File Coverage

blib/lib/Moo.pm
Criterion Covered Total %
statement 154 156 98.7
branch 52 52 100.0
condition 25 31 80.6
subroutine 93 110 84.5
pod 0 2 0.0
total 324 351 92.3


line stmt bran cond sub pod time code
1             package Moo;
2 216     220   16659873 use strict;
  216         509  
  216         6635  
3 216     220   1109 use warnings;
  216         404  
  216         6115  
4 216     220   1035 no warnings 'once';
  216         478  
  216         9966  
5              
6 216         18176 use Moo::_Utils qw(
7             _check_tracked
8             _getglob
9             _getstash
10             _install_coderef
11             _install_modifier
12             _install_tracked
13             _linear_isa
14             _load_module
15             _set_loaded
16             _unimport_coderefs
17 216     220   59438 );
  216         505  
18 216     220   1406 use Carp qw(croak);
  216         398  
  216         12085  
19             BEGIN {
20 216     220   66410 our @CARP_NOT = qw(
21             Method::Generate::Constructor
22             Method::Generate::Accessor
23             Moo::sification
24             Moo::_Utils
25             Moo::Role
26             );
27             }
28              
29             our $VERSION = '2.005003';
30             $VERSION =~ tr/_//d;
31              
32             require Moo::sification;
33             Moo::sification->import;
34              
35             our %MAKERS;
36              
37             sub import {
38 780     784   1294995 my $target = caller;
39 780         1500 my $class = shift;
40 780 100 100     4121 if ($INC{'Role/Tiny.pm'} and Role::Tiny->is_role($target)) {
41 6         1165 croak "Cannot import Moo into a role";
42             }
43              
44 774         6254 _set_loaded(caller);
45              
46 774         4628 strict->import;
47 774         8875 warnings->import;
48              
49 774         2727 $class->_install_subs($target, @_);
50 774         2519 $class->make_class($target);
51 774         538040 return;
52             }
53              
54             sub make_class {
55 774     778 0 1648 my ($me, $target) = @_;
56              
57 774   100     3994 my $makers = $MAKERS{$target} ||= {};
58 774 100       2526 return $target if $makers->{is_class};
59              
60 770         2391 my $stash = _getstash($target);
61             $makers->{non_methods} = {
62 6468         16636 map +($_ => \&{"${target}::${_}"}),
63 770   66     12975 grep exists &{"${target}::${_}"},
  7414         14012  
64             grep !/::\z/ && !/\A\(/,
65             keys %$stash
66             };
67              
68 770         2344 $makers->{is_class} = 1;
69             {
70 216     220   1727 no strict 'refs';
  216         506  
  216         195593  
  770         1141  
71 766         13915 @{"${target}::ISA"} = do {
72 766         76181 require Moo::Object; ('Moo::Object');
  766         1747  
73 770 100       1274 } unless @{"${target}::ISA"};
  770         5288  
74             }
75 770 100 100     4330 if ($INC{'Moo/HandleMoose.pm'} && !$Moo::sification::disabled) {
76 68         331 Moo::HandleMoose::inject_fake_metaclass_for($target);
77             }
78 770         154084 return $target;
79             }
80              
81             sub is_class {
82 0     4 0 0 my ($me, $class) = @_;
83 0   0     0 return $MAKERS{$class} && $MAKERS{$class}{is_class};
84             }
85              
86             sub _install_subs {
87 774     778   1828 my ($me, $target) = @_;
88 774         2220 my %install = $me->_gen_subs($target);
89             _install_tracked $target => $_ => $install{$_}
90 774         7641 for sort keys %install;
91 774         2492 return;
92             }
93              
94             sub _gen_subs {
95 774     778   1641 my ($me, $target) = @_;
96             return (
97             extends => sub {
98 152     156   135684 $me->_set_superclasses($target, @_);
        156      
        154      
        146      
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        78      
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        60      
        60      
        42      
        42      
        26      
        0      
        0      
        0      
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        0      
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        0      
        0      
        0      
99 142         572 $me->_maybe_reset_handlemoose($target);
100 142         3498 return;
101             },
102             with => sub {
103 112     112   25832 require Moo::Role;
        112      
        106      
        94      
        78      
        60      
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        8      
104 112         1012 Moo::Role->apply_roles_to_package($target, @_);
105 100         5285 $me->_maybe_reset_handlemoose($target);
106             },
107             has => sub {
108 526     530   309397 my $name_proto = shift;
        530      
        524      
        466      
        350      
        286      
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109 526 100       2218 my @name_proto = ref $name_proto eq 'ARRAY' ? @$name_proto : $name_proto;
110 526 100       2198 if (@_ % 2 != 0) {
111 4         630 croak "Invalid options for " . join(', ', map "'$_'", @name_proto)
112             . " attribute(s): even number of arguments expected, got " . scalar @_;
113             }
114 522         2216 my %spec = @_;
115 522         1464 foreach my $name (@name_proto) {
116             # Note that when multiple attributes specified, each attribute
117             # needs a separate \%specs hashref
118 524 100       1614 my $spec_ref = @name_proto > 1 ? +{%spec} : \%spec;
119 524         2039 $me->_constructor_maker_for($target)
120             ->register_attribute_specs($name, $spec_ref);
121 508         2210 $me->_accessor_maker_for($target)
122             ->generate_method($target, $name, $spec_ref);
123 474         2012 $me->_maybe_reset_handlemoose($target);
124             }
125 472         8462 return;
