first released in 2006</li>
74 <li>Moose builds on Perl 5's native OO</li>
75 <li>Borrows ideas from other languages, notably Perl 6</li>
76 <li>Provides semantics for common operations</li>
80 <div class="slide fake-slide0">
81 <h1>Part 0: Moose Concepts</h1>
94 <li>Method modifiers</li>
95 <li>Constructor and destructor</li>
96 <li>One metaclass object</li>
99 <li>Classes do roles</li>
104 <h1>Class Example</h1>
106 <pre><code>package Person;
107 <span class="highlight">use Moose;</span></code></pre>
110 <li>Poof, a Moose-based class!</li>
118 <li>Aka property, slot, field, member variable</li>
119 <li>A piece of data owned by an object</li>
130 <li>Access-control (read-only vs read-write)</li>
131 <li>An optional type</li>
132 <li>Accessor methods</li>
133 <li>Delegation methods</li>
134 <li>Optional default value</li>
135 <li>Many more features</li>
138 <li>Stored in the object, but don't worry about that</li>
143 <h1>Attribute Example</h1>
145 <pre><code>package Person;
148 <span class="highlight">has first_name => ( is => 'rw' );</span></code></pre>
156 <li>Nothing fancy here, just Perl subroutines</li>
159 <pre><code>package Person;
162 <span class="highlight">sub greet { ... }</span></code></pre>
169 <li>Classes <strong>do</strong> (or consume) roles</li>
170 <li>Similar to mixins and Java interfaces</li>
178 <li>Like classes, can have attributes, methods, do roles</li>
179 <li>Roles can require methods</li>
180 <li>Roles are composed (flattened) into classes</li>
185 <h1>Role Example</h1>
187 <pre><code>package HasPermissions;
188 <span class="highlight">use Moose::Role;</span>
190 has is_admin => ( is => 'rw' );</code></pre>
194 <h1>Role Example</h1>
200 <pre><code>package Person;
203 <span class="highlight">with 'HasPermissions';</span></code></pre>
207 <h1>Method Modifiers</h1>
211 <li>"<strong>Before</strong> foo(), do this first"</li>
212 <li>"Do this <strong>after</strong> foo()</li>
213 <li>"Put this code <strong>around</strong> foo()"</li>
218 <h1>Before and After</h1>
220 <pre><code>before 'foo'
221 => sub { warn 'About to call foo()' };
224 => sub { warn 'Leaving foo()' };</code></pre>
231 <pre><code>around 'foo' => sub {
232 my $real_foo = shift;
235 warn 'Just before foo()';
237 $self->$real_foo( @_, bar => 42 );
239 return ( @return, 'modify return values' );
244 <h1>Type Constraints</h1>
247 <li>NOT A FULL-BLOWN TYPE SYSTEM!</li>
248 <li>But still darn useful</li>
249 <li>Constrain attribute values</li>
250 <li>Coerce from other types</li>
255 <h1>Type Constraint Example</h1>
257 <pre><code>package Person;
262 <span class="highlight">isa => 'Int'</span>,
266 Person->new( weight => 'fat' );</code></pre>
273 <li>Attributes can define delegations</li>
274 <li>Lets you hide some implementation details</li>
275 <li>Fewer objects to chase around</li>
282 <pre><code>package Person;
288 <span class="highlight">handles => { 'blog_hostname' => 'host' },</span>
291 <span class="highlight">$person->blog_hostname;</span>
292 # really calls $person->blog_uri->host</code></pre>
296 <h1>Constructors</h1>
299 <li>Moose creates <code>new()</code> for you</li>
300 <li>Provide an optional <code>BUILDARGS()</code> and <code>BUILD()</code></li>
308 <li>Provide an optional <code>DEMOLISH()</code></li>
313 <h1>Moose Meta-API</h1>
316 <li>Answers questions like ...
318 <li>What methods does this class have?</li>
319 <li>What are its parents?</li>
320 <li>What attributes does it have (including inherited attributes)?</li>
321 <li>What roles does it do?</li>
322 <li>Much, much, more</li>
329 <h1>Moose Meta-API</h1>
332 <li>Not just for introspection ...
334 <li>Add methods, attributes, roles, etc</li>
335 <li>Extend and alter core features</li>
345 <li>A quick bit of propaganda ...</li>
352 <pre><code>package Person;
355 has last_name => (
362 <h1>Without Moose</h1>
364 <pre class="small"><code>package Person;
374 if (exists $args{last_name}) {
375 confess "Attribute (last_name) does not pass the type constraint because: "
376 . "Validation failed for 'Str' with value $args{last_name}"
377 if ref($args{last_name});
378 $self->{last_nane} = $args{last_name};
381 return bless $self, $class;
389 confess "Attribute (last_name) does not pass the type constraint because: "
390 . "Validation failed for 'Str' with value $value"
392 $self->{last_name} = $value;
395 return $self->{last_name};
401 <h1>Side by side</h1>
403 <table class="side-by-side">
406 <pre><code>package Person;
409 has last_name => (
415 <pre class="small"><code>package Person;
425 if (exists $args{last_name}) {
426 confess "Attribute (last_name) does not pass the type constraint because: "
427 . "Validation failed for 'Str' with value $args{last_name}"
428 if ref($args{last_name});
429 $self->{last_nane} = $args{last_name};
432 return bless $self, $class;
440 confess "Attribute (last_name) does not pass the type constraint because: "
441 . "Validation failed for 'Str' with value $value"
443 $self->{last_name} = $value;
446 return $self->{last_name};
455 <h1>Side by side</h1>
457 <table class="side-by-side">
460 <pre><code><span class="match-moose">package Person;</span>
463 has last_name => (
469 <pre class="small"><code><span class="match-unsweet">package Person;</span>
479 if (exists $args{last_name}) {
480 confess "Attribute (last_name) does not pass the type constraint because: "
481 . "Validation failed for 'Str' with value $args{last_name}"
482 if ref($args{last_name});
483 $self->{last_nane} = $args{last_name};
486 return bless $self, $class;
494 confess "Attribute (last_name) does not pass the type constraint because: "
495 . "Validation failed for 'Str' with value $value"
497 $self->{last_name} = $value;
500 return $self->{last_name};
508 <h1>Side by side</h1>
510 <table class="side-by-side">
513 <pre><code>package Person;
514 <span class="match-moose">use Moose;</span>
516 has last_name => (
522 <pre class="small"><code>package Person;
523 <span class="match-unsweet">use strict;
530 my $self = {};</span>
532 if (exists $args{last_name}) {
533 confess "Attribute (last_name) does not pass the type constraint because: "
534 . "Validation failed for 'Str' with value $args{last_name}"
535 if ref($args{last_name});
536 $self->{last_nane} = $args{last_name};
539 <span class="match-unsweet">return bless $self, $class;
547 confess "Attribute (last_name) does not pass the type constraint because: "
548 . "Validation failed for 'Str' with value $value"
550 $self->{last_name} = $value;
553 return $self->{last_name};
561 <h1>Side by side</h1>
563 <table class="side-by-side">
566 <pre><code>package Person;
569 <span class="match-moose">has last_name => (</span>
572 <span class="match-moose">);</span></code></pre>
575 <pre class="small"><code>package Person;
585 <span class="match-unsweet">if (exists $args{last_name}) {</span>
