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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>
55 <h2><a href="git://git.moose.perl.org/moose-presentations.git"><tt>git://git.moose.perl.org/moose-presentations.git</tt></a></h2>
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 => 'fat' );</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 => (
845 <div class="slide fake-slide0">
846 <h1>Part 1: Moose Classes</h1>
850 <h1>Moose Classes</h1>
853 <li>Moose classes are Perl packages which <code>use Moose</code></li>
858 <h1>Moose.pm and Your Class</h1>
860 <pre><code>package Person;
861 use Moose;</code></pre>
864 <li><code>Moose.pm</code> provides declarative sugar</li>
865 <li>Turns on <code>strict</code> and <code>warnings</code></li>
866 <li>Creates metaclasses for your class: <code>Person->meta</code></li>
867 <li>Moose classes automatically inherit from <code>Moose::Object</code></li>
872 <h1>What <code>Moose::Object</code> Provides</h1>
875 <li>Constructor - <code>new()</code></li>
876 <li>Calls your <code>BUILDARGS()</code> and/or <code>BUILD()</code></li>
877 <li>Calls your <code>DEMOLISH</code> during object destruction</li>
885 <li>Takes <code>@_</code>, returns a hash reference of attribute names/value</li>
886 <li>Accepts a hash or hashref; throws otherwise</li>
887 <li>Provide your own for other cases</li>
888 <li><strong>Always</strong> call <code>$class->SUPER::BUILDARGS(@_)</code> as a fallback!</li>
893 <h1>BUILDARGS Example</h1>
895 <pre><code>package Person;
901 if ( @_ == 1 && ! ref $_[0] ) {
902 <span class="highlight">return { ssn => $_[0] };</span>
904 <span class="highlight">return $class->SUPER::BUILDARGS(@_)</span>;
907 <span class="highlight">Person->new('123-45-6789')</span></code></pre>
914 <li>Called after object is created, before <code>new</code> returns</li>
915 <li>Chance to do more complex validation, set complex attributes</li>
916 <li>Called in reverse inheritance order, parents to children</li>
917 <li>Return value is ignored</li>
922 <h1>BUILD Example</h1>
924 <pre><code>package Person;
930 if ( $self->country_of_residence
932 die 'All US residents'
933 . ' must have an SSN'
934 unless $self->has_ssn;
940 <h1>Object Construction a la Moose</h1>
942 <pre><code>Person->new(@_)</code></pre>
945 <li>Calls <code>Person->BUILDARGS(@_)</code> to turn <code>@_</code> into a hashref</li>
946 <li>Blesses a reference</li>
947 <li>Populates attributes based on the hashref from #1</li>
948 <li>Calls <code>$new_object->BUILDALL($constructor_args)</code>
949 <br />... which calls all <code>BUILD</code> methods</li>
950 <li>Returns the object</li>
955 <h1>The Object is Opaque</h1>
958 <li>Technically it's a hash reference</li>
959 <li><span class="wrong">If you <em>ever</em> treat it as one <strong>you are doing it wrong!</strong></span></li>
967 <li>Like <code>DESTROY</code>, but Moose makes sure all <code>DEMOLISH</code> methods in a hierarchy are called</li>
968 <li>Called in normal inheritance order, children to parents</li>
976 <li><code>extends</code> is sugar for declaring parent classes</li>
977 <li>Also ensures metaclass compatibility between parent and child</li>
978 <li>Do not <code>use base</code></li>
981 <pre><code>package Employee;
983 <span class="highlight">extends 'Person';</span></code></pre>
990 <li>Each call to <code>extends</code> <strong>resets</strong> your parents</li>
993 <h2 class="wrong">Wrong</h2>
995 <pre><code>package EvilEmployee;
998 extends 'Thief';</code></pre>
1000 <h2 class="right">Right</h2>
1002 <pre><code>package EvilEmployee;
1004 extends 'Person', 'Thief';</code></pre>
1008 <h1>Extending un-Moose-y Parents</h1>
1010 <pre><code>package My::LWP;
1012 extends 'LWP';</code></pre>
1015 <li>No <code>Moose::Object</code>, so ...
1017 <li>No attribute-handling <code>new()</code></li>
1018 <li>No <code>BUILDARGS()</code> or <code>BUILD()</code></li>
1019 <li>No <code>DEMOLISH()</code></li>
1022 <li>But see <code>MooseX::NonMoose</code> for a workaround</li>
1027 <h1><code>override</code> and <code>super</code></h1>
1030 <li><code>override</code> is another method modifier</li>
1031 <li>An alternative to Perl's <code>SUPER::</code></li>
1036 <h1><code>override</code> and <code>super</code></h1>
1038 <pre><code>package Employee;
1041 <span class="current incremental">extends 'Person';</span>
1043 <span class="incremental">override</span> work => sub {
1047 unless $self->got_paid;
1048 <span class="incremental">super();</span>
1049 }<span class="incremental">;</span></code></pre>
1053 <h1>Caveat <code>super</code></h1>
1056 <li>Mostly like <code>$self->SUPER::work(@_)</code></li>
1057 <li><strong>But</strong> cannot change <code>@_</code>!</li>
1058 <li>Binds the parent's method at compile time</li>
1063 <h1>Minimal Attributes</h1>
1066 <li><code>has 'foo'</code></li>
1067 <li>Use <code>is => 'ro'</code> or <code>is => 'rw'</code></li>
1068 <li>Attributes without "is" have no accessors</li>
1073 <h1>Read-write attributes</h1>
1075 <pre><code>package Person;
1078 has first_name => ( <span class="highlight">is => 'rw'</span> );
1081 Person->new( first_name => 'Dave' );
1083 $person->first_name('Stevan');
1084 print $person->first_name; # Stevan</code></pre>
1089 <h1>Read-only attributes</h1>
1091 <pre><code>package Person;
1094 has first_name => ( <span class="highlight">is => 'ro'</span> );
1097 Person->new( first_name => 'Dave' );
1099 $person->first_name('Stevan');
1100 print $person->first_name; # Dave</code></pre>
1105 <h1>There is More to Come</h1>
1108 <li>Attributes have a <em>lot</em> of features</li>
1113 <h1>Cleaning Up Moose Droppings</h1>
1115 <pre><code>package Person;
1119 Person->can('extends');</code></pre>
1122 <li>Not very hygienic</li>
1127 <h1>Cleaning Up Moose Droppings</h1>
1129 <pre><code>package Person;
1137 Person->can('extends');</code></pre>
1144 <li><code>no Moose</code> at the end of a package is a best practice</li>
1145 <li>Or <code>use namespace::autoclean</code> at the top</li>
1151 <h1>Immutability</h1>
1154 <li><span style="font-family: URW Chancery L; font-size: 140%">Stevan's Incantation of Fleet-Footedness</span></li>
1157 <pre><code>package Person;
1160 <span class="highlight">__PACKAGE__->meta->make_immutable;</span></code></pre>
1164 <h1>What <code>make_immutable</code> does</h1>
1168 <li>Uses <code>eval</code> to "inline" a constructor</li>
1169 <li>Memoizes a lot of meta-information</li>
1170 <li>Makes loading your class slower</li>
1171 <li>Makes object creation <em>much</em> faster</li>
1176 <h1>When to Immutabilize?</h1>
1179 <li><em>Almost</em> always</li>
1180 <li>Startup time vs execution time</li>
1185 <h1>Classes Summary</h1>
1188 <li><code>use Moose</code></li>
1189 <li><code>Class->meta</code></li>
1190 <li><code>Moose::Object</code> base class</li>
1191 <li><code>extends</code>, <code>override</code>, and <code>super</code></li>
