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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 propoganda ...</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><code>extends</code> is sugar for declaring parent classes</li>
875 <pre><code>package Employee;
877 <span class="highlight">extends 'Person';</span></code></pre>
884 <li>Each call to <code>extends</code> <strong>resets</strong> your parents</li>
887 <h2 class="wrong">Wrong</h2>
889 <pre><code>package EvilEmployee;
892 extends 'Thief';</code></pre>
894 <h2 class="right">Right</h2>
896 <pre><code>package EvilEmployee;
898 extends 'Person', 'Thief';</code></pre>
902 <h1>Extending un-Moose-y Parents</h1>
904 <pre><code>package My::LWP;
906 extends 'LWP';</code></pre>
909 <li>No <code>Moose::Object</code>, so ...
911 <li>No attribute-handling <code>new()</code></li>
912 <li>No <code>BUILDARGS()</code> or <code>BUILD()</code></li>
913 <li>No <code>DEMOLISH()</code></li>
916 <li>But see <code>MooseX::NonMoose</code> for a workaround</li>
921 <h1><code>overrides</code> and <code>super</code></h1>
924 <li><code>overrides</code> is another method modifier</li>
925 <li>An alternative to Perl's <code>SUPER::</code></li>
930 <h1><code>overrides</code> and <code>super</code></h1>
932 <pre><code>package Employee;
935 <span class="current incremental">extends 'Person';</span>
937 <span class="incremental">overrides</span> work => sub {
940 die "Pay me first" unless $self->got_paid;
941 <span class="incremental">super();</span>
942 }<span class="incremental">;</span></code></pre>
946 <h1>Caveat <code>super</code></h1>
949 <li>Mostly like <code>$self->SUPER::work(@_)</code></li>
950 <li><strong>But</strong> cannot change <code>@_</code>!</li>
951 <li>Binds the parent's method at compile time</li>
956 <h1>Minimal Attributes</h1>
959 <li><code>has 'foo'</code></li>
960 <li>Use <code>is => 'ro'</code> or <code>is => 'rw'</code></li>
961 <li>Attributes without "is" have no accessors</li>
966 <h1>Read-write attributes</h1>
968 <pre><code>package Person;
971 has first_name => ( <span class="highlight">is => 'rw'</span> );
974 Person->new( first_name => 'Dave' );
976 $person->first_name('Stevan');
977 print $person->first_name; # Stevan</code></pre>
982 <h1>Read-only attributes</h1>
984 <pre><code>package Person;
987 has first_name => ( <span class="highlight">is => 'ro'</span> );
990 Person->new( first_name => 'Dave' );
992 $person->first_name('Stevan');
993 print $person->first_name; # Dave</code></pre>
998 <h1>There is More to Come</h1>
1001 <li>Attributes have a <em>lot</em> of features</li>
1006 <h1>Cleaning Up Moose Droppings</h1>
1008 <pre><code>package Person;
1012 Person->can('extends');</code></pre>
1015 <li>Not very hygienic</li>
1020 <h1>Cleaning Up Moose Droppings</h1>
1022 <pre><code>package Person;
1030 Person->can('extends');</code></pre>
1037 <li><code>no Moose</code> at the end of a package is a best practice</li>
1043 <h1>Immutability</h1>
1046 <li><span style="font-family: URW Chancery L; font-size: 140%">Stevan's Incantation of Fleet-Footedness</span></li>
1049 <pre><code>package Person;
1052 <span class="highlight">__PACKAGE__->meta->make_immutable;</span></code></pre>
1056 <h1>What <code>make_immutable</code> does</h1>
1060 <li>Uses <code>eval</code> to "inline" a constructor</li>
1061 <li>Memoizes a lot of meta-information</li>
1062 <li>Makes loading your class slower</li>
1063 <li>Makes object creation <em>much</em> faster</li>
1068 <h1>When to Immutabilize?</h1>
1071 <li><em>Almost</em> always</li>
1072 <li>Startup time vs execution time</li>
1077 <h1>Classes Summary</h1>
1080 <li><code>use Moose</code></li>
1081 <li><code>Class->meta</code></li>
1082 <li><code>Moose::Object</code> base class</li>
1083 <li><code>extends</code>, <code>overrides</code>, and <code>super</code></li>
1084 <li>Simple attributes: <code>has</code>, <code>is => 'ro'</code>, & <code>is => 'rw'</code></li>
1085 <li><code>no Moose</code></li>
1086 <li><code>__PACKAGE__->meta->make_immutable</code></li>
1098 $ perl bin/prove -lv t/00-prereq.t
1100 Missing anything? Install it. (see tarballs/)
1102 # perl bin/prove -lv t/01-classes.t
1104 Iterate til this passes all its tests</pre>