586 confess "Attribute (last_name) does not pass the type constraint because: "
587 . "Validation failed for 'Str' with value $args{last_name}"
588 if ref($args{last_name});
589 <span class="match-unsweet">$self->{last_nane} = $args{last_name};
592 return bless $self, $class;
600 confess "Attribute (last_name) does not pass the type constraint because: "
601 . "Validation failed for 'Str' with value $value"
603 $self->{last_name} = $value;
606 return $self->{last_name};
614 <h1>Side by side</h1>
616 <table class="side-by-side">
619 <pre><code>package Person;
622 has last_name => (
623 <span class="match-moose">is => 'rw',</span>
628 <pre class="small"><code>package Person;
638 if (exists $args{last_name}) {
639 confess "Attribute (last_name) does not pass the type constraint because: "
640 . "Validation failed for 'Str' with value $args{last_name}"
641 if ref($args{last_name});
642 $self->{last_nane} = $args{last_name};
645 return bless $self, $class;
648 <span class="match-unsweet">sub last_name {
652 my $value = shift;</span>
653 confess "Attribute (last_name) does not pass the type constraint because: "
654 . "Validation failed for 'Str' with value $value"
656 <span class="match-unsweet">$self->{last_name} = $value;
659 return $self->{last_name};
660 }</span></code></pre>
667 <h1>Side by side</h1>
669 <table class="side-by-side">
672 <pre><code>package Person;
675 has last_name => (
677 <span class="match-moose">isa => 'Str',</span>
681 <pre class="small"><code>package Person;
691 if (exists $args{last_name}) {
692 <span class="match-unsweet">confess "Attribute (last_name) does not pass the type constraint because: "
693 . "Validation failed for 'Str' with value $args{last_name}"
694 if ref($args{last_name});</span>
695 $self->{last_nane} = $args{last_name};
698 return bless $self, $class;
706 <span class="match-unsweet">confess "Attribute (last_name) does not pass the type constraint because: "
707 . "Validation failed for 'Str' with value $value"
708 if ref($value);</span>
709 $self->{last_name} = $value;
712 return $self->{last_name};
720 <h1>Side by side</h1>
722 <table class="side-by-side">
723 <tr class="incremental">
727 <tr class="incremental">
728 <td>92 characters</td>
729 <td>741 characters</td>
733 <pre><code>package Person;
736 has last_name => (
742 <pre class="small"><code>package Person;
752 if (exists $args{last_name}) {
753 confess "Attribute (last_name) does not pass the type constraint because: "
754 . "Validation failed for 'Str' with value $args{last_name}"
755 if ref($args{last_name});
756 $self->{last_nane} = $args{last_name};
759 return bless $self, $class;
767 confess "Attribute (last_name) does not pass the type constraint because: "
768 . "Validation failed for 'Str' with value $value"
770 $self->{last_name} = $value;
773 return $self->{last_name};
783 <pre class="small"><code>sub new {
788 if (exists $args{last_name}) {
789 confess "Attribute (last_name) does not pass the type constraint because: "
790 . "Validation failed for 'Str' with value $args{last_name}"
791 if ref($args{last_name});
792 $self->{last_nane} = $args{last_name};
795 return bless $self, $class;
802 <pre class="small"><code>if (exists $args{last_name}) {
803 confess "Attribute (last_name) does not pass the type constraint because: "
804 . "Validation failed for 'Str' with value $args{last_name}"
805 if ref($args{last_name});
806 $self->{last_nane} = $args{last_name};
813 <code>$self->{last_nane} = $args{last_name};</code>
818 <code>$self->{last_na<span class="wrong">n</span>e}</code>
824 <pre><code>package Person;
827 has last_name => (
833 <div class="slide fake-slide0">
834 <h1>Part 1: Moose Classes</h1>
838 <h1>Moose Classes</h1>
841 <li>Moose classes are Perl packages which <code>use Moose</code></li>
846 <h1>Moose.pm and Your Class</h1>
848 <pre><code>package Person;
849 use Moose;</code></pre>
852 <li><code>Moose.pm</code> provides declarative sugar</li>
853 <li>Turns on <code>strict</code> and <code>warnings</code></li>
854 <li>Creates metaclasses for your class: <code>Person->meta</code></li>
855 <li>Moose classes automatically inherit from <code>Moose::Object</code></li>
860 <h1>What <code>Moose::Object</code> Provides</h1>
863 <li>Constructor - <code>new()</code></li>
864 <li>Calls your <code>BUILDARGS()</code> and/or <code>BUILD()</code></li>
865 <li>Calls your <code>DEMOLISH</code> during object destruction</li>
873 <li>Takes <code>@_</code>, returns a hash reference of attribute names/value</li>
874 <li>Accepts a hash or hashref; throws otherwise</li>
875 <li>Provide your own for other cases</li>
876 <li><strong>Always</strong> call <code>$class->SUPER::BUILDARGS(@_)</code> as a fallback!</li>
881 <h1>BUILDARGS Example</h1>
883 <pre><code>package Person;
889 if ( @_ == 1 && ! ref $_[0] ) {
890 <span class="highlight">return { ssn => $_[0] };</span>
893 <span class="highlight">return $class->SUPER::BUILDARGS(@_)</span>;
896 <span class="highlight">Person->new('123-45-6789')</span></code></pre>
903 <li>Called after object is created, before <code>new</code> returns</li>
904 <li>Chance to do more complex validation, set complex attributes</li>
905 <li>Called in reverse inheritance order, parents to children</li>
906 <li>Return value is ignored</li>
911 <h1>BUILD Example</h1>
913 <pre><code>package Person;
919 if ( $self->country_of_residence
921 die 'All US residents'
922 . ' must have an SSN'
923 unless $self->has_ssn;
929 <h1>Object Construction a la Moose</h1>
931 <pre><code>Person->new(@_)</code></pre>
934 <li>Calls <code>Person->BUILDARGS(@_)</code> to turn <code>@_</code> into a hashref</li>
935 <li>Blesses a reference</li>
936 <li>Populates attributes based on the hashref from #1</li>
937 <li>Calls <code>$new_object->BUILDALL($constructor_args)</code>
938 <br />... which calls all <code>BUILD</code> methods</li>
939 <li>Returns the object</li>
944 <h1>The Object is Opaque</h1>
947 <li>Technically it's a hash reference</li>
948 <li><span class="wrong">If you <em>ever</em> treat it as one <strong>you are doing it wrong!</strong></span></li>
956 <li>Like <code>DESTROY</code>, but Moose makes sure all <code>DEMOLISH</code> methods in a hierarchy are called</li>
957 <li>Called in normal inheritance order, children to parents</li>
965 <li><code>extends</code> is sugar for declaring parent classes</li>
968 <pre><code>package Employee;
970 <span class="highlight">extends 'Person';</span></code></pre>
977 <li>Each call to <code>extends</code> <strong>resets</strong> your parents</li>
980 <h2 class="wrong">Wrong</h2>
982 <pre><code>package EvilEmployee;
985 extends 'Thief';</code></pre>
987 <h2 class="right">Right</h2>
989 <pre><code>package EvilEmployee;
991 extends 'Person', 'Thief';</code></pre>
995 <h1>Extending un-Moose-y Parents</h1>
997 <pre><code>package My::LWP;
999 extends 'LWP';</code></pre>
1002 <li>No <code>Moose::Object</code>, so ...