1192 <li>Simple attributes: <code>has</code>, <code>is => 'ro'</code>, & <code>is => 'rw'</code></li>
1193 <li><code>no Moose</code></li>
1194 <li><code>__PACKAGE__->meta->make_immutable</code></li>
1207 # perl bin/prove -lv t/00-prereq.t
1209 # perl install-moose (if needed)
1211 # perl bin/prove -lv t/01-classes.t
1213 # edit lib/Person.pm and lib/Employee.pm
1215 Iterate til this passes all its tests</pre>
1218 <div class="slide fake-slide0">
1219 <h1>Part 2: Roles</h1>
1223 <h1>Just What Is a Role?</h1>
1226 <li>Mixin? Interface? Trait?</li>
1227 <li>Yes ... and more!</li>
1232 <h1>Roles - State <strong>and</strong> Behavior</h1>
1234 <pre><code>package HasPermissions;
1236 <span class="current incremental"># state
1237 has access_level => ( is => 'rw' );</span>
1239 <span class="incremental"># behavior
1242 my $required = shift;
1244 return $self->access_level
1246 }</span></code></pre>
1251 <h1>Roles Can Define Interfaces</h1>
1253 <pre><code>package Printable;
1256 requires 'as_string';</code></pre>
1260 <h1>Roles Can Do All Three</h1>
1262 <pre><code>package Printable;
1265 requires 'as_string';
1267 has has_been_printed => ( is => 'rw' );
1271 print $self->as_string;
1272 $self->has_been_printed(1);
1277 <h1>Classes Consume Roles</h1>
1279 <pre><code>package Person;
1282 with 'HasPermissions';</code></pre>
1286 <h1>Classes Consume Roles</h1>
1288 <pre><code>my $person = Person->new(
1289 first_name => 'Kenichi',
1290 last_name => 'Asai',
1291 access_level => 42,
1294 print $person->full_name
1296 . $person->can_access(42)
1298 : 'little power';</code></pre>
1302 <h1>Roles in Practice</h1>
1305 <li>Consuming a role =~ inlining the role</li>
1310 <h1>In Other Words ...</h1>
1312 <pre><code>package Person;
1315 <span class="highlight">with 'Printable';</span></code></pre>
1319 <h1>In Other Words ...</h1>
1321 <pre><code>package Person;
1324 <span class="delete">with 'Printable';</span>
1326 <span class="highlight">has has_been_printed => ( is => 'rw' );
1330 print $self->as_string;
1331 $self->has_been_printed(1);
1332 }</span></code></pre>
1339 <li>Role consumption is introspectable</li>
1342 <pre><code>if ( Person->does('Printable') ) { ... }
1346 Person->meta->does('Printable')</code></pre>
1351 <h1>These Names Are the Same</h1>
1354 <li>What if a role and class define the same method?</li>
1355 <li>A class's <em>local</em> methods win over the role's</li>
1356 <li>The role's methods win over the class's <em>inherited</em> methods</li>
1361 <h1>Conflicts Between Roles</h1>
1364 <li>Two roles with a method of the same name</li>
1365 <li>Generates a compile-time error when consumed by a class</li>
1370 <h1>Conflict Example</h1>
1372 <pre><code>package IsFragile;
1377 package CanBreakdance;
1380 sub break { ... }</code></pre>
1384 <h1>Conflict Example</h1>
1386 <pre><code>package FragileDancer;
1389 <span class="highlight">with 'IsFragile', 'CanBreakdance';</span></code></pre>
1392 <li>Only one <code>with</code>!</li>
1397 <h1>Conflict Resolution</h1>
1400 <li>The consuming class must resolve the conflict by implementing the method</li>
1401 <li>Can use some combination of method exclusion and aliasing</li>
1406 <h1>Method Aliasing</h1>
1408 <pre><code>package FragileDancer;
1411 <span class="highlight">with 'IsFragile' =>
1413 { break => 'break_bone' } },
1416 { break => 'break_it_down' } };</span></code></pre>
1419 <li>Renames the roles' methods</li>
1420 <li>Still conflicts, need to <code>exclude</code> as well</li>
1425 <h1>Method Exclusion</h1>
1427 <pre><code>package FragileDancer;
1430 <span class="highlight">with 'IsFragile' =>
1432 { break => 'break_bone' },
1433 -excludes => 'break' },
1436 { break => 'break_it_down' },
1437 -excludes => 'break' };</span></code></pre>
1441 <h1>And then ...</h1>
1443 <pre><code>package FragileDancer;
1449 $self->break_it_down;
1450 if ( rand(1) < 0.5 ) {
1457 <h1>Still Full of Fail</h1>
1460 <li>Roles are also about semantics!</li>
1461 <li>We've fulfilled the letter and lost the spirit</li>
1462 <li>Roles have a <em>meaning</em></li>
1463 <li>Think twice before blindly aliasing and excluding methods!</li>
1468 <h1>Hot Role-on-Role Action</h1>
1470 <pre><code>package Comparable;
1473 requires 'compare';</code></pre>
1477 <h1>Hot Role-on-Role Action</h1>
1479 <pre><code>package TestsEquality;
1486 return $self->compare(@_) == 0;
1491 <h1>And then ...</h1>
1493 <pre><code>package Integer;
1496 with 'TestsEquality';
1498 # Satisfies the Comparable role
1501 Integer->does('TestsEquality'); # true
1502 Integer->does('Comparable'); # also true!</code></pre>
1506 <h1>Name Conflicts Between Roles</h1>
1508 <pre><code>package HasSubProcess;
1511 <span class="highlight">sub execute { ... }</span>
1516 with 'HasSubProcess';
1518 <span class="highlight">sub execute { ... }</span></code></pre>
1522 <h1>Delayed Conflict</h1>
1524 <pre><code>package StateOfTexas;
1525 with 'Killer';</code></pre>
1528 <li><code>StateOfTexas</code> must implement its own <code>execute</code></li>
1529 <li>But loading the <code>Killer</code> role by itself does not cause an error</li>
1534 <h1>Roles as Interfaces</h1>
1537 <li>Roles can <code>require</code> methods of their consumers</li>
1538 <li>Compile-time checks</li>
1539 <li>Method must exist when the role is consumed</li>
1544 <h1>The Attribute Gotcha</h1>
1546 <pre><code>package HasSize;
1549 <span class="current incremental">requires 'size';</span>
1554 <span class="incremental">with 'HasSize';
1556 has size => ( is => 'ro' );</span></code></pre>
1560 <h1>The Attribute Gotcha Workaround</h1>
1562 <pre><code>package HasSize;
1570 has size => ( is => 'ro' );
1572 with 'HasSize';</code></pre>
1576 <h1>Compile-time Is a Lie</h1>
1579 <li>Really, it's <em>package load</em> time</li>
1580 <li>That's run-time, but before the "real" run-time</li>
1581 <li>Moose does not rewire Perl, it's just sugar!</li>
1582 <li>(but <code>MooseX::Declare</code> <em>does</em> rewire Perl)</li>
1587 <h1>Enforcing Roles</h1>
1589 <pre><code>package Comparison;
1592 has [ 'left', 'right' ] => (
1594 <span class="highlight">does => 'Comparable',</span>
1599 <li>A sneak peek at type constraints</li>
1605 <h1>Roles Can Be Applied to Objects</h1>
1607 <pre><code>use Moose::Util qw( apply_all_roles );
1609 my $fragile_person = Person->new( ... );
1610 apply_all_roles( $fragile_person,
1611 'IsFragile' );</code></pre>
1614 <li>Does not change the <code>Person</code> class</li>
1615 <li>Works with non-Moose classes, great for monkey-patching!</li>
1620 <h1>Roles Are Dirty Too</h1>
1623 <li>Once again, clean up those Moose droppings</li>
1626 <pre><code>package Comparable;
1631 <span class="highlight">no Moose::Role;</span></code></pre>
1634 <li>But roles cannot be made immutable</li>
1639 <h1>The Zen of Roles</h1>
1642 <li>Roles represent discrete units of ...
