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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>Introduce Yourselves</h1>
63 <li>What you do with Perl</li>
64 <li>Why you're here today (optional)</li>
69 <h1>Moose Summed Up</h1>
72 <li><strong>Declarative</strong> OO sugar</li>
73 <li>Introspectable</li>
74 <li>Extensible (MooseX::* on CPAN)</li>
79 <h1>Moose Background</h1>
82 <li>Created by Stevan Little, first released in 2006</li>
83 <li>Moose builds on Perl 5's native OO</li>
84 <li>Borrows ideas from other languages, notably Perl 6</li>
85 <li>Provides semantics for common operations</li>
89 <div class="slide fake-slide0">
90 <h1>Part 0: Moose Concepts</h1>
102 <li>Superclasses</li>
103 <li>Method modifiers</li>
104 <li>Constructor and destructor</li>
105 <li>One metaclass object</li>
108 <li>Classes do roles</li>
113 <h1>Class Example</h1>
115 <pre><code>package Person;
116 <span class="highlight">use Moose;</span></code></pre>
119 <li>Poof, a Moose-based class!</li>
127 <li>Aka property, slot, field, member variable</li>
128 <li>A piece of data owned by an object</li>
139 <li>Mutability (read-only vs read-write)</li>
140 <li>An optional type</li>
141 <li>Accessor methods</li>
142 <li>Delegation methods</li>
143 <li>Optional default value</li>
144 <li>Many more features</li>
147 <li>Stored in the object, but don't worry about that</li>
152 <h1>Attribute Example</h1>
154 <pre><code>package Person;
157 <span class="highlight">has first_name => ( is => 'rw' );</span></code></pre>
165 <li>Nothing fancy here, just Perl subroutines</li>
168 <pre><code>package Person;
171 <span class="highlight">sub greet { ... }</span></code></pre>
178 <li>Classes <strong>do</strong> (or consume) roles</li>
179 <li>Similar to mixins and Java interfaces</li>
187 <li>Like classes, can have attributes, methods, do roles</li>
188 <li>Roles can require methods</li>
189 <li>Roles are composed (flattened) into classes</li>
194 <h1>Role Example</h1>
196 <pre><code>package HasPermissions;
197 <span class="highlight">use Moose::Role;</span>
199 has is_admin => ( is => 'rw' );</code></pre>
203 <h1>Role Example</h1>
209 <pre><code>package Person;
212 <span class="highlight">with 'HasPermissions';</span></code></pre>
216 <h1>Method Modifiers</h1>
220 <li>"<strong>Before</strong> foo(), do this first"</li>
221 <li>"Do this <strong>after</strong> foo()"</li>
222 <li>"Put this code <strong>around</strong> foo()"</li>
227 <h1>Before and After</h1>
229 <pre><code>before 'foo'
230 => sub { warn 'About to call foo()' };
233 => sub { warn 'Leaving foo()' };</code></pre>
240 <pre><code>around 'foo' => sub {
241 my $real_foo = shift;
244 warn 'Just before foo()';
246 $self->$real_foo( @_, bar => 42 );
250 'modify return values'
256 <h1>Type Constraints</h1>
259 <li>NOT A FULL-BLOWN TYPE SYSTEM!</li>
260 <li>But still darn useful</li>
261 <li>Constrain attribute values</li>
262 <li>Coerce from other types</li>
267 <h1>Type Constraint Example</h1>
269 <pre><code>package Person;
274 <span class="highlight">isa => 'Int'</span>,
278 Person->new( weight => 'heavy' );</code></pre>
285 <li>Attributes can define delegations</li>
286 <li>Lets you hide some implementation details</li>
287 <li>Fewer objects to chase around</li>
294 <pre><code>package Person;
300 <span class="highlight">handles => { 'blog_host' => 'host' },</span>
303 <span class="highlight">$person->blog_host;</span>
304 # really calls $person->blog_uri->host</code></pre>
308 <h1>Constructors</h1>
311 <li>Moose creates <code>new()</code> for you</li>
312 <li>Provide an optional <code>BUILDARGS()</code> and <code>BUILD()</code></li>
320 <li>Provide an optional <code>DEMOLISH()</code></li>
325 <h1>Moose Meta-API</h1>
328 <li>Answers questions like ...
330 <li>What methods does this class have?</li>
331 <li>What are its parents?</li>
332 <li>What attributes does it have (including inherited attributes)?</li>
333 <li>What roles does it do?</li>
334 <li>Much, much, more</li>
341 <h1>Moose Meta-API</h1>
344 <li>Not just for introspection ...
346 <li>Add methods, attributes, roles, etc</li>
347 <li>Extend and alter core features</li>
357 <li>A quick bit of propaganda ...</li>
364 <pre><code>package Person;
367 has last_name => (
374 <h1>Without Moose</h1>
376 <pre class="small"><code>package Person;
386 if (exists $args{last_name}) {
387 confess "Attribute (last_name) does not pass the type constraint because: "
388 . "Validation failed for 'Str' with value $args{last_name}"
389 if ref($args{last_name});
390 $self->{last_nane} = $args{last_name};
393 return bless $self, $class;
401 confess "Attribute (last_name) does not pass the type constraint because: "
402 . "Validation failed for 'Str' with value $value"
404 $self->{last_name} = $value;
407 return $self->{last_name};
413 <h1>Side by side</h1>
415 <table class="side-by-side">
418 <pre><code>package Person;
421 has last_name => (
427 <pre class="small"><code>package Person;
437 if (exists $args{last_name}) {
438 confess "Attribute (last_name) does not pass the type constraint because: "
439 . "Validation failed for 'Str' with value $args{last_name}"
440 if ref($args{last_name});
441 $self->{last_nane} = $args{last_name};
444 return bless $self, $class;
452 confess "Attribute (last_name) does not pass the type constraint because: "
453 . "Validation failed for 'Str' with value $value"
455 $self->{last_name} = $value;
458 return $self->{last_name};
467 <h1>Side by side</h1>
469 <table class="side-by-side">
472 <pre><code><span class="match-moose">package Person;</span>
475 has last_name => (
481 <pre class="small"><code><span class="match-unsweet">package Person;</span>
491 if (exists $args{last_name}) {
492 confess "Attribute (last_name) does not pass the type constraint because: "
493 . "Validation failed for 'Str' with value $args{last_name}"
494 if ref($args{last_name});
495 $self->{last_nane} = $args{last_name};
498 return bless $self, $class;
506 confess "Attribute (last_name) does not pass the type constraint because: "
507 . "Validation failed for 'Str' with value $value"
509 $self->{last_name} = $value;
512 return $self->{last_name};
520 <h1>Side by side</h1>
522 <table class="side-by-side">
525 <pre><code>package Person;
526 <span class="match-moose">use Moose;</span>
528 has last_name => (
534 <pre class="small"><code>package Person;
535 <span class="match-unsweet">use strict;
542 my $self = {};</span>
544 if (exists $args{last_name}) {
545 confess "Attribute (last_name) does not pass the type constraint because: "
546 . "Validation failed for 'Str' with value $args{last_name}"
547 if ref($args{last_name});
548 $self->{last_nane} = $args{last_name};
551 <span class="match-unsweet">return bless $self, $class;
559 confess "Attribute (last_name) does not pass the type constraint because: "
560 . "Validation failed for 'Str' with value $value"
562 $self->{last_name} = $value;
565 return $self->{last_name};
573 <h1>Side by side</h1>
575 <table class="side-by-side">
578 <pre><code>package Person;
581 <span class="match-moose">has last_name => (</span>
584 <span class="match-moose">);</span></code></pre>
587 <pre class="small"><code>package Person;
597 <span class="match-unsweet">if (exists $args{last_name}) {</span>