126             },
127             (map {
128 774         9023 my $type = $_;
  2322         3728  
129             (
130             $type => sub {
131 26     66   8197 _install_modifier($target, $type, @_);
        66      
        60      
        54      
        52      
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        12      
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        0      
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        0      
        0      
        0      
132 24         3154 return;
133             },
134             )
135 2322         11309 } qw(before after around)),
136             );
137             }
138              
139             sub unimport {
140 16     16   463 my $target = caller;
141 16         57 _unimport_coderefs($target);
142             }
143              
144             sub _set_superclasses {
145 152     152   368 my $class = shift;
146 152         291 my $target = shift;
147 152         510 foreach my $superclass (@_) {
148 164         728 _load_module($superclass);
149 160 100 100     986 if ($INC{'Role/Tiny.pm'} && Role::Tiny->is_role($superclass)) {
150 4         910 croak "Can't extend role '$superclass'";
151             }
152             }
153 144         709 @{*{_getglob("${target}::ISA")}} = @_;
  144         198  
  144         543  
154 144 100       2430 if (my $old = delete $Moo::MAKERS{$target}{constructor}) {
    100          
155 6         30 $old->assert_constructor;
156 4         14 delete _getstash($target)->{new};
157             Moo->_constructor_maker_for($target)
158 4         20 ->register_attribute_specs(%{$old->all_attribute_specs});
  4         14  
159             }
160             elsif (!$target->isa('Moo::Object')) {
161 44         174 Moo->_constructor_maker_for($target);
162             }
163 142 100       1196 $Moo::HandleMoose::MOUSE{$target} = [
164             grep defined, map Mouse::Util::find_meta($_), @_
165             ] if Mouse::Util->can('find_meta');
166             }
167              
168             sub _maybe_reset_handlemoose {
169 716     716   1669 my ($class, $target) = @_;
170 716 100 100     7896 if ($INC{'Moo/HandleMoose.pm'} && !$Moo::sification::disabled) {
171 116         464 Moo::HandleMoose::maybe_reinject_fake_metaclass_for($target);
172             }
173             }
174              
175             sub _accessor_maker_for {
176 1372     1372   3098 my ($class, $target) = @_;
177 1372 100       3728 return unless $MAKERS{$target};
178 1360   66     6337 $MAKERS{$target}{accessor} ||= do {
179 682         1042 my $maker_class = do {
180 216     220   1810 no strict 'refs';
  216         487  
  216         80375  
181 682 100       1005 if (my $m = do {
182 682         985 my @isa = @{_linear_isa($target)};
  682         4261  
183 682         1311 shift @isa;
184 682 100       1542 if (my ($parent_new) = grep +(defined &{$_.'::new'}), @isa) {
  844         4297  
185 672 100       3152 $MAKERS{$parent_new} && $MAKERS{$parent_new}{accessor};
186             }
187             else {
188 10         29 undef;
189             }
190             }) {
191 76         198 ref($m);
192             } else {
193 606         77171 require Method::Generate::Accessor;
194 606         1879 'Method::Generate::Accessor'
195             }
196             };
197 682         5586 $maker_class->new;
198             }
199             }
200              
201             sub _constructor_maker_for {
202 984     984   76922 my ($class, $target) = @_;
203 984 100       3255 return unless $MAKERS{$target};
204 962   66     4120 $MAKERS{$target}{constructor} ||= do {
205 662         86600 require Method::Generate::Constructor;
206              
207 662         2811 my %construct_opts = (
208             package => $target,
209             accessor_generator => $class->_accessor_maker_for($target),
210             subconstructor_handler => (
211             ' if ($Moo::MAKERS{$class}) {'."\n"
212             .' if ($Moo::MAKERS{$class}{constructor}) {'."\n"
213             .' package '.$target.';'."\n"
214             .' return $invoker->SUPER::new(@_);'."\n"
215             .' }'."\n"
216             .' '.$class.'->_constructor_maker_for($class);'."\n"
217             .' return $invoker->new(@_)'.";\n"
218             .' } elsif ($INC{"Moose.pm"} and my $meta = Class::MOP::get_metaclass_by_name($class)) {'."\n"
219             .' return $meta->new_object('."\n"
220             .' $class->can("BUILDARGS") ? $class->BUILDARGS(@_)'."\n"
221             .' : $class->Moo::Object::BUILDARGS(@_)'."\n"
222             .' );'."\n"
223             .' }'."\n"
224             ),
225             );
226              
227 662         1477 my $con;
228 662         1085 my @isa = @{_linear_isa($target)};
  662         2689  
229 662         1199 shift @isa;
230 216     220   2248 no strict 'refs';
  216         472  
  216         69492  
231 662 100       1429 if (my ($parent_new) = grep +(defined &{$_.'::new'}), @isa) {
  826         4925  
232 658 100       2845 if ($parent_new eq 'Moo::Object') {
    100          
    100          
233             # no special constructor needed
234             }
235             elsif (my $makers = $MAKERS{$parent_new}) {
236 80         180 $con = $makers->{constructor};
237 80 100       429 $construct_opts{construction_string} = $con->construction_string
238             if $con;
239             }
240             elsif ($parent_new->can('BUILDALL')) {
241             $construct_opts{construction_builder} = sub {
242 14 100   14   94 my $inv = $target->can('BUILDARGS') ? '' : 'Moo::Object::';
243 14         140 'do {'
244             .' my $args = $class->'.$inv.'BUILDARGS(@_);'
245             .' $args->{__no_BUILD__} = 1;'
246             .' $invoker->'.$target.'::SUPER::new($args);'
247             .'}'
248 14         109 };
249             }
250             else {
251             $construct_opts{construction_builder} = sub {
252 24 100   24   292 '$invoker->'.$target.'::SUPER::new('
253             .($target->can('FOREIGNBUILDARGS') ?