1649 <li>Roles are shareable between unrelated classes</li>
1650 <li>Roles are what a class <em>does</em>, not what it <em>is</em></li>
1651 <li>Roles <em>add</em> functionality, inheritance <em>specializes</em></li>
1656 <h1>Abstract Examples</h1>
1659 <li>Human <em>@ISA</em> Animal</li>
1660 <li>Human <em>does</em> Toolmaker (as <em>does</em> Chimpanzee)</li>
1661 <li>Car <em>@ISA</em> Vehicle</li>
1662 <li>Car <em>does</em> HasEngine</li>
1667 <h1>Real Examples</h1>
1670 <li>Objects representing SQL database components and queries
1672 <li>Schema, Table, Column, ColumnAlias</li>
1673 <li>Select, Insert, Update, Delete</li>
1680 <h1>Real Examples</h1>
1683 <li>Column and ColumnAlias both <em>do</em> ColumnLike</li>
1684 <li>ColumnLike things can be used in certain parts of queries</li>
1685 <li>All queries <em>do</em> HasWhereClause</li>
1686 <li>Select <em>does</em> Comparable and Selectable (for subselects)</li>
1687 <li>A where clause requires its components to <em>do</em> Comparable</li>
1692 <h1>Roles Summary</h1>
1695 <li>Roles can define an interface with <code>requires</code></li>
1696 <li>Roles can have state (attributes) and behavior (methods)</li>
1697 <li>Roles can mix interface, state, & behavior</li>
1698 <li>Roles are composed (flattened) into classes</li>
1699 <li>Roles can do other roles</li>
1700 <li>Roles can be used as a type in APIs (must do Comparable)</li>
1712 # perl bin/prove -lv t/02-roles.t
1714 Iterate til this passes all its tests</pre>
1717 <div class="slide fake-slide0">
1718 <h1>Part 3: Basic Attributes</h1>
1722 <h1>Attributes Are Huge</h1>
1725 <li>Moose's biggest feature</li>
1726 <li>The target of <em>many</em> MooseX modules</li>
1731 <h1>Quick Review</h1>
1734 <li>Declared with <code>has</code></li>
1735 <li>Read-only or read-write</li>
1738 <pre><code>package Shirt;
1741 has 'color' => ( is => 'ro' );
1742 has 'is_ripped' => ( is => 'rw' );</code></pre>
1746 <h1>Required-ness</h1>
1749 <li>Required means "must be passed to the constructor"</li>
1750 <li>But can be <code>undef</code></li>
1755 <h1>Required-ness</h1>
1757 <pre><code>package Person;
1760 has first_name => (
1762 <span class="current incremental">required => 1,</span>
1765 <span class="incremental">Person->new( first_name => undef ); # ok
1766 Person->new(); # kaboom</span></code></pre>
1770 <h1>Default and Builder</h1>
1773 <li>Attributes can have defaults</li>
1774 <li>Simple non-reference scalars (number, string)</li>
1775 <li>Subroutine reference</li>
1776 <li>A builder method</li>
1784 <li>Can be a non-reference scalar (including <code>undef</code>)</li>
1787 <pre><code>package Person;
1792 default => 'Spire FCU',
1800 <li>Can be a subroutine reference</li>
1803 <pre><code>package Person;
1810 name => 'Spire FCU' ) },
1815 <h1>Subroutine Reference Default</h1>
1818 <li>Called as a method on the object</li>
1819 <li>Called anew for each object</li>
1824 <h1>Why No Other Reference Types?</h1>
1826 <pre><code>package Person;
1831 <span class="wrong">default => Bank->new(
1832 name => 'Spire FCU' ),</span>
1836 <li>Now <strong>every</strong> person shares the <strong>same</strong> Bank object!</li>
1841 <h1>Defaulting to an Empty Reference</h1>
1843 <pre><code>package Person;
1846 has packages => (
1848 default => <span class="highlight">sub { [] }</span>,
1853 <h1>What if I Want to Share?</h1>
1855 <pre><code>package Person;
1858 my $highlander_bank =
1859 Bank->new( name => 'Spire FCU' );
1863 default => sub { $highlander_bank },
1871 <li>A method <em>name</em> which returns the default</li>
1878 <pre><code>package Person;
1883 builder => '_build_bank',
1888 return Bank->new(
1889 name => 'Spire FCU' );
1894 <h1>Default vs Builder</h1>
1897 <li>Use default for simple scalars</li>
1898 <li>Use default to return empty references</li>
1899 <li>Use default for <em>very</em> trivial subroutine references</li>
1900 <li>Use builder for everything else</li>
1905 <h1>Builder Bonuses</h1>
1908 <li>Can be overridden and method modified, because it's called by <em>name</em></li>
1909 <li>Roles can require a builder</li>
1914 <h1>Role Requires Builder</h1>
1916 <pre><code>package HasBank;
1919 requires '_build_bank';
1923 builder => '_build_bank',
1928 <h1>Lazy, Good for Nothin' Attributes</h1>
1931 <li>Normally, defaults are generated during object construction</li>
1932 <li>This can be expensive</li>
1933 <li>We want to default to <code>$self->size * 2</code>, but attribute initialization order is unpredictable</li>
1934 <li>Use lazy attributes!</li>
1939 <h1>The Power of Dynamic Defaults</h1>
1941 <pre><code>package Person;
1944 has shoe_size => (
1950 <h1>The Power of Dynamic Defaults</h1>
1952 <pre><code>has shoes => (
1954 <span class="highlight">lazy => 1,</span>
1955 builder => '_build_shoes',
1961 return Shoes->new(
1962 size => <span class="highlight">$self->shoe_size</span> );
1967 <h1>Lazy is Good</h1>
1970 <li>Lazy defaults are executed when the attribute is read</li>
1971 <li>Can see other object attributes</li>
1972 <li>Still need to watch out for circular laziness</li>
1977 <h1>Clearer and Predicate</h1>
1980 <li>Attributes can have a value, including <code>undef</code>, or not</li>