1107 <div class="slide fake-slide0">
1108 <h1>Part 2: Roles</h1>
1112 <h1>Just What Is a Role?</h1>
1115 <li>Mixin? Interface? Trait?</li>
1116 <li>Yes ... and more!</li>
1121 <h1>Roles Can Have State <strong>and</strong> Behavior</h1>
1123 <pre><code>package HasPermissions;
1126 <span class="current incremental"># state
1127 has access_level => ( is => 'rw' );</span>
1129 <span class="incremental"># behavior
1132 my $required = shift;
1134 return $self->access_level >= $required;
1135 }</span></code></pre>
1140 <h1>Roles Can Define Interfaces</h1>
1142 <pre><code>package Printable;
1145 requires 'as_string';</code></pre>
1149 <h1>Roles Can Do All Three</h1>
1151 <pre><code>package Printable;
1154 requires 'as_string';
1156 has has_been_printed => ( is => 'rw' );
1160 print $self->as_string;
1161 $self->has_been_printed(1);
1166 <h1>Classes Consume Roles</h1>
1168 <pre><code>package Person;
1171 with 'HasPermissions';</code></pre>
1175 <h1>Classes Consume Roles</h1>
1177 <pre><code>my $person = Person->new(
1178 first_name => 'Kenichi',
1179 last_name => 'Asai',
1180 access_level => 42,
1183 print $person->full_name
1185 . $person->can_access(42)
1187 : 'little power';</code></pre>
1191 <h1>Roles in Practice</h1>
1194 <li>Consuming a role =~ inlining the role</li>
1199 <h1>In Other Words ...</h1>
1201 <pre><code>package Person;
1204 <span class="highlight">with 'Printable';</span></code></pre>
1208 <h1>In Other Words ...</h1>
1210 <pre><code>package Person;
1213 <span class="delete">with 'Printable';</span>
1215 <span class="highlight">has has_been_printed => ( is => 'rw' );
1219 print $self->as_string;
1220 $self->has_been_printed(1);
1221 }</span></code></pre>
1228 <li>Role consumption is introspectable</li>
1231 <pre><code>if ( Person->does('Printable') ) { ... }
1235 if ( Person->meta->does('Printable') ) { ... }</code></pre>
1240 <h1>These Names Are the Same</h1>
1243 <li>What if a role and class define the same method?</li>
1244 <li>A class's <em>local</em> methods win over the role's</li>
1245 <li>The role's methods win over the class's <em>inherited</em> methods</li>
1250 <h1>Conflicts Between Roles</h1>
1253 <li>Two roles with a method of the same name</li>
1254 <li>Generates a compile-time error when consumed by a class</li>
1259 <h1>Conflict Example</h1>
1261 <pre><code>package IsFragile;
1266 package CanBreakdance;
1269 sub break { ... }</code></pre>
1273 <h1>Conflict Example</h1>
1275 <pre><code>package FragileDancer;
1278 <span class="highlight">with 'IsFragile', 'CanBreakdance';</span></code></pre>
1281 <li>Only one <code>with</code>!</li>
1286 <h1>Conflict Resolution</h1>
1289 <li>The consuming class must resolve the conflict by implementing th emethod</li>
1290 <li>Can use some combination of method exclusion and aliasing</li>
1295 <h1>Method Aliasing</h1>
1297 <pre><code>package FragileDancer;
1300 <span class="highlight">with 'IsFragile' =>
1302 { break => 'break_bone' } },
1305 { break => 'break_it_down' } };</span></code></pre>
1308 <li>Renames the roles' methods</li>
1309 <li>Still conflicts, need to <code>exclude</code> as well</li>
1314 <h1>Method Exclusion</h1>
1316 <pre><code>package FragileDancer;
1319 <span class="highlight">with 'IsFragile' =>
1321 { break => 'break_bone' },
1322 exclude => 'break' },
1325 { break => 'break_dance' },
1326 exclude => 'break' };</span></code></pre>
1330 <h1>And then ...</h1>
1332 <pre><code>package FragileDancer;
1339 if ( rand(1) < 0.5 ) {
1346 <h1>Still Full of Fail</h1>
1349 <li>Roles are also about semantics!</li>
1350 <li>We've fulfilled the letter and lost the spirit</li>
1351 <li>Roles have a <em>meaning</em></li>
1352 <li>Think twice before blindly aliasing and excluding methods!</li>
1357 <h1>Hot Role-on-Role Action</h1>
1359 <pre><code>package Comparable;
1362 requires 'compare';</code></pre>
1366 <h1>Hot Role-on-Role Action</h1>
1368 <pre><code>package TestsEquality;
1375 return $self->compare(@_) == 0;
1380 <h1>And then ...</h1>
1382 <pre><code>package Integer;
1385 with 'TestsEquality';
1387 # Satisfies the Comparable role
1390 Integer->does('TestsEquality'); # true
1391 Integer->does('Comparable'); # also true!</code></pre>
1395 <h1>Name Conflicts Between Roles</h1>