598 confess "Attribute (last_name) does not pass the type constraint because: "
599 . "Validation failed for 'Str' with value $args{last_name}"
600 if ref($args{last_name});
601 <span class="match-unsweet">$self->{last_nane} = $args{last_name};
604 return bless $self, $class;
612 confess "Attribute (last_name) does not pass the type constraint because: "
613 . "Validation failed for 'Str' with value $value"
615 $self->{last_name} = $value;
618 return $self->{last_name};
626 <h1>Side by side</h1>
628 <table class="side-by-side">
631 <pre><code>package Person;
634 has last_name => (
635 <span class="match-moose">is => 'rw',</span>
640 <pre class="small"><code>package Person;
650 if (exists $args{last_name}) {
651 confess "Attribute (last_name) does not pass the type constraint because: "
652 . "Validation failed for 'Str' with value $args{last_name}"
653 if ref($args{last_name});
654 $self->{last_nane} = $args{last_name};
657 return bless $self, $class;
660 <span class="match-unsweet">sub last_name {
664 my $value = shift;</span>
665 confess "Attribute (last_name) does not pass the type constraint because: "
666 . "Validation failed for 'Str' with value $value"
668 <span class="match-unsweet">$self->{last_name} = $value;
671 return $self->{last_name};
672 }</span></code></pre>
679 <h1>Side by side</h1>
681 <table class="side-by-side">
684 <pre><code>package Person;
687 has last_name => (
689 <span class="match-moose">isa => 'Str',</span>
693 <pre class="small"><code>package Person;
703 if (exists $args{last_name}) {
704 <span class="match-unsweet">confess "Attribute (last_name) does not pass the type constraint because: "
705 . "Validation failed for 'Str' with value $args{last_name}"
706 if ref($args{last_name});</span>
707 $self->{last_nane} = $args{last_name};
710 return bless $self, $class;
718 <span class="match-unsweet">confess "Attribute (last_name) does not pass the type constraint because: "
719 . "Validation failed for 'Str' with value $value"
720 if ref($value);</span>
721 $self->{last_name} = $value;
724 return $self->{last_name};
732 <h1>Side by side</h1>
734 <table class="side-by-side">
735 <tr class="incremental">
739 <tr class="incremental">
740 <td>92 characters</td>
741 <td>741 characters</td>
745 <pre><code>package Person;
748 has last_name => (
754 <pre class="small"><code>package Person;
764 if (exists $args{last_name}) {
765 confess "Attribute (last_name) does not pass the type constraint because: "
766 . "Validation failed for 'Str' with value $args{last_name}"
767 if ref($args{last_name});
768 $self->{last_nane} = $args{last_name};
771 return bless $self, $class;
779 confess "Attribute (last_name) does not pass the type constraint because: "
780 . "Validation failed for 'Str' with value $value"
782 $self->{last_name} = $value;
785 return $self->{last_name};
795 <pre class="small"><code>sub new {
800 if (exists $args{last_name}) {
801 confess "Attribute (last_name) does not pass the type constraint because: "
802 . "Validation failed for 'Str' with value $args{last_name}"
803 if ref($args{last_name});
804 $self->{last_nane} = $args{last_name};
807 return bless $self, $class;
814 <pre class="small"><code>if (exists $args{last_name}) {
815 confess "Attribute (last_name) does not pass the type constraint because: "
816 . "Validation failed for 'Str' with value $args{last_name}"
817 if ref($args{last_name});
818 $self->{last_nane} = $args{last_name};
825 <code>$self->{last_nane} = $args{last_name};</code>
830 <code>$self->{last_na<span class="wrong">n</span>e}</code>
836 <pre><code>package Person;
839 has last_name => (
846 <h1>More Why Moose?</h1>
849 <li>Less code == fewer bugs</li>
850 <li>Moose is well-tested, test your own code, not Moose</li>
851 <li>Focus on <strong>what</strong>, not <strong>how</strong></li>
855 <div class="slide fake-slide0">
856 <h1>Part 1: Moose Classes</h1>
860 <h1>Moose Classes</h1>
863 <li>Moose classes are Perl packages which <code>use Moose</code></li>
868 <h1>Moose.pm and Your Class</h1>
870 <pre><code>package Person;
871 use Moose;</code></pre>
874 <li><code>Moose.pm</code> provides declarative sugar</li>
875 <li>Turns on <code>strict</code> and <code>warnings</code></li>
876 <li>Creates metaclasses for your class: <code>Person->meta</code></li>
877 <li>Moose classes automatically inherit from <code>Moose::Object</code></li>
882 <h1>What <code>Moose::Object</code> Provides</h1>
885 <li>Constructor - <code>new()</code></li>
886 <li>Calls your <code>BUILDARGS()</code> and/or <code>BUILD()</code></li>
887 <li>Calls your <code>DEMOLISH</code> during object destruction</li>
895 <li>Takes <code>@_</code>, returns a hash reference of attribute name/value pairs</li>
896 <li>Accepts a hash or hashref; throws otherwise</li>
897 <li>Provide your own for other cases</li>
898 <li><strong>Always</strong> call <code>$class->SUPER::BUILDARGS(@_)</code> as a fallback!</li>
903 <h1>BUILDARGS Example</h1>
905 <pre><code>package Person;
911 if ( @_ == 1 && ! ref $_[0] ) {
912 <span class="highlight">return { ssn => $_[0] };</span>
914 <span class="highlight">return $class->SUPER::BUILDARGS(@_)</span>;
917 <span class="highlight">Person->new('123-45-6789')</span></code></pre>
924 <li>Called after object is created, before <code>new</code> returns</li>
925 <li>Chance to do more complex validation, set complex attributes</li>
926 <li>Called in reverse inheritance order, parents to children</li>
927 <li>Return value is ignored</li>
932 <h1>BUILD Example</h1>
934 <pre><code>package Person;
940 if ( $self->country_of_residence
942 die 'All US residents'
943 . ' must have an SSN'
944 unless $self->has_ssn;
950 <h1>Object Construction a la Moose</h1>
952 <pre><code>Person->new(@_)</code></pre>
954 <ol style="margin-top: 0">
955 <li>Calls <code>Person->BUILDARGS(@_)</code> to turn <code>@_</code> into a hashref</li>
956 <li>Blesses a reference</li>
957 <li>Populates attributes based on the hashref from #1</li>
958 <li>Calls <code>$new_object->BUILDALL($constructor_args)</code>
959 <br />... which calls all <code>BUILD</code> methods</li>
960 <li>Returns the object</li>
965 <h1>The Object is Opaque</h1>
968 <li>Technically it's a hash reference</li>
969 <li><span class="wrong">If you <em>ever</em> treat it as one <strong>you are doing it wrong!</strong></span></li>
977 <li>Like <code>DESTROY</code>, but Moose makes sure all <code>DEMOLISH</code> methods in a hierarchy are called</li>
978 <li>Called in normal inheritance order, children to parents</li>
986 <li><code>extends</code> is sugar for declaring parent classes</li>
987 <li>Also ensures metaclass compatibility between parent and child</li>
988 <li>Do not <code>use base</code></li>
991 <pre><code>package Employee;
993 <span class="highlight">extends 'Person';</span></code></pre>
1000 <li>Each call to <code>extends</code> <strong>resets</strong> your parents</li>
1003 <h2 class="wrong">Wrong</h2>
1005 <pre><code>package EvilEmployee;
1008 extends 'Thief';</code></pre>
1010 <h2 class="right">Right</h2>
1012 <pre><code>package EvilEmployee;
1014 extends 'Person', 'Thief';</code></pre>
1018 <h1>Extending un-Moose-y Parents</h1>
1020 <pre><code>package My::LWP;
1022 extends 'LWP';</code></pre>
1025 <li>No <code>Moose::Object</code>, so ...