1981 <li>Can clear the value with a clearer method</li>
1982 <li>Can check for the existence of a value with a predicate method</li>
1983 <li>By default, these methods are not created</li>
1988 <h1>Clearer and Predicate</h1>
1990 <pre><code>package Person;
1996 builder => '_build_account',
1997 <span class="highlight">clearer => '_clear_account',
1998 predicate => 'has_account',</span>
2003 <h1>Clearer and Lazy Defaults</h1>
2006 <li>Lazy defaults are good for computed attributes</li>
2007 <li>Clear the attribute when the source data changes</li>
2008 <li>Recalculated at next access</li>
2013 <h1>Renaming constructor arguments</h1>
2016 <li>By default, constructor names = attribute names</li>
2017 <li>Use <code>init_arg</code> to change this</li>
2018 <li>Set <code>init_arg => undef</code> to make it unconstructable</li>
2023 <h1>Some <code>init_arg</code> examples</h1>
2025 <pre><code>package Person;
2030 <span class="highlight">init_arg => 'foot_size',</span>
2033 Person->new( <span class="wrong">shoe_size => 13</span> );
2036 Person->new( <span class="right">foot_size => 13</span> );
2037 print $person->shoe_size;</code></pre>
2041 <h1>Some <code>init_arg</code> examples</h1>
2043 <pre><code>package Person;
2048 <span class="highlight">init_arg => undef,</span>
2051 Person->new( <span class="wrong">shoes => Shoes->new</span> );</code></pre>
2055 <h1>Why Set <code>init_arg => undef</code>?</h1>
2058 <li>Use this with a lazy default for attributes-as-cache</li>
2059 <li>Compute the value as needed</li>
2060 <li>Ensure that it is always generated correctly (not set by constructor)</li>
2061 <li>Use triggers or method modifiers (coming soon) to clear the value</li>
2066 <h1>Attribute Inheritance</h1>
2069 <li>By default, subclasses inherit attribute as-is</li>
2070 <li>Can change some attribute parameters in subclasses
2076 <li>others we've not yet covered</li>
2083 <h1>Attribute Inheritance Example</h1>
2085 <pre><code>package Employee;
2090 has '<span class="highlight">+first_name</span>' => (
2091 default => 'Joe',
2096 <h1>Attribute Inheritance Warning</h1>
2099 <li>An attribute is a contract about a class's API</li>
2100 <li>Don't break that contract in a subclass</li>
2101 <li>Especially important in the context of types</li>
2106 <h1>Changing Accessor Names</h1>
2108 <pre><code>package Person;
2111 has first_name => (
2112 <span class="highlight">accessor</span> => 'first_name',
2116 <li>The long-hand version of <code>is => 'rw'</code></li>
2121 <h1>Changing Accessor Names</h1>
2123 <pre><code>package Person;
2126 has first_name => (
2127 <span class="highlight">reader</span> => 'first_name',
2128 <span class="highlight">writer</span> => undef,
2132 <li>The long-hand version of <code>is => 'ro'</code></li>
2138 <h1>Changing Accessor Names</h1>
2140 <pre><code>package Person;
2143 has first_name => (
2144 <span class="highlight">reader</span> => 'get_first_name',
2145 <span class="highlight">writer</span> => 'set_first_name',
2150 <h1>Changing Accessor Names</h1>
2152 <pre><code>package Person;
2155 has first_name => (
2156 <span class="highlight">is</span> => 'rw',
2157 <span class="highlight">writer</span> => '_first_name',
2161 <li>Can also mix-and-match <code>is</code> and explicit names</li>
2166 <h1>ETOOMUCHTYPING</h1>
2169 <li><code>MooseX::FollowPBP</code><br /><code>get_foo</code> and <code>set_foo</code></li>
2170 <li><code>MooseX::SemiAffordanceAccessor</code><br /><code>foo</code> and <code>set_foo</code></li>
2175 <h1>ETOOMUCHTYPING</h1>
2177 <pre><code>package Person;
2179 <span class="highlight">use MooseX::SemiAffordanceAccessor;</span>
2181 has first_name => (
2186 <li>Creates <code>first_name</code> and <code>set_first_name</code></li>
2191 <h1>Basic Attributes Summary</h1>
2194 <li>Attributes can be <code>required</code></li>
2195 <li>Attributes can have a <code>default</code> or <code>builder</code></li>
2196 <li>Attributes with a default or builder can be <code>lazy</code></li>
2197 <li>Attributes can have a <code>clearer</code> and/or <code>predicate</code></li>
2198 <li>An attribute's constructor name can be changed with <code>init_arg</code></li>
2199 <li>A subclass can alter its parents' attributes</li>
2200 <li>Attribute accessor names can be changed</li>
2212 # perl bin/prove -lv \
2213 t/03-basic-attributes.t
2215 Iterate til this passes all its tests</pre>
2218 <div class="slide fake-slide0">
2219 <h1>Part 4: Method Modifiers</h1>
2223 <h1>What is a Method Modifier</h1>
2226 <li>Apply to an existing method</li>
2227 <li>... from a parent class, the current class, or a role</li>
2228 <li>Roles can provide modifiers that are applied at composition time</li>
2233 <h1>What is a Method Modifier</h1>
2236 <li>"Inject" behavior</li>
2237 <li>Add behavior to generated methods (accessors, delegations)</li>
2238 <li>Provide roles which modify existing behavior</li>
2243 <h1>Before and After</h1>
2246 <li>Simplest modifiers - <code>before</code> and <code>after</code></li>
2247 <li>Guess when they run!</li>
2252 <h1>Uses for <code>before</code></h1>
2255 <li>As a pre-call check</li>
2258 <pre><code>package Person;
2261 before work => sub {
2263 die 'I have no job!'