1397 <pre><code>package HasSubProcess;
1400 <span class="highlight">sub execute { ... }</span>
1405 with 'HasSubProcess';
1407 <span class="highlight">sub execute { ... }</span></code></pre>
1411 <h1>Delayed Conflict</h1>
1413 <pre><code>package StateOfTexas;
1414 with 'Killer';</code></pre>
1417 <li><code>StateOfTexas</code> must implement its own <code>execute</code></li>
1418 <li>But loading the <code>Killer</code> role by itself does not cause an error</li>
1423 <h1>Roles as Interfaces</h1>
1426 <li>Roles can <code>require</code> methods of their consumers</li>
1427 <li>Compile-time checks</li>
1428 <li>Method must exist when the role is consumed</li>
1433 <h1>The Attribute Gotcha</h1>
1435 <pre><code>package HasSize;
1438 <span class="current incremental">requires 'size';</span>
1443 <span class="incremental">with 'HasSize';
1445 has size => ( is => 'ro' );</span></code></pre>
1449 <h1>The Attribute Gotcha Workaround</h1>
1451 <pre><code>package HasSize;
1459 has size => ( is => 'ro' );
1461 with 'HasSize';</code></pre>
1465 <h1>Compile-time Is a Lie</h1>
1468 <li>Really, it's <em>package load</em> time</li>
1469 <li>That's run-time, but before the "real" run-time</li>
1470 <li>Moose does not rewire Perl, it's just sugar!</li>
1471 <li>(but <code>MooseX::Declare</code> <em>does</em> rewire Perl)</li>
1476 <h1>Enforcing Roles</h1>
1478 <pre><code>package Comparison;
1481 has [ 'left', 'right' ] => (
1483 <span class="highlight">does => 'Comparable',</span>
1488 <li>A sneak peek at type constraints</li>
1494 <h1>Roles Can Be Applied to Objects</h1>
1496 <pre><code>use Moose::Util qw( apply_all_roles );
1498 my $fragile_person = Person->new( ... );
1499 apply_all_roles( $fragile_person, 'IsFragile' );</code></pre>
1502 <li>Does not change the <code>Person</code> class</li>
1503 <li>Works with non-Moose classes, great for monkey-patching!</li>
1508 <h1>Roles Are Dirty Too</h1>
1511 <li>Once again, clean up those Moose droppings</li>
1514 <pre><code>package Comparable;
1519 <span class="highlight">no Moose::Role;</span></code></pre>
1522 <li>But roles cannot be made immutable</li>
1527 <h1>The Zen of Roles</h1>
1530 <li>Roles represent discrete units of ...
1537 <li>Roles are shareable between unrelated classes</li>
1538 <li>Roles are what a class <em>does</em>, not what it <em>is</em></li>
1539 <li>Roles <em>add</em> functionality, inheritance <em>specializes</em></li>
1544 <h1>Abstract Examples</h1>
1547 <li>Human <em>@ISA</em> Animal</li>
1548 <li>Human <em>does</em> Toolmaker (as <em>does</em> Chimpanzee)</li>
1549 <li>Car <em>@ISA</em> Vehicle</li>
1550 <li>Car <em>does</em> HasEngine</li>
1555 <h1>Real Examples</h1>
1558 <li>Objects representing SQL database components and queries
1560 <li>Schema, Table, Column, ColumnAlias</li>
1561 <li>Select, Insert, Update, Delete</li>
1568 <h1>Real Examples</h1>
1571 <li>Column and ColumnAlias both <em>do</em> ColumnLike</li>
1572 <li>ColumnLike things can be used in certain parts of queries</li>
1573 <li>All queries <em>do</em> HasWhereClause</li>
1574 <li>Select <em>does</em> Comparable and Selectable (for subselects)</li>
1575 <li>A where clause requires its components to <em>do</em> Comparable</li>
1580 <h1>Roles Summary</h1>
1583 <li>Roles can define an interface with <code>requires</code></li>
1584 <li>Roles can have state (attributes) and behavior (methods)</li>
1585 <li>Roles can mix interface, state, & behavior</li>
1586 <li>Roles are composed (flattened) into classes</li>
1587 <li>Roles can do other roles</li>
1588 <li>Roles can be used as a type in APIs (must do Comparable)</li>
1600 # perl bin/prove -lv t/02-roles.t
1602 Iterate til this passes all its tests</pre>
1605 <div class="slide fake-slide0">
1606 <h1>Part 3: Basic Attributes</h1>
1610 <h1>Attributes Are Huge</h1>
1613 <li>Moose's biggest feature</li>
1614 <li>The target of <em>many</em> MooseX modules</li>
1619 <h1>Quick Review</h1>
1622 <li>Declared with <code>has</code></li>
1623 <li>Read-only or read-write</li>
1626 <pre><code>package Shirt;
1629 has 'color' => ( is => 'ro' );
1630 has 'is_ripped' => ( is => 'rw' );</code></pre>
1634 <h1>Required-ness</h1>