254             '$class->FOREIGNBUILDARGS(@_)' : '@_')
255             .')'
256 28         251 };
257             }
258             }
259             ($con ? ref($con) : 'Method::Generate::Constructor')
260             ->new(%construct_opts)
261             ->install_delayed
262 662 100       10991 ->register_attribute_specs(%{$con?$con->all_attribute_specs:{}})
  652 100       3278  
263             }
264             }
265              
266             sub _concrete_methods_of {
267 82     82   686 my ($me, $class) = @_;
268 82         247 my $makers = $MAKERS{$class};
269              
270 82   100     347 my $non_methods = $makers->{non_methods} || {};
271 82         409 my $stash = _getstash($class);
272              
273             my $subs = {
274             map {;
275 216     220   1724 no strict 'refs';
  216         487  
  216         51849  
276 838         961 ${"${class}::${_}"} = ${"${class}::${_}"};
  838         2969  
  838         1524  
277 838         889 ($_ => \&{"${class}::${_}"});
  838         2136  
278             }
279 82         780 grep exists &{"${class}::${_}"},
  1183         2351  
280             grep !/::\z/,
281             keys %$stash
282             };
283              
284 82         773 my %tracked = map +($_ => 1), _check_tracked($class, [ keys %$subs ]);
285              
286             return {
287 380         1536 map +($_ => \&{"${class}::${_}"}),
288             grep !($non_methods->{$_} && $non_methods->{$_} == $subs->{$_}),
289 82   100     1058 grep !exists $tracked{$_},
290             keys %$subs
291             };
292             }
293              
294             1;
295             __END__
296              
297             =pod
298              
299             =encoding utf-8
300              
301             =head1 NAME
302              
303             Moo - Minimalist Object Orientation (with Moose compatibility)
304              
305             =head1 SYNOPSIS
306              
307             package Cat::Food;
308              
309             use Moo;
310             use strictures 2;
311             use namespace::clean;
312              
313             sub feed_lion {
314             my $self = shift;
315             my $amount = shift || 1;
316              
317             $self->pounds( $self->pounds - $amount );
318             }
319              
320             has taste => (
321             is => 'ro',
322             );
323              
324             has brand => (
325             is => 'ro',
326             isa => sub {
327             die "Only SWEET-TREATZ supported!" unless $_[0] eq 'SWEET-TREATZ'
328             },
329             );
330              
331             has pounds => (
332             is => 'rw',
333             isa => sub { die "$_[0] is too much cat food!" unless $_[0] < 15 },
334             );
335              
336             1;
337              
338             And elsewhere:
339              
340             my $full = Cat::Food->new(
341             taste => 'DELICIOUS.',
342             brand => 'SWEET-TREATZ',
343             pounds => 10,
344             );
345              
346             $full->feed_lion;
347              
348             say $full->pounds;
349              
350             =head1 DESCRIPTION
351              
352             C<Moo> is an extremely light-weight Object Orientation system. It allows one to
353             concisely define objects and roles with a convenient syntax that avoids the
354             details of Perl's object system. C<Moo> contains a subset of L<Moose> and is
355             optimised for rapid startup.
356              
357             C<Moo> avoids depending on any XS modules to allow for simple deployments. The
358             name C<Moo> is based on the idea that it provides almost -- but not quite --
359             two thirds of L<Moose>. As such, the L<Moose::Manual> can serve as an effective
360             guide to C<Moo> aside from the MOP and Types sections.
361              
362             Unlike L<Mouse> this module does not aim at full compatibility with
363             L<Moose>'s surface syntax, preferring instead to provide full interoperability
364             via the metaclass inflation capabilities described in L</MOO AND MOOSE>.
365              
366             For a full list of the minor differences between L<Moose> and L<Moo>'s surface
367             syntax, see L</INCOMPATIBILITIES WITH MOOSE>.
368              
369             =head1 WHY MOO EXISTS
370              
371             If you want a full object system with a rich Metaprotocol, L<Moose> is
372             already wonderful.
373              
374             But if you don't want to use L<Moose>, you may not want "less metaprotocol"
375             like L<Mouse> offers, but you probably want "no metaprotocol", which is what
376             Moo provides. C<Moo> is ideal for some situations where deployment or startup
377             time precludes using L<Moose> and L<Mouse>:
378              
379             =over 2
380              
381             =item a command line or CGI script where fast startup is essential
382              
383             =item code designed to be deployed as a single file via L<App::FatPacker>
384              
385             =item a CPAN module that may be used by others in the above situations
386              
387             =back
388              
389             C<Moo> maintains transparent compatibility with L<Moose> so if you install and
390             load L<Moose> you can use Moo classes and roles in L<Moose> code without
391             modification.
392              
393             Moo -- Minimal Object Orientation -- aims to make it smooth to upgrade to
394             L<Moose> when you need more than the minimal features offered by Moo.
395              
396             =head1 MOO AND MOOSE
397              
398             If L<Moo> detects L<Moose> being loaded, it will automatically register
399             metaclasses for your L<Moo> and L<Moo::Role> packages, so you should be able
400             to use them in L<Moose> code without modification.
401              
402             L<Moo> will also create L<Moose type constraints|Moose::Manual::Types> for
403             L<Moo> classes and roles, so that in Moose classes C<< isa => 'MyMooClass' >>
404             and C<< isa => 'MyMooRole' >> work the same as for L<Moose> classes and roles.