1027 <li>No attribute-handling <code>new()</code></li>
1028 <li>No <code>BUILDARGS()</code> or <code>BUILD()</code></li>
1029 <li>No <code>DEMOLISH()</code></li>
1032 <li>But see <code>MooseX::NonMoose</code> for a workaround</li>
1037 <h1><code>override</code> and <code>super</code></h1>
1040 <li><code>override</code> is another method modifier</li>
1041 <li>An alternative to Perl's <code>SUPER::</code></li>
1046 <h1><code>override</code> and <code>super</code></h1>
1048 <pre><code>package Employee;
1051 <span class="current incremental">extends 'Person';</span>
1053 <span class="incremental">override</span> work => sub {
1057 unless $self->got_paid;
1058 <span class="incremental">super();</span>
1059 }<span class="incremental">;</span></code></pre>
1063 <h1>Caveat <code>super</code></h1>
1066 <li>Mostly like <code>$self->SUPER::work(@_)</code></li>
1067 <li><strong>But</strong> cannot change <code>@_</code>!</li>
1068 <li>Binds the parent's method at compile time</li>
1069 <li>Parent determined by checking <code>Child->meta()->superclasses()</code></li>
1074 <h1>Minimal Attributes</h1>
1077 <li><code>has 'foo'</code></li>
1078 <li>Use <code>is => 'ro'</code> or <code>is => 'rw'</code></li>
1079 <li>Attributes without "is" have no accessors</li>
1084 <h1>Read-write attributes</h1>
1086 <pre><code>package Person;
1089 has first_name => ( <span class="highlight">is => 'rw'</span> );
1092 Person->new( first_name => 'Dave' );
1094 $person->first_name('Stevan');
1095 print $person->first_name; # Stevan</code></pre>
1100 <h1>Read-only attributes</h1>
1102 <pre><code>package Person;
1105 has first_name => ( <span class="highlight">is => 'ro'</span> );
1108 Person->new( first_name => 'Dave' );
1110 $person->first_name('Stevan'); # dies</code></pre>
1115 <h1>There is More to Come</h1>
1118 <li>Attributes have a <em>lot</em> of features</li>
1123 <h1>Cleaning Up Moose Droppings</h1>
1125 <pre><code>package Person;
1129 Person->can('extends');</code></pre>
1132 <li>Not very hygienic</li>
1137 <h1>Cleaning Up Moose Droppings</h1>
1139 <pre><code>package Person;
1144 <span class="highlight">no Moose;</span>
1147 Person->can('extends');</code></pre>
1151 <h1>Cleaning Up Moose Droppings</h1>
1153 <pre><code>package Person;
1154 <span class="highlight">use namespace::autoclean;</span>
1160 Person->can('extends');</code></pre>
1167 <li>Cleaning up is a best practice</li>
1168 <li>Say <code>no Moose</code> at the end of a package</li>
1169 <li>Or <code>use namespace::autoclean</code> at the top</li>
1175 <h1>Immutability</h1>
1178 <li><span style="font-family: URW Chancery L; font-size: 120%">Stevan's Incantation of Fleet-Footedness</span></li>
1181 <pre><code>package Person;
1184 <span class="highlight">__PACKAGE__->meta->make_immutable;</span></code></pre>
1188 <h1>What <code>make_immutable</code> does</h1>
1192 <li>Uses <code>eval</code> to "inline" a constructor</li>
1193 <li>Memoizes a lot of meta-information</li>
1194 <li>Makes loading your class slower</li>
1195 <li>Makes object creation <em>much</em> faster</li>
1200 <h1>When to Immutabilize?</h1>
1203 <li><em>Almost</em> always</li>
1204 <li>Startup time vs execution time</li>
1209 <h1>Classes Summary</h1>
1212 <li><code>use Moose</code></li>
1213 <li><code>Class->meta</code></li>
1214 <li><code>Moose::Object</code> base class</li>
1215 <li><code>extends</code>, <code>override</code>, and <code>super</code></li>
1216 <li>Simple attributes: <code>has</code>, <code>is => 'ro'</code>, & <code>is => 'rw'</code></li>
1217 <li><code>no Moose</code></li>
1218 <li><code>__PACKAGE__->meta->make_immutable</code></li>
1231 # perl bin/prove -lv t/00-prereq.t
1233 # perl install-moose (if needed)
1235 # perl bin/prove -lv t/01-classes.t
1237 # edit lib/Person.pm and lib/Employee.pm
1239 Iterate til this passes all its tests</pre>
1242 <div class="slide fake-slide0">
1243 <h1>Part 2: Roles</h1>
1247 <h1>Just What Is a Role?</h1>
1250 <li>Mixin? Interface? Trait?</li>
1251 <li>Yes ... and more!</li>
1256 <h1>Roles - State <strong>and</strong> Behavior</h1>
1258 <pre><code>package HasPermissions;
1260 <span class="current incremental"># state
1261 has access_level => ( is => 'rw' );</span>
1263 <span class="incremental"># behavior
1266 my $required = shift;
1268 return $self->access_level
1270 }</span></code></pre>
1275 <h1>Roles Can Define Interfaces</h1>
1277 <pre><code>package Printable;
1280 requires 'as_string';</code></pre>
1284 <h1>Roles Can Do All Three</h1>
1286 <pre><code>package Printable;
1289 requires 'as_string';
1291 has has_been_printed => ( is => 'rw' );
1295 print $self->as_string;
1296 $self->has_been_printed(1);
1301 <h1>Classes Consume Roles</h1>
1303 <pre><code>package Person;
1306 with 'HasPermissions';</code></pre>
1310 <h1>Classes Consume Roles</h1>
1312 <pre><code>my $person = Person->new(
1313 first_name => 'Kenichi',
1314 last_name => 'Asai',
1315 access_level => 42,
1318 print $person->full_name
1320 . $person->can_access(42)
1322 : 'little power';</code></pre>
1326 <h1>Roles in Practice</h1>
1329 <li>Consuming a role =~ inlining the role</li>
1334 <h1>In Other Words ...</h1>
1336 <pre><code>package Person;
1339 <span class="highlight">with 'Printable';</span></code></pre>
1343 <h1>In Other Words ...</h1>
1345 <pre><code>package Person;
1348 <span class="delete">with 'Printable';</span>
1350 <span class="highlight">has has_been_printed => ( is => 'rw' );
1354 print $self->as_string;
1355 $self->has_been_printed(1);
1356 }</span></code></pre>
1363 <li>Role consumption is introspectable</li>
1366 <pre><code>if ( Person->does('Printable') ) { ... }
1370 Person->meta->does_role('Printable')</code></pre>
1375 <h1>These Names Are the Same</h1>
1378 <li>What if a role and class define the same method?</li>
1379 <li>A class's <em>local</em> methods win over the role's</li>
1380 <li>The role's methods win over the class's <em>inherited</em> methods</li>
1385 <h1>Conflicts Between Roles</h1>
1388 <li>Two roles with a method of the same name</li>
1389 <li>Generates a compile-time error when consumed by a class</li>
1394 <h1>Conflict Example</h1>
1396 <pre><code>package IsFragile;
1401 package CanBreakdance;
1404 sub break { ... }</code></pre>
1408 <h1>Conflict Example</h1>
1410 <pre><code>package FragileDancer;
1413 <span class="highlight">with 'IsFragile', 'CanBreakdance';</span></code></pre>
1416 <li>Only one <code>with</code>!</li>
1421 <h1>Conflict Resolution</h1>
1424 <li>The consuming class must resolve the conflict by implementing the method</li>
1425 <li>Can use some combination of method exclusion and aliasing</li>
1430 <h1>Conflicts Are a Smell</h1>
1433 <li>Roles are about semantics!</li>
1434 <li>Roles have a <em>meaning</em></li>
1435 <li>Method name conflicts smell like bad design</li>
1440 <h1>Roles With Roles</h1>
1442 <pre><code>package Comparable;
1445 requires 'compare';</code></pre>
1449 <h1>Roles With Roles</h1>
1451 <pre><code>package TestsEquality;
1458 return $self->compare(@_) == 0;
1463 <h1>And then ...</h1>
1465 <pre><code>package Integer;
1468 with 'TestsEquality';
1470 # Satisfies the Comparable role
1473 Integer->does('TestsEquality'); # true
1474 Integer->does('Comparable'); # also true!</code></pre>
1478 <h1>Name Conflicts Between Roles</h1>
1480 <pre><code>package HasSubProcess;
1483 <span class="highlight">sub execute { ... }</span>
1488 with 'HasSubProcess';
1490 <span class="highlight">sub execute { ... }</span></code></pre>
1494 <h1>Delayed Conflict</h1>
1496 <pre><code>package SysadminAssassin;
1497 with 'Killer';</code></pre>
1500 <li><code>SysadminAssassin</code> must implement its own <code>execute</code></li>
1501 <li>But loading the <code>Killer</code> role by itself does not cause an error</li>
1506 <h1>Roles as Interfaces</h1>
1509 <li>Roles can <code>require</code> methods of their consumers</li>
1510 <li>Compile-time checks</li>
1511 <li>Method must exist when the role is consumed</li>
1516 <h1>The Attribute Gotcha</h1>
1518 <pre><code>package HasSize;
1521 <span class="current incremental">requires 'size';</span>
1526 <span class="incremental">with 'HasSize';
1528 has size => ( is => 'ro' );</span></code></pre>
1532 <h1>The Attribute Gotcha Workaround</h1>
1534 <pre><code>package HasSize;
1542 has size => ( is => 'ro' );
1544 with 'HasSize';</code></pre>
1548 <h1>Compile-time Is a Lie</h1>
1551 <li>Really, it's <em>package load</em> time</li>
1552 <li>That's run-time, but before the "real" run-time</li>
1553 <li>Moose does not rewire Perl, it's just sugar!</li>
1554 <li>(but <code>MooseX::Declare</code> <em>does</em> rewire Perl)</li>
1559 <h1>Enforcing Roles</h1>
1561 <pre><code>package Comparison;
1564 has [ 'left', 'right' ] => (
1566 <span class="highlight">does => 'Comparable',</span>
1571 <li>A sneak peek at type constraints</li>
1577 <h1>Roles Can Be Applied to Objects</h1>
1579 <pre><code>use Moose::Util qw( apply_all_roles );
1581 my $fragile_person = Person->new( ... );
1582 apply_all_roles( $fragile_person,
1583 'IsFragile' );</code></pre>
1586 <li>Does not change the <code>Person</code> class</li>
1587 <li>Works with non-Moose classes, great for monkey-patching!</li>
1592 <h1>Roles Are Dirty Too</h1>
1595 <li>Once again, clean up those Moose droppings</li>
1598 <pre><code>package Comparable;
1603 <span class="highlight">no Moose::Role;</span></code></pre>
1606 <li>But roles cannot be made immutable</li>
1611 <h1>The Zen of Roles</h1>
1614 <li>Roles represent discrete units of ...