1004 <li>No attribute-handling <code>new()</code></li>
1005 <li>No <code>BUILDARGS()</code> or <code>BUILD()</code></li>
1006 <li>No <code>DEMOLISH()</code></li>
1009 <li>But see <code>MooseX::NonMoose</code> for a workaround</li>
1014 <h1><code>override</code> and <code>super</code></h1>
1017 <li><code>override</code> is another method modifier</li>
1018 <li>An alternative to Perl's <code>SUPER::</code></li>
1023 <h1><code>override</code> and <code>super</code></h1>
1025 <pre><code>package Employee;
1028 <span class="current incremental">extends 'Person';</span>
1030 <span class="incremental">override</span> work => sub {
1033 die "Pay me first" unless $self->got_paid;
1034 <span class="incremental">super();</span>
1035 }<span class="incremental">;</span></code></pre>
1039 <h1>Caveat <code>super</code></h1>
1042 <li>Mostly like <code>$self->SUPER::work(@_)</code></li>
1043 <li><strong>But</strong> cannot change <code>@_</code>!</li>
1044 <li>Binds the parent's method at compile time</li>
1049 <h1>Minimal Attributes</h1>
1052 <li><code>has 'foo'</code></li>
1053 <li>Use <code>is => 'ro'</code> or <code>is => 'rw'</code></li>
1054 <li>Attributes without "is" have no accessors</li>
1059 <h1>Read-write attributes</h1>
1061 <pre><code>package Person;
1064 has first_name => ( <span class="highlight">is => 'rw'</span> );
1067 Person->new( first_name => 'Dave' );
1069 $person->first_name('Stevan');
1070 print $person->first_name; # Stevan</code></pre>
1075 <h1>Read-only attributes</h1>
1077 <pre><code>package Person;
1080 has first_name => ( <span class="highlight">is => 'ro'</span> );
1083 Person->new( first_name => 'Dave' );
1085 $person->first_name('Stevan');
1086 print $person->first_name; # Dave</code></pre>
1091 <h1>There is More to Come</h1>
1094 <li>Attributes have a <em>lot</em> of features</li>
1099 <h1>Cleaning Up Moose Droppings</h1>
1101 <pre><code>package Person;
1105 Person->can('extends');</code></pre>
1108 <li>Not very hygienic</li>
1113 <h1>Cleaning Up Moose Droppings</h1>
1115 <pre><code>package Person;
1123 Person->can('extends');</code></pre>
1130 <li><code>no Moose</code> at the end of a package is a best practice</li>
1131 <li>Or <code>namespace::clean</code> at the top</li>
1137 <h1>Immutability</h1>
1140 <li><span style="font-family: URW Chancery L; font-size: 140%">Stevan's Incantation of Fleet-Footedness</span></li>
1143 <pre><code>package Person;
1146 <span class="highlight">__PACKAGE__->meta->make_immutable;</span></code></pre>
1150 <h1>What <code>make_immutable</code> does</h1>
1154 <li>Uses <code>eval</code> to "inline" a constructor</li>
1155 <li>Memoizes a lot of meta-information</li>
1156 <li>Makes loading your class slower</li>
1157 <li>Makes object creation <em>much</em> faster</li>
1162 <h1>When to Immutabilize?</h1>
1165 <li><em>Almost</em> always</li>
1166 <li>Startup time vs execution time</li>
1171 <h1>Classes Summary</h1>
1174 <li><code>use Moose</code></li>
1175 <li><code>Class->meta</code></li>
1176 <li><code>Moose::Object</code> base class</li>
1177 <li><code>extends</code>, <code>override</code>, and <code>super</code></li>
1178 <li>Simple attributes: <code>has</code>, <code>is => 'ro'</code>, & <code>is => 'rw'</code></li>
1179 <li><code>no Moose</code></li>
1180 <li><code>__PACKAGE__->meta->make_immutable</code></li>
1193 # perl bin/prove -lv t/00-prereq.t
1195 # perl install-moose (if needed)
1197 # perl bin/prove -lv t/01-classes.t
1199 Iterate til this passes all its tests</pre>
1202 <div class="slide fake-slide0">
1203 <h1>Part 2: Roles</h1>
1207 <h1>Just What Is a Role?</h1>
1210 <li>Mixin? Interface? Trait?</li>
1211 <li>Yes ... and more!</li>
1216 <h1>Roles Can Have State <strong>and</strong> Behavior</h1>
1218 <pre><code>package HasPermissions;
1221 <span class="current incremental"># state
1222 has access_level => ( is => 'rw' );</span>
1224 <span class="incremental"># behavior
1227 my $required = shift;
1229 return $self->access_level >= $required;
1230 }</span></code></pre>
1235 <h1>Roles Can Define Interfaces</h1>
1237 <pre><code>package Printable;
1240 requires 'as_string';</code></pre>
1244 <h1>Roles Can Do All Three</h1>
1246 <pre><code>package Printable;
1249 requires 'as_string';
1251 has has_been_printed => ( is => 'rw' );
1255 print $self->as_string;
1256 $self->has_been_printed(1);
1261 <h1>Classes Consume Roles</h1>
1263 <pre><code>package Person;
1266 with 'HasPermissions';</code></pre>
1270 <h1>Classes Consume Roles</h1>
1272 <pre><code>my $person = Person->new(
1273 first_name => 'Kenichi',
1274 last_name => 'Asai',
1275 access_level => 42,
1278 print $person->full_name
1280 . $person->can_access(42)
1282 : 'little power';</code></pre>
1286 <h1>Roles in Practice</h1>
1289 <li>Consuming a role =~ inlining the role</li>
1294 <h1>In Other Words ...</h1>
1296 <pre><code>package Person;
1299 <span class="highlight">with 'Printable';</span></code></pre>
1303 <h1>In Other Words ...</h1>
1305 <pre><code>package Person;
1308 <span class="delete">with 'Printable';</span>
1310 <span class="highlight">has has_been_printed => ( is => 'rw' );
1314 print $self->as_string;
1315 $self->has_been_printed(1);
1316 }</span></code></pre>
1323 <li>Role consumption is introspectable</li>
1326 <pre><code>if ( Person->does('Printable') ) { ... }
1330 if ( Person->meta->does('Printable') ) { ... }</code></pre>
1335 <h1>These Names Are the Same</h1>
1338 <li>What if a role and class define the same method?</li>
1339 <li>A class's <em>local</em> methods win over the role's</li>
1340 <li>The role's methods win over the class's <em>inherited</em> methods</li>
1345 <h1>Conflicts Between Roles</h1>
1348 <li>Two roles with a method of the same name</li>
1349 <li>Generates a compile-time error when consumed by a class</li>
1354 <h1>Conflict Example</h1>
1356 <pre><code>package IsFragile;
1361 package CanBreakdance;
1364 sub break { ... }</code></pre>
1368 <h1>Conflict Example</h1>
1370 <pre><code>package FragileDancer;
1373 <span class="highlight">with 'IsFragile', 'CanBreakdance';</span></code></pre>
1376 <li>Only one <code>with</code>!</li>
1381 <h1>Conflict Resolution</h1>
1384 <li>The consuming class must resolve the conflict by implementing the method</li>
1385 <li>Can use some combination of method exclusion and aliasing</li>
1390 <h1>Method Aliasing</h1>
1392 <pre><code>package FragileDancer;
1395 <span class="highlight">with 'IsFragile' =>
1397 { break => 'break_bone' } },
1400 { break => 'break_it_down' } };</span></code></pre>
1403 <li>Renames the roles' methods</li>
1404 <li>Still conflicts, need to <code>exclude</code> as well</li>
1409 <h1>Method Exclusion</h1>
1411 <pre><code>package FragileDancer;
1414 <span class="highlight">with 'IsFragile' =>
1416 { break => 'break_bone' },