2264 unless $self->has_title;
2269 <h1>Uses for <code>before</code></h1>
2272 <li>Logging/Debugging</li>
2275 <pre><code>package Person;
2278 before work => sub {
2280 return unless $DEBUG;
2282 warn "Called work on ",
2283 $self->full_name,
2284 "with the arguments: [@_]\n";
2289 <h1>Uses for <code>after</code></h1>
2292 <li>Also works for logging/debugging</li>
2293 <li>Post-X side-effects (recording audit info)</li>
2296 <pre><code>package Person;
2299 after work => sub {
2301 $self->work_count(
2302 $self->work_count + 1 );
2310 <li>Modifiers are useful for adding behavior to generated methods</li>
2315 <h1>More Modifier Examples</h1>
2317 <pre><code>has password => (
2319 clearer => 'clear_password',
2321 has hashed_password => (
2323 builder => '_build_hashed_password',
2324 clearer => '_clear_hashed_password',
2326 after clear_password => sub {
2328 $self->_clear_hashed_password;
2333 <h1><code>before</code> and <code>after</code> Limitations</h1>
2336 <li>Cannot alter method parameters</li>
2337 <li>Cannot alter return value</li>
2338 <li>But <strong>can</strong> throw an exception</li>
2343 <h1>The <code>around</code> Modifier</h1>
2346 <li>The big gun</li>
2347 <li>Can alter parameters <strong>and/or</strong> return values</li>
2348 <li>Can skip calling the wrapped method entirely</li>
2353 <h1>The power of <code>around</code></h1>
2355 <pre><code>around insert => sub {
2359 $self->_validate_insert(@_);
2363 $self->_munge_insert(@_) );
2365 $new_user->_assign_uri;
2371 <h1>Modifier Order</h1>
2374 <li>Before runs in order from last to first</li>
2375 <li>After runs in order from first to last</li>
2376 <li>Around runs in order from last to first</li>
2381 <h1>Modifier Order Illustrated</h1>
2384 <span class="current incremental">before 2
2386 <span class="incremental">around 2
2388 <span class="incremental">wrapped method</span>
2389 <span class="incremental">around 1
2391 <span class="incremental">after 1
2397 <h1>Modifiers in Roles</h1>
2400 <li>Roles can use these modifiers</li>
2401 <li>Very powerful!</li>
2406 <h1>Modifiers in Roles</h1>
2408 <pre><code>package IsUnreliable;
2411 <span class="highlight">requires 'run';
2413 around run</span> => sub {
2417 return if rand(1) < 0.5;
2419 return $self->$orig(@_);
2424 <h1>Augment and Inner</h1>
2427 <li>Inverted <code>super</code></li>
2428 <li>From least- to most-specific</li>
2429 <li>Grandparent to parent to child</li>
2430 <li>Not allowed in roles</li>
2435 <h1>Augment and Inner</h1>
2437 <pre><code>package Document;
2439 sub xml { '<doc>' . <span class="highlight">inner()</span> . '</doc>' }
2443 <span class="highlight">augment xml</span> =>
2444 sub { title() . <span class="highlight">inner()</span> . summary() };
2448 <span class="highlight">augment xml</span> =>
2449 sub { tps_xml() . <span class="highlight">inner()</span> };</code></pre>
2453 <h1>Augment and Inner</h1>
2456 <li>When we call <code>$tps->xml</code> ...
2458 <li><code>Document->xml</code></li>
2459 <li><code>Report->xml</code></li>
2460 <li><code>TPSReport->xml</code></li>
2467 <h1>Augment and Inner Usage</h1>
2470 <li>Call <code>inner()</code> to "fill in the blank"</li>
2471 <li>Requires designing for subclassing</li>
2472 <li>Call <code>inner()</code> in the terminal class, just in case</li>
2477 <h1>Method Modifiers Summary</h1>
2480 <li>Use <code>before</code> and <code>after</code> for ...
2483 <li>pre- or post-validation</li>
2484 <li>to add behavior to generated methods</li>
2487 <li>These two modifiers cannot change parameters or return values</li>
2492 <h1>Method Modifiers Summary</h1>
2495 <li>Use <code>around</code> to ...
2497 <li>alter parameters passed to the original method</li>
2498 <li>alter the return value of the original method</li>
2499 <li>not call the original method at all (or call a <em>different</em> method)</li>
2506 <h1>Method Modifiers Summary</h1>
2509 <li>When using modifiers in a role, require the modified method</li>
2510 <li>Use <code>augment</code> and <code>inner</code> to invert the normal subclassing flow ...
2512 <li>Least- to most-specific (parents to children)</li>
2513 <li>Build in "insertability" (stick more stuff in the "middle")</li>
2516 <li>Always call <code>inner</code> in the most specific subclass to allow for future extension</li>
2528 # perl bin/prove -lv \
2529 t/04-method-modifiers.t
2531 Iterate til this passes all its tests</pre>
2534 <div class="slide fake-slide0">
2535 <h1>Part 5: Types</h1>
2539 <h1>A Type System for Perl</h1>
2542 <li>Sort of ...</li>
2543 <li><em>Variables</em> are not typed</li>
2544 <li>Attributes can have types</li>
2545 <li>MooseX modules let you define method signatures</li>
2550 <h1>Components of a Moose Type</h1>
2553 <li>A type is a name and a constraint</li>
2554 <li>Types have a hierarchy</li>
2555 <li>Constraints are cumulative from parents</li>
2556 <li>Types can have associated coercions</li>
2561 <h1>Built-in Type Hierarchy</h1>
2580 <h1>Built-in Type Hierarchy</h1>
2614 <li>Like Perl's <code>if ($foo)</code></li>
2619 <h1>Value (and subtypes)</h1>
2622 <li><code>Value</code> is true when <code>! ref $thing</code></li>
2623 <li><code>Value</code> and <code>Str</code> are effectively the same, but <code>Str</code> is more expressive</li>
2624 <li>An overloaded object which numifies does not pass the <code>Num</code> constraint!</li>
2625 <li>Perl 5's overloading is hopelessly broken</li>
2630 <h1>ClassName and RoleName</h1>
2633 <li>A string with a package name</li>
2634 <li>The package <strong>must already be loaded</strong></li>
2639 <h1>Parameterizable Types</h1>
2642 <li>What does <code>ArrayRef[`a]</code> mean?</li>
2643 <li><code>s/`a/Int/</code> (or <code>Str</code> or ...)</li>
2644 <li>When you use it you can write ...