1621 <li>Roles are shareable between unrelated classes</li>
1622 <li>Roles are what a class <em>does</em>, not what it <em>is</em></li>
1623 <li>Roles <em>add</em> functionality, inheritance <em>specializes</em></li>
1628 <h1>Abstract Examples</h1>
1631 <li>Human <em>@ISA</em> Animal</li>
1632 <li>Human <em>does</em> Toolmaker (as <em>does</em> Chimpanzee)</li>
1633 <li>Car <em>@ISA</em> Vehicle</li>
1634 <li>Car <em>does</em> HasEngine</li>
1639 <h1>Real Examples</h1>
1642 <li>Objects representing SQL database components and queries
1644 <li>Schema, Table, Column, ColumnAlias</li>
1645 <li>Select, Insert, Update, Delete</li>
1652 <h1>Real Examples</h1>
1655 <li>Column and ColumnAlias both <em>do</em> ColumnLike</li>
1656 <li>ColumnLike things can be used in certain parts of queries</li>
1657 <li>All queries <em>do</em> HasWhereClause</li>
1658 <li>Select <em>does</em> Comparable and Selectable (for subselects)</li>
1659 <li>A where clause requires its components to <em>do</em> Comparable</li>
1664 <h1>Roles Summary</h1>
1667 <li>Roles can define an interface with <code>requires</code></li>
1668 <li>Roles can have state (attributes) and behavior (methods)</li>
1669 <li>Roles can mix interface, state, & behavior</li>
1670 <li>Roles are composed (flattened) into classes</li>
1671 <li>Roles can do other roles</li>
1672 <li>Roles can be used as a type in APIs (must do Comparable)</li>
1684 # perl bin/prove -lv t/02-roles.t
1686 Iterate til this passes all its tests</pre>
1689 <div class="slide fake-slide0">
1690 <h1>Part 3: Basic Attributes</h1>
1694 <h1>Attributes Are Huge</h1>
1697 <li>Moose's biggest feature</li>
1698 <li>The target of <em>many</em> MooseX modules</li>
1703 <h1>Quick Review</h1>
1706 <li>Declared with <code>has</code></li>
1707 <li>Read-only or read-write</li>
1710 <pre><code>package Shirt;
1713 has 'color' => ( is => 'ro' );
1714 has 'is_ripped' => ( is => 'rw' );</code></pre>
1718 <h1>Required-ness</h1>
1721 <li>Required means "must be passed to the constructor"</li>
1722 <li>But can be <code>undef</code></li>
1727 <h1>Required-ness</h1>
1729 <pre><code>package Person;
1732 has first_name => (
1734 <span class="current incremental">required => 1,</span>
1737 <span class="incremental">Person->new( first_name => undef ); # ok
1738 Person->new(); # kaboom</span></code></pre>
1742 <h1>Default and Builder</h1>
1745 <li>Attributes can have defaults</li>
1746 <li>Simple non-reference scalars (number, string)</li>
1747 <li>Subroutine reference</li>
1748 <li>A builder method</li>
1756 <li>Can be a non-reference scalar (including <code>undef</code>)</li>
1759 <pre><code>package Person;
1764 default => 'Spire FCU',
1772 <li>Can be a subroutine reference</li>
1775 <pre><code>package Person;
1782 name => 'Spire FCU' ) },
1787 <h1>Subroutine Reference Default</h1>
1790 <li>Called as a method on the object</li>
1791 <li>Called anew for each object</li>
1796 <h1>Why No Other Reference Types?</h1>
1798 <pre><code>package Person;
1803 <span class="wrong">default => Bank->new(
1804 name => 'Spire FCU' ),</span>
1808 <li>Now <strong>every</strong> person shares the <strong>same</strong> Bank object!</li>
1813 <h1>Defaulting to an Empty Reference</h1>
1815 <pre><code>package Person;
1818 has packages => (
1820 default => <span class="highlight">sub { [] }</span>,
1825 <h1>What if I Want to Share?</h1>
1827 <pre><code>package Person;
1830 my $highlander_bank =
1832 name => 'Clan MacLeod Trust' );
1836 default => sub { $highlander_bank },
1844 <li>A method <em>name</em></li>
1845 <li>When called, this method returns the default value</li>
1852 <pre><code>package Person;
1857 builder => '_build_bank',
1862 return Bank->new(
1863 name => 'Spire FCU' );
1868 <h1>Default vs Builder</h1>
1871 <li>Use default for simple scalars</li>
1872 <li>Use default to return empty references</li>
1873 <li>Use default for <em>very</em> trivial subroutine references</li>
1874 <li>Use builder for everything else</li>
1879 <h1>Builder Bonuses</h1>
1882 <li>Can be overridden and method modified, because it's called by <em>name</em></li>
1883 <li>Roles can require a builder</li>
1888 <h1>Role Requires Builder</h1>
1890 <pre><code>package HasBank;
1893 requires '_build_bank';
1897 builder => '_build_bank',
1902 <h1>Lazy, Good for Nothin' Attributes</h1>
1905 <li>Normally, defaults are generated during object construction</li>
1906 <li>This can be expensive</li>
1907 <li>We want to default to <code>$self->size * 2</code>, but attribute initialization order is unpredictable</li>
1908 <li>Use lazy attributes!</li>
1913 <h1>The Power of Dynamic Defaults</h1>
1915 <pre><code>package Person;
1918 has shoe_size => (
1925 <h1>The Power of Dynamic Defaults</h1>
1927 <pre><code>has shoes => (
1929 <span class="highlight">lazy => 1,</span>
1930 builder => '_build_shoes',
1936 return Shoes->new(
1937 size => <span class="highlight">$self->shoe_size</span> );
1942 <h1>Lazy is Good</h1>
1945 <li>Lazy defaults are executed when the attribute is read</li>
1946 <li>Can see other object attributes</li>
1947 <li>Still need to watch out for circular laziness</li>
1952 <h1>Clearer and Predicate</h1>
1955 <li>Attributes can have a value, including <code>undef</code>, or not</li>
1956 <li>Can clear the value with a clearer method</li>
1957 <li>Can check for the existence of a value with a predicate method</li>
1958 <li>By default, these methods are not created</li>
1963 <h1>Clearer and Predicate</h1>
1965 <pre><code>package Person;
1971 builder => '_build_account',
1972 <span class="highlight">clearer => '_clear_account',
1973 predicate => 'has_account',</span>
1978 <h1>Clearer and Lazy Defaults</h1>
1981 <li>Lazy defaults are good for computed attributes</li>
1982 <li>Clear the attribute when the source data changes</li>
1983 <li>Recalculated at next access</li>
1988 <h1>Renaming constructor arguments</h1>
1991 <li>By default, constructor names = attribute names</li>
1992 <li>Use <code>init_arg</code> to change this</li>
1993 <li>Set <code>init_arg => undef</code> to make it unconstructable</li>
1998 <h1>Some <code>init_arg</code> examples</h1>
2000 <pre><code>package Person;
2005 <span class="highlight">init_arg => 'foot_size',</span>
2008 Person->new( <span class="wrong">shoe_size => 13</span> );
2011 Person->new( <span class="right">foot_size => 13</span> );
2012 print $person->shoe_size;</code></pre>
2016 <h1>Some <code>init_arg</code> examples</h1>
2018 <pre><code>package Person;
2023 <span class="highlight">init_arg => undef,</span>
2026 Person->new( <span class="wrong">shoes => Shoes->new</span> );</code></pre>
2030 <h1>Why Set <code>init_arg => undef</code>?</h1>
2033 <li>Use this with a lazy default for attributes-as-cache</li>
2034 <li>Compute the value as needed</li>
2035 <li>Ensure that it is always generated correctly (not set by constructor)</li>
2036 <li>Use triggers or method modifiers (coming soon) to clear the value</li>
2041 <h1>Attribute Inheritance</h1>
2044 <li>By default, subclasses inherit attribute as-is</li>
2045 <li>Can change some attribute parameters in subclasses
2051 <li>others we've not yet covered</li>
