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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>Moose Summed Up</h1>
62 <li><strong>Declarative</strong> OO sugar</li>
63 <li>Introspectable</li>
64 <li>Extensible (MooseX::* on CPAN)</li>
69 <h1>Moose Background</h1>
72 <li>Created by Stevan Little, first released in 2006</li>
73 <li>Moose builds on Perl 5's native OO</li>
74 <li>Borrows ideas from other languages, notably Perl 6</li>
75 <li>Provides semantics for common operations</li>
79 <div class="slide fake-slide0">
80 <h1>Part 0: Moose Concepts</h1>
93 <li>Method modifiers</li>
94 <li>Constructor and destructor</li>
95 <li>One metaclass object</li>
98 <li>Classes do roles</li>
103 <h1>Class Example</h1>
105 <pre><code>package Person;
106 <span class="highlight">use Moose;</span></code></pre>
109 <li>Poof, a Moose-based class!</li>
117 <li>Aka property, slot, field, member variable</li>
118 <li>A piece of data owned by an object</li>
129 <li>Access-control (read-only vs read-write)</li>
130 <li>An optional type</li>
131 <li>Accessor methods</li>
132 <li>Delegation methods</li>
133 <li>Optional default value</li>
134 <li>Many more features</li>
137 <li>Stored in the object, but don't worry about that</li>
142 <h1>Attribute Example</h1>
144 <pre><code>package Person;
147 <span class="highlight">has first_name => ( is => 'rw' );</span></code></pre>
155 <li>Nothing fancy here, just Perl subroutines</li>
158 <pre><code>package Person;
161 <span class="highlight">sub greet { ... }</span></code></pre>
168 <li>Classes <strong>do</strong> (or consume) roles</li>
169 <li>Similar to mixins and Java interfaces</li>
177 <li>Like classes, can have attributes, methods, do roles</li>
178 <li>Roles can require methods</li>
179 <li>Roles are composed (flattened) into classes</li>
184 <h1>Role Example</h1>
186 <pre><code>package HasPermissions;
187 <span class="highlight">use Moose::Role;</span>
189 has is_admin => ( is => 'rw' );</code></pre>
193 <h1>Role Example</h1>
199 <pre><code>package Person;
202 <span class="highlight">with 'HasPermissions';</span></code></pre>
206 <h1>Method Modifiers</h1>
210 <li>"<strong>Before</strong> foo(), do this first"</li>
211 <li>"Do this <strong>after</strong> foo()</li>
212 <li>"Put this code <strong>around</strong> foo()"</li>
217 <h1>Before and After</h1>
219 <pre><code>before 'foo'
220 => sub { warn 'About to call foo()' };
223 => sub { warn 'Leaving foo()' };</code></pre>
230 <pre><code>around 'foo' => sub {
231 my $real_foo = shift;
234 warn 'Just before foo()';
236 $self->$real_foo( @_, bar => 42 );
238 return ( @return, 'modify return values' );
243 <h1>Type Constraints</h1>
246 <li>NOT A FULL-BLOWN TYPE SYSTEM!</li>
247 <li>But still darn useful</li>
248 <li>Constrain attribute values</li>
249 <li>Coerce from other types</li>
254 <h1>Type Constraint Example</h1>
256 <pre><code>package Person;
261 <span class="highlight">isa => 'Int'</span>,
265 Person->new( weight => 'fat' );</code></pre>
272 <li>Attributes can define delegations</li>
273 <li>Lets you hide some implementation details</li>
274 <li>Fewer objects to chase around</li>
281 <pre><code>package Person;
287 <span class="highlight">handles => { 'blog_hostname' => 'host' },</span>
290 <span class="highlight">$person->blog_hostname;</span>
291 # really calls $person->blog_uri->host</code></pre>
295 <h1>Constructors</h1>
298 <li>Moose creates <code>new()</code> for you</li>
299 <li>Provide an optional <code>BUILDARGS()</code> and <code>BUILD()</code></li>
307 <li>Provide an optional <code>DEMOLISH()</code></li>
312 <h1>Moose Meta-API</h1>
315 <li>Answers questions like ...
317 <li>What methods does this class have?</li>
318 <li>What are its parents?</li>
319 <li>What attributes does it have (including inherited attributes)?</li>
320 <li>What roles does it do?</li>
321 <li>Much, much, more</li>
328 <h1>Moose Meta-API</h1>
331 <li>Not just for introspection ...
333 <li>Add methods, attributes, roles, etc</li>
334 <li>Extend and alter core features</li>
344 <li>A quick bit of propaganda ...</li>
351 <pre><code>package Person;
354 has last_name => (
361 <h1>Without Moose</h1>
363 <pre class="small"><code>package Person;
373 if (exists $args{last_name}) {
374 confess "Attribute (last_name) does not pass the type constraint because: "
375 . "Validation failed for 'Str' with value $args{last_name}"
376 if ref($args{last_name});
377 $self->{last_nane} = $args{last_name};
380 return bless $self, $class;
388 confess "Attribute (last_name) does not pass the type constraint because: "
389 . "Validation failed for 'Str' with value $value"
391 $self->{last_name} = $value;
394 return $self->{last_name};
400 <h1>Side by side</h1>
402 <table class="side-by-side">
405 <pre><code>package Person;
408 has last_name => (
414 <pre class="small"><code>package Person;
424 if (exists $args{last_name}) {
425 confess "Attribute (last_name) does not pass the type constraint because: "
426 . "Validation failed for 'Str' with value $args{last_name}"
427 if ref($args{last_name});
428 $self->{last_nane} = $args{last_name};
431 return bless $self, $class;
439 confess "Attribute (last_name) does not pass the type constraint because: "
440 . "Validation failed for 'Str' with value $value"
442 $self->{last_name} = $value;
445 return $self->{last_name};
454 <h1>Side by side</h1>
456 <table class="side-by-side">
459 <pre><code><span class="match-moose">package Person;</span>
462 has last_name => (
468 <pre class="small"><code><span class="match-unsweet">package Person;</span>
478 if (exists $args{last_name}) {
479 confess "Attribute (last_name) does not pass the type constraint because: "
480 . "Validation failed for 'Str' with value $args{last_name}"
481 if ref($args{last_name});
482 $self->{last_nane} = $args{last_name};
485 return bless $self, $class;
493 confess "Attribute (last_name) does not pass the type constraint because: "
494 . "Validation failed for 'Str' with value $value"
496 $self->{last_name} = $value;
499 return $self->{last_name};
507 <h1>Side by side</h1>
509 <table class="side-by-side">
512 <pre><code>package Person;
513 <span class="match-moose">use Moose;</span>
515 has last_name => (
521 <pre class="small"><code>package Person;
522 <span class="match-unsweet">use strict;
529 my $self = {};</span>
531 if (exists $args{last_name}) {
532 confess "Attribute (last_name) does not pass the type constraint because: "
533 . "Validation failed for 'Str' with value $args{last_name}"
534 if ref($args{last_name});
535 $self->{last_nane} = $args{last_name};
538 <span class="match-unsweet">return bless $self, $class;
546 confess "Attribute (last_name) does not pass the type constraint because: "