405              
406             Extending a L<Moose> class or consuming a L<Moose::Role> will also work.
407              
408             Extending a L<Mouse> class or consuming a L<Mouse::Role> will also work. But
409             note that we don't provide L<Mouse> metaclasses or metaroles so the other way
410             around doesn't work. This feature exists for L<Any::Moose> users porting to
411             L<Moo>; enabling L<Mouse> users to use L<Moo> classes is not a priority for us.
412              
413             This means that there is no need for anything like L<Any::Moose> for Moo
414             code - Moo and Moose code should simply interoperate without problem. To
415             handle L<Mouse> code, you'll likely need an empty Moo role or class consuming
416             or extending the L<Mouse> stuff since it doesn't register true L<Moose>
417             metaclasses like L<Moo> does.
418              
419             If you need to disable the metaclass creation, add:
420              
421             no Moo::sification;
422              
423             to your code before Moose is loaded, but bear in mind that this switch is
424             global and turns the mechanism off entirely so don't put this in library code.
425              
426             =head1 MOO AND CLASS::XSACCESSOR
427              
428             If a new enough version of L<Class::XSAccessor> is available, it will be used
429             to generate simple accessors, readers, and writers for better performance.
430             Simple accessors are those without lazy defaults, type checks/coercions, or
431             triggers. Simple readers are those without lazy defaults. Readers and writers
432             generated by L<Class::XSAccessor> will behave slightly differently: they will
433             reject attempts to call them with the incorrect number of parameters.
434              
435             =head1 MOO VERSUS ANY::MOOSE
436              
437             L<Any::Moose> will load L<Mouse> normally, and L<Moose> in a program using
438             L<Moose> - which theoretically allows you to get the startup time of L<Mouse>
439             without disadvantaging L<Moose> users.
440              
441             Sadly, this doesn't entirely work, since the selection is load order dependent
442             - L<Moo>'s metaclass inflation system explained above in L</MOO AND MOOSE> is
443             significantly more reliable.
444              
445             So if you want to write a CPAN module that loads fast or has only pure perl
446             dependencies but is also fully usable by L<Moose> users, you should be using
447             L<Moo>.
448              
449             For a full explanation, see the article
450             L<https://shadow.cat/blog/matt-s-trout/moo-versus-any-moose> which explains
451             the differing strategies in more detail and provides a direct example of
452             where L<Moo> succeeds and L<Any::Moose> fails.
453              
454             =head1 PUBLIC METHODS
455              
456             Moo provides several methods to any class using it.
457              
458             =head2 new
459              
460             Foo::Bar->new( attr1 => 3 );
461              
462             or
463              
464             Foo::Bar->new({ attr1 => 3 });
465              
466             The constructor for the class. By default it will accept attributes either as a
467             hashref, or a list of key value pairs. This can be customized with the
468             L</BUILDARGS> method.
469              
470             =head2 does
471              
472             if ($foo->does('Some::Role1')) {
473             ...
474             }
475              
476             Returns true if the object composes in the passed role.
477              
478             =head2 DOES
479              
480             if ($foo->DOES('Some::Role1') || $foo->DOES('Some::Class1')) {
481             ...
482             }
483              
484             Similar to L</does>, but will also return true for both composed roles and
485             superclasses.
486              
487             =head2 meta
488              
489             my $meta = Foo::Bar->meta;
490             my @methods = $meta->get_method_list;
491              
492             Returns an object that will behave as if it is a
493             L<Moose metaclass|Moose::Meta::Class> object for the class. If you call
494             anything other than C<make_immutable> on it, the object will be transparently
495             upgraded to a genuine L<Moose::Meta::Class> instance, loading Moose in the
496             process if required. C<make_immutable> itself is a no-op, since we generate
497             metaclasses that are already immutable, and users converting from Moose had
498             an unfortunate tendency to accidentally load Moose by calling it.
499              
500             =head1 LIFECYCLE METHODS
501              
502             There are several methods that you can define in your class to control
503             construction and destruction of objects. They should be used rather than trying
504             to modify C<new> or C<DESTROY> yourself.
505              
506             =head2 BUILDARGS
507              
508             around BUILDARGS => sub {
509             my ( $orig, $class, @args ) = @_;
510              
511             return { attr1 => $args[0] }
512             if @args == 1 && !ref $args[0];
513              
514             return $class->$orig(@args);
515             };
516              
517             Foo::Bar->new( 3 );
518              
519             This class method is used to transform the arguments to C<new> into a hash
520             reference of attribute values.
521              
522             The default implementation accepts a hash or hash reference of named parameters.
523             If it receives a single argument that isn't a hash reference it will throw an
524             error.
525              
526             You can override this method in your class to handle other types of options
527             passed to the constructor.
528              
529             This method should always return a hash reference of named options.
530              
531             =head2 FOREIGNBUILDARGS
532              
533             sub FOREIGNBUILDARGS {
534             my ( $class, $options ) = @_;
535             return $options->{foo};
536             }
537              
538             If you are inheriting from a non-Moo class, the arguments passed to the parent
539             class constructor can be manipulated by defining a C<FOREIGNBUILDARGS> method.
540             It will receive the same arguments as L</BUILDARGS>, and should return a list
541             of arguments to pass to the parent class constructor.
542              
543             =head2 BUILD
544              
545             sub BUILD {
546             my ($self, $args) = @_;
547             die "foo and bar cannot be used at the same time"
548             if exists $args->{foo} && exists $args->{bar};
549             }
550              
551             On object creation, any C<BUILD> methods in the class's inheritance hierarchy
552             will be called on the object and given the results of L</BUILDARGS>. They each
553             will be called in order from the parent classes down to the child, and thus
554             should not themselves call the parent's method. Typically this is used for
555             object validation or possibly logging.