2058 <h1>Attribute Inheritance Example</h1>
2060 <pre><code>package Employee;
2065 has '<span class="highlight">+first_name</span>' => (
2066 default => 'Joe',
2071 <h1>Attribute Inheritance Warning</h1>
2074 <li>An attribute is a contract about a class's API</li>
2075 <li>Don't break that contract in a subclass</li>
2076 <li>Especially important in the context of types</li>
2081 <h1>Changing Accessor Names</h1>
2083 <pre><code>package Person;
2086 has first_name => (
2087 <span class="highlight">accessor</span> => 'first_name',
2091 <li>The long-hand version of <code>is => 'rw'</code></li>
2096 <h1>Changing Accessor Names</h1>
2098 <pre><code>package Person;
2101 has first_name => (
2102 <span class="highlight">reader</span> => 'first_name',
2103 <span class="highlight">writer</span> => undef,
2107 <li>The long-hand version of <code>is => 'ro'</code></li>
2113 <h1>Changing Accessor Names</h1>
2115 <pre><code>package Person;
2118 has first_name => (
2119 <span class="highlight">reader</span> => 'get_first_name',
2120 <span class="highlight">writer</span> => 'set_first_name',
2125 <h1>Changing Accessor Names</h1>
2127 <pre><code>package Person;
2130 has first_name => (
2131 <span class="highlight">is</span> => 'rw',
2132 <span class="highlight">writer</span> => '_first_name',
2136 <li>Can also mix-and-match <code>is</code> and explicit names</li>
2141 <h1>ETOOMUCHTYPING</h1>
2144 <li><code>MooseX::FollowPBP</code><br /><code>get_foo</code> and <code>set_foo</code></li>
2145 <li><code>MooseX::SemiAffordanceAccessor</code><br /><code>foo</code> and <code>set_foo</code></li>
2150 <h1>ETOOMUCHTYPING</h1>
2152 <pre><code>package Person;
2154 <span class="highlight">use MooseX::SemiAffordanceAccessor;</span>
2156 has first_name => (
2161 <li>Creates <code>first_name</code> and <code>set_first_name</code></li>
2166 <h1>Basic Attributes Summary</h1>
2169 <li>Attributes can be <code>required</code></li>
2170 <li>Attributes can have a <code>default</code> or <code>builder</code></li>
2171 <li>Attributes with a default or builder can be <code>lazy</code></li>
2172 <li>Attributes can have a <code>clearer</code> and/or <code>predicate</code></li>
2177 <h1>Basic Attributes Summary</h1>
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 \
2195 t/03-basic-attributes.t
2197 Iterate til this passes all its tests</pre>
2200 <div class="slide fake-slide0">
2201 <h1>Part 4: Method Modifiers</h1>
2205 <h1>What is a Method Modifier</h1>
2208 <li>Apply to an existing method</li>
2209 <li>... that comes from a parent class, the current class, or a role</li>
2210 <li>Roles can provide modifiers that are applied at composition time</li>
2215 <h1>What Are Method Modifiers For?</h1>
2218 <li>"Inject" behavior</li>
2219 <li>Add behavior to generated methods (accessors, delegations)</li>
2220 <li>Added from a role, can modify existing behavior</li>
2225 <h1>Before and After</h1>
2228 <li>Simplest modifiers - <code>before</code> and <code>after</code></li>
2229 <li>Guess when they run!</li>
2234 <h1>Uses for <code>before</code></h1>
2237 <li>As a pre-call check</li>
2240 <pre><code>package Person;
2243 before work => sub {
2245 die 'I have no job!'
2246 unless $self->has_title;
2251 <h1>Uses for <code>before</code></h1>
2254 <li>Logging/Debugging</li>
2257 <pre><code>package Person;
2260 before work => sub {
2262 return unless $DEBUG;
2264 warn "Called work on ",
2265 $self->full_name,
2266 "with the arguments: [@_]\n";
2271 <h1>Uses for <code>after</code></h1>
2274 <li>Also works for logging/debugging</li>
2275 <li>Post-X side-effects (recording audit info)</li>
2278 <pre><code>package Person;
2281 after work => sub {
2283 $self->work_count(
2284 $self->work_count + 1 );
2292 <li>Modifiers are useful for adding behavior to generated methods</li>
2297 <h1>More Modifier Examples</h1>
2299 <pre><code>has password => (
2301 clearer => 'clear_password',
2303 has hashed_password => (
2305 builder => '_build_hashed_password',
2306 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;
2353 <h1>Modifier Order</h1>
2356 <li>Before runs in order from last to first</li>
2357 <li>After runs in order from first to last</li>
2358 <li>Around runs in order from last to first</li>
2363 <h1>Modifier Order Illustrated</h1>
2366 <span class="current incremental">before 2
2368 <span class="incremental">around 2
2370 <span class="incremental">wrapped method</span>
2371 <span class="incremental">around 1
2373 <span class="incremental">after 1
2379 <h1>Modifiers in Roles</h1>
2382 <li>Roles can use these modifiers</li>
2383 <li>Very powerful!</li>
2388 <h1>Modifiers in Roles</h1>
2390 <pre><code>package IsUnreliable;
2393 <span class="highlight">requires 'run';
2395 around run</span> => sub {
2399 return if rand(1) < 0.5;
2401 return $self->$orig(@_);
2406 <h1>Augment and Inner</h1>
2409 <li>Inverted <code>super</code></li>
2410 <li>From least- to most-specific</li>
2411 <li>Like Mason's autohandler feature</li>
2412 <li>Grandparent to parent to child</li>
2413 <li>Not allowed in roles</li>
2418 <h1>Augment and Inner</h1>
2420 <pre class="medium"><code>package Document;
2422 sub xml { '<doc>' . <span class="highlight">inner()</span> . '</doc>' }
2426 <span class="highlight">augment xml</span> =>
2427 sub { my $self = shift;
2428 $self->title() . <span class="highlight">inner()</span> . $self->summary() };
2432 <span class="highlight">augment xml</span> =>
2433 sub { my $self = shift;
2434 $self->tps_xml() . <span class="highlight">inner()</span> };</code></pre>
2438 <h1>Augment and Inner</h1>
2441 <li>When we call <code>$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 \
2514 t/04-method-modifiers.t
2516 Iterate til this passes all its tests</pre>
2519 <div class="slide fake-slide0">
2520 <h1>Part 5: Types</h1>
2524 <h1>A Type System for Perl</h1>
2527 <li>Sort of ...</li>
2528 <li><em>Variables</em> are not typed</li>
2529 <li>Attributes can have types</li>
2530 <li>MooseX modules let you define method signatures</li>
2535 <h1>Components of a Moose Type</h1>
2538 <li>A type is a name and a constraint</li>
2539 <li>Types have a hierarchy</li>
2540 <li>Constraints are cumulative from parents</li>
2541 <li>Types can have associated coercions</li>
2546 <h1>Built-in Type Hierarchy</h1>
2565 <h1>Built-in Type Hierarchy</h1>
2599 <li>Like Perl's <code>if ($foo)</code></li>
2604 <h1>Value (and subtypes)</h1>
2607 <li><code>Value</code> is true when <code>! ref $thing</code></li>
2608 <li><code>Value</code> and <code>Str</code> are effectively the same, but <code>Str</code> is more expressive</li>
2609 <li><code>Num</code> is true when a <code>$scalar</code> looks like a number</li>
2610 <li>An overloaded object which numifies does not pass the <code>Num</code> constraint!</li>
2611 <li>Perl 5's overloading is hopelessly broken</li>
2616 <h1>ClassName and RoleName</h1>
2619 <li>A string with a package name</li>
2620 <li>The package <strong>must already be loaded</strong></li>
2625 <h1>Parameterizable Types</h1>
2628 <li>What does <code>ArrayRef[`a]</code> mean?</li>
2629 <li><code>s/`a/Int/</code> (or <code>Str</code> or ...)</li>
2630 <li>When you use it you can write ...
