5 Moose::Manual::Types - Moose's type system
9 Moose provides its own type system for attributes. You can also use
10 these types to validate method parameters with the help of a MooseX
13 Moose's type system is based on a combination of Perl 5's own
14 I<implicit> types and some Perl 6 concepts. You can easily create your
15 own subtypes with custom constraints, making it easy to express any
18 Types have names, and you can re-use them by name, making it easy to
19 share types throughout a large application.
21 Let us be clear that is not a "real" type system. Moose does not
22 magically make Perl start associating types with variables. This is
23 just an advanced parameter checking system which allows you to
24 associate a name with a constraint.
26 That said, it's still pretty damn useful, and we think it's one of the
27 things that makes Moose both fun and powerful. Taking advantage of the
28 type system makes it much easier to ensure that you are getting valid
29 data, and it also contributes greatly to code maintainability.
33 The basic Moose type hierarchy looks like this
58 In practice, the only difference between C<Any> and C<Item> is
59 conceptual. C<Item> is used as the top-level type in the hierarchy.
61 The rest of these types correspond to existing Perl concepts. For
62 example, a C<Num> is anything that Perl thinks looks like a number, an
63 C<Object> is a blessed reference, etc.
65 The types followed by "[`a]" can be parameterized. So instead of just
66 plain C<ArrayRef> we can say that we want C<ArrayRef[Int]> instead. We
67 can even do something like C<HashRef[ArrayRef[Str]]>.
69 The C<Maybe[`a]> type deserves a special mention. Used by itself, it
70 doesn't really mean anything (and is equivalent to C<Item>). When it
71 is parameterized, it means that the value is either C<undef> or the
72 parameterized type. So C<Maybe[Int]> means an integer or C<undef>.
74 For more details on the type hierarchy, see
75 L<Moose::Util::TypeConstraints>.
77 =head1 WHAT IS A TYPE?
79 It's important to realize that types are not classes (or
80 packages). Types are just objects (L<Moose::Meta::TypeConstraint>
81 objects, to be exact) with a name and a constraint. Moose maintains a
82 global type registry that lets it convert names like C<Num> into the
85 However, class names I<can be> type names. When you define a new class
86 using Moose, it defines an associated type name behind the scenes:
92 Now you can use C<'MyApp::User'> as a type name:
99 However, for non-Moose classes there's no magic. You may have to
100 explicitly declare the class type. This is a bit muddled because Moose
101 assumes that any unknown type name passed as the C<isa> value for an
102 attribute is a class. So this works:
104 has 'birth_date' => (
109 In general, when Moose is presented with an unknown name, it assumes
110 that the name is a class:
112 subtype 'ModernDateTime'
114 => where { $_->year() >= 1980 }
115 => message { 'The date you provided is not modern enough' };
117 has 'valid_dates' => (
119 isa => 'ArrayRef[DateTime]',
122 Moose will assume that C<DateTime> is a class name in both of these
127 Moose uses subtypes in its built-in hierarchy. For example, C<Int> is
130 A subtype is defined in terms of a parent type and a constraint. Any
131 constraints defined by the parent(s) will be checked first, followed by
132 constraints defined by the subtype. A value must pass I<all> of these
133 checks to be valid for the subtype.
135 Typically, a subtype takes the parent's constraint and makes it more
138 A subtype can also define its own constraint failure message. This
139 lets you do things like have an error "The value you provided (20),
140 was not a valid rating, which must be a number from 1-10." This is
141 much friendlier than the default error, which just says that the value
142 failed a validation check for the type.
144 Here's a simple (and useful) subtype example:
146 subtype 'PositiveInt'
149 => message { "The number you provided, $_, was not a positive number" }
151 Note that the sugar functions for working with types are all exported
152 by L<Moose::Util::TypeConstraints>.
154 =head2 Creating a new type (that isn't a subtype)
156 You can also create new top-level types:
158 type 'FourCharacters' => where { defined $_ && length $_ == 4 };
160 In practice, this example is more or less the same as subtyping
161 C<Str>, except you have to check definedness yourself.
163 It's hard to find a case where you wouldn't want to subtype a very
164 broad type like C<Defined>, C<Ref> or C<Object>.
166 Defining a new top-level type is conceptually the same as subtyping
171 Type names are global throughout the current Perl
172 interpreter. Internally, Moose maps names to type objects via a
173 L<registry|Moose::Meta::TypeConstraint::Registry>.
175 If you have multiple apps or libraries all using Moose in the same
176 process, you could have problems with collisions. We recommend that
177 you prefix names with some sort of namespace indicator to prevent
178 these sorts of collisions.