547 . "Validation failed for 'Str' with value $value"
549 $self->{last_name} = $value;
552 return $self->{last_name};
560 <h1>Side by side</h1>
562 <table class="side-by-side">
565 <pre><code>package Person;
568 <span class="match-moose">has last_name => (</span>
571 <span class="match-moose">);</span></code></pre>
574 <pre class="small"><code>package Person;
584 <span class="match-unsweet">if (exists $args{last_name}) {</span>
585 confess "Attribute (last_name) does not pass the type constraint because: "
586 . "Validation failed for 'Str' with value $args{last_name}"
587 if ref($args{last_name});
588 <span class="match-unsweet">$self->{last_nane} = $args{last_name};
591 return bless $self, $class;
599 confess "Attribute (last_name) does not pass the type constraint because: "
600 . "Validation failed for 'Str' with value $value"
602 $self->{last_name} = $value;
605 return $self->{last_name};
613 <h1>Side by side</h1>
615 <table class="side-by-side">
618 <pre><code>package Person;
621 has last_name => (
622 <span class="match-moose">is => 'rw',</span>
627 <pre class="small"><code>package Person;
637 if (exists $args{last_name}) {
638 confess "Attribute (last_name) does not pass the type constraint because: "
639 . "Validation failed for 'Str' with value $args{last_name}"
640 if ref($args{last_name});
641 $self->{last_nane} = $args{last_name};
644 return bless $self, $class;
647 <span class="match-unsweet">sub last_name {
651 my $value = shift;</span>
652 confess "Attribute (last_name) does not pass the type constraint because: "
653 . "Validation failed for 'Str' with value $value"
655 <span class="match-unsweet">$self->{last_name} = $value;
658 return $self->{last_name};
659 }</span></code></pre>
666 <h1>Side by side</h1>
668 <table class="side-by-side">
671 <pre><code>package Person;
674 has last_name => (
676 <span class="match-moose">isa => 'Str',</span>
680 <pre class="small"><code>package Person;
690 if (exists $args{last_name}) {
691 <span class="match-unsweet">confess "Attribute (last_name) does not pass the type constraint because: "
692 . "Validation failed for 'Str' with value $args{last_name}"
693 if ref($args{last_name});</span>
694 $self->{last_nane} = $args{last_name};
697 return bless $self, $class;
705 <span class="match-unsweet">confess "Attribute (last_name) does not pass the type constraint because: "
706 . "Validation failed for 'Str' with value $value"
707 if ref($value);</span>
708 $self->{last_name} = $value;
711 return $self->{last_name};
719 <h1>Side by side</h1>
721 <table class="side-by-side">
722 <tr class="incremental">
726 <tr class="incremental">
727 <td>92 characters</td>
728 <td>741 characters</td>
732 <pre><code>package Person;
735 has last_name => (
741 <pre class="small"><code>package Person;
751 if (exists $args{last_name}) {
752 confess "Attribute (last_name) does not pass the type constraint because: "
753 . "Validation failed for 'Str' with value $args{last_name}"
754 if ref($args{last_name});
755 $self->{last_nane} = $args{last_name};
758 return bless $self, $class;
766 confess "Attribute (last_name) does not pass the type constraint because: "
767 . "Validation failed for 'Str' with value $value"
769 $self->{last_name} = $value;
772 return $self->{last_name};
782 <pre class="small"><code>sub new {
787 if (exists $args{last_name}) {
788 confess "Attribute (last_name) does not pass the type constraint because: "
789 . "Validation failed for 'Str' with value $args{last_name}"
790 if ref($args{last_name});
791 $self->{last_nane} = $args{last_name};
794 return bless $self, $class;
801 <pre class="small"><code>if (exists $args{last_name}) {
802 confess "Attribute (last_name) does not pass the type constraint because: "
803 . "Validation failed for 'Str' with value $args{last_name}"
804 if ref($args{last_name});
805 $self->{last_nane} = $args{last_name};
812 <code>$self->{last_nane} = $args{last_name};</code>
817 <code>$self->{last_na<span class="wrong">n</span>e}</code>
823 <pre><code>package Person;
826 has last_name => (
832 <div class="slide fake-slide0">
833 <h1>Part 1: Moose Classes</h1>
837 <h1>Moose Classes</h1>
840 <li>Moose classes are Perl packages which <code>use Moose</code></li>
845 <h1>Moose.pm and Your Class</h1>
847 <pre><code>package Person;
848 use Moose;</code></pre>
851 <li><code>Moose.pm</code> provides declarative sugar</li>
852 <li>Turns on <code>strict</code> and <code>warnings</code></li>
853 <li>Creates metaclasses for your class: <code>Person->meta</code></li>
854 <li>Moose classes automatically inherit from <code>Moose::Object</code></li>
859 <h1>What <code>Moose::Object</code> Provides</h1>
862 <li>Constructor - <code>new()</code></li>
863 <li>Calls your <code>BUILDARGS()</code> and/or <code>BUILD()</code></li>
864 <li>Calls your <code>DEMOLISH</code> during object destruction</li>
872 <li>Takes <code>@_</code>, returns a hash reference of attribute names/value</li>
873 <li>Accepts a hash or hashref; throws otherwise</li>
874 <li>Provide your own for other cases</li>
875 <li><strong>Always</strong> call <code>$class->SUPER::BUILDARGS(@_)</code> as a fallback!</li>
880 <h1>BUILDARGS Example</h1>
882 <pre><code>package Person;
888 if ( @_ == 1 && ! ref $_[0] ) {
889 <span class="highlight">return { ssn => $_[0] };</span>
892 <span class="highlight">return $class->SUPER::BUILDARGS(@_)</span>;
895 <span class="highlight">Person->new('123-45-6789')</span></code></pre>
902 <li>Called after object is created, before <code>new</code> returns</li>
903 <li>Chance to do more complex validation, set complex attributes</li>
904 <li>Called in reverse inheritance order, parents to children</li>
905 <li>Return value is ignored</li>
910 <h1>BUILD Example</h1>
912 <pre><code>package Person;
918 if ( $self->country_of_residence
920 die 'All US residents'
921 . ' must have an SSN'
922 unless $self->has_ssn;
931 <li>Like <code>DESTROY</code>, but Moose makes sure all <code>DEMOLISH</code> methods in a hierarchy are called</li>
932 <li>Called in normal inheritance order, children to parents</li>
940 <li><code>extends</code> is sugar for declaring parent classes</li>
943 <pre><code>package Employee;
945 <span class="highlight">extends 'Person';</span></code></pre>
952 <li>Each call to <code>extends</code> <strong>resets</strong> your parents</li>
955 <h2 class="wrong">Wrong</h2>
957 <pre><code>package EvilEmployee;
960 extends 'Thief';</code></pre>
962 <h2 class="right">Right</h2>
964 <pre><code>package EvilEmployee;
966 extends 'Person', 'Thief';</code></pre>
970 <h1>Extending un-Moose-y Parents</h1>
972 <pre><code>package My::LWP;
974 extends 'LWP';</code></pre>
977 <li>No <code>Moose::Object</code>, so ...