1637 <li>Required means "must be passed to the constructor"</li>
1638 <li>But can be <code>undef</code></li>
1643 <h1>Required-ness</h1>
1645 <pre><code>package Person;
1648 has first_name => (
1650 <span class="current incremental">required => 1,</span>
1653 <span class="incremental">Person->new( first_name => undef ); # ok
1654 Person->new(); # kaboom</span></code></pre>
1658 <h1>Default and Builder</h1>
1661 <li>Attributes can have defaults</li>
1662 <li>Simple non-referecne scalars (number, string)</li>
1663 <li>Subroutine reference</li>
1664 <li>A builder method</li>
1672 <li>Can be a non-reference scalar (including <code>undef</code>)</li>
1675 <pre><code>package Person;
1680 default => 'Spire FCU',
1688 <li>Can be a subroutine reference</li>
1691 <pre><code>package Person;
1698 name => 'Spire FCU' ) },
1703 <h1>Default as a Subroutine Reference</h1>
1706 <li>Called as a method on the object</li>
1707 <li>Called anew for each object</li>
1712 <h1>Why No Other Reference Types?</h1>
1714 <pre><code>package Person;
1719 <span class="wrong">default => Bank->new(
1720 name => 'Spire FCU' ),</span>
1724 <li>Now <strong>every</strong> person shares the <strong>same</strong> Bank object!</li>
1729 <h1>Defaulting to an Empty Reference</h1>
1731 <pre><code>package Person;
1734 has packages => (
1736 default => <span class="highlight">sub { [] }</span>,
1741 <h1>What if I Want to Share?</h1>
1743 <pre><code>package Person;
1746 my $highlander_bank =
1747 Bank->new( name => 'Spire FCU' );
1751 default => sub { $highlander_bank },
1759 <li>A method <em>name</em> which returns the default</li>
1766 <pre><code>package Person;
1771 builder => '_build_bank',
1776 return Bank->new( name => 'Spire FCU' );
1781 <h1>Default vs Builder</h1>
1784 <li>Use default for simple scalars</li>
1785 <li>Use default to return empty references</li>
1786 <li>Use default for <em>very</em> trivial subroutine references</li>
1787 <li>Use builder for everything else</li>
1792 <h1>Builder Bonuses</h1>
1795 <li>Can be overridden and method modified, because it's called by <em>name</em></li>
1796 <li>Roles can require a builder</li>
1801 <h1>Role Requires Builder</h1>
1803 <pre><code>package HasBank;
1806 requires '_build_bank';
1810 builder => '_build_bank',
1815 <h1>Lazy, Good for Nothing Attributes</h1>
1818 <li>Normally, defaults are generated during object construction</li>
1819 <li>This can be expensive</li>
1820 <li>We want to default to <code>$self->size * 2</code>, but attribute initialization order is unpredictable</li>
1821 <li>Use lazy attributes!</li>
1826 <h1>The Power of Dynamic Defaults</h1>
1828 <pre><code>package Person;
1831 has shoe_size => (
1837 <h1>The Power of Dynamic Defaults</h1>
1839 <pre><code>has shoes => (
1841 <span class="highlight">lazy => 1,</span>
1842 builder => '_build_shoes',
1848 return Shoes->new(
1849 size => <span class="highlight">$_[0]->shoe_size</span> );
1854 <h1>Lazy is Good</h1>
1857 <li>Lazy defaults are executed when the attribute is read</li>
1858 <li>Can see other object attributes</li>
1859 <li>Still need to watch out for circular laziness</li>
1864 <h1>Clearer and Predicate</h1>
1867 <li>Attributes can have a value, including <code>undef</code>, or not</li>
1868 <li>Can clear the value with a clearer method</li>
1869 <li>Can check for the existence of a value with a predicate method</li>
1870 <li>By default, these methods are not created</li>
1875 <h1>Clearer and Predicate</h1>
1877 <pre><code>package Person;
1883 builder => '_build_account',
1884 <span class="highlight">clearer => '_clear_account',
1885 predicate => 'has_account',</span>
1890 <h1>Clearer and Lazy Defaults</h1>
1893 <li>Lazy defaults are good for computed attributes</li>
1894 <li>Clear the attribute when the source data changes</li>
1895 <li>Recalculated at next access</li>
1900 <h1>Renaming constructor arguments</h1>
1903 <li>By default, constructor names = attribute names</li>
1904 <li>Use <code>init_arg</code> to change this</li>
1905 <li>Set <code>init_arg => undef</code> to make it unconstructable</li>
1910 <h1>Some <code>init_arg</code> examples</h1>
1912 <pre><code>package Person;
1917 <span class="highlight">init_arg => 'foot_size',</span>