1417 exclude => 'break' },
1420 { break => 'break_dance' },
1421 exclude => 'break' };</span></code></pre>
1425 <h1>And then ...</h1>
1427 <pre><code>package FragileDancer;
1434 if ( rand(1) < 0.5 ) {
1441 <h1>Still Full of Fail</h1>
1444 <li>Roles are also about semantics!</li>
1445 <li>We've fulfilled the letter and lost the spirit</li>
1446 <li>Roles have a <em>meaning</em></li>
1447 <li>Think twice before blindly aliasing and excluding methods!</li>
1452 <h1>Hot Role-on-Role Action</h1>
1454 <pre><code>package Comparable;
1457 requires 'compare';</code></pre>
1461 <h1>Hot Role-on-Role Action</h1>
1463 <pre><code>package TestsEquality;
1470 return $self->compare(@_) == 0;
1475 <h1>And then ...</h1>
1477 <pre><code>package Integer;
1480 with 'TestsEquality';
1482 # Satisfies the Comparable role
1485 Integer->does('TestsEquality'); # true
1486 Integer->does('Comparable'); # also true!</code></pre>
1490 <h1>Name Conflicts Between Roles</h1>
1492 <pre><code>package HasSubProcess;
1495 <span class="highlight">sub execute { ... }</span>
1500 with 'HasSubProcess';
1502 <span class="highlight">sub execute { ... }</span></code></pre>
1506 <h1>Delayed Conflict</h1>
1508 <pre><code>package StateOfTexas;
1509 with 'Killer';</code></pre>
1512 <li><code>StateOfTexas</code> must implement its own <code>execute</code></li>
1513 <li>But loading the <code>Killer</code> role by itself does not cause an error</li>
1518 <h1>Roles as Interfaces</h1>
1521 <li>Roles can <code>require</code> methods of their consumers</li>
1522 <li>Compile-time checks</li>
1523 <li>Method must exist when the role is consumed</li>
1528 <h1>The Attribute Gotcha</h1>
1530 <pre><code>package HasSize;
1533 <span class="current incremental">requires 'size';</span>
1538 <span class="incremental">with 'HasSize';
1540 has size => ( is => 'ro' );</span></code></pre>
1544 <h1>The Attribute Gotcha Workaround</h1>
1546 <pre><code>package HasSize;
1554 has size => ( is => 'ro' );
1556 with 'HasSize';</code></pre>
1560 <h1>Compile-time Is a Lie</h1>
1563 <li>Really, it's <em>package load</em> time</li>
1564 <li>That's run-time, but before the "real" run-time</li>
1565 <li>Moose does not rewire Perl, it's just sugar!</li>
1566 <li>(but <code>MooseX::Declare</code> <em>does</em> rewire Perl)</li>
1571 <h1>Enforcing Roles</h1>
1573 <pre><code>package Comparison;
1576 has [ 'left', 'right' ] => (
1578 <span class="highlight">does => 'Comparable',</span>
1583 <li>A sneak peek at type constraints</li>
1589 <h1>Roles Can Be Applied to Objects</h1>
1591 <pre><code>use Moose::Util qw( apply_all_roles );
1593 my $fragile_person = Person->new( ... );
1594 apply_all_roles( $fragile_person, 'IsFragile' );</code></pre>
1597 <li>Does not change the <code>Person</code> class</li>
1598 <li>Works with non-Moose classes, great for monkey-patching!</li>
1603 <h1>Roles Are Dirty Too</h1>
1606 <li>Once again, clean up those Moose droppings</li>
1609 <pre><code>package Comparable;
1614 <span class="highlight">no Moose::Role;</span></code></pre>
1617 <li>But roles cannot be made immutable</li>
1622 <h1>The Zen of Roles</h1>
1625 <li>Roles represent discrete units of ...
1632 <li>Roles are shareable between unrelated classes</li>
1633 <li>Roles are what a class <em>does</em>, not what it <em>is</em></li>
1634 <li>Roles <em>add</em> functionality, inheritance <em>specializes</em></li>
1639 <h1>Abstract Examples</h1>
1642 <li>Human <em>@ISA</em> Animal</li>
1643 <li>Human <em>does</em> Toolmaker (as <em>does</em> Chimpanzee)</li>
1644 <li>Car <em>@ISA</em> Vehicle</li>
1645 <li>Car <em>does</em> HasEngine</li>
1650 <h1>Real Examples</h1>
1653 <li>Objects representing SQL database components and queries
1655 <li>Schema, Table, Column, ColumnAlias</li>
1656 <li>Select, Insert, Update, Delete</li>
1663 <h1>Real Examples</h1>
1666 <li>Column and ColumnAlias both <em>do</em> ColumnLike</li>
1667 <li>ColumnLike things can be used in certain parts of queries</li>
1668 <li>All queries <em>do</em> HasWhereClause</li>
1669 <li>Select <em>does</em> Comparable and Selectable (for subselects)</li>
1670 <li>A where clause requires its components to <em>do</em> Comparable</li>
1675 <h1>Roles Summary</h1>
1678 <li>Roles can define an interface with <code>requires</code></li>
1679 <li>Roles can have state (attributes) and behavior (methods)</li>
1680 <li>Roles can mix interface, state, & behavior</li>
1681 <li>Roles are composed (flattened) into classes</li>
1682 <li>Roles can do other roles</li>
1683 <li>Roles can be used as a type in APIs (must do Comparable)</li>
1695 # perl bin/prove -lv t/02-roles.t
1697 Iterate til this passes all its tests</pre>
1700 <div class="slide fake-slide0">
1701 <h1>Part 3: Basic Attributes</h1>
1705 <h1>Attributes Are Huge</h1>
1708 <li>Moose's biggest feature</li>
1709 <li>The target of <em>many</em> MooseX modules</li>
1714 <h1>Quick Review</h1>
1717 <li>Declared with <code>has</code></li>
1718 <li>Read-only or read-write</li>
1721 <pre><code>package Shirt;
1724 has 'color' => ( is => 'ro' );
1725 has 'is_ripped' => ( is => 'rw' );</code></pre>
1729 <h1>Required-ness</h1>
1732 <li>Required means "must be passed to the constructor"</li>
1733 <li>But can be <code>undef</code></li>
1738 <h1>Required-ness</h1>
1740 <pre><code>package Person;
1743 has first_name => (
1745 <span class="current incremental">required => 1,</span>
1748 <span class="incremental">Person->new( first_name => undef ); # ok
1749 Person->new(); # kaboom</span></code></pre>
1753 <h1>Default and Builder</h1>
1756 <li>Attributes can have defaults</li>
1757 <li>Simple non-referecne scalars (number, string)</li>
1758 <li>Subroutine reference</li>
1759 <li>A builder method</li>
1767 <li>Can be a non-reference scalar (including <code>undef</code>)</li>
1770 <pre><code>package Person;
1775 default => 'Spire FCU',
1783 <li>Can be a subroutine reference</li>
1786 <pre><code>package Person;
1793 name => 'Spire FCU' ) },
1798 <h1>Default as a Subroutine Reference</h1>
1801 <li>Called as a method on the object</li>
1802 <li>Called anew for each object</li>
1807 <h1>Why No Other Reference Types?</h1>
1809 <pre><code>package Person;
1814 <span class="wrong">default => Bank->new(
1815 name => 'Spire FCU' ),</span>
1819 <li>Now <strong>every</strong> person shares the <strong>same</strong> Bank object!</li>
1824 <h1>Defaulting to an Empty Reference</h1>
1826 <pre><code>package Person;
1829 has packages => (
1831 default => <span class="highlight">sub { [] }</span>,
1836 <h1>What if I Want to Share?</h1>
1838 <pre><code>package Person;
1841 my $highlander_bank =
1842 Bank->new( name => 'Spire FCU' );
1846 default => sub { $highlander_bank },
1854 <li>A method <em>name</em> which returns the default</li>
1861 <pre><code>package Person;