979 <li>No attribute-handling <code>new()</code></li>
980 <li>No <code>BUILDARGS()</code> or <code>BUILD()</code></li>
981 <li>No <code>DEMOLISH()</code></li>
984 <li>But see <code>MooseX::NonMoose</code> for a workaround</li>
989 <h1><code>override</code> and <code>super</code></h1>
992 <li><code>override</code> is another method modifier</li>
993 <li>An alternative to Perl's <code>SUPER::</code></li>
998 <h1><code>override</code> and <code>super</code></h1>
1000 <pre><code>package Employee;
1003 <span class="current incremental">extends 'Person';</span>
1005 <span class="incremental">override</span> work => sub {
1008 die "Pay me first" unless $self->got_paid;
1009 <span class="incremental">super();</span>
1010 }<span class="incremental">;</span></code></pre>
1014 <h1>Caveat <code>super</code></h1>
1017 <li>Mostly like <code>$self->SUPER::work(@_)</code></li>
1018 <li><strong>But</strong> cannot change <code>@_</code>!</li>
1019 <li>Binds the parent's method at compile time</li>
1024 <h1>Minimal Attributes</h1>
1027 <li><code>has 'foo'</code></li>
1028 <li>Use <code>is => 'ro'</code> or <code>is => 'rw'</code></li>
1029 <li>Attributes without "is" have no accessors</li>
1034 <h1>Read-write attributes</h1>
1036 <pre><code>package Person;
1039 has first_name => ( <span class="highlight">is => 'rw'</span> );
1042 Person->new( first_name => 'Dave' );
1044 $person->first_name('Stevan');
1045 print $person->first_name; # Stevan</code></pre>
1050 <h1>Read-only attributes</h1>
1052 <pre><code>package Person;
1055 has first_name => ( <span class="highlight">is => 'ro'</span> );
1058 Person->new( first_name => 'Dave' );
1060 $person->first_name('Stevan');
1061 print $person->first_name; # Dave</code></pre>
1066 <h1>There is More to Come</h1>
1069 <li>Attributes have a <em>lot</em> of features</li>
1074 <h1>Cleaning Up Moose Droppings</h1>
1076 <pre><code>package Person;
1080 Person->can('extends');</code></pre>
1083 <li>Not very hygienic</li>
1088 <h1>Cleaning Up Moose Droppings</h1>
1090 <pre><code>package Person;
1098 Person->can('extends');</code></pre>
1105 <li><code>no Moose</code> at the end of a package is a best practice</li>
1111 <h1>Immutability</h1>
1114 <li><span style="font-family: URW Chancery L; font-size: 140%">Stevan's Incantation of Fleet-Footedness</span></li>
1117 <pre><code>package Person;
1120 <span class="highlight">__PACKAGE__->meta->make_immutable;</span></code></pre>
1124 <h1>What <code>make_immutable</code> does</h1>
1128 <li>Uses <code>eval</code> to "inline" a constructor</li>
1129 <li>Memoizes a lot of meta-information</li>
1130 <li>Makes loading your class slower</li>
1131 <li>Makes object creation <em>much</em> faster</li>
1136 <h1>When to Immutabilize?</h1>
1139 <li><em>Almost</em> always</li>
1140 <li>Startup time vs execution time</li>
1145 <h1>Classes Summary</h1>
1148 <li><code>use Moose</code></li>
1149 <li><code>Class->meta</code></li>
1150 <li><code>Moose::Object</code> base class</li>
1151 <li><code>extends</code>, <code>override</code>, and <code>super</code></li>
1152 <li>Simple attributes: <code>has</code>, <code>is => 'ro'</code>, & <code>is => 'rw'</code></li>
1153 <li><code>no Moose</code></li>
1154 <li><code>__PACKAGE__->meta->make_immutable</code></li>
1166 $ perl bin/prove -lv t/00-prereq.t
1168 Missing anything? Install it. (see tarballs/)
1170 # perl bin/prove -lv t/01-classes.t
1172 Iterate til this passes all its tests</pre>
1175 <div class="slide fake-slide0">
1176 <h1>Part 2: Roles</h1>
1180 <h1>Just What Is a Role?</h1>
1183 <li>Mixin? Interface? Trait?</li>
1184 <li>Yes ... and more!</li>
1189 <h1>Roles Can Have State <strong>and</strong> Behavior</h1>
1191 <pre><code>package HasPermissions;
1194 <span class="current incremental"># state
1195 has access_level => ( is => 'rw' );</span>
1197 <span class="incremental"># behavior
1200 my $required = shift;
1202 return $self->access_level >= $required;
1203 }</span></code></pre>
1208 <h1>Roles Can Define Interfaces</h1>
1210 <pre><code>package Printable;
1213 requires 'as_string';</code></pre>
1217 <h1>Roles Can Do All Three</h1>
1219 <pre><code>package Printable;
1222 requires 'as_string';
1224 has has_been_printed => ( is => 'rw' );
1228 print $self->as_string;
1229 $self->has_been_printed(1);
1234 <h1>Classes Consume Roles</h1>
1236 <pre><code>package Person;
1239 with 'HasPermissions';</code></pre>
1243 <h1>Classes Consume Roles</h1>
1245 <pre><code>my $person = Person->new(
1246 first_name => 'Kenichi',
1247 last_name => 'Asai',
1248 access_level => 42,
1251 print $person->full_name
1253 . $person->can_access(42)
1255 : 'little power';</code></pre>
1259 <h1>Roles in Practice</h1>
1262 <li>Consuming a role =~ inlining the role</li>
1267 <h1>In Other Words ...</h1>
1269 <pre><code>package Person;
1272 <span class="highlight">with 'Printable';</span></code></pre>
1276 <h1>In Other Words ...</h1>
1278 <pre><code>package Person;