1920 Person->new( <span class="wrong">shoe_size => 13</span> );
1923 Person->new( <span class="right">foot_size => 13</span> );
1924 print $person->shoe_size;</code></pre>
1928 <h1>Some <code>init_arg</code> examples</h1>
1930 <pre><code>package Person;
1935 <span class="highlight">init_arg => undef,</span>
1938 Person->new( <span class="wrong">shoes => Shoes->new</span> );</code></pre>
1942 <h1>Why Set <code>init_arg => undef</code>?</h1>
1945 <li>Use this with a lazy default for attributes-as-cache</li>
1946 <li>Compute the value as needed</li>
1947 <li>Ensure that it is always generated correctly (not set by constructor)</li>
1948 <li>Use triggers or method modifiers (coming soon) to clear the value</li>
1953 <h1>Attribute Inheritance</h1>
1956 <li>By default, subclasses inherit attribute as-is</li>
1957 <li>Can change some attribute parameters in subclasses
1963 <li>others we've not yet covered</li>
1970 <h1>Attribute Inheritance Example</h1>
1972 <pre><code>package Employee;
1977 has '<span class="highlight">+first_name</span>' => (
1978 default => 'Joe',
1983 <h1>Attribute Inheritance Warning</h1>
1986 <li>An attribute is a contract about a class's API</li>
1987 <li>Don't break that contract in a subclass</li>
1988 <li>Especially important in the context of types</li>
1993 <h1>Changing Accessor Names</h1>
1995 <pre><code>package Person;
1998 has first_name => (
1999 <span class="highlight">reader</span> => 'first_name',
2000 <span class="highlight">writer</span> => 'first_name',
2004 <li>The long-hand version of <code>is => 'rw'</code></li>
2009 <h1>Changing Accessor Names</h1>
2011 <pre><code>package Person;
2014 has first_name => (
2015 <span class="highlight">reader</span> => 'first_name',
2016 <span class="highlight">writer</span> => undef,
2020 <li>The long-hand version of <code>is => 'ro'</code></li>
2026 <h1>Changing Accessor Names</h1>
2028 <pre><code>package Person;
2031 has first_name => (
2032 <span class="highlight">reader</span> => 'get_first_name',
2033 <span class="highlight">writer</span> => 'set_first_name,
2038 <h1>Changing Accessor Names</h1>
2040 <pre><code>package Person;
2043 has first_name => (
2044 <span class="highlight">is</span> => 'rw',
2045 <span class="highlight">writer</span> => '_first_name',
2049 <li>Can also mix-and-match</li>
2054 <h1>ETOOMUCHTYPING</h1>
2057 <li><code>MooseX::FollowPBP</code><br /><code>get_foo</code> and <code>set_foo</code></li>
2058 <li><code>MooseX::SemiAffordanceAccessor</code><br /><code>foo</code> and <code>set_foo</code></li>
2063 <h1>ETOOMUCHTYPING</h1>
2065 <pre><code>package Person;
2067 <span class="highlight">use MooseX::SemiAffordanceAccessor;</span>
2069 has first_name => (
2074 <li>Creates <code>first_name</code> and <code>set_first_name</code></li>
2079 <h1>Basic Attributes Summary</h1>
2082 <li>Attributes can be <code>required</code></li>
2083 <li>Attributes can have a <code>default</code> or <code>builder</code></li>
2084 <li>Attributes with a default or builder can be <code>lazy</code></li>
2085 <li>Attributes can have a <code>clearer</code> and/or <code>predicate</code></li>
2086 <li>An attribute's constructor name can be changed with <code>init_arg</code></li>
2087 <li>A subclass can alter its parents' attributes</li>
2088 <li>Attribute accessor names can be changed</li>
2100 # perl bin/prove -lv t/03-basic-attributes.t
2102 Iterate til this passes all its tests</pre>
2105 <div class="slide fake-slide0">
2106 <h1>Part 4: Method Modifiers</h1>
2110 <h1>What is a Method Modifier</h1>
2113 <li>Apply to an existing method</li>
2114 <li>... from a parent class, the current class, or a role</li>
2115 <li>Roles can provide modifiers that are applied at composition time</li>
2120 <h1>What is a Method Modifier</h1>
2123 <li>"Iinject" behavior</li>
2124 <li>Add behavior to generated methods (accessors, delegations)</li>
2125 <li>Provide roles which modify existing behavior</li>
2130 <h1>Before and After</h1>
2133 <li>Simplest modifiers - <code>before</code> and <code>after</code></li>
2134 <li>Guess when they run!</li>
2139 <h1>Uses for <code>before</code></h1>
2142 <li>As a pre-call check</li>
2145 <pre><code>package Person;
2148 before work => sub {
2150 die 'I have no job!'