2646 <li><code>ArrayRef</code> (== <code>ArrayRef[Item]</code>)</li>
2647 <li><code>ArrayRef[Str]</code></li>
2648 <li><code>ArrayRef[MyTypeName]</code></li>
2649 <li><code>ArrayRef[HashRef[Maybe[Int]]]</code></li>
2659 <li>Maybe means either the named type or <code>undef</code></li>
2660 <li><code>Maybe[Int]</code> accepts integers or <code>undef</code></li>
2668 <li>This or that (or that or ...)</li>
2669 <li><code>Int | ArrayRef[Int]</code></li>
2670 <li>But use a coercion instead when possible</li>
2671 <li>Or use a <code>role_type</code>, <code>duck_type</code>, or anything not a union</li>
2672 <li>A union is often a code smell</li>
2677 <h1>Making Your Own Types</h1>
2679 <pre><code>use Moose::Util::TypeConstraints;
2681 <span class="incremental current">subtype 'PositiveInt',</span>
2682 <span class="incremental">as 'Int',</span>
2683 <span class="incremental">where { $_ > 0 },</span>
2684 <span class="incremental">message
2685 { "The value you provided ($_)"
2686 . " was not a positive int." };</span>
2690 <span class="incremental">isa => 'PositiveInt',</span>
2695 <h1>Automatic Types</h1>
2698 <li>Moose creates a type for every Moose class and role</li>
2699 <li>Unknown names are assumed to be classes</li>
2704 <h1>Automatic Types</h1>
2706 <pre><code>package Employee;
2711 <span class="highlight">isa => 'Employee',</span>
2714 has start_date => (
2716 <span class="highlight">isa => 'DateTime',</span>
2721 <h1>Subtype Shortcuts - <code>class_type</code></h1>
2723 <pre><code>use Moose::Util::TypeConstraints;
2724 class_type 'DateTime';
2728 where { $_->isa('DateTime') },
2729 message { ... };</code></pre>
2733 <h1>Subtype Shortcuts - <code>role_type</code></h1>
2735 <pre><code>use Moose::Util::TypeConstraints;
2736 role_type 'Printable';
2738 subtype 'Printable',
2741 { Moose::Util::does_role(
2742 $_, 'Printable' ) },
2743 message { ... };</code></pre>
2747 <h1>Subtype Shortcuts - <code>duck_type</code></h1>
2749 <pre><code>use Moose::Util::TypeConstraints;
2750 duck_type Car => qw( run break_down );
2754 where { all { $_->can($_) }
2755 qw( run break_down ) },
2756 message { ... };</code></pre>
2760 <h1>Subtype Shortcuts - <code>enum</code></h1>
2762 <pre><code>use Moose::Util::TypeConstraints;
2763 enum Color => qw( red blue green ) );
2765 my %ok = map { $_ => 1 }
2766 qw( red blue green );
2771 message { ... };</code></pre>
2775 <h1>Anonymous Subtypes</h1>
2777 <pre><code>package Person;
2779 <span class="highlight">my $posint =
2780 subtype as 'Int', where { $_ > 0 };</span>
2784 <span class="highlight">isa => $posint,</span>
2788 <li>Shortcuts have anonymous forms as well</li>
2795 <pre><code>use Moose::Util::TypeConstraints;
2799 where { ! /[a-z]/ };</code></pre>
2805 <pre><code><span class="incremental current">coerce 'UCStr',</span>
2806 <span class="incremental">from 'Str',</span>
2807 <span class="incremental">via { uc };</span>
2809 has shouty_name => (
2812 <span class="incremental">coerce => 1,</span>
2817 <h1>Coercion Examples</h1>
2819 <pre><code>subtype 'My::DateTime',
2820 as class_type 'DateTime';
2822 coerce 'My::DateTime',
2824 via { DateTime->new( %{$_} ) };
2826 coerce 'My::DateTime',
2828 via { DateTime->from_epoch(
2829 epoch => $_ ) };</code></pre>
2832 <li>Use coercion to inflate a value</li>
2837 <h1>Coercion Examples</h1>
2839 <pre><code>coerce 'ArrayRef[Int]',
2841 via { [ $_ ] };</code></pre>
2844 <li>Instead of union - <code style="white-space: nowrap">Int | ArrayRef[Int]</code></li>
2849 <h1>Using Types with Attributes</h1>
2851 <pre><code>package Person;
2855 <span class="highlight">isa => 'Num',</span>
2858 has favorite_numbers => (
2860 <span class="highlight">isa => 'ArrayRef[Int]',
2861 coerce => 1,</span>
2866 <h1>More Droppings</h1>
2869 <li><code>Moose::Util::TypeConstraints</code> also needs cleanup</li>
2872 <pre><code>package Person;
2875 use Moose::Util::TypeConstraints;
2880 <span class="highlight">no Moose::Util::TypeConstraints;</span></code></pre>
2884 <h1>Typed Methods (Low-tech)</h1>
2886 <pre class="medium"><code>package Person;
2887 <span class="highlight">use MooseX::Params::Validate qw( validated_list );</span>
2891 <span class="highlight">my ( $tasks, $can_rest ) =
2895 { isa => 'ArrayRef[Task]',
2906 <h1>Typed Methods (High-tech)</h1>
2908 <pre class="medium"><code>package Person;
2910 <span class="highlight">use MooseX::Method::Signatures;</span>
2912 <span class="highlight">method work ( ArrayRef[Task] :$tasks,
2913 Bool :$can_rest = 0 )</span> {
2921 <h1>Digression: The Type Registry</h1>
2924 <li>Types are actually <code>Moose::Meta::TypeConstraints</code> <em>objects</em></li>
2925 <li>Stored in an interpreter-global registry mapping names to objects</li>
2933 <li>Coercions are attached to type objects</li>
2934 <li>Therefore also global</li>
2935 <li>Name conflicts between modules!</li>
2936 <li>Coercion conflicts between modules!</li>
2941 <h1>Namespace Fix</h1>
2944 <li>Use some sort of pseudo-namespacing scheme</li>
2945 <li>Never coerce directly to a class name, or <em>to</em> built-in types</li>
2950 <h1>Namespace Fix</h1>
2952 <pre><code>use Moose::Util::TypeConstraints;
2953 subtype <span class="highlight">'MyApp::Type::DateTime',</span>
2956 <span class="highlight">coerce 'MyApp::Type::DateTime',</span>
2958 via { DateTime->new( %{$_} ) }
2960 has creation_date => (
2962 <span class="highlight">isa => 'MyApp::Type::DateTime',</span>
2968 <h1>Namespace Fix</h1>
2970 <pre><code>subtype 'MyApp::Type::ArrayOfInt',
2973 coerce 'MyApp::Type::ArrayOfInt',
2975 via { [ $_ ] };</code></pre>
2979 <h1>Namespace Fix Pros and Cons</h1>
2982 <li><span class="right">Relatively simple</span></li>
2983 <li><span class="right">Already built into Moose</span></li>
2984 <li><span class="wrong">Conflates type and module namespaces</span></li>
2985 <li><span class="wrong">Type names are strings, so typos are easy to make and may be hard to find</span></li>
2990 <h1>MooseX::Types</h1>
2992 <pre><code>package MyApp::Types;
2995 <span class="highlight">-declare => [ qw( ArrayOfInt ) ]</span>;
2996 use MooseX::Types::Moose
2999 subtype <span class="highlight">ArrayOfInt</span>,
3002 coerce <span class="highlight">ArrayOfInt</span>
3004 via { [ $_ ] };</code></pre>
3008 <h1>MooseX::Types</h1>
3010 <pre><code>package MyApp::Account;
3012 use MyApp::Types qw( ArrayOfInt );
3014 has transaction_history => (
3021 <h1>MooseX::Types</h1>
3024 <li>Type names are exported functions, catches typos early</li>
3025 <li>Types must be pre-declared</li>
3026 <li>Types are stored with namespaces internally, but externally are short</li>
3027 <li>Import existing Moose types as functions from <code>MooseX::Types::Moose</code></li>
3028 <li>Still need string names for things like <code>ArrayRef['Email::Address']</code></li>
3033 <h1>MooseX::Types Pros and Cons</h1>
3036 <li><span class="right">Catches typos at compile time</span></li>
3037 <li><span class="right">Automatic namespacing</span></li>
3038 <li><span class="wrong">One more thing to install and learn</span></li>
3039 <li><span class="wrong">Every name gets types twice (declared and then defined)</span></li>
3040 <li><span class="wrong">Still stuck with strings when referring to class or role names</span></li>
3041 <li><span class="wrong">Coercion gotcha from earlier still applies to types exported from <code>MooseX::Types::Moose</code></span></li>
3046 <h1>Recommendation</h1>
3049 <li>Use <code>MooseX::Types</code></li>
3050 <li>Compile time error catching and automatic namespacing are huge wins</li>
3051 <li>Docs from <code>Moose::Util::TypeConstraints</code> are 98% compatible with <code>MooseX::Types</code> anyway</li>
3052 <li>A function exported by a type library works wherever a type name would</li>
3064 # perl bin/prove -lv t/05-types.t
3066 Iterate til this passes all its tests</pre>
3069 <div class="slide fake-slide0">
3070 <h1>Part 6: Advanced Attributes</h1>
3074 <h1>Weak References</h1>
3077 <li>A weak reference lets you avoid circular references</li>
3078 <li>Weak references do not increase the reference count</li>
3083 <h1>Circular Reference Illustrated</h1>
3085 <pre><code>my $foo = {};
3086 my $bar = { foo => $foo };
3087 $foo->{bar} = $bar;</code></pre>
3090 <li>Neither <code>$foo</code> nor <code>$bar</code> go out of scope<br />
3091 (until the program exits)</li>
3096 <h1>Weakening Circular References</h1>
3098 <pre><code>use Scalar::Util qw( weaken );
3101 my $bar = { foo => $foo };
3102 $foo->{bar} = $bar;
3103 weaken $foo->{bar}</code></pre>
3106 <li>When <code>$bar</code> goes out of scope, <code>$foo->{bar}</code> becomes <code>undef</code></li>
3111 <h1>Circular References in Attributes</h1>
3113 <pre><code>package Person;
3116 has name => ( is => 'ro' );
3117 has friend => ( is => 'rw' );
3119 my $alice = Person->new( name => 'Alice' );
3120 my $bob = Person->new( name => 'Bob' );
3121 $bob->friend($alice);
3122 $alice->friend($bob);</code></pre>
3128 <pre><code>package Person;
3131 has name => ( is => 'ro' );
3132 has friend => ( is => 'rw',
3133 <span class="highlight">weak_ref => 1</span> );
3135 my $alice = Person->new( name => 'Alice' );
3136 my $bob = Person->new( name => 'Bob' );
3137 $bob->friend($alice);
3138 $alice->friend($bob);</code></pre>
3142 <h1>Under the Hood</h1>
3145 <li>A <code>weak_ref</code> attribute calls <code>weaken</code> ...