2632 <li><code>ArrayRef</code> (== <code>ArrayRef[Item]</code>)</li>
2633 <li><code>ArrayRef[Str]</code></li>
2634 <li><code>ArrayRef[MyTypeName]</code></li>
2635 <li><code>ArrayRef[HashRef[Maybe[Int]]]</code></li>
2645 <li>Maybe means either the named type or <code>undef</code></li>
2646 <li><code>Maybe[Int]</code> accepts integers or <code>undef</code></li>
2654 <li>This or that (or that or ...)</li>
2655 <li><code>Int | ArrayRef[Int]</code></li>
2656 <li>But use a coercion instead when possible</li>
2657 <li>Or use a <code>role_type</code>, <code>duck_type</code>, or anything not a union</li>
2658 <li>A union is often a code smell</li>
2663 <h1>Making Your Own Types</h1>
2665 <pre><code>use Moose::Util::TypeConstraints;
2667 <span class="incremental current">subtype 'PositiveInt',</span>
2668 <span class="incremental">as 'Int',</span>
2669 <span class="incremental">where { $_ > 0 },</span>
2670 <span class="incremental">message
2671 { "The value you provided ($_)"
2672 . " was not a positive int." };</span>
2676 <span class="incremental">isa => 'PositiveInt',</span>
2681 <h1>Automatic Types</h1>
2684 <li>Moose creates a type for every Moose class and role</li>
2685 <li>Unknown names are assumed to be classes</li>
2690 <h1>Automatic Types</h1>
2692 <pre><code>package Employee;
2697 <span class="highlight">isa => 'Employee',</span>
2700 has start_date => (
2702 <span class="highlight">isa => 'DateTime',</span>
2707 <h1>Subtype Shortcuts - <code>class_type</code></h1>
2709 <pre><code>use Moose::Util::TypeConstraints;
2710 class_type 'DateTime';</code></pre>
2714 <pre><code>subtype 'DateTime',
2716 where { $_->isa('DateTime') },
2717 message { ... };</code></pre>
2721 <h1>Subtype Shortcuts - <code>role_type</code></h1>
2723 <pre><code>use Moose::Util::TypeConstraints;
2724 role_type 'Printable';</coe></pre>
2728 <pre><code>subtype 'Printable',
2731 { Moose::Util::does_role(
2732 $_, 'Printable' ) },
2733 message { ... };</code></pre>
2737 <h1>Subtype Shortcuts - <code>duck_type</code></h1>
2739 <pre><code>use Moose::Util::TypeConstraints;
2740 duck_type Car => qw( run break_down );</code></pre>
2744 <pre><code>subtype 'Car',
2746 where { all { $_->can($_) }
2747 qw( run break_down ) },
2748 message { ... };</code></pre>
2752 <h1>Subtype Shortcuts - <code>enum</code></h1>
2754 <pre><code>use Moose::Util::TypeConstraints;
2755 enum Color => qw( red blue green );</code></pre>
2759 <pre><code>my %ok = map { $_ => 1 }
2760 qw( red blue green );
2765 message { ... };</code></pre>
2769 <h1>Anonymous Subtypes</h1>
2771 <pre><code>package Person;
2773 <span class="highlight">my $posint =
2774 subtype as 'Int', where { $_ > 0 };</span>
2778 <span class="highlight">isa => $posint,</span>
2782 <li>Shortcuts have anonymous forms as well</li>
2789 <pre><code>use Moose::Util::TypeConstraints;
2793 where { ! /[a-z]/ };</code></pre>
2799 <pre><code><span class="incremental current">coerce 'UCStr',</span>
2800 <span class="incremental">from 'Str',</span>
2801 <span class="incremental">via { uc };</span>
2803 has shouty_name => (
2806 <span class="incremental">coerce => 1,</span>
2811 <h1>Coercion Examples</h1>
2813 <pre><code>subtype 'My::DateTime',
2814 as class_type 'DateTime';
2816 coerce 'My::DateTime',
2818 via { DateTime->new( %{$_} ) };
2820 coerce 'My::DateTime',
2822 via { DateTime->from_epoch(
2823 epoch => $_ ) };</code></pre>
2826 <li>Use coercion to inflate a value</li>
2831 <h1>Coercion Examples</h1>
2833 <pre><code>coerce 'ArrayRef[Int]',
2835 via { [ $_ ] };</code></pre>
2838 <li>Instead of union - <code style="white-space: nowrap">Int | ArrayRef[Int]</code></li>
2843 <h1>Using Types with Attributes</h1>
2845 <pre><code>package Person;
2849 <span class="highlight">isa => 'Num',</span>
2852 has favorite_numbers => (
2854 <span class="highlight">isa => 'ArrayRef[Int]',
2855 coerce => 1,</span>
2860 <h1>More Droppings</h1>
2863 <li><code>Moose::Util::TypeConstraints</code> also needs cleanup</li>
2866 <pre><code>package Person;
2869 use Moose::Util::TypeConstraints;
2874 <span class="highlight">no Moose::Util::TypeConstraints;</span></code></pre>
2878 <h1>Questions So Far?</h1>
2885 # perl bin/prove -lv t/05-types.t
2887 Iterate til this passes all its tests</pre>
2891 <h1>Typed Methods (Low-tech)</h1>
2893 <pre class="medium"><code>package Person;
2894 <span class="highlight">use MooseX::Params::Validate qw( validated_list );</span>
2898 <span class="highlight">my ( $tasks, $can_rest ) =
2902 { isa => 'ArrayRef[Task]',
2913 <h1>Typed Methods (High-tech)</h1>
2915 <pre class="medium"><code>package Person;
2917 <span class="highlight">use MooseX::Method::Signatures;</span>
2919 <span class="highlight">method work ( ArrayRef[Task] :$tasks,
2920 Bool :$can_rest = 0 )</span> {
2928 <h1>Digression: The Type Registry</h1>
2931 <li>Types are actually <code>Moose::Meta::TypeConstraints</code> <em>objects</em></li>
2932 <li>Stored in an interpreter-global registry mapping names to objects</li>
2940 <li>Coercions are attached to type objects</li>
2941 <li>Therefore also global</li>
2942 <li>Name conflicts between modules!</li>
2943 <li>Coercion conflicts between modules!</li>
2948 <h1>Namespace Fix</h1>
2951 <li>Use some sort of pseudo-namespacing scheme</li>
2952 <li>Never coerce directly to a class name, or <em>to</em> built-in types</li>
2957 <h1>Namespace Fix</h1>
2959 <pre><code>use Moose::Util::TypeConstraints;
2960 subtype <span class="highlight">'MyApp::Type::DateTime',</span>
2963 <span class="highlight">coerce 'MyApp::Type::DateTime',</span>
2965 via { DateTime->new( %{$_} ) }
2967 has creation_date => (
2969 <span class="highlight">isa => 'MyApp::Type::DateTime',</span>
2975 <h1>Namespace Fix</h1>
2977 <pre><code>subtype 'MyApp::Type::ArrayOfInt',
2980 coerce 'MyApp::Type::ArrayOfInt',
2982 via { [ $_ ] };</code></pre>
2986 <h1>Namespace Fix Pros and Cons</h1>
2989 <li><span class="right">Relatively simple</span></li>
2990 <li><span class="right">Already built into Moose</span></li>
2991 <li><span class="wrong">Conflates type and module namespaces</span></li>
2992 <li><span class="wrong">Type names are strings, so typos are easy to make and may be hard to find</span></li>
2997 <h1>MooseX::Types</h1>
2999 <pre><code>package MyApp::Types;
3002 <span class="highlight">-declare => [ qw( ArrayOfInt ) ]</span>;
3003 use MooseX::Types::Moose
3006 subtype <span class="highlight">ArrayOfInt</span>,
3009 coerce <span class="highlight">ArrayOfInt</span>
3011 via { [ $_ ] };</code></pre>
3015 <h1>MooseX::Types</h1>
3017 <pre><code>package MyApp::Account;
3019 use MyApp::Types qw( ArrayOfInt );
3021 has transaction_history => (
3028 <h1>MooseX::Types</h1>
3031 <li>Type names are exported functions, catches typos early</li>
3032 <li>Types must be pre-declared</li>
3033 <li>Types are stored with namespaces internally, but you use short names</li>