1281 <span class="delete">with 'Printable';</span>
1283 <span class="highlight">has has_been_printed => ( is => 'rw' );
1287 print $self->as_string;
1288 $self->has_been_printed(1);
1289 }</span></code></pre>
1296 <li>Role consumption is introspectable</li>
1299 <pre><code>if ( Person->does('Printable') ) { ... }
1303 if ( Person->meta->does('Printable') ) { ... }</code></pre>
1308 <h1>These Names Are the Same</h1>
1311 <li>What if a role and class define the same method?</li>
1312 <li>A class's <em>local</em> methods win over the role's</li>
1313 <li>The role's methods win over the class's <em>inherited</em> methods</li>
1318 <h1>Conflicts Between Roles</h1>
1321 <li>Two roles with a method of the same name</li>
1322 <li>Generates a compile-time error when consumed by a class</li>
1327 <h1>Conflict Example</h1>
1329 <pre><code>package IsFragile;
1334 package CanBreakdance;
1337 sub break { ... }</code></pre>
1341 <h1>Conflict Example</h1>
1343 <pre><code>package FragileDancer;
1346 <span class="highlight">with 'IsFragile', 'CanBreakdance';</span></code></pre>
1349 <li>Only one <code>with</code>!</li>
1354 <h1>Conflict Resolution</h1>
1357 <li>The consuming class must resolve the conflict by implementing the method</li>
1358 <li>Can use some combination of method exclusion and aliasing</li>
1363 <h1>Method Aliasing</h1>
1365 <pre><code>package FragileDancer;
1368 <span class="highlight">with 'IsFragile' =>
1370 { break => 'break_bone' } },
1373 { break => 'break_it_down' } };</span></code></pre>
1376 <li>Renames the roles' methods</li>
1377 <li>Still conflicts, need to <code>exclude</code> as well</li>
1382 <h1>Method Exclusion</h1>
1384 <pre><code>package FragileDancer;
1387 <span class="highlight">with 'IsFragile' =>
1389 { break => 'break_bone' },
1390 exclude => 'break' },
1393 { break => 'break_dance' },
1394 exclude => 'break' };</span></code></pre>
1398 <h1>And then ...</h1>
1400 <pre><code>package FragileDancer;
1407 if ( rand(1) < 0.5 ) {
1414 <h1>Still Full of Fail</h1>
1417 <li>Roles are also about semantics!</li>
1418 <li>We've fulfilled the letter and lost the spirit</li>
1419 <li>Roles have a <em>meaning</em></li>
1420 <li>Think twice before blindly aliasing and excluding methods!</li>
1425 <h1>Hot Role-on-Role Action</h1>
1427 <pre><code>package Comparable;
1430 requires 'compare';</code></pre>
1434 <h1>Hot Role-on-Role Action</h1>
1436 <pre><code>package TestsEquality;
1443 return $self->compare(@_) == 0;
1448 <h1>And then ...</h1>
1450 <pre><code>package Integer;
1453 with 'TestsEquality';
1455 # Satisfies the Comparable role
1458 Integer->does('TestsEquality'); # true
1459 Integer->does('Comparable'); # also true!</code></pre>
1463 <h1>Name Conflicts Between Roles</h1>
1465 <pre><code>package HasSubProcess;
1468 <span class="highlight">sub execute { ... }</span>
1473 with 'HasSubProcess';
1475 <span class="highlight">sub execute { ... }</span></code></pre>
1479 <h1>Delayed Conflict</h1>
1481 <pre><code>package StateOfTexas;
1482 with 'Killer';</code></pre>
1485 <li><code>StateOfTexas</code> must implement its own <code>execute</code></li>
1486 <li>But loading the <code>Killer</code> role by itself does not cause an error</li>
1491 <h1>Roles as Interfaces</h1>
1494 <li>Roles can <code>require</code> methods of their consumers</li>
1495 <li>Compile-time checks</li>
1496 <li>Method must exist when the role is consumed</li>
1501 <h1>The Attribute Gotcha</h1>
1503 <pre><code>package HasSize;
1506 <span class="current incremental">requires 'size';</span>
1511 <span class="incremental">with 'HasSize';
1513 has size => ( is => 'ro' );</span></code></pre>
1517 <h1>The Attribute Gotcha Workaround</h1>
1519 <pre><code>package HasSize;
1527 has size => ( is => 'ro' );
1529 with 'HasSize';</code></pre>
1533 <h1>Compile-time Is a Lie</h1>
1536 <li>Really, it's <em>package load</em> time</li>
1537 <li>That's run-time, but before the "real" run-time</li>
1538 <li>Moose does not rewire Perl, it's just sugar!</li>
1539 <li>(but <code>MooseX::Declare</code> <em>does</em> rewire Perl)</li>
1544 <h1>Enforcing Roles</h1>
1546 <pre><code>package Comparison;
1549 has [ 'left', 'right' ] => (
1551 <span class="highlight">does => 'Comparable',</span>
1556 <li>A sneak peek at type constraints</li>
1562 <h1>Roles Can Be Applied to Objects</h1>
1564 <pre><code>use Moose::Util qw( apply_all_roles );
1566 my $fragile_person = Person->new( ... );
1567 apply_all_roles( $fragile_person, 'IsFragile' );</code></pre>
1570 <li>Does not change the <code>Person</code> class</li>
1571 <li>Works with non-Moose classes, great for monkey-patching!</li>
1576 <h1>Roles Are Dirty Too</h1>
1579 <li>Once again, clean up those Moose droppings</li>
1582 <pre><code>package Comparable;
1587 <span class="highlight">no Moose::Role;</span></code></pre>
1590 <li>But roles cannot be made immutable</li>
1595 <h1>The Zen of Roles</h1>
1598 <li>Roles represent discrete units of ...