3147 <li>during object construction</li>
3148 <li>when the attribute is set via a writer</li>
3158 <li>A code reference run after an attribute is <em>set</em></li>
3159 <li>Like an <code>after</code> modifier, but makes intentions clearer</li>
3162 <h2 class="wrong">Gross</h2>
3164 <pre><code>after salary_level => {
3167 $self->clear_salary;
3172 <h1>Use a Trigger Instead</h1>
3174 <h2 class="right">Cleaner</h2>
3176 <pre><code>has salary_level => (
3178 trigger => sub { $_[0]->clear_salary },
3186 <li>Attributes can be objects</li>
3187 <li>Delegation transparently calls methods on those objects</li>
3192 <h1>Delegation Examples</h1>
3194 <pre><code>package Person;
3199 <span class="highlight">handles => [ 'inhale', 'exhale' ],</span>
3203 <li>Creates <code>$person->inhale</code> and <code>->exhale</code> methods</li>
3204 <li>Internally calls <code>$person->lungs->inhale</code></li>
3209 <h1>Why Delegation?</h1>
3212 <li>Reduce the number of classes exposed</li>
3213 <li>Re-arrange class internals -<br />
3214 turn a method into an attribute with delegation</li>
3215 <li>Provide convenenience methods</li>
3220 <h1>Moose's <code>handles</code> Parameter</h1>
3223 <li>Accepts many arguments ...
3225 <li>Array reference - list of methods to delegate as-is</li>
3226 <li>Hash reference - map of method names</li>
3227 <li>Regex - delegates all matching methods</li>
3228 <li>Role name - delegates all methods in the role</li>
3229 <li>Sub reference - does something complicated ;)</li>
3236 <h1>Array Reference</h1>
3239 <li>Takes each method name and creates a simple delegation from the delegating class to the delegatee attribute</li>
3244 <h1>Hash Reference</h1>
3247 <li>Mapping of names in the delegating class to the delegatee class</li>
3250 <pre><code>package Person;
3254 isa => 'BankAccount',
3255 <span class="highlight">handles => {
3256 receive_money => 'deposit',
3257 give_money => 'withdraw',
3263 <h1>Hash Reference Detailed</h1>
3265 <pre><code> handles => {
3266 receive_money => 'deposit',
3267 give_money => 'withdraw',
3271 <li><code>$person->receive_money</code> = <code>$person->account->deposit</code></li>
3272 <li><code>$person->give_money</code> = <code>$person->account->withdraw</code></li>
3279 <pre><code>package Person;
3285 handles => qr/.*/,
3289 <li>Creates a delegation for every method in the Name class</li>
3290 <li>Excludes <code>meta</code> and methods inherited from <code>Moose::Object</code></li>
3297 <pre><code>package Auditor;
3299 sub record_change { ... }
3300 sub change_history { ... }
3307 does => 'Auditor',
3308 <span class="highlight">handles => 'Auditor',</span>
3313 <h1>Role Name Detailed</h1>
3316 <li>Account gets delegate methods for each method in the <code>Auditor</code> role
3318 <li>record_history</li>
3319 <li>change_history</li>
3326 <h1>Native Delegation</h1>
3329 <li>Delegate to <em>unblessed</em> Perl types</li>
3330 <li>Scalar, array or hash ref, etc</li>
3331 <li>Treat Perl types as objects</li>
3332 <li>Still uses <code>handles</code></li>
3333 <li>Pretend that native Perl types have methods</li>
3338 <h1>Native Delegation - Array(Ref)</h1>
3341 <li>Methods include:
3343 <li><code>push</code></li>
3344 <li><code>shift</code></li>
3345 <li><code>elements</code> - returns all elements</li>
3346 <li><code>count</code></li>
3347 <li><code>is_empty</code></li>
3348 <li>quite a few more</li>
3355 <h1>Native Delegation - Array(Ref)</h1>
3357 <pre><code>package Person;
3359 has _favorite_numbers => (
3360 traits => [ 'Array' ],
3362 isa => 'ArrayRef[Int]',
3363 default => sub { [] },
3364 init_arg => undef,
3365 <span class="highlight">handles =>
3366 { favorite_numbers => 'elements',
3367 add_favorite_number => 'push',
3373 <h1>Native Delegation - Array(Ref)</h1>
3375 <pre><code>my $person = Person->new();
3377 $person->add_favorite_number(7);
3378 $person->add_favorite_number(42);
3381 for $person->favorite_numbers;
3388 <h1>Native Delegation</h1>
3391 <li>Native types are ...