1866 builder => '_build_bank',
1871 return Bank->new( name => 'Spire FCU' );
1876 <h1>Default vs Builder</h1>
1879 <li>Use default for simple scalars</li>
1880 <li>Use default to return empty references</li>
1881 <li>Use default for <em>very</em> trivial subroutine references</li>
1882 <li>Use builder for everything else</li>
1887 <h1>Builder Bonuses</h1>
1890 <li>Can be overridden and method modified, because it's called by <em>name</em></li>
1891 <li>Roles can require a builder</li>
1896 <h1>Role Requires Builder</h1>
1898 <pre><code>package HasBank;
1901 requires '_build_bank';
1905 builder => '_build_bank',
1910 <h1>Lazy, Good for Nothing Attributes</h1>
1913 <li>Normally, defaults are generated during object construction</li>
1914 <li>This can be expensive</li>
1915 <li>We want to default to <code>$self->size * 2</code>, but attribute initialization order is unpredictable</li>
1916 <li>Use lazy attributes!</li>
1921 <h1>The Power of Dynamic Defaults</h1>
1923 <pre><code>package Person;
1926 has shoe_size => (
1932 <h1>The Power of Dynamic Defaults</h1>
1934 <pre><code>has shoes => (
1936 <span class="highlight">lazy => 1,</span>
1937 builder => '_build_shoes',
1943 return Shoes->new(
1944 size => <span class="highlight">$self->shoe_size</span> );
1949 <h1>Lazy is Good</h1>
1952 <li>Lazy defaults are executed when the attribute is read</li>
1953 <li>Can see other object attributes</li>
1954 <li>Still need to watch out for circular laziness</li>
1959 <h1>Clearer and Predicate</h1>
1962 <li>Attributes can have a value, including <code>undef</code>, or not</li>
1963 <li>Can clear the value with a clearer method</li>
1964 <li>Can check for the existence of a value with a predicate method</li>
1965 <li>By default, these methods are not created</li>
1970 <h1>Clearer and Predicate</h1>
1972 <pre><code>package Person;
1978 builder => '_build_account',
1979 <span class="highlight">clearer => '_clear_account',
1980 predicate => 'has_account',</span>
1985 <h1>Clearer and Lazy Defaults</h1>
1988 <li>Lazy defaults are good for computed attributes</li>
1989 <li>Clear the attribute when the source data changes</li>
1990 <li>Recalculated at next access</li>
1995 <h1>Renaming constructor arguments</h1>
1998 <li>By default, constructor names = attribute names</li>
1999 <li>Use <code>init_arg</code> to change this</li>
2000 <li>Set <code>init_arg => undef</code> to make it unconstructable</li>
2005 <h1>Some <code>init_arg</code> examples</h1>
2007 <pre><code>package Person;
2012 <span class="highlight">init_arg => 'foot_size',</span>
2015 Person->new( <span class="wrong">shoe_size => 13</span> );
2018 Person->new( <span class="right">foot_size => 13</span> );
2019 print $person->shoe_size;</code></pre>
2023 <h1>Some <code>init_arg</code> examples</h1>
2025 <pre><code>package Person;
2030 <span class="highlight">init_arg => undef,</span>
2033 Person->new( <span class="wrong">shoes => Shoes->new</span> );</code></pre>
2037 <h1>Why Set <code>init_arg => undef</code>?</h1>
2040 <li>Use this with a lazy default for attributes-as-cache</li>
2041 <li>Compute the value as needed</li>
2042 <li>Ensure that it is always generated correctly (not set by constructor)</li>
2043 <li>Use triggers or method modifiers (coming soon) to clear the value</li>
2048 <h1>Attribute Inheritance</h1>
2051 <li>By default, subclasses inherit attribute as-is</li>
2052 <li>Can change some attribute parameters in subclasses
2058 <li>others we've not yet covered</li>
2065 <h1>Attribute Inheritance Example</h1>
2067 <pre><code>package Employee;
2072 has '<span class="highlight">+first_name</span>' => (
2073 default => 'Joe',
2078 <h1>Attribute Inheritance Warning</h1>
2081 <li>An attribute is a contract about a class's API</li>
2082 <li>Don't break that contract in a subclass</li>
2083 <li>Especially important in the context of types</li>
2088 <h1>Changing Accessor Names</h1>
2090 <pre><code>package Person;
2093 has first_name => (
2094 <span class="highlight">accessor</span> => 'first_name',
2098 <li>The long-hand version of <code>is => 'rw'</code></li>
2103 <h1>Changing Accessor Names</h1>
2105 <pre><code>package Person;
2108 has first_name => (
2109 <span class="highlight">reader</span> => 'first_name',
2110 <span class="highlight">writer</span> => undef,
2114 <li>The long-hand version of <code>is => 'ro'</code></li>
2120 <h1>Changing Accessor Names</h1>
2122 <pre><code>package Person;
2125 has first_name => (
2126 <span class="highlight">reader</span> => 'get_first_name',
2127 <span class="highlight">writer</span> => 'set_first_name',
2132 <h1>Changing Accessor Names</h1>
2134 <pre><code>package Person;
2137 has first_name => (
2138 <span class="highlight">is</span> => 'rw',
2139 <span class="highlight">writer</span> => '_first_name',
2143 <li>Can also mix-and-match <code>is</code> and explicit names</li>
2148 <h1>ETOOMUCHTYPING</h1>
2151 <li><code>MooseX::FollowPBP</code><br /><code>get_foo</code> and <code>set_foo</code></li>
2152 <li><code>MooseX::SemiAffordanceAccessor</code><br /><code>foo</code> and <code>set_foo</code></li>
2157 <h1>ETOOMUCHTYPING</h1>
2159 <pre><code>package Person;
2161 <span class="highlight">use MooseX::SemiAffordanceAccessor;</span>
2163 has first_name => (
2168 <li>Creates <code>first_name</code> and <code>set_first_name</code></li>
2173 <h1>Basic Attributes Summary</h1>
2176 <li>Attributes can be <code>required</code></li>
2177 <li>Attributes can have a <code>default</code> or <code>builder</code></li>
2178 <li>Attributes with a default or builder can be <code>lazy</code></li>
2179 <li>Attributes can have a <code>clearer</code> and/or <code>predicate</code></li>
2180 <li>An attribute's constructor name can be changed with <code>init_arg</code></li>
2181 <li>A subclass can alter its parents' attributes</li>
2182 <li>Attribute accessor names can be changed</li>
2194 # perl bin/prove -lv t/03-basic-attributes.t
2196 Iterate til this passes all its tests</pre>
2199 <div class="slide fake-slide0">
2200 <h1>Part 4: Method Modifiers</h1>
2204 <h1>What is a Method Modifier</h1>
2207 <li>Apply to an existing method</li>
2208 <li>... from a parent class, the current class, or a role</li>
2209 <li>Roles can provide modifiers that are applied at composition time</li>
2214 <h1>What is a Method Modifier</h1>
2217 <li>"Inject" behavior</li>
2218 <li>Add behavior to generated methods (accessors, delegations)</li>
2219 <li>Provide roles which modify existing behavior</li>
2224 <h1>Before and After</h1>
2227 <li>Simplest modifiers - <code>before</code> and <code>after</code></li>
2228 <li>Guess when they run!</li>
2233 <h1>Uses for <code>before</code></h1>
2236 <li>As a pre-call check</li>
2239 <pre><code>package Person;
2242 before work => sub {
2244 die 'I have no job!'