1605 <li>Roles are shareable between unrelated classes</li>
1606 <li>Roles are what a class <em>does</em>, not what it <em>is</em></li>
1607 <li>Roles <em>add</em> functionality, inheritance <em>specializes</em></li>
1612 <h1>Abstract Examples</h1>
1615 <li>Human <em>@ISA</em> Animal</li>
1616 <li>Human <em>does</em> Toolmaker (as <em>does</em> Chimpanzee)</li>
1617 <li>Car <em>@ISA</em> Vehicle</li>
1618 <li>Car <em>does</em> HasEngine</li>
1623 <h1>Real Examples</h1>
1626 <li>Objects representing SQL database components and queries
1628 <li>Schema, Table, Column, ColumnAlias</li>
1629 <li>Select, Insert, Update, Delete</li>
1636 <h1>Real Examples</h1>
1639 <li>Column and ColumnAlias both <em>do</em> ColumnLike</li>
1640 <li>ColumnLike things can be used in certain parts of queries</li>
1641 <li>All queries <em>do</em> HasWhereClause</li>
1642 <li>Select <em>does</em> Comparable and Selectable (for subselects)</li>
1643 <li>A where clause requires its components to <em>do</em> Comparable</li>
1648 <h1>Roles Summary</h1>
1651 <li>Roles can define an interface with <code>requires</code></li>
1652 <li>Roles can have state (attributes) and behavior (methods)</li>
1653 <li>Roles can mix interface, state, & behavior</li>
1654 <li>Roles are composed (flattened) into classes</li>
1655 <li>Roles can do other roles</li>
1656 <li>Roles can be used as a type in APIs (must do Comparable)</li>
1668 # perl bin/prove -lv t/02-roles.t
1670 Iterate til this passes all its tests</pre>
1673 <div class="slide fake-slide0">
1674 <h1>Part 3: Basic Attributes</h1>
1678 <h1>Attributes Are Huge</h1>
1681 <li>Moose's biggest feature</li>
1682 <li>The target of <em>many</em> MooseX modules</li>
1687 <h1>Quick Review</h1>
1690 <li>Declared with <code>has</code></li>
1691 <li>Read-only or read-write</li>
1694 <pre><code>package Shirt;
1697 has 'color' => ( is => 'ro' );
1698 has 'is_ripped' => ( is => 'rw' );</code></pre>
1702 <h1>Required-ness</h1>
1705 <li>Required means "must be passed to the constructor"</li>
1706 <li>But can be <code>undef</code></li>
1711 <h1>Required-ness</h1>
1713 <pre><code>package Person;
1716 has first_name => (
1718 <span class="current incremental">required => 1,</span>
1721 <span class="incremental">Person->new( first_name => undef ); # ok
1722 Person->new(); # kaboom</span></code></pre>
1726 <h1>Default and Builder</h1>
1729 <li>Attributes can have defaults</li>
1730 <li>Simple non-referecne scalars (number, string)</li>
1731 <li>Subroutine reference</li>
1732 <li>A builder method</li>
1740 <li>Can be a non-reference scalar (including <code>undef</code>)</li>
1743 <pre><code>package Person;
1748 default => 'Spire FCU',
1756 <li>Can be a subroutine reference</li>
1759 <pre><code>package Person;
1766 name => 'Spire FCU' ) },
1771 <h1>Default as a Subroutine Reference</h1>
1774 <li>Called as a method on the object</li>
1775 <li>Called anew for each object</li>
1780 <h1>Why No Other Reference Types?</h1>
1782 <pre><code>package Person;
1787 <span class="wrong">default => Bank->new(
1788 name => 'Spire FCU' ),</span>
1792 <li>Now <strong>every</strong> person shares the <strong>same</strong> Bank object!</li>
1797 <h1>Defaulting to an Empty Reference</h1>
1799 <pre><code>package Person;
1802 has packages => (
1804 default => <span class="highlight">sub { [] }</span>,
1809 <h1>What if I Want to Share?</h1>
1811 <pre><code>package Person;
1814 my $highlander_bank =
1815 Bank->new( name => 'Spire FCU' );
1819 default => sub { $highlander_bank },
1827 <li>A method <em>name</em> which returns the default</li>
1834 <pre><code>package Person;
1839 builder => '_build_bank',
1844 return Bank->new( name => 'Spire FCU' );
1849 <h1>Default vs Builder</h1>
1852 <li>Use default for simple scalars</li>
1853 <li>Use default to return empty references</li>
1854 <li>Use default for <em>very</em> trivial subroutine references</li>
1855 <li>Use builder for everything else</li>
1860 <h1>Builder Bonuses</h1>
1863 <li>Can be overridden and method modified, because it's called by <em>name</em></li>
1864 <li>Roles can require a builder</li>
1869 <h1>Role Requires Builder</h1>
1871 <pre><code>package HasBank;
1874 requires '_build_bank';
1878 builder => '_build_bank',
1883 <h1>Lazy, Good for Nothing Attributes</h1>
1886 <li>Normally, defaults are generated during object construction</li>
1887 <li>This can be expensive</li>
1888 <li>We want to default to <code>$self->size * 2</code>, but attribute initialization order is unpredictable</li>
1889 <li>Use lazy attributes!</li>
1894 <h1>The Power of Dynamic Defaults</h1>
1896 <pre><code>package Person;
1899 has shoe_size => (
1905 <h1>The Power of Dynamic Defaults</h1>
1907 <pre><code>has shoes => (
1909 <span class="highlight">lazy => 1,</span>
1910 builder => '_build_shoes',
1916 return Shoes->new(
1917 size => <span class="highlight">$self->shoe_size</span> );
1922 <h1>Lazy is Good</h1>
1925 <li>Lazy defaults are executed when the attribute is read</li>
1926 <li>Can see other object attributes</li>
1927 <li>Still need to watch out for circular laziness</li>
1932 <h1>Clearer and Predicate</h1>
1935 <li>Attributes can have a value, including <code>undef</code>, or not</li>