3393 <li>Number - <code>add</code>, <code>mul</code>, ...</li>
3394 <li>String - <code>append</code>, <code>chop</code>, ...</li>
3395 <li>Counter - <code>inc</code>, <code>dec</code>, ...</li>
3396 <li>Bool - <code>set</code>, <code>toggle</code>, ...</li>
3397 <li>Hash - <code>get</code>, <code>set</code>, ...</li>
3398 <li>Array - already saw it</li>
3399 <li>Code - <code>execute</code>, that's it</li>
3406 <h1>Curried Delegation</h1>
3409 <li>A delegation with some preset arguments</li>
3410 <li>Works with object or Native delegation</li>
3415 <h1>Curried Delegation</h1>
3417 <pre><code>package Person;
3421 isa => 'BankAccount',
3424 <span class="highlight">[ 'deposit', 100 ]</span>
3426 <span class="highlight">[ 'withdraw', 100 ]</span>
3432 <h1>Traits and Metaclasses</h1>
3435 <li>The ultimate in customization</li>
3436 <li>Per attribute metaclasses</li>
3437 <li>Per attribute roles applied to the attribute metaclass</li>
3438 <li>Change the meta-level behavior</li>
3443 <h1>Traits and Metaclasses</h1>
3446 <li>The default metaclass is <code>Moose::Meta::Attribute</code></li>
3447 <li>Controls accessor generation, defaults, delegation, etc.</li>
3448 <li>Adding a role to this metaclass (or replacing it) allows for infinite customization</li>
3453 <h1>Traits and Metaclasses</h1>
3456 <li>Can add/alter/remove attribute parameter (from <code>has</code>)</li>
3457 <li>Can change behavior of created attribute</li>
3462 <h1>Simple Trait Example</h1>
3464 <pre><code>package Person;
3466 use MooseX::LabeledAttributes;
3469 <span class="highlight">traits => [ 'Labeled' ],</span>
3472 <span class="highlight">label => 'Social Security Number',</span>
3474 print <span class="highlight">Person->meta
3475 ->get_attribute('ssn')->label;</span></code></pre>
3479 <h1>Simple Metaclass Example</h1>
3481 <pre><code>package Person;
3483 use MooseX::LabeledAttributes;
3486 <span class="highlight">metaclass =>
3487 'MooseX::Meta::Attribute::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>Traits vs Metaclass</h1>
3500 <li>Can apply any mix of traits to an attribute</li>
3501 <li>But just one metaclass</li>
3502 <li>Traits (aka roles) can cooperate</li>
3503 <li>Metaclasses require you to pick just one</li>
3508 <h1>Advanced Attributes Summary</h1>
3511 <li>Use <code>weak_ref</code> to avoid circular references</li>
3512 <li>Use trigger to do an action post-attribute write</li>
3513 <li>Use delegations to hide "internal" objects</li>
3514 <li>Traits and metaclasses let you extend Moose's core attribute features</li>
3526 # perl bin/prove -lv \
3527 t/06-advanced-attributes.t
3529 Iterate til this passes all its tests</pre>
3532 <div class="slide fake-slide0">
3533 <h1>Part 7: Introspection</h1>
3536 <div class="slide fake-slide0">
3537 <h1>Part 8: A Brief Tour of MooseX</h1>
3541 <h1>Notable Moose Extensions on CPAN</h1>
3544 <li><strong>Not comprehensive</strong></li>
3545 <li>128 MooseX distributions on CPAN as of 09/24/2009</li>
3546 <li>Some of them are crap</li>
3551 <h1>Already Mentioned Several</h1>
3554 <li>MooseX::NonMoose - best solution for subclassing non-Moose parents</li>
3555 <li>MooseX::Declare - <em>real</em> Perl 5 OO</li>
3556 <li>MooseX::FollowPBP and MooseX::SemiAffordanceAccessor</li>
3557 <li>MooseX::Params::Validate and MooseX::Method::Signatures</li>
3558 <li>MooseX::Types</li>
3563 <h1>MooseX::Declare</h1>
3565 <pre><code>use MooseX::Declare;
3566 use 5.10.0; # for say
3570 => ( is => 'ro', isa => 'Str' );
3573 say $self->greeting;
3579 <h1>MooseX::Declare</h1>
3582 <li>Still experimental-ish, but seeing more and more use</li>
3583 <li><strong>Not</strong> a source filter!</li>
3584 <li>Hooks into the Perl parser rather than filtering all your code</li>
3589 <h1>MooseX::StrictConstructor</h1>
3592 <li>By default, unknown constructor arguments are ignore</li>
3593 <li>MX::StrictConstructor turns these into an error</li>
3598 <h1>MooseX::StrictConstructor</h1>
3600 <pre><code>package Person;
3603 <span class="highlight">use MooseX::StrictConstructor;</span>
3605 has name => ( is => 'ro' );
3608 ( na<span class="wrong">n</span>e => 'Ringo Shiina' ); # kaboom</code></pre>
3612 <h1>MooseX::Traits</h1>
3615 <li>Combines object construction and role application</li>
3616 <li>Makes it easy to create one-off customized objects</li>
3621 <h1>MooseX::Traits</h1>
3623 <pre><code>package MyApp::Thingy;
3626 <span class="highlight">with 'MooseX::Traits';</span>
3629 MyApp::Thingy-><span class="highlight">new_with_traits</span>
3630 ( <span class="highlight">traits => [ 'Foo', 'Bar' ],</span>
3631 size => 42 );</code></pre>
3635 <h1>MooseX::Getopt</h1>
3638 <li>Makes command-line interface programs easy!</li>
3639 <li>Construct an object from CLI arguments</li>
3644 <h1>MooseX::Getopt</h1>
3646 <pre><code>package App::CLI;
3649 <span class="highlight">with 'MooseX::Getopt';</span>
3652 ( is => 'ro', required => 1 );
3654 ( is => 'ro', isa => 'Str' );
3656 sub run { ... }</code></pre>
3660 <h1>MooseX::Getopt</h1>
3663 <li>Then call it like this:</li>
3666 <pre><code>#!/usr/bin/perl
3670 <span class="highlight">App::CLI->new_with_options()</span>->run();</code></pre>
3674 --filters compress \
3675 --filters sanitize</pre>
3679 <h1>MooseX::Clone</h1>
3681 <pre><code>package Person;
3684 <span class="highlight">with 'MooseX::Clone';</span>
3686 my $person = Person->new;
3687 my $clone = <span class="highlight">$person->clone;</span></code></pre>
3691 <h1>MooseX::NonMoose</h1>
3694 <li>Highly recommended for subclassing non-Moose parents</li>
3695 <li>Gets all the little annoying details right</li>
3700 <h1>MooseX::Role::Parameterized</h1>
3702 <pre><code>package HasCollection;
3703 use MooseX::Role::Parameterized;
3705 parameter type => ( isa => 'Str',
3706 default => 'Item' );
3710 my $type = 'ArrayRef[' . $p->type() . ']';
3711 has collection =>
3718 <h1>MooseX::Role::Parameterized</h1>
3720 <pre><code>package Person;
3723 with HasCollection => { type => 'Int' };</code></pre>
3730 <div class="slide fake-slide0">
3731 <h1>Part 9: Writing Moose Extensions</h1>
3734 <div class="slide fake-slide0">
3739 <h1>More Information</h1>
3742 <li><a href="http://moose.perl.org/">http://moose.perl.org/</a></li>
3743 <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>
3744 <li><a href="irc://irc.perl.org/#moose">irc://irc.perl.org/#moose</a></li>
3745 <li>mailing list - <a href="mailto:moose@perl.org">moose@perl.org</a></li>
3746 <li>Slides and exercises are in Moose's git repo:
3748 <span style="white-space: nowrap">git://jules.scsys.co.uk/gitmo/moose-presentations</span></li>
3758 Copyright 2009 David Rolsky. All Rights Reserved.
3760 This work is licensed under a Creative Commons Attribution-Share Alike
3761 3.0 United States License See
3762 http://creativecommons.org/licenses/by-sa/3.0/us/ for details.