556              
557             =head2 DEMOLISH
558              
559             sub DEMOLISH {
560             my ($self, $in_global_destruction) = @_;
561             ...
562             }
563              
564             When an object is destroyed, any C<DEMOLISH> methods in the inheritance
565             hierarchy will be called on the object. They are given boolean to inform them
566             if global destruction is in progress, and are called from the child class upwards
567             to the parent. This is similar to L</BUILD> methods but in the opposite order.
568              
569             Note that this is implemented by a C<DESTROY> method, which is only created on
570             on the first construction of an object of your class. This saves on overhead for
571             classes that are never instantiated or those without C<DEMOLISH> methods. If you
572             try to define your own C<DESTROY>, this will cause undefined results.
573              
574             =head1 IMPORTED SUBROUTINES
575              
576             =head2 extends
577              
578             extends 'Parent::Class';
579              
580             Declares a base class. Multiple superclasses can be passed for multiple
581             inheritance but please consider using L<roles|Moo::Role> instead. The class
582             will be loaded but no errors will be triggered if the class can't be found and
583             there are already subs in the class.
584              
585             Calling extends more than once will REPLACE your superclasses, not add to
586             them like 'use base' would.
587              
588             =head2 with
589              
590             with 'Some::Role1';
591              
592             or
593              
594             with 'Some::Role1', 'Some::Role2';
595              
596             Composes one or more L<Moo::Role> (or L<Role::Tiny>) roles into the current
597             class. An error will be raised if these roles cannot be composed because they
598             have conflicting method definitions. The roles will be loaded using the same
599             mechanism as C<extends> uses.
600              
601             =head2 has
602              
603             has attr => (
604             is => 'ro',
605             );
606              
607             Declares an attribute for the class.
608              
609             package Foo;
610             use Moo;
611             has 'attr' => (
612             is => 'ro'
613             );
614              
615             package Bar;
616             use Moo;
617             extends 'Foo';
618             has '+attr' => (
619             default => sub { "blah" },
620             );
621              
622             Using the C<+> notation, it's possible to override an attribute.
623              
624             has [qw(attr1 attr2 attr3)] => (
625             is => 'ro',
626             );
627              
628             Using an arrayref with multiple attribute names, it's possible to declare
629             multiple attributes with the same options.
630              
631             The options for C<has> are as follows:
632              
633             =over 2
634              
635             =item C<is>
636              
637             B<required>, may be C<ro>, C<lazy>, C<rwp> or C<rw>.
638              
639             C<ro> stands for "read-only" and generates an accessor that dies if you attempt
640             to write to it - i.e. a getter only - by defaulting C<reader> to the name of
641             the attribute.
642              
643             C<lazy> generates a reader like C<ro>, but also sets C<lazy> to 1 and
644             C<builder> to C<_build_${attribute_name}> to allow on-demand generated
645             attributes. This feature was my attempt to fix my incompetence when
646             originally designing C<lazy_build>, and is also implemented by
647             L<MooseX::AttributeShortcuts>. There is, however, nothing to stop you
648             using C<lazy> and C<builder> yourself with C<rwp> or C<rw> - it's just that
649             this isn't generally a good idea so we don't provide a shortcut for it.
650              
651             C<rwp> stands for "read-write protected" and generates a reader like C<ro>, but
652             also sets C<writer> to C<_set_${attribute_name}> for attributes that are
653             designed to be written from inside of the class, but read-only from outside.
654             This feature comes from L<MooseX::AttributeShortcuts>.
655              
656             C<rw> stands for "read-write" and generates a normal getter/setter by
657             defaulting the C<accessor> to the name of the attribute specified.
658              
659             =item C<isa>
660              
661             Takes a coderef which is used to validate the attribute. Unlike L<Moose>, Moo
662             does not include a basic type system, so instead of doing C<< isa => 'Num' >>,
663             one should do
664              
665             use Scalar::Util qw(looks_like_number);
666             ...
667             isa => sub {
668             die "$_[0] is not a number!" unless looks_like_number $_[0]
669             },
670              
671             Note that the return value for C<isa> is discarded. Only if the sub dies does
672             type validation fail.
673              
674             L<Sub::Quote aware|/SUB QUOTE AWARE>
675              
676             Since L<Moo> does B<not> run the C<isa> check before C<coerce> if a coercion
677             subroutine has been supplied, C<isa> checks are not structural to your code
678             and can, if desired, be omitted on non-debug builds (although if this results
679             in an uncaught bug causing your program to break, the L<Moo> authors guarantee
680             nothing except that you get to keep both halves).
681              
682             If you want L<Moose> compatible or L<MooseX::Types> style named types, look at
683             L<Type::Tiny>.
684              
685             To cause your C<isa> entries to be automatically mapped to named
686             L<Moose::Meta::TypeConstraint> objects (rather than the default behaviour
687             of creating an anonymous type), set:
688              
689             $Moo::HandleMoose::TYPE_MAP{$isa_coderef} = sub {
690             require MooseX::Types::Something;
691             return MooseX::Types::Something::TypeName();
692             };
693              
694             Note that this example is purely illustrative; anything that returns a
695             L<Moose::Meta::TypeConstraint> object or something similar enough to it to
696             make L<Moose> happy is fine.