1936 <li>Can clear the value with a clearer method</li>
1937 <li>Can check for the existence of a value with a predicate method</li>
1938 <li>By default, these methods are not created</li>
1943 <h1>Clearer and Predicate</h1>
1945 <pre><code>package Person;
1951 builder => '_build_account',
1952 <span class="highlight">clearer => '_clear_account',
1953 predicate => 'has_account',</span>
1958 <h1>Clearer and Lazy Defaults</h1>
1961 <li>Lazy defaults are good for computed attributes</li>
1962 <li>Clear the attribute when the source data changes</li>
1963 <li>Recalculated at next access</li>
1968 <h1>Renaming constructor arguments</h1>
1971 <li>By default, constructor names = attribute names</li>
1972 <li>Use <code>init_arg</code> to change this</li>
1973 <li>Set <code>init_arg => undef</code> to make it unconstructable</li>
1978 <h1>Some <code>init_arg</code> examples</h1>
1980 <pre><code>package Person;
1985 <span class="highlight">init_arg => 'foot_size',</span>
1988 Person->new( <span class="wrong">shoe_size => 13</span> );
1991 Person->new( <span class="right">foot_size => 13</span> );
1992 print $person->shoe_size;</code></pre>
1996 <h1>Some <code>init_arg</code> examples</h1>
1998 <pre><code>package Person;
2003 <span class="highlight">init_arg => undef,</span>
2006 Person->new( <span class="wrong">shoes => Shoes->new</span> );</code></pre>
2010 <h1>Why Set <code>init_arg => undef</code>?</h1>
2013 <li>Use this with a lazy default for attributes-as-cache</li>
2014 <li>Compute the value as needed</li>
2015 <li>Ensure that it is always generated correctly (not set by constructor)</li>
2016 <li>Use triggers or method modifiers (coming soon) to clear the value</li>
2021 <h1>Attribute Inheritance</h1>
2024 <li>By default, subclasses inherit attribute as-is</li>
2025 <li>Can change some attribute parameters in subclasses
2031 <li>others we've not yet covered</li>
2038 <h1>Attribute Inheritance Example</h1>
2040 <pre><code>package Employee;
2045 has '<span class="highlight">+first_name</span>' => (
2046 default => 'Joe',
2051 <h1>Attribute Inheritance Warning</h1>
2054 <li>An attribute is a contract about a class's API</li>
2055 <li>Don't break that contract in a subclass</li>
2056 <li>Especially important in the context of types</li>
2061 <h1>Changing Accessor Names</h1>
2063 <pre><code>package Person;
2066 has first_name => (
2067 <span class="highlight">accessor</span> => 'first_name',
2071 <li>The long-hand version of <code>is => 'rw'</code></li>
2076 <h1>Changing Accessor Names</h1>
2078 <pre><code>package Person;
2081 has first_name => (
2082 <span class="highlight">reader</span> => 'first_name',
2083 <span class="highlight">writer</span> => undef,
2087 <li>The long-hand version of <code>is => 'ro'</code></li>
2093 <h1>Changing Accessor Names</h1>
2095 <pre><code>package Person;
2098 has first_name => (
2099 <span class="highlight">reader</span> => 'get_first_name',
2100 <span class="highlight">writer</span> => 'set_first_name',
2105 <h1>Changing Accessor Names</h1>
2107 <pre><code>package Person;
2110 has first_name => (
2111 <span class="highlight">is</span> => 'rw',
2112 <span class="highlight">writer</span> => '_first_name',
2116 <li>Can also mix-and-match</li>
2121 <h1>ETOOMUCHTYPING</h1>
2124 <li><code>MooseX::FollowPBP</code><br /><code>get_foo</code> and <code>set_foo</code></li>
2125 <li><code>MooseX::SemiAffordanceAccessor</code><br /><code>foo</code> and <code>set_foo</code></li>
2130 <h1>ETOOMUCHTYPING</h1>
2132 <pre><code>package Person;
2134 <span class="highlight">use MooseX::SemiAffordanceAccessor;</span>
2136 has first_name => (
2141 <li>Creates <code>first_name</code> and <code>set_first_name</code></li>
2146 <h1>Basic Attributes Summary</h1>
2149 <li>Attributes can be <code>required</code></li>
2150 <li>Attributes can have a <code>default</code> or <code>builder</code></li>
2151 <li>Attributes with a default or builder can be <code>lazy</code></li>
2152 <li>Attributes can have a <code>clearer</code> and/or <code>predicate</code></li>
2153 <li>An attribute's constructor name can be changed with <code>init_arg</code></li>
2154 <li>A subclass can alter its parents' attributes</li>
2155 <li>Attribute accessor names can be changed</li>
2167 # perl bin/prove -lv t/03-basic-attributes.t
2169 Iterate til this passes all its tests</pre>
2172 <div class="slide fake-slide0">
2173 <h1>Part 4: Method Modifiers</h1>
2177 <h1>What is a Method Modifier</h1>
2180 <li>Apply to an existing method</li>
2181 <li>... from a parent class, the current class, or a role</li>
2182 <li>Roles can provide modifiers that are applied at composition time</li>
2187 <h1>What is a Method Modifier</h1>
2190 <li>"Inject" behavior</li>
2191 <li>Add behavior to generated methods (accessors, delegations)</li>
2192 <li>Provide roles which modify existing behavior</li>
2197 <h1>Before and After</h1>
2200 <li>Simplest modifiers - <code>before</code> and <code>after</code></li>
2201 <li>Guess when they run!</li>
2206 <h1>Uses for <code>before</code></h1>
2209 <li>As a pre-call check</li>
2212 <pre><code>package Person;
2215 before work => sub {
2217 die 'I have no job!'