2245 unless $self->has_title;
2250 <h1>Uses for <code>before</code></h1>
2253 <li>Logging/Debugging</li>
2256 <pre><code>package Person;
2259 before work => sub {
2261 return unless $DEBUG;
2263 warn "Called work on ", $self->full_name,
2264 "with the arguments: [@_]\n";
2269 <h1>Uses for <code>after</code></h1>
2272 <li>Also works for logging/debugging</li>
2273 <li>Post-X side-effects (recording audit info)</li>
2276 <pre><code>package Person;
2279 after work => sub {
2281 $self->work_count(
2282 $self->work_count + 1 );
2290 <li>Modifiers are useful for adding behavior to generated methods</li>
2295 <h1>Other Uses Example</h1>
2297 <pre><code>has password => (
2299 clearer => 'clear_password',
2302 has hashed_password => (
2304 builder => '_build_hashed_password',
2305 clearer => '_clear_hashed_password',
2308 after clear_password => sub {
2310 $self->_clear_hashed_password;
2315 <h1><code>before</code> and <code>after</code> Limitations</h1>
2318 <li>Cannot alter method parameters</li>
2319 <li>Cannot alter return value</li>
2320 <li>But <strong>can</strong> throw an exception</li>
2325 <h1>The <code>around</code> Modifier</h1>
2328 <li>The big gun</li>
2329 <li>Can alter parameters <strong>and/or</strong> return values</li>
2330 <li>Can skip calling the wrapped method entirely</li>
2335 <h1>The power of <code>around</code></h1>
2337 <pre><code>around insert => sub {
2341 $self->_validate_insert(@_);
2345 $self->_munge_insert(@_) );
2347 $new_user->_assign_uri;
2354 <h1>Modifier Order</h1>
2357 <li>Before runs order from last to first</li>
2358 <li>After runs in order from first to last</li>
2359 <li>Around runs in order from last to first</li>
2364 <h1>Modifier Order Illustrated</h1>
2367 <span class="current incremental">before 2
2369 <span class="incremental">around 2
2371 <span class="incremental">wrapped method</span>
2372 <span class="incremental">around 1
2374 <span class="incremental">after 1
2380 <h1>Modifiers in Roles</h1>
2383 <li>Roles can use these modifiers</li>
2384 <li>Very powerful!</li>
2389 <h1>Modifiers in Roles</h1>
2391 <pre><code>package IsUnreliable;
2394 <span class="highlight">requires 'run';
2396 around run</span> => sub {
2400 return if rand(1) < 0.5;
2402 return $self->$orig(@_);
2407 <h1>Augment and Inner</h1>
2410 <li>Inverted <code>super</code></li>
2411 <li>From least- to most-specific</li>
2412 <li>Grandparent to parent to child</li>
2413 <li>Not allowed in roles</li>
2418 <h1>Augment and Inner</h1>
2420 <pre><code>package Document;
2422 sub xml { '<doc>' . <span class="highlight">inner()</span> . '</doc>' }
2427 <span class="highlight">augment xml</span> =>
2428 sub { title() . <span class="highlight">inner()</span> . summary() };
2433 <span class="highlight">augment xml</span> =>
2434 sub { tps_xml() . <span class="highlight">inner()</span> };</code></pre>
2438 <h1>Augment and Inner</h1>
2441 <li>When we call <code>$tps->xml</code> ...
2443 <li><code>Document->xml</code></li>
2444 <li><code>Report->xml</code></li>
2445 <li><code>TPSReport->xml</code></li>
2452 <h1>Augment and Inner Usage</h1>
2455 <li>Call <code>inner()</code> to "fill in the blank"</li>
2456 <li>Requires designing for subclassing</li>
2457 <li>Call <code>inner()</code> in the terminal class, just in case</li>
2462 <h1>Method Modifiers Summary</h1>
2465 <li>Use <code>before</code> and <code>after</code> for ...
2468 <li>pre- or post-validation</li>
2469 <li>to add behavior to generated methods</li>
2472 <li>These two modifiers cannot change parameters or return values</li>
2477 <h1>Method Modifiers Summary</h1>
2480 <li>Use <code>around</code> to ...
2482 <li>alter parameters passed to the original method</li>
2483 <li>alter the return value of the original method</li>
2484 <li>not call the original method at all (or call a <em>different</em> method)</li>
2491 <h1>Method Modifiers Summary</h1>
2494 <li>When using modifiers in a role, require the modified method</li>
2495 <li>Use <code>augment</code> and <code>inner</code> to invert the normal subclassing flow ...
2497 <li>Least- to most-specific (parents to children)</li>
2498 <li>Build in "insertability" (stick more stuff in the "middle")</li>
2501 <li>Always call <code>inner</code> in the most specific subclass to allow for future extension</li>
2513 # perl bin/prove -lv t/04-method-modifiers.t
2515 Iterate til this passes all its tests</pre>
2518 <div class="slide fake-slide0">
2519 <h1>Part 5: Types</h1>
2523 <h1>A Type System for Perl</h1>
2526 <li>Sort of ...</li>
2527 <li><em>Variables</em> are not typed</li>
2528 <li>Attributes can have types</li>
2529 <li>MooseX modules let you define method signatures</li>
2534 <h1>Components of a Moose Type</h1>
2537 <li>A type is a name and a constraint</li>
2538 <li>Types have a hierarchy</li>
2539 <li>Constraints are cumulative from parents</li>
2540 <li>Types can have associated coercions</li>
2545 <h1>Built-in Type Hierarchy</h1>
2564 <h1>Built-in Type Hierarchy</h1>
2597 <li>Like Perl's <code>if ($foo)</code></li>
2602 <h1>Value (and subtypes)</h1>
2605 <li><code>Value</code> is true when <code>! ref $thing</code></li>
2606 <li><code>Value</code> and <code>Str</code> are effectively the same, but <code>Str</code> is more expressive</li>
2607 <li>An overloaded object which numifies does not pass the <code>Num</code> constraint!</li>
2608 <li>Perl 5's overloading is hopelessly broken</li>
2613 <h1>ClassName and RoleName</h1>
2616 <li>A string with a package name</li>
2617 <li>The package <strong>must already be loaded</strong></li>
2622 <h1>Parameterizable Types</h1>
2625 <li>What does <code>ArrayRef[`a]</code> mean?</li>
2626 <li><code>s/`a/Int/</code> (or <code>Str</code> or ...)</li>
2627 <li>When you use it you can write ...