697              
698             =item C<coerce>
699              
700             Takes a coderef which is meant to coerce the attribute. The basic idea is to
701             do something like the following:
702              
703             coerce => sub {
704             $_[0] % 2 ? $_[0] : $_[0] + 1
705             },
706              
707             Note that L<Moo> will always execute your coercion: this is to permit
708             C<isa> entries to be used purely for bug trapping, whereas coercions are
709             always structural to your code. We do, however, apply any supplied C<isa>
710             check after the coercion has run to ensure that it returned a valid value.
711              
712             L<Sub::Quote aware|/SUB QUOTE AWARE>
713              
714             If the C<isa> option is a blessed object providing a C<coerce> or
715             C<coercion> method, then the C<coerce> option may be set to just C<1>.
716              
717             =item C<handles>
718              
719             Takes a string
720              
721             handles => 'RobotRole'
722              
723             Where C<RobotRole> is a L<role|Moo::Role> that defines an interface which
724             becomes the list of methods to handle.
725              
726             Takes a list of methods
727              
728             handles => [ qw( one two ) ]
729              
730             Takes a hashref
731              
732             handles => {
733             un => 'one',
734             }
735              
736             =item C<trigger>
737              
738             Takes a coderef which will get called any time the attribute is set. This
739             includes the constructor, but not default or built values. The coderef will be
740             invoked against the object with the new value as an argument.
741              
742             If you set this to just C<1>, it generates a trigger which calls the
743             C<_trigger_${attr_name}> method on C<$self>. This feature comes from
744             L<MooseX::AttributeShortcuts>.
745              
746             Note that Moose also passes the old value, if any; this feature is not yet
747             supported.
748              
749             L<Sub::Quote aware|/SUB QUOTE AWARE>
750              
751             =item C<default>
752              
753             Takes a coderef which will get called with $self as its only argument to
754             populate an attribute if no value for that attribute was supplied to the
755             constructor. Alternatively, if the attribute is lazy, C<default> executes when
756             the attribute is first retrieved if no value has yet been provided.
757              
758             If a simple scalar is provided, it will be inlined as a string. Any non-code
759             reference (hash, array) will result in an error - for that case instead use
760             a code reference that returns the desired value.
761              
762             Note that if your default is fired during new() there is no guarantee that
763             other attributes have been populated yet so you should not rely on their
764             existence.
765              
766             L<Sub::Quote aware|/SUB QUOTE AWARE>
767              
768             =item C<predicate>
769              
770             Takes a method name which will return true if an attribute has a value.
771              
772             If you set this to just C<1>, the predicate is automatically named
773             C<has_${attr_name}> if your attribute's name does not start with an
774             underscore, or C<_has_${attr_name_without_the_underscore}> if it does.
775             This feature comes from L<MooseX::AttributeShortcuts>.
776              
777             =item C<builder>
778              
779             Takes a method name which will be called to create the attribute - functions
780             exactly like default except that instead of calling
781              
782             $default->($self);
783              
784             Moo will call
785              
786             $self->$builder;
787              
788             The following features come from L<MooseX::AttributeShortcuts>:
789              
790             If you set this to just C<1>, the builder is automatically named
791             C<_build_${attr_name}>.
792              
793             If you set this to a coderef or code-convertible object, that variable will be
794             installed under C<$class::_build_${attr_name}> and the builder set to the same
795             name.
796              
797             =item C<clearer>
798              
799             Takes a method name which will clear the attribute.
800              
801             If you set this to just C<1>, the clearer is automatically named
802             C<clear_${attr_name}> if your attribute's name does not start with an
803             underscore, or C<_clear_${attr_name_without_the_underscore}> if it does.
804             This feature comes from L<MooseX::AttributeShortcuts>.
805              
806             B<NOTE:> If the attribute is C<lazy>, it will be regenerated from C<default> or
807             C<builder> the next time it is accessed. If it is not lazy, it will be C<undef>.
808              
809             =item C<lazy>
810              
811             B<Boolean>. Set this if you want values for the attribute to be grabbed
812             lazily. This is usually a good idea if you have a L</builder> which requires
813             another attribute to be set.
814              
815             =item C<required>
816              
817             B<Boolean>. Set this if the attribute must be passed on object instantiation.
818              
819             =item C<reader>
820              
821             The name of the method that returns the value of the attribute. If you like
822             Java style methods, you might set this to C<get_foo>
823              
824             =item C<writer>
825              
826             The value of this attribute will be the name of the method to set the value of
827             the attribute. If you like Java style methods, you might set this to
828             C<set_foo>.
829              
830             =item C<weak_ref>
831              
832             B<Boolean>. Set this if you want the reference that the attribute contains to
833             be weakened. Use this when circular references, which cause memory leaks, are
834             possible.
835              
836             =item C<init_arg>
837              
838             Takes the name of the key to look for at instantiation time of the object. A
839             common use of this is to make an underscored attribute have a non-underscored
840             initialization name. C<undef> means that passing the value in on instantiation
841             is ignored.
842              
843             =item C<moosify>
844              
845             Takes either a coderef or array of coderefs which is meant to transform the
846             given attributes specifications if necessary when upgrading to a Moose role or
847             class. You shouldn't need this by default, but is provided as a means of
848             possible extensibility.
849              
850             =back
851              
852             =head2 before
853              
854             before foo => sub { ... };
855              
856             See L<< Class::Method::Modifiers/before method(s) => sub { ... }; >> for full
857             documentation.
858              
859             =head2 around
860              
861             around foo => sub { ... };
862              
863             See L<< Class::Method::Modifiers/around method(s) => sub { ... }; >> for full
864             documentation.
865              
866             =head2 after
867              
868             after foo => sub { ... };
869              
870             See L<< Class::Method::Modifiers/after method(s) => sub { ... }; >> for full
871             documentation.