2218 unless $self->has_title;
2223 <h1>Uses for <code>before</code></h1>
2226 <li>Logging/Debugging</li>
2229 <pre><code>package Person;
2232 before work => sub {
2234 return unless $DEBUG;
2236 warn "Called work on ", $self->full_name,
2237 "with the arguments: [@_]\n";
2242 <h1>Uses for <code>after</code></h1>
2245 <li>Also works for logging/debugging</li>
2246 <li>Post-X side-effects (recording audit info)</li>
2249 <pre><code>package Person;
2252 after work => sub {
2254 $self->work_count(
2255 $self->work_count + 1 );
2263 <li>Modifiers are useful for adding behavior to generated methods</li>
2268 <h1>Other Uses Example</h1>
2270 <pre><code>has password => (
2272 clearer => 'clear_password',
2275 has hashed_password => (
2277 builder => '_build_hashed_password',
2278 clearer => '_clear_hashed_password',
2281 after clear_password => sub {
2283 $self->_clear_hashed_password;
2288 <h1><code>before</code> and <code>after</code> Limitations</h1>
2291 <li>Cannot alter method parameters</li>
2292 <li>Cannot alter return value</li>
2293 <li>But <strong>can</strong> throw an exception</li>
2298 <h1>The <code>around</code> Modifier</h1>
2301 <li>The big gun</li>
2302 <li>Can alter parameters <strong>and/or</strong> return values</li>
2303 <li>Can skip calling the wrapped method entirely</li>
2308 <h1>The power of <code>around</code></h1>
2310 <pre><code>around insert => sub {
2314 $self->_validate_insert(@_);
2318 $self->_munge_insert(@_) );
2320 $new_user->_assign_uri;
2327 <h1>Modifier Order</h1>
2330 <li>Before runs order from last to first</li>
2331 <li>After runs in order from first to last</li>
2332 <li>Around runs in order from last to first</li>
2337 <h1>Modifier Order Illustrated</h1>
2340 <span class="current incremental">before 2
2342 <span class="incremental">around 2
2344 <span class="incremental">wrapped method</span>
2345 <span class="incremental">around 1
2347 <span class="incremental">after 1
2353 <h1>Modifiers in Roles</h1>
2356 <li>Roles can use these modifiers</li>
2357 <li>Very powerful!</li>
2362 <h1>Modifiers in Roles</h1>
2364 <pre><code>package IsUnreliable;
2367 <span class="highlight">requires 'run';
2369 around run</span> => sub {
2373 return if rand(1) < 0.5;
2375 return $self->$orig(@_);
2380 <h1>Augment and Inner</h1>
2383 <li>Inverted <code>super</code></li>
2384 <li>From least- to most-specific</li>
2385 <li>Grandparent to parent to child</li>
2386 <li>Not allowed in roles</li>
2391 <h1>Augment and Inner</h1>
2393 <pre><code>package Document;
2395 sub xml { '<doc>' . <span class="highlight">inner()</span> . '</doc>' }
2400 <span class="highlight">augment xml</span> => { title() . <span class="highlight">inner()</span> . summary() };
2405 <span class="highlight">augment xml</span> => { tps_xml() . <span class="highlight">inner()</span> };</code></pre>
2409 <h1>Augment and Inner</h1>
2412 <li>When we call <code>$tps->xml</code> ...
2414 <li><code>Document->xml</code></li>
2415 <li><code>Report->xml</code></li>
2416 <li><code>TPSReport->xml</code></li>
2423 <h1>Augment and Inner Usage</h1>
2426 <li>Call <code>inner()</code> to "fill in the blank"</li>
2427 <li>Requires designing for subclassing</li>
2428 <li>Call <code>inner()</code> in the terminal class, just in case</li>
2433 <h1>Method Modifiers Summary</h1>
2436 <li>Use <code>before</code> and <code>after</code> for ...
2439 <li>pre- or post-validation</li>
2440 <li>to add behavior to generated methods</li>
2443 <li>These two modifiers cannot change parameters or return values</li>
2448 <h1>Method Modifiers Summary</h1>
2451 <li>Use <code>around</code> to ...
2453 <li>alter parameters passed to the original method</li>
2454 <li>alter the return value of the original method</li>
2455 <li>not call the original method at all (or call a <em>different</em> method)</li>
2462 <h1>Method Modifiers Summary</h1>
2465 <li>When using modifiers in a role, require the modified method</li>
2466 <li>Use <code>augment</code> and <code>inner</code> to invert the normal subclassing flow ...
2468 <li>Least- to most-specific (parents to children)</li>
2469 <li>Build in "insertability" (stick more stuff in the "middle")</li>
2472 <li>Always call <code>inner</code> in the most specific subclass to allow for future extension</li>
2484 # perl bin/prove -lv t/04-method-modifiers.t
2486 Iterate til this passes all its tests</pre>
2489 <div class="slide fake-slide0">
2490 <h1>Part 5: Types</h1>
2493 <div class="slide fake-slide0">
2494 <h1>Part 6: Advanced Attributes</h1>
2498 <h1>Weak References</h1>
2501 <li>A weak reference lets you avoid circular references</li>
2502 <li>Weak references do not increase the reference count</li>
2507 <h1>Circular Reference Illustrated</h1>
2509 <pre><code>my $foo = {};
2510 my $bar = { foo => $foo };
2511 $foo->{bar} = $bar;</code></pre>
2514 <li>Neither <code>$foo</code> nor <code>$bar</code> go out of scope<br />
2515 (until the program exits)</li>
2520 <h1>Weakening Circular References</h1>
2522 <pre><code>use Scalar::Util qw( weaken );
2525 my $bar = { foo => $foo };
2526 $foo->{bar} = $bar;
2527 weaken $foo->{bar}</code></pre>
2530 <li>When <code>$bar</code> goes out of scope, <code>$foo->{bar}</code> becomes <code>undef</code></li>
2535 <h1>Circular References in Attributes</h1>
2537 <pre><code>package Person;
2540 has name => ( is => 'ro' );
2541 has friend => ( is => 'rw' );
2543 my $alice = Person->new( name => 'Alice' );
2544 my $bob = Person->new( name => 'Bob' );
2545 $bob->friend($alice);
2546 $alice->friend($bob);</code></pre>
2552 <pre><code>package Person;
2555 has name => ( is => 'ro' );
2556 has friend => ( is => 'rw', <span class="highlight">weak_ref => 1</span> );
2558 my $alice = Person->new( name => 'Alice' );
2559 my $bob = Person->new( name => 'Bob' );
2560 $bob->friend($alice);
2561 $alice->friend($bob);</code></pre>
2565 <h1>Under the Hood</h1>
2568 <li>A <code>weak_ref</code> attribute calls <code>weaken</code> ...