2629 <li><code>ArrayRef</code> (== <code>ArrayRef[Item]</code>)</li>
2630 <li><code>ArrayRef[Str]</code></li>
2631 <li><code>ArrayRef[MyTypeName]</code></li>
2632 <li><code>ArrayRef[HashRef[Maybe[Int]]]</code></li>
2642 <li>Maybe means either the named type or <code>undef</code></li>
2643 <li><code>Maybe[Int]</code> accepts integers or <code>undef</code></li>
2651 <li>This or that (or that or ...)</li>
2652 <li><code>Int | ArrayRef[Int]</code></li>
2653 <li>But use a coercion instead when possible</li>
2654 <li>Or use a <code>role_type</code>, <code>duck_type</code>, or anything not a union</li>
2655 <li>A union is often a code smell</li>
2660 <h1>Making Your Own Types</h1>
2662 <pre><code>use Moose::Util::TypeConstraints;
2664 <span class="incremental current">subtype 'PositiveInt',</span>
2665 <span class="incremental">as 'Int',</span>
2666 <span class="incremental">where { $_ > 0 },</span>
2667 <span class="incremental">message { "The value you provided ($_)"
2668 . " was not a positive number." };</span>
2672 <span class="incremental">isa => 'PositiveInt',</span>
2677 <h1>Automatic Types</h1>
2680 <li>Moose creates a type for every Moose class and role</li>
2681 <li>Unknown names are assumed to be classes</li>
2686 <h1>Automatic Types</h1>
2688 <pre><code>package Employee;
2693 <span class="highlight">isa => 'Employee',</span>
2696 has start_date => (
2698 <span class="highlight">isa => 'DateTime',</span>
2703 <h1>Subtype Shortcuts - <code>class_type</code></h1>
2705 <pre><code>use Moose::Util::TypeConstraints;
2706 class_type 'DateTime';
2710 where { $_->isa('DateTime') },
2711 message { ... };</code></pre>
2715 <h1>Subtype Shortcuts - <code>role_type</code></h1>
2717 <pre><code>use Moose::Util::TypeConstraints;
2718 role_type 'Printable';
2720 subtype 'Printable',
2723 { Moose::Util::does_role(
2724 $_, 'Printable' ) },
2725 message { ... };</code></pre>
2729 <h1>Subtype Shortcuts - <code>duck_type</code></h1>
2731 <pre><code>use Moose::Util::TypeConstraints;
2732 duck_type Car => qw( run break_down );
2736 where { all { $_->can($_) }
2737 qw( run break_down ) },
2738 message { ... };</code></pre>
2742 <h1>Subtype Shortcuts - <code>enum</code></h1>
2744 <pre><code>use Moose::Util::TypeConstraints;
2745 enum Color => qw( red blue green ) );
2747 my %ok = map { $_ => 1 } qw( red blue green );
2751 message { ... };</code></pre>
2755 <h1>Anonymous Subtypes</h1>
2757 <pre><code>package Person;
2759 <span class="highlight">my $posint =
2760 subtype as 'Int', where { $_ > 0 };</span>
2764 <span class="highlight">isa => $posint,</span>
2768 <li>Shortcuts have anonymous forms as well</li>
2775 <pre><code>use Moose::Util::TypeConstraints;
2779 where { ! /[a-z]/ };
2781 <span class="incremental current">coerce 'UCStr',</span>
2782 <span class="incremental">from 'Str',</span>
2783 <span class="incremental">via { uc };</span>
2785 has shouty_name => (
2788 <span class="incremental">coerce => 1,</span>
2793 <h1>Coercion Examples</h1>
2795 <pre><code>subtype 'My::DateTime',
2796 as class_type 'DateTime';
2798 coerce 'My::DateTime',
2800 via { DateTime->new( %{$_} ) };
2802 coerce 'My::DateTime',
2804 via { DateTime->from_epoch(
2805 epoch => $_ ) };</code></pre>
2808 <li>Use coercion to inflate a value</li>
2813 <h1>Coercion Examples</h1>
2815 <pre><code>coerce 'ArrayRef[Int]',
2817 via { [ $_ ] };</code></pre>
2820 <li>Coerce instead of a union like <code style="white-space: nowrap">Int | ArrayRef[Int]</code></li>
2825 <h1>Using Types with Attributes</h1>
2827 <pre><code>package Person;
2829 use Moose::Util::TypeConstraints;
2833 <span class="highlight">isa => 'Num',</span>
2836 has favorite_numbers => (
2838 <span class="highlight">isa => 'ArrayRef[Int]',
2839 coerce => 1,</span>
2844 <h1>More Droppings</h1>
2847 <li><code>Moose::Util::TypeConstraint</code> also needs cleanup</li>
2850 <pre><code>package Person;
2853 use Moose::Util::TypeConstraints;
2858 <span class="highlight">no Moose::Util::TypeConstraints;</span></code></pre>
2862 <h1>Typed Methods (Low-tech)</h1>
2864 <pre class="medium"><code>package Person;
2865 <span class="highlight">use MooseX::Params::Validate qw( validated_list );</span>
2869 <span class="highlight">my ( $tasks, $can_rest ) =
2873 { isa => 'ArrayRef[Task]',
2885 <h1>Typed Methods (High-tech)</h1>
2887 <pre class="medium"><code>package Person;
2889 <span class="highlight">use MooseX::Method::Signatures;</span>
2891 <span class="highlight">method work ( ArrayRef[Task] :$tasks,
2892 Bool :$can_rest = 0 )</span> {
2900 <h1>Digression: The Type Registry</h1>
2903 <li>Types are actually <code>Moose::Meta::TypeConstraint</code> <em>objects</em></li>
2904 <li>Stored in an interpreter-global registry mapping names to objects</li>
2912 <li>Coercions are attached to type objects</li>
2913 <li>Therefore also global</li>
2914 <li>Name conflicts between modules!</li>
2915 <li>Coercion conflicts between modules!</li>
2920 <h1>Namespace Fix</h1>
2923 <li>Use some sort of pseudo-namespacing scheme</li>
2924 <li>Never coerce directly to a class name, or <em>to</em> built-in types</li>
2929 <h1>Namespace Fix</h1>
2931 <pre><code>use Moose::Util::TypeConstraints;
2933 subtype <span class="highlight">'MyApp::Type::DateTime',</span>
2936 <span class="highlight">coerce 'MyApp::Type::DateTime',</span>
2938 via { DateTime->new( %{$_} ) }
2940 has creation_date => (
2942 <span class="highlight">isa => 'MyApp::Type::DateTime',</span>
2948 <h1>Namespace Fix</h1>
2950 <pre><code>subtype 'MyApp::Type::ArrayOfInt',
2953 coerce 'MyApp::Type::ArrayOfInt',
2955 via { [ $_ ] };</code></pre>
2959 <h1>Namespace Fix Pros and Cons</h1>
2962 <li><span class="right">Relatively simple</span></li>
2963 <li><span class="right">Already built into Moose</span></li>
2964 <li><span class="wrong">Conflates type and module namespaces</span></li>
2965 <li><span class="wrong">Type names are strings, so typos are easy to make and may be hard to find</span></li>
2970 <h1>MooseX::Types</h1>
2972 <pre><code>package MyApp::Types;
2975 <span class="highlight">-declare => [ qw( ArrayOfInt ) ]</span>;
2976 use MooseX::Types::Moose
2979 subtype <span class="highlight">ArrayOfInt</span>,
2982 coerce <span class="highlight">ArrayOfInt</span>
2984 via { [ $_ ] };</code></pre>
2988 <h1>MooseX::Types</h1>
2990 <pre><code>package MyApp::Account;
2992 use MyApp::Types qw( ArrayOfInt );
2994 has transaction_history => (
3001 <h1>MooseX::Types</h1>
3004 <li>Type names are exported functions, catches typos early</li>
3005 <li>Types must be pre-declared</li>
3006 <li>Types are stored with namespaces internally, but externally are short</li>
3007 <li>Import existing Moose types as functions from <code>MooseX::Types::Moose</code></li>
3008 <li>Still need string names for things like <code>ArrayRef['Email::Address']</code></li>
3013 <h1>MooseX::Types Pros and Cons</h1>
3016 <li><span class="right">Catches typos at compile time</span></li>
3017 <li><span class="right">Automatic namespacing</span></li>
3018 <li><span class="wrong">One more thing to install and learn</span></li>
3019 <li><span class="wrong">Every name gets types twice (declared and then defined)</span></li>
3020 <li><span class="wrong">Still stuck with strings when referring to class or role names</span></li>
3021 <li><span class="wrong">Coercion gotcha from earlier still applies to types exported from <code>MooseX::Types::Moose</code></span></li>
3026 <h1>Recommendation</h1>
3029 <li>Use <code>MooseX::Types</code></li>
3030 <li>Compile time error catching and automatic namespacing are huge wins</li>
3031 <li>Docs from <code>Moose::Util::TypeConstraints</code> are 98% compatible with <code>MooseX::Types</code> anyway</li>
3032 <li>A function exported by a type library works wherever a type name would</li>
3044 # perl bin/prove -lv t/05-types.t
3046 Iterate til this passes all its tests</pre>
3049 <div class="slide fake-slide0">
3050 <h1>Part 6: Advanced Attributes</h1>
3054 <h1>Weak References</h1>
3057 <li>A weak reference lets you avoid circular references</li>
3058 <li>Weak references do not increase the reference count</li>
3063 <h1>Circular Reference Illustrated</h1>
3065 <pre><code>my $foo = {};
3066 my $bar = { foo => $foo };
3067 $foo->{bar} = $bar;</code></pre>
3070 <li>Neither <code>$foo</code> nor <code>$bar</code> go out of scope<br />
3071 (until the program exits)</li>
3076 <h1>Weakening Circular References</h1>
3078 <pre><code>use Scalar::Util qw( weaken );
3081 my $bar = { foo => $foo };
3082 $foo->{bar} = $bar;
3083 weaken $foo->{bar}</code></pre>
3086 <li>When <code>$bar</code> goes out of scope, <code>$foo->{bar}</code> becomes <code>undef</code></li>
3091 <h1>Circular References in Attributes</h1>
3093 <pre><code>package Person;
3096 has name => ( is => 'ro' );
3097 has friend => ( is => 'rw' );
3099 my $alice = Person->new( name => 'Alice' );
3100 my $bob = Person->new( name => 'Bob' );
3101 $bob->friend($alice);
3102 $alice->friend($bob);</code></pre>
3108 <pre><code>package Person;
3111 has name => ( is => 'ro' );
3112 has friend => ( is => 'rw', <span class="highlight">weak_ref => 1</span> );
3114 my $alice = Person->new( name => 'Alice' );
3115 my $bob = Person->new( name => 'Bob' );
3116 $bob->friend($alice);
3117 $alice->friend($bob);</code></pre>
3121 <h1>Under the Hood</h1>
3124 <li>A <code>weak_ref</code> attribute calls <code>weaken</code> ...