872              
873             =head1 SUB QUOTE AWARE
874              
875             L<Sub::Quote/quote_sub> allows us to create coderefs that are "inlineable,"
876             giving us a handy, XS-free speed boost. Any option that is L<Sub::Quote>
877             aware can take advantage of this.
878              
879             To do this, you can write
880              
881             use Sub::Quote;
882              
883             use Moo;
884             use namespace::clean;
885              
886             has foo => (
887             is => 'ro',
888             isa => quote_sub(q{ die "Not <3" unless $_[0] < 3 })
889             );
890              
891             which will be inlined as
892              
893             do {
894             local @_ = ($_[0]->{foo});
895             die "Not <3" unless $_[0] < 3;
896             }
897              
898             or to avoid localizing @_,
899              
900             has foo => (
901             is => 'ro',
902             isa => quote_sub(q{ my ($val) = @_; die "Not <3" unless $val < 3 })
903             );
904              
905             which will be inlined as
906              
907             do {
908             my ($val) = ($_[0]->{foo});
909             die "Not <3" unless $val < 3;
910             }
911              
912             See L<Sub::Quote> for more information, including how to pass lexical
913             captures that will also be compiled into the subroutine.
914              
915             =head1 CLEANING UP IMPORTS
916              
917             L<Moo> will not clean up imported subroutines for you; you will have
918             to do that manually. The recommended way to do this is to declare your
919             imports first, then C<use Moo>, then C<use namespace::clean>.
920             Anything imported before L<namespace::clean> will be scrubbed.
921             Anything imported or declared after will be still be available.
922              
923             package Record;
924              
925             use Digest::MD5 qw(md5_hex);
926              
927             use Moo;
928             use namespace::clean;
929              
930             has name => (is => 'ro', required => 1);
931             has id => (is => 'lazy');
932             sub _build_id {
933             my ($self) = @_;
934             return md5_hex($self->name);
935             }
936              
937             1;
938              
939             For example if you were to import these subroutines after
940             L<namespace::clean> like this
941              
942             use namespace::clean;
943              
944             use Digest::MD5 qw(md5_hex);
945             use Moo;
946              
947             then any C<Record> C<$r> would have methods such as C<< $r->md5_hex() >>,
948             C<< $r->has() >> and C<< $r->around() >> - almost certainly not what you
949             intend!
950              
951             L<Moo::Role>s behave slightly differently. Since their methods are
952             composed into the consuming class, they can do a little more for you
953             automatically. As long as you declare your imports before calling
954             C<use Moo::Role>, those imports and the ones L<Moo::Role> itself
955             provides will not be composed into consuming classes so there's usually
956             no need to use L<namespace::clean>.
957              
958             B<On L<namespace::autoclean>:> Older versions of L<namespace::autoclean> would
959             inflate Moo classes to full L<Moose> classes, losing the benefits of Moo. If
960             you want to use L<namespace::autoclean> with a Moo class, make sure you are
961             using version 0.16 or newer.
962              
963             =head1 INCOMPATIBILITIES WITH MOOSE
964              
965             =head2 TYPES
966              
967             There is no built-in type system. C<isa> is verified with a coderef; if you
968             need complex types, L<Type::Tiny> can provide types, type libraries, and
969             will work seamlessly with both L<Moo> and L<Moose>. L<Type::Tiny> can be
970             considered the successor to L<MooseX::Types> and provides a similar API, so
971             that you can write
972              
973             use Types::Standard qw(Int);
974             has days_to_live => (is => 'ro', isa => Int);
975              
976             =head2 API INCOMPATIBILITIES
977              
978             C<initializer> is not supported in core since the author considers it to be a
979             bad idea and Moose best practices recommend avoiding it. Meanwhile C<trigger> or
980             C<coerce> are more likely to be able to fulfill your needs.
981              
982             No support for C<super>, C<override>, C<inner>, or C<augment> - the author
983             considers augment to be a bad idea, and override can be translated:
984              
985             override foo => sub {
986             ...
987             super();
988             ...
989             };
990              
991             around foo => sub {
992             my ($orig, $self) = (shift, shift);
993             ...
994             $self->$orig(@_);
995             ...
996             };
997              
998             The C<dump> method is not provided by default. The author suggests loading
999             L<Devel::Dwarn> into C<main::> (via C<perl -MDevel::Dwarn ...> for example) and
1000             using C<< $obj->$::Dwarn() >> instead.
1001              
1002             L</default> only supports coderefs and plain scalars, because passing a hash
1003             or array reference as a default is almost always incorrect since the value is
1004             then shared between all objects using that default.
1005              
1006             C<lazy_build> is not supported; you are instead encouraged to use the
1007             C<< is => 'lazy' >> option supported by L<Moo> and
1008             L<MooseX::AttributeShortcuts>.
1009              
1010             C<auto_deref> is not supported since the author considers it a bad idea and
1011             it has been considered best practice to avoid it for some time.
1012              
1013             C<documentation> will show up in a L<Moose> metaclass created from your class
1014             but is otherwise ignored. Then again, L<Moose> ignores it as well, so this
1015             is arguably not an incompatibility.
1016              
1017             Since C<coerce> does not require C<isa> to be defined but L<Moose> does
1018             require it, the metaclass inflation for coerce alone is a trifle insane
1019             and if you attempt to subtype the result will almost certainly break.