2151 unless $self->has_title;
2156 <h1>Uses for <code>before</code></h1>
2159 <li>Logging/Debugging</li>
2162 <pre><code>package Person;
2165 before work => sub {
2167 return unless $DEBUG;
2169 warn "Called work on ", $self->full_name,
2170 "with the arguments: [@_]\n";
2175 <h1>Uses for <code>after</code></h1>
2178 <li>Also works for logging/debugging</li>
2179 <li>Post-X side-effects (recording audit info)</li>
2182 <pre><code>package Person;
2185 after work => sub {
2187 $self->work_count(
2188 $self->work_count + 1 );
2196 <li>Modifiers are useful for adding behavior to generated methods</li>
2201 <h1>Other Uses Example</h1>
2203 <pre><code>has password => (
2205 clearer => 'clear_password',
2208 has hashed_password => (
2210 builder => '_build_hashed_password',
2211 clearer => '_clear_hashed_password',
2214 after clear_password => sub {
2216 $self->_clear_hashed_password;
2221 <h1><code>before</code> and <code>after</code> Limitations</h1>
2224 <li>Cannot alter method parameters</li>
2225 <li>Cannot alter return value</li>
2226 <li>But <strong>can</strong> throw an exception</li>
2231 <h1>The <code>around</code> Modifier</h1>
2234 <li>The big gun</li>
2235 <li>Can alter parameters <strong>and/or</strong> return values</li>
2236 <li>Can skip calling the wrapped method entirely</li>
2241 <h1>The power of <code>around</code></h1>
2243 <pre><code>around insert => sub {
2247 $self->_validate_insert(@_);
2251 $self->_munge_insert(@_) );
2253 $new_user->_assign_uri;
2260 <h1>Modifier Order</h1>
2263 <li>Before runs order from last to first</li>
2264 <li>After runs in order from first to last</li>
2265 <li>Around runs in order from last to first</li>
2270 <h1>Modifier Order Illustrated</h1>
2273 <span class="current incremental">before 2
2275 <span class="incremental">around 2
2277 <span class="incremental">wrapped method</span>
2278 <span class="incremental">around 1
2280 <span class="incremental">after 1
2286 <h1>Modifiers in Roles</h1>
2289 <li>Roles can use these modifiers</li>
2290 <li>Very powerful!</li>
2295 <h1>Modifiers in Roles</h1>
2297 <pre><code>package IsUnreliable;
2300 <span class="highlight">requires 'run';
2302 around run</span> => sub {
2306 return if rand(1) < 0.5;
2308 return $self->$orig(@_);
2313 <h1>Augment and Inner</h1>
2316 <li>Inverted <code>super</code></li>
2317 <li>From least- to most-specific</li>
2318 <li>Grandparent to parent to child</li>
2319 <li>Not allowed in roles</li>
2324 <h1>Augment and Inner</h1>
2326 <pre><code>package Document;
2328 sub xml { '<doc>' . <span class="highlight">inner()</span> . '</doc>' }
2333 <span class="highlight">augment xml</span> => { title() . <span class="highlight">inner()</span> . summary() };
2338 <span class="highlight">augment xml</span> => { tps_xml() . <span class="highlight">inner()</span> };</code></pre>
2342 <h1>Augment and Inner</h1>
2345 <li>When we call <code>$tps->xml</code> ...