2570 <li>during object construction</li>
2571 <li>when the attribute is set via a writer</li>
2581 <li>A code reference run after an attribute is <em>set</em></li>
2582 <li>Like an <code>after</code> modifier, but makes intentions clearer</li>
2585 <h2 class="wrong">Gross</h2>
2587 <pre><code>after salary_level => {
2590 $self->clear_salary;
2595 <h1>Use a Trigger Instead</h1>
2597 <h2 class="right">Cleaner</h2>
2599 <pre><code>has salary_level => (
2601 trigger => sub { $_[0]->clear_salary },
2609 <li>Attributes can be objects</li>
2610 <li>Delegation transparently calls methods on those objects</li>
2615 <h1>Delegation Examples</h1>
2617 <pre><code>package Person;
2622 <span class="highlight">handles => [ 'inhale', 'exhale' ],</span>
2626 <li>Creates <code>$person->inhale</code> and <code>->exhale</code> methods</li>
2627 <li>Internally calls <code>$person->lungs->inhale</code></li>
2632 <h1>Why Delegation?</h1>
2635 <li>Reduce the number of classes exposed</li>
2636 <li>Re-arrange class internals -<br />
2637 turn a method into an attribute with delegation</li>
2638 <li>Provide convenenience methods</li>
2643 <h1>Moose's <code>handles</code> Parameter</h1>
2646 <li>Accepts many arguments ...
2648 <li>Array reference - list of methods to delegate as-is</li>
2649 <li>Hash reference - map of method names</li>
2650 <li>Regex - delegates all matching methods</li>
2651 <li>Role name - delegates all methods in the role</li>
2652 <li>Sub reference - does something complicated ;)</li>
2659 <h1>Array Reference</h1>
2662 <li>Takes each method name and creates a simple delegation from the delegating class to the delegatee attribute</li>
2667 <h1>Hash Reference</h1>
2670 <li>Mapping of names in the delegating class to the delegatee class</li>
2673 <pre><code>package Person;
2678 isa => 'BankAccount',
2679 <span class="highlight">handles => {
2680 receive_money => 'deposit',
2681 give_money => 'withdraw',
2687 <h1>Hash Reference Detailed</h1>
2689 <pre><code> handles => {
2690 receive_money => 'deposit',
2691 give_money => 'withdraw',
2695 <li><code>$person->receive_money</code> = <code>$person->account->deposit</code></li>
2696 <li><code>$person->give_money</code> = <code>$person->account->withdraw</code></li>
2703 <pre><code>package Person;
2709 handles => qr/.*/,
2713 <li>Creates a delegation for every method in the Name class</li>
2714 <li>Excludes <code>meta</code> and methods inherited from <code>Moose::Object</code></li>
2721 <pre><code>package Auditor;
2724 sub record_change { ... }
2725 sub change_history { ... }
2732 does => 'Auditor',
2733 <span class="highlight">handles => 'Auditor',</span>
2738 <h1>Role Name Detailed</h1>
2741 <li>Account gets delegate methods for each method in the <code>Auditor</code> role
2743 <li>record_history</li>
2744 <li>change_history</li>
2751 <h1>Traits and Metaclasses</h1>
2754 <li>The ultimate in customization</li>
2755 <li>Per attribute metaclasses</li>
2756 <li>Per attribute roles applied to the attribute metaclass</li>
2757 <li>Change the meta-level behavior</li>
2762 <h1>Traits and Metaclasses</h1>
2765 <li>The default metaclass is <code>Moose::Meta::Attribute</code></li>
2766 <li>Controls accessor generation, defaults, delegation, etc.</li>
2767 <li>Adding a role to this metaclass (or replacing it) allows for infinite customization</li>
2772 <h1>Traits and Metaclasses</h1>
2775 <li>Can add/alter/remove attribute parameter (from <code>has</code>)</li>
2776 <li>Can change behavior of created attribute</li>
2781 <h1>Simple Trait Example</h1>
2783 <pre><code>package Person;
2785 use MooseX::LabeledAttributes;
2788 <span class="highlight">traits => [ 'Labeled' ],</span>
2791 <span class="highlight">label => 'Social Security Number',</span>
2794 print <span class="highlight">Person->meta
2795 ->get_attribute('ssn')->label;</span></code></pre>
2799 <h1>Simple Metaclass Example</h1>
2801 <pre><code>package Person;
2803 use MooseX::LabeledAttributes;
2806 <span class="highlight">metaclass =>
2807 'MooseX::Meta::Attribute::Labeled',</span>
2810 <span class="highlight">label => 'Social Security Number',</span>
2813 print <span class="highlight">Person->meta
2814 ->get_attribute('ssn')->label;</span></code></pre>
2818 <h1>Traits vs Metaclass</h1>
2821 <li>Can apply any mix of traits to an attribute</li>
2822 <li>But just one metaclass</li>
2823 <li>Traits (aka roles) can cooperate</li>
2824 <li>Metaclasses require you to pick just one</li>
2829 <h1>Advanced Attributes Summary</h1>
2832 <li>Use <code>weak_ref</code> to avoid circular references</li>
2833 <li>Use trigger to do an action post-attribute write</li>
2834 <li>Use delegations to hide "internal" objects</li>
2835 <li>Traits and metaclasses let you extend Moose's core attribute features</li>
2847 # perl bin/prove -lv t/06-advanced-attributes.t
2849 Iterate til this passes all its tests</pre>
2852 <div class="slide fake-slide0">
2853 <h1>Part 7: Introspection</h1>
2856 <div class="slide fake-slide0">
2857 <h1>Part 8: A Tour of MooseX</h1>
2860 <div class="slide fake-slide0">
2861 <h1>Part 9: Writing Moose Extensions</h1>
2870 Copyright 2009 David Rolsky. All Rights Reserved.
2872 This work is licensed under a Creative Commons Attribution-Share Alike
2873 3.0 United States License See
2874 http://creativecommons.org/licenses/by-sa/3.0/us/ for details.