1020              
1021             Handling of warnings: when you C<use Moo> we enable strict and warnings, in a
1022             similar way to Moose. The authors recommend the use of C<strictures>, which
1023             enables FATAL warnings, and several extra pragmas when used in development:
1024             L<indirect>, L<multidimensional>, and L<bareword::filehandles>.
1025              
1026             Additionally, L<Moo> supports a set of attribute option shortcuts intended to
1027             reduce common boilerplate. The set of shortcuts is the same as in the L<Moose>
1028             module L<MooseX::AttributeShortcuts> as of its version 0.009+. So if you:
1029              
1030             package MyClass;
1031             use Moo;
1032             use strictures 2;
1033              
1034             The nearest L<Moose> invocation would be:
1035              
1036             package MyClass;
1037              
1038             use Moose;
1039             use warnings FATAL => "all";
1040             use MooseX::AttributeShortcuts;
1041              
1042             or, if you're inheriting from a non-Moose class,
1043              
1044             package MyClass;
1045              
1046             use Moose;
1047             use MooseX::NonMoose;
1048             use warnings FATAL => "all";
1049             use MooseX::AttributeShortcuts;
1050              
1051             =head2 META OBJECT
1052              
1053             There is no meta object. If you need this level of complexity you need
1054             L<Moose> - Moo is small because it explicitly does not provide a metaprotocol.
1055             However, if you load L<Moose>, then
1056              
1057             Class::MOP::class_of($moo_class_or_role)
1058              
1059             will return an appropriate metaclass pre-populated by L<Moo>.
1060              
1061             =head2 IMMUTABILITY
1062              
1063             Finally, Moose requires you to call
1064              
1065             __PACKAGE__->meta->make_immutable;
1066              
1067             at the end of your class to get an inlined (i.e. not horribly slow)
1068             constructor. Moo does it automatically the first time ->new is called
1069             on your class. (C<make_immutable> is a no-op in Moo to ease migration.)
1070              
1071             An extension L<MooX::late> exists to ease translating Moose packages
1072             to Moo by providing a more Moose-like interface.
1073              
1074             =head1 COMPATIBILITY WITH OLDER PERL VERSIONS
1075              
1076             Moo is compatible with perl versions back to 5.6. When running on older
1077             versions, additional prerequisites will be required. If you are packaging a
1078             script with its dependencies, such as with L<App::FatPacker>, you will need to
1079             be certain that the extra prerequisites are included.
1080              
1081             =over 4
1082              
1083             =item L<MRO::Compat>
1084              
1085             Required on perl versions prior to 5.10.0.
1086              
1087             =item L<Devel::GlobalDestruction>
1088              
1089             Required on perl versions prior to 5.14.0.
1090              
1091             =back
1092              
1093             =head1 SUPPORT
1094              
1095             IRC: #moose on irc.perl.org
1096              
1097             =for :html
1098             L<(click for instant chatroom login)|https://chat.mibbit.com/#moose@irc.perl.org>
1099              
1100             Bugtracker: L<https://rt.cpan.org/Public/Dist/Display.html?Name=Moo>
1101              
1102             Git repository: L<git://github.com/moose/Moo.git>
1103              
1104             Git browser: L<https://github.com/moose/Moo>
1105              
1106             =head1 AUTHOR
1107              
1108             mst - Matt S. Trout (cpan:MSTROUT) <mst@shadowcat.co.uk>
1109              
1110             =head1 CONTRIBUTORS
1111              
1112             dg - David Leadbeater (cpan:DGL) <dgl@dgl.cx>
1113              
1114             frew - Arthur Axel "fREW" Schmidt (cpan:FREW) <frioux@gmail.com>
1115              
1116             hobbs - Andrew Rodland (cpan:ARODLAND) <arodland@cpan.org>
1117              
1118             jnap - John Napiorkowski (cpan:JJNAPIORK) <jjn1056@yahoo.com>
1119              
1120             ribasushi - Peter Rabbitson (cpan:RIBASUSHI) <ribasushi@cpan.org>
1121              
1122             chip - Chip Salzenberg (cpan:CHIPS) <chip@pobox.com>
1123              
1124             ajgb - Alex J. G. Burzyński (cpan:AJGB) <ajgb@cpan.org>
1125              
1126             doy - Jesse Luehrs (cpan:DOY) <doy at tozt dot net>
1127              
1128             perigrin - Chris Prather (cpan:PERIGRIN) <chris@prather.org>
1129              
1130             Mithaldu - Christian Walde (cpan:MITHALDU) <walde.christian@googlemail.com>
1131              
1132             ilmari - Dagfinn Ilmari Mannsåker (cpan:ILMARI) <ilmari@ilmari.org>
1133              
1134             tobyink - Toby Inkster (cpan:TOBYINK) <tobyink@cpan.org>
1135              
1136             haarg - Graham Knop (cpan:HAARG) <haarg@cpan.org>
1137              
1138             mattp - Matt Phillips (cpan:MATTP) <mattp@cpan.org>
1139              
1140             bluefeet - Aran Deltac (cpan:BLUEFEET) <bluefeet@gmail.com>
1141              
1142             bubaflub - Bob Kuo (cpan:BUBAFLUB) <bubaflub@cpan.org>
1143              
1144             ether = Karen Etheridge (cpan:ETHER) <ether@cpan.org>
1145              
1146             =head1 COPYRIGHT
1147              
1148             Copyright (c) 2010-2015 the Moo L</AUTHOR> and L</CONTRIBUTORS>
1149             as listed above.
1150              
1151             =head1 LICENSE
1152              
1153             This library is free software and may be distributed under the same terms
1154             as perl itself. See L<https://dev.perl.org/licenses/>.
1155              
1156             =cut