2347 <li><code>Document->xml</code></li>
2348 <li><code>Report->xml</code></li>
2349 <li><code>TPSReport->xml</code></li>
2356 <h1>Augment and Inner Usage</h1>
2359 <li>Call <code>inner()</code> to "fill in the blank"</li>
2360 <li>Requires designing for subclassing</li>
2361 <li>Call <code>inner()</code> in the terminal class, just in case</li>
2366 <h1>Method Modifiers Summary</h1>
2369 <li>Use <code>before</code> and <code>after</code> for ...
2372 <li>pre- or post-validation</li>
2373 <li>to add behavior to generated methods</li>
2376 <li>These two modifiers cannot change parameters or return values</li>
2381 <h1>Method Modifiers Summary</h1>
2384 <li>Use <code>around</code> to ...
2386 <li>alter parameters passed to the original method</li>
2387 <li>alter the return value of the original method</li>
2388 <li>not call the original method at all (or call a <em>different</em> method)</li>
2395 <h1>Method Modifiers Summary</h1>
2398 <li>When using modifiers in a role, require the modified method</li>
2399 <li>Use <code>augment</code> and <code>inner</code> to invert the normal subclassing flow ...
2401 <li>Least- to most-specific (parents to children)</li>
2402 <li>Build in "insertability" (stick more stuff in the "middle")</li>
2405 <li>Always call <code>inner</code> in the most specific subclass to allow for future extension</li>
2417 # perl bin/prove -lv t/04-method-modifiers.t
2419 Iterate til this passes all its tests</pre>
2422 <div class="slide fake-slide0">
2423 <h1>Part 5: Types</h1>
2426 <div class="slide fake-slide0">
2427 <h1>Part 6: Advanced Attributes</h1>
2431 <h1>Weak References</h1>
2434 <li>A weak reference lets you avoid circular references</li>
2435 <li>Weak references do not increase the reference count</li>
2440 <h1>Circular Reference Illustrated</h1>
2442 <pre><code>my $foo = {};
2443 my $bar = { foo => $foo };
2444 $foo->{bar} = $bar;</code></pre>
2447 <li>Neither <code>$foo</code> nor <code>$bar</code> go out of scope<br />
2448 (until the program exits)</li>
2453 <h1>Weakening Circular References</h1>
2455 <pre><code>use Scalar::Util qw( weaken );
2458 my $bar = { foo => $foo };
2459 $foo->{bar} = $bar;
2460 weaken $foo->{bar}</code></pre>
2463 <li>When <code>$bar</code> goes out of scope, <code>$foo->{bar}</code> becomes <code>undef</code></li>
2468 <h1>Circular References in Attributes</h1>
2470 <pre><code>package Person;
2473 has name => ( is => 'ro' );
2474 has friend => ( is => 'rw' );
2476 my $alice = Person->new( name => 'Alice' );
2477 my $bob = Person->new( name => 'Bob' );
2478 $bob->friend($alice);
2479 $alice->friend($bob);</code></pre>
2485 <pre><code>package Person;
2488 has name => ( is => 'ro' );
2489 has friend => ( is => 'rw', <span class="highlight">weak_ref => 1</span> );
2491 my $alice = Person->new( name => 'Alice' );
2492 my $bob = Person->new( name => 'Bob' );
2493 $bob->friend($alice);
2494 $alice->friend($bob);</code></pre>
2498 <h1>Under the Hood</h1>
2501 <li>A <code>weak_ref</code> attribute calls <code>weaken</code> ...
2503 <li>during object construction</li>
2504 <li>when the attribute is set via a writer</li>
2514 <li>A code reference run after an attribute is <em>set</em></li>
2515 <li>Like an <code>after</code> modifier, but makes intentions clearer</li>
2518 <h2 class="wrong">Gross</h2>
2520 <pre><code>after salary_level => {
2523 $self->clear_salary;
2528 <h1>Use a Trigger Instead</h1>
2530 <h2 class="right">Cleaner</h2>
2532 <pre><code>has salary_level => (
2534 trigger => sub { $_[0]->clear_salary },
2542 <li>Attributes can be objects</li>
2543 <li>Delegation transparently calls methods on those objects</li>
2548 <h1>Delegation Examples</h1>
2550 <pre><code>package Person;
2555 <span class="highlight">handles => [ 'inhale', 'exhale' ],</span>
2559 <li>Creates <code>$person->inhale</code> and <code>->exhale</code> methods</li>
2560 <li>Internally calls <code>$person->lungs->inhale</code></li>
2565 <h1>Why Delegation?</h1>
2568 <li>Reduce the number of classes exposed</li>
2569 <li>Re-arrange class internals -<br />
2570 turn a method into an attribute with delegation</li>
2571 <li>Provide convenenience methods</li>
2576 <h1>Moose's <code>handles</code> Parameter</h1>
2579 <li>Accepts many arguments ...