3126 <li>during object construction</li>
3127 <li>when the attribute is set via a writer</li>
3137 <li>A code reference run after an attribute is <em>set</em></li>
3138 <li>Like an <code>after</code> modifier, but makes intentions clearer</li>
3141 <h2 class="wrong">Gross</h2>
3143 <pre><code>after salary_level => {
3146 $self->clear_salary;
3151 <h1>Use a Trigger Instead</h1>
3153 <h2 class="right">Cleaner</h2>
3155 <pre><code>has salary_level => (
3157 trigger => sub { $_[0]->clear_salary },
3165 <li>Attributes can be objects</li>
3166 <li>Delegation transparently calls methods on those objects</li>
3171 <h1>Delegation Examples</h1>
3173 <pre><code>package Person;
3178 <span class="highlight">handles => [ 'inhale', 'exhale' ],</span>
3182 <li>Creates <code>$person->inhale</code> and <code>->exhale</code> methods</li>
3183 <li>Internally calls <code>$person->lungs->inhale</code></li>
3188 <h1>Why Delegation?</h1>
3191 <li>Reduce the number of classes exposed</li>
3192 <li>Re-arrange class internals -<br />
3193 turn a method into an attribute with delegation</li>
3194 <li>Provide convenenience methods</li>
3199 <h1>Moose's <code>handles</code> Parameter</h1>
3202 <li>Accepts many arguments ...
3204 <li>Array reference - list of methods to delegate as-is</li>
3205 <li>Hash reference - map of method names</li>
3206 <li>Regex - delegates all matching methods</li>
3207 <li>Role name - delegates all methods in the role</li>
3208 <li>Sub reference - does something complicated ;)</li>
3215 <h1>Array Reference</h1>
3218 <li>Takes each method name and creates a simple delegation from the delegating class to the delegatee attribute</li>
3223 <h1>Hash Reference</h1>
3226 <li>Mapping of names in the delegating class to the delegatee class</li>
3229 <pre><code>package Person;
3234 isa => 'BankAccount',
3235 <span class="highlight">handles => {
3236 receive_money => 'deposit',
3237 give_money => 'withdraw',
3243 <h1>Hash Reference Detailed</h1>
3245 <pre><code> handles => {
3246 receive_money => 'deposit',
3247 give_money => 'withdraw',
3251 <li><code>$person->receive_money</code> = <code>$person->account->deposit</code></li>
3252 <li><code>$person->give_money</code> = <code>$person->account->withdraw</code></li>
3259 <pre><code>package Person;
3265 handles => qr/.*/,
3269 <li>Creates a delegation for every method in the Name class</li>
3270 <li>Excludes <code>meta</code> and methods inherited from <code>Moose::Object</code></li>
3277 <pre><code>package Auditor;
3280 sub record_change { ... }
3281 sub change_history { ... }
3288 does => 'Auditor',
3289 <span class="highlight">handles => 'Auditor',</span>
3294 <h1>Role Name Detailed</h1>
3297 <li>Account gets delegate methods for each method in the <code>Auditor</code> role
3299 <li>record_history</li>
3300 <li>change_history</li>
3307 <h1>Traits and Metaclasses</h1>
3310 <li>The ultimate in customization</li>
3311 <li>Per attribute metaclasses</li>
3312 <li>Per attribute roles applied to the attribute metaclass</li>
3313 <li>Change the meta-level behavior</li>
3318 <h1>Traits and Metaclasses</h1>
3321 <li>The default metaclass is <code>Moose::Meta::Attribute</code></li>
3322 <li>Controls accessor generation, defaults, delegation, etc.</li>
3323 <li>Adding a role to this metaclass (or replacing it) allows for infinite customization</li>
3328 <h1>Traits and Metaclasses</h1>
3331 <li>Can add/alter/remove attribute parameter (from <code>has</code>)</li>
3332 <li>Can change behavior of created attribute</li>
3337 <h1>Simple Trait Example</h1>
3339 <pre><code>package Person;
3341 use MooseX::LabeledAttributes;
3344 <span class="highlight">traits => [ '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>Simple Metaclass Example</h1>
3357 <pre><code>package Person;
3359 use MooseX::LabeledAttributes;
3362 <span class="highlight">metaclass =>
3363 'MooseX::Meta::Attribute::Labeled',</span>
3366 <span class="highlight">label => 'Social Security Number',</span>
3369 print <span class="highlight">Person->meta
3370 ->get_attribute('ssn')->label;</span></code></pre>
3374 <h1>Traits vs Metaclass</h1>
3377 <li>Can apply any mix of traits to an attribute</li>
3378 <li>But just one metaclass</li>
3379 <li>Traits (aka roles) can cooperate</li>
3380 <li>Metaclasses require you to pick just one</li>
3385 <h1>Advanced Attributes Summary</h1>
3388 <li>Use <code>weak_ref</code> to avoid circular references</li>
3389 <li>Use trigger to do an action post-attribute write</li>
3390 <li>Use delegations to hide "internal" objects</li>
3391 <li>Traits and metaclasses let you extend Moose's core attribute features</li>
3403 # perl bin/prove -lv t/06-advanced-attributes.t
3405 Iterate til this passes all its tests</pre>
3408 <div class="slide fake-slide0">
3409 <h1>Part 7: Introspection</h1>
3412 <div class="slide fake-slide0">
3413 <h1>Part 8: A Tour of MooseX</h1>
3416 <div class="slide fake-slide0">
3417 <h1>Part 9: Writing Moose Extensions</h1>
3420 <div class="slide fake-slide0">
3425 <h1>More Information</h1>
3428 <li><a href="http://moose.perl.org/">http://moose.perl.org/</a></li>
3429 <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>
3430 <li><a href="irc://irc.perl.org/#moose">irc://irc.perl.org/#moose</a></li>
3431 <li>mailing list - <a href="mailto:moose@perl.org">moose@perl.org</a></li>
3432 <li>Slides and exercises are in Moose's git repo:
3434 <span style="white-space: nowrap">git://jules.scsys.co.uk/gitmo/moose-presentations</span></li>
3444 Copyright 2009 David Rolsky. All Rights Reserved.
3446 This work is licensed under a Creative Commons Attribution-Share Alike
3447 3.0 United States License See
3448 http://creativecommons.org/licenses/by-sa/3.0/us/ for details.