3034 <li>Import existing Moose types as functions from <code>MooseX::Types::Moose</code></li>
3035 <li>Still need string names for things like <code>ArrayRef['Email::Address']</code></li>
3040 <h1>MooseX::Types Pros and Cons</h1>
3043 <li><span class="right">Catches typos at compile time</span></li>
3044 <li><span class="right">Automatic namespacing</span></li>
3045 <li><span class="wrong">One more thing to install and learn</span></li>
3046 <li><span class="wrong">Every name is typed twice (declared and then defined)</span></li>
3047 <li><span class="wrong">Still stuck with strings when referring to class or role names</span></li>
3048 <li><span class="wrong">Coercion gotcha from earlier still applies to types exported from <code>MooseX::Types::Moose</code></span></li>
3053 <h1>Recommendation</h1>
3056 <li>Use <code>MooseX::Types</code></li>
3057 <li>Compile time error catching and automatic namespacing are huge wins</li>
3058 <li>Docs from <code>Moose::Util::TypeConstraints</code> are 98% compatible with <code>MooseX::Types</code> anyway</li>
3059 <li>A function exported by a type library works wherever a type name would</li>
3067 <div class="slide fake-slide0">
3068 <h1>Part 6: Advanced Attributes</h1>
3072 <h1>Weak References</h1>
3075 <li>A weak reference lets you avoid circular references</li>
3076 <li>Weak references do not increase the reference count</li>
3081 <h1>Circular Reference Illustrated</h1>
3083 <pre><code>my $foo = {};
3084 my $bar = { foo => $foo };
3085 $foo->{bar} = $bar;</code></pre>
3088 <li>Neither <code>$foo</code> nor <code>$bar</code> go out of scope<br />
3089 (until the program exits)</li>
3094 <h1>Weakening Circular References</h1>
3096 <pre><code>use Scalar::Util qw( weaken );
3099 my $bar = { foo => $foo };
3100 $foo->{bar} = $bar;
3101 weaken $foo->{bar}</code></pre>
3104 <li>When <code>$bar</code> goes out of scope, <code>$foo->{bar}</code> becomes <code>undef</code></li>
3109 <h1>Circular References in Attributes</h1>
3111 <pre><code>package Person;
3114 has name => ( is => 'ro' );
3115 has friend => ( is => 'rw' );
3117 my $alice = Person->new( name => 'Alice' );
3118 my $bob = Person->new( name => 'Bob' );
3119 $bob->friend($alice);
3120 $alice->friend($bob);</code></pre>
3126 <pre><code>package Person;
3129 has name => ( is => 'ro' );
3130 has friend => ( is => 'rw',
3131 <span class="highlight">weak_ref => 1</span> );
3133 my $alice = Person->new( name => 'Alice' );
3134 my $bob = Person->new( name => 'Bob' );
3135 $bob->friend($alice);
3136 $alice->friend($bob);</code></pre>
3140 <h1>Under the Hood</h1>
3143 <li>A <code>weak_ref</code> attribute calls <code>weaken</code> ...
3145 <li>during object construction</li>
3146 <li>when the attribute is set via a writer</li>
3156 <li>A code reference run after an attribute is <em>set</em></li>
3157 <li>Like an <code>after</code> modifier, but makes intentions clearer</li>
3160 <h2 class="wrong">Gross</h2>
3162 <pre><code>after salary_level => {
3164 <span class="highlight">return unless @_;</span>
3165 $self->clear_salary;
3170 <h1>Use a Trigger Instead</h1>
3172 <h2 class="right">Cleaner</h2>
3174 <pre><code>has salary_level => (
3177 sub { $_[0]->clear_salary },
3182 <h1>Trigger Arguments</h1>
3185 <li><code>$self</code></li>
3186 <li><code>$new_value</code></li>
3187 <li><code>$old_value</code> - if one exists</li>
3195 <li>Attributes can be objects</li>
3196 <li>Delegation transparently calls methods on those objects</li>
3201 <h1>Delegation Examples</h1>
3203 <pre><code>package Person;
3208 <span class="highlight">handles => [ 'inhale', 'exhale' ],</span>
3212 <li>Creates <code>$person->inhale</code> and <code>->exhale</code> methods</li>
3213 <li>Internally calls <code>$person->lungs->inhale</code></li>
3218 <h1>Why Delegation?</h1>
3221 <li>Reduce the number of classes exposed</li>
3222 <li>Re-arrange class internals -<br />
3223 turn a method into an attribute with delegation</li>
3224 <li>Provide convenenience methods</li>
3229 <h1>Moose's <code>handles</code> Parameter</h1>
3232 <li>Accepts many arguments ...
3234 <li>Array reference - list of methods to delegate as-is</li>
3235 <li>Hash reference - map of method names</li>
3236 <li>Regex - delegates all matching methods</li>
3237 <li>Role name - delegates all methods in the role</li>
3238 <li>Sub reference - does something complicated ;)</li>
3245 <h1>Array Reference</h1>
3248 <li>1-to-1 mapping</li>
3249 <li>Takes each method name and creates a simple delegation from the delegating class to the delegatee attribute</li>
3254 <h1>Hash Reference</h1>
3257 <li>Mapping of names in the delegating class to the delegatee class</li>
3260 <pre><code>package Person;
3264 isa => 'BankAccount',
3265 <span class="highlight">handles => {
3266 receive_money => 'deposit',
3267 give_money => 'withdraw',
3273 <h1>Hash Reference Detailed</h1>
3275 <pre><code> handles => {
3276 receive_money => 'deposit',
3277 give_money => 'withdraw',
3281 <li><code>$person->receive_money</code> = <code>$person->account->deposit</code></li>
3282 <li><code>$person->give_money</code> = <code>$person->account->withdraw</code></li>
3289 <pre><code>package Person;
3295 handles => qr/.*/,
3299 <li>Creates a delegation for every method in the Name class</li>
3300 <li>Excludes <code>meta</code> and methods inherited from <code>Moose::Object</code></li>
3307 <pre><code>package Auditor;
3309 sub record_change { ... }
3310 sub change_history { ... }
3317 does => 'Auditor',
3318 <span class="highlight">handles => 'Auditor',</span>
3323 <h1>Role Name Detailed</h1>
3326 <li>Account gets delegate methods for each method in the <code>Auditor</code> role
3328 <li>record_history</li>
3329 <li>change_history</li>
3336 <h1>Native Delegation</h1>
3339 <li>Delegate to <em>unblessed</em> Perl types</li>
3340 <li>Scalar, array or hash ref, etc</li>
3341 <li>Treat Perl types as objects</li>
3342 <li>Still uses <code>handles</code></li>
3343 <li>Pretend that native Perl types have methods</li>
3348 <h1>Native Delegation - Array(Ref)</h1>
3351 <li>Methods include:
3353 <li><code>push</code></li>
3354 <li><code>shift</code></li>
3355 <li><code>elements</code> - returns all elements</li>
3356 <li><code>count</code></li>
3357 <li><code>is_empty</code></li>
3358 <li>quite a few more</li>
3365 <h1>Native Delegation - Array(Ref)</h1>
3367 <pre><code>package Person;
3369 has _favorite_numbers => (
3370 traits => [ 'Array' ],
3372 isa => 'ArrayRef[Int]',
3373 default => sub { [] },
3374 init_arg => undef,
3375 <span class="highlight">handles =>
3376 { favorite_numbers => 'elements',
3377 add_favorite_number => 'push',
3383 <h1>Native Delegation - Array(Ref)</h1>
3385 <pre><code>my $person = Person->new();
3387 $person->add_favorite_number(7);
3388 $person->add_favorite_number(42);
3391 for $person->favorite_numbers;
3398 <h1>Native Delegation</h1>
3401 <li>Native types are ...