2581 <li>Array reference - list of methods to delegate as-is</li>
2582 <li>Hash reference - map of method names</li>
2583 <li>Regex - delegates all matching methods</li>
2584 <li>Role name - delegates all methods in the role</li>
2585 <li>Sub reference - does something complicated ;)</li>
2592 <h1>Array Reference</h1>
2595 <li>Takes each method name and creates a simple delegation from the delegating class to the delegatee attribute</li>
2600 <h1>Hash Reference</h1>
2603 <li>Mapping of names in the delegating class to the delegatee class</li>
2606 <pre><code>package Person;
2611 isa => 'BankAccount',
2612 <span class="highlight">handles => {
2613 receive_money => 'deposit',
2614 give_money => 'withdraw',
2620 <h1>Hash Reference Detailed</h1>
2622 <pre><code> handles => {
2623 receive_money => 'deposit',
2624 give_money => 'withdraw',
2628 <li><code>$person->receive_money</code> = <code>$person->account->deposit</code></li>
2629 <li><code>$person->give_money</code> = <code>$person->account->withdraw</code></li>
2636 <pre><code>package Person;
2642 handles => qr/.*/,
2646 <li>Creates a delegation for every method in the Name class</li>
2647 <li>Excludes <code>meta</code> and methods inherited from <code>Moose::Object</code></li>
2654 <pre><code>package Auditor;
2657 sub record_change { ... }
2658 sub change_history { ... }
2665 does => 'Auditor',
2666 <span class="highlight">handles => 'Auditor',</span>
2671 <h1>Role Name Detailed</h1>
2674 <li>Account gets delegate methods for each method in the <code>Auditor</code> role
2676 <li>record_history</li>
2677 <li>change_history</li>
2684 <h1>Traits and Metaclasses</h1>
2687 <li>The ultimate in customization</li>
2688 <li>Per attribute metaclasses</li>
2689 <li>Per attribute roles applied to the attribute metaclass</li>
2690 <li>Change the meta-level behavior</li>
2695 <h1>Traits and Metaclasses</h1>
2698 <li>The default metaclass is <code>Moose::Meta::Attribute</code></li>
2699 <li>Controls accessor generation, defaults, delegation, etc.</li>
2700 <li>Adding a role to this metaclass (or replacing it) allows for infinite customization</li>
2705 <h1>Traits and Metaclasses</h1>
2708 <li>Can add/alter/remove attribute parameter (from <code>has</code>)</li>
2709 <li>Can change behavior of created attribute</li>
2714 <h1>Simple Trait Example</h1>
2716 <pre><code>package Person;
2718 use MooseX::LabeledAttributes;
2721 <span class="highlight">traits => [ 'Labeled' ],</span>
2724 <span class="highlight">label => 'Social Security Number',</span>
2727 print <span class="highlight">Person->meta
2728 ->get_attribute('ssn')->label;</span></code></pre>
2732 <h1>Simple Metaclass Example</h1>
2734 <pre><code>package Person;
2736 use MooseX::LabeledAttributes;
2739 <span class="highlight">metaclass =>
2740 'MooseX::Meta::Attribute::Labeled',</span>
2743 <span class="highlight">label => 'Social Security Number',</span>
2746 print <span class="highlight">Person->meta
2747 ->get_attribute('ssn')->label;</span></code></pre>
2751 <h1>Traits vs Metaclass</h1>
2754 <li>Can apply any mix of traits to an attribute</li>
2755 <li>But just one metaclass</li>
2756 <li>Traits (aka roles) can cooperate</li>
2757 <li>Metaclasses require you to pick just one</li>
2762 <h1>Advanced Attributes Summary</h1>
2765 <li>Use <code>weak_ref</code> to avoid circular references</li>
2766 <li>Use trigger to do an action post-attribute write</li>
2767 <li>Use delegations to hide "internal" objects</li>
2768 <li>Traits and metaclasses let you extend Moose's core attribute features</li>
2780 # perl bin/prove -lv t/06-advanced-attributes.t
2782 Iterate til this passes all its tests</pre>
2785 <div class="slide fake-slide0">
2786 <h1>Part 7: Introspection</h1>
2789 <div class="slide fake-slide0">
2790 <h1>Part 8: A Tour of MooseX</h1>
2793 <div class="slide fake-slide0">
2794 <h1>Part 9: Writing Moose Extensions</h1>
2803 Copyright 2009 David Rolsky. All Rights Reserved.
2805 This work is licensed under a Creative Commons Attribution-Share Alike
2806 3.0 United States License See
2807 http://creativecommons.org/licenses/by-sa/3.0/us/ for details.