3403 <li>Number - <code>add</code>, <code>mul</code>, ...</li>
3404 <li>String - <code>append</code>, <code>chop</code>, ...</li>
3405 <li>Counter - <code>inc</code>, <code>dec</code>, ...</li>
3406 <li>Bool - <code>set</code>, <code>toggle</code>, ...</li>
3407 <li>Hash - <code>get</code>, <code>set</code>, ...</li>
3408 <li>Array - already saw it</li>
3409 <li>Code - <code>execute</code> and <code>execute_method</code></li>
3416 <h1>Curried Delegation</h1>
3419 <li>A delegation with some preset arguments</li>
3420 <li>Works with object or Native delegation</li>
3425 <h1>Curried Delegation</h1>
3427 <pre><code>package Person;
3431 isa => 'BankAccount',
3434 <span class="highlight">[ 'deposit', 100 ]</span>
3436 <span class="highlight">[ 'withdraw', 100 ]</span>
3442 <h1>Curried Delegation</h1>
3444 <pre><code>$person->receive_100;
3446 $person->account->deposit(100);</code></pre>
3450 <h1>Traits and Metaclasses</h1>
3453 <li>The ultimate in customization</li>
3454 <li>Per attribute metaclasses</li>
3455 <li>Per attribute roles applied to the attribute metaclass</li>
3456 <li>Change the meta-level behavior</li>
3461 <h1>Traits and Metaclasses</h1>
3464 <li>The default metaclass is <code>Moose::Meta::Attribute</code></li>
3465 <li>Controls accessor generation, defaults, delegation, etc.</li>
3466 <li>Adding a role to this metaclass (or replacing it) allows for infinite customization</li>
3471 <h1>Traits and Metaclasses</h1>
3474 <li>Can add/alter/remove an attribute parameter (from <code>has</code>)</li>
3475 <li>Can change behavior of created attribute</li>
3480 <h1>Simple Trait Example</h1>
3482 <pre><code>package Person;
3484 use MooseX::LabeledAttributes;
3487 <span class="highlight">traits => [ 'Labeled' ],</span>
3490 <span class="highlight">label => 'Social Security Number',</span>
3492 print <span class="highlight">Person->meta
3493 ->get_attribute('ssn')->label;</span></code></pre>
3497 <h1>Simple Metaclass Example</h1>
3499 <pre><code>package Person;
3501 use MooseX::LabeledAttributes;
3504 <span class="highlight">metaclass =>
3505 'MooseX::Meta::Attribute::Labeled',</span>
3508 <span class="highlight">label => 'Social Security Number',</span>
3510 print <span class="highlight">Person->meta
3511 ->get_attribute('ssn')->label;</span></code></pre>
3515 <h1>Traits vs Metaclass</h1>
3518 <li>Can apply any mix of traits to an attribute</li>
3519 <li>But just one metaclass</li>
3520 <li>Traits (aka roles) can cooperate</li>
3521 <li>Metaclasses require you to pick just one</li>
3526 <h1>Advanced Attributes Summary</h1>
3529 <li>Use <code>weak_ref</code> to avoid circular references</li>
3530 <li>Use trigger to do an action post-attribute write</li>
3531 <li>Use delegations to hide "internal" objects</li>
3532 <li>Use native delegations to treat Perl types as objects</li>
3533 <li>Traits and metaclasses let you extend Moose's core attribute features</li>
3545 # perl bin/prove -lv \
3546 t/06-advanced-attributes.t
3548 Iterate til this passes all its tests</pre>
3555 <div class="slide fake-slide0">
3560 <h1>More Information</h1>
3563 <li><a href="http://moose.perl.org/">http://moose.perl.org/</a></li>
3564 <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>
3565 <li><a href="irc://irc.perl.org/#moose">irc://irc.perl.org/#moose</a></li>
3566 <li>mailing list - <a href="mailto:moose@perl.org">moose@perl.org</a></li>
3567 <li>Slides and exercises are in Moose's git repo:
3569 <span style="font-size:80%; white-space: nowrap">git://jules.scsys.co.uk/gitmo/moose-presentations</span></li>
3573 <div class="slide fake-slide0">
3574 <h1>Bonus: A Brief Tour of MooseX</h1>
3578 <h1>Notable MX Modules on CPAN</h1>
3581 <li><strong>Not comprehensive</strong></li>
3582 <li>152 MooseX distributions on CPAN as of 02/02/2010</li>
3583 <li>Some of them are crap</li>
3588 <h1>Already Mentioned Several</h1>
3591 <li><code>MooseX::NonMoose</code> - best solution for subclassing non-Moose parents</li>
3592 <li><code>MooseX::Declare</code> - <em>real</em> Perl 5 OO</li>
3593 <li><code>MooseX::FollowPBP</code> and <code>MooseX::SemiAffordanceAccessor</code></li>
3594 <li><code>MooseX::Params::Validate</code> and <code>MooseX::Method::Signatures</code></li>
3595 <li><code>MooseX::Types</code></li>
3600 <h1>MooseX::Declare</h1>
3602 <pre><code>use MooseX::Declare;
3603 use 5.10.0; # for say
3607 ( is => 'ro', isa => 'Str' );
3610 say $self->greeting;
3616 <h1>MooseX::Declare</h1>
3619 <li>Still experimental-ish, but seeing more and more use</li>
3620 <li><strong>Not</strong> a source filter!</li>
3621 <li>Hooks into the Perl parser rather than filtering all your code</li>
3622 <li>But not supported by <code>PPI</code>, <code>perltidy</code>, etc.</li> (yet?)
3627 <h1>MooseX::StrictConstructor</h1>
3630 <li>By default, unknown constructor arguments are ignored</li>
3631 <li>MX::StrictConstructor turns these into an error</li>
3636 <h1>MooseX::StrictConstructor</h1>
3638 <pre><code>package Person;
3641 <span class="highlight">use MooseX::StrictConstructor;</span>
3643 has name => ( is => 'ro' );
3646 ( na<span class="wrong">n</span>e => 'Ringo Shiina' ); # kaboom</code></pre>
3650 <h1>MooseX::Traits</h1>
3653 <li>Combines object construction and role application</li>
3654 <li>Makes it easy to create one-off customized objects</li>
3659 <h1>MooseX::Traits</h1>
3661 <pre><code>package MyApp::Thingy;
3664 <span class="highlight">with 'MooseX::Traits';</span>
3667 MyApp::Thingy-><span class="highlight">new_with_traits</span>
3668 ( <span class="highlight">traits => [ 'Foo', 'Bar' ],</span>
3669 size => 42 );</code></pre>
3673 <h1>MooseX::Getopt</h1>
3676 <li>Makes command-line interface programs easy!</li>
3677 <li>Construct an object from CLI arguments</li>
3682 <h1>MooseX::Getopt</h1>
3684 <pre><code>package App::CLI;
3687 <span class="highlight">with 'MooseX::Getopt';</span>
3690 ( is => 'ro', required => 1 );
3692 ( is => 'ro', isa => 'ArrayRef[Str]' );
3694 sub run { ... }</code></pre>
3698 <h1>MooseX::Getopt</h1>
3701 <li>Then call it like this:</li>
3704 <pre><code>#!/usr/bin/perl
3708 <span class="highlight">App::CLI->new_with_options()</span>->run();</code></pre>
3712 --filters compress \
3713 --filters sanitize</pre>
3717 <h1>MooseX::Clone</h1>
3719 <pre><code>package Person;
3722 <span class="highlight">with 'MooseX::Clone';</span>
3724 my $person = Person->new;
3725 my $clone = <span class="highlight">$person->clone;</span></code></pre>
3729 <h1>MooseX::NonMoose</h1>
3732 <li>Highly recommended for subclassing non-Moose parents</li>
3733 <li>Gets all the little annoying details right</li>
3738 <h1>MooseX::Role::Parameterized</h1>
3740 <pre><code>package HasCollection;
3741 <span class="current incremental">use MooseX::Role::Parameterized;</span>
3742 <span class="incremental">parameter type => ( isa => 'Str',
3743 default => 'Item' );</span>
3744 <span class="incremental">role {
3748 'ArrayRef[' . $p->type() . ']';
3749 has collection =>
3752 };</span></code></pre>
3756 <h1>MooseX::Role::Parameterized</h1>
3758 <pre><code>package Person;
3761 with HasCollection => { type => 'Int' };</code></pre>
3764 <div class="slide fake-slide0">
3765 <h1>The End (Really)</h1>
3769 <h1>More Information</h1>
3772 <li><a href="http://moose.perl.org/">http://moose.perl.org/</a></li>
3773 <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>
3774 <li><a href="irc://irc.perl.org/#moose">irc://irc.perl.org/#moose</a></li>
3775 <li>mailing list - <a href="mailto:moose@perl.org">moose@perl.org</a></li>
3776 <li>Slides and exercises are in Moose's git repo:
3778 <span style="font-size:80%; white-space: nowrap">git://jules.scsys.co.uk/gitmo/moose-presentations</span></li>
3788 Copyright 2009 David Rolsky. All Rights Reserved.
3790 This work is licensed under a Creative Commons Attribution-Share Alike
3791 3.0 United States License See
3792 http://creativecommons.org/licenses/by-sa/3.0/us/ for details.