180 For example, instead of calling a type "PositiveInt", call it
181 "MyApp::Type::PositiveInt" or "MyApp::Types::PositiveInt". We
182 recommend that you centralize all of these definitions in a single
183 package, C<MyApp::Types>, which can be loaded by other classes in your
186 Once you're doing this, you should almost certainly look at the
187 L<MooseX::Types> extension which allows easy declaration of type libraries
188 and can export your types as perl constants so that you can refer to them
191 has 'counter' => (is => 'rw', isa => PositiveInt);
193 rather than needing to fully qualify them everywhere. It also allows
195 has 'counts' => (is => 'ro', isa => HashRef[PositiveInt]);
197 and similarly for the union and other syntaxes discussed below, which
198 will compile time check your use of names and is generally more robust
199 than the string type parsing for complex cases.
203 One of the most powerful features of Moose's type system is its
204 coercions. A coercion is a way to convert from one type to another.
206 subtype 'ArrayRefOfInts'
207 => as 'ArrayRef[Int]';
209 coerce 'ArrayRefOfInts'
213 You'll note that we had to create a subtype rather than coercing
214 C<ArrayRef[Int]> directly. This is just a quirk of how Moose
217 Coercions, like type names, are global. This is I<another> reason why
218 it is good to namespace your types. Moose will I<never> try to coerce
219 a value unless you explicitly ask for it. This is done by setting the
220 C<coerce> attribute option to a true value:
226 isa => 'ArrayRefOfInts',
230 Foo->new( sizes => 42 );
232 This code example will do the right thing, and the newly created
233 object will have C<[ 42 ]> as its C<sizes> attribute.
237 Deep coercion is the coercion of type parameters for parameterized
238 types. Let's take these types as an example:
242 => where { /[a-f0-9]/i };
250 isa => 'ArrayRef[Int]',
254 If we try passing an array reference of hex numbers for the C<sizes>
255 attribute, Moose will not do any coercion.
257 However, you can define a set of subtypes to enable coercion between
258 two parameterized types.
260 subtype 'ArrayRefOfHexNums'
261 => as 'ArrayRef[HexNum]';
263 subtype 'ArrayRefOfInts'
264 => as 'ArrayRef[Int]';
266 coerce 'ArrayRefOfInts'
267 => from 'ArrayRefOfHexNums'
268 => via { [ map { hex } @{$_} ] };
270 Foo->new( sizes => [ 'a1', 'ff', '22' ] );
272 Now Moose will coerce the hex numbers to integers.
274 However, Moose does not attempt to chain coercions, so it will not
275 coerce a single hex number. To do that, we need to define a separate
278 coerce 'ArrayRefOfInts'
280 => via { [ hex $_ ] };
282 Yes, this can all get verbose, but coercion is tricky magic, and we
283 think it's best to make it explicit.
287 Moose allows you to say that an attribute can be of two or more
288 disparate types. For example, we might allow an C<Object> or
293 isa => 'Object | FileHandle',
296 Moose actually parses that string and recognizes that you are creating
297 a type union. The C<output> attribute will accept any sort of object,
298 as well as an unblessed file handle. It is up to you to do the right
299 thing for each of them in your code.
301 Whenever you use a type union, you should consider whether or not
302 coercion might be a better answer.
304 For our example above, we might want to be more specific, and insist
305 that output be an object with a C<print> method:
309 => where { $_->can('print') };
311 We can coerce file handles to an object that satisfies this condition
312 with a simple wrapper class:
325 my $fh = $self->handle();
330 Now we can define a coercion from C<FileHandle> to our wrapper class:
334 => via { FHWrapper->new( handle => $_ ) };
342 This pattern of using a coercion instead of a type union will help
343 make your class internals simpler.
345 =head1 TYPE CREATION HELPERS
347 The L<Moose::Util::TypeConstraints> module exports a number of helper
348 functions for creating specific kinds of types. These include
349 C<class_type>, C<role_type>, and C<maybe_type>. See the docs for
352 One helper worth noting is C<enum>, which allows you to create a
353 subtype of C<Str> that only allows the specified values:
355 enum 'RGB' => qw( red green blue );
357 This creates a type named C<RGB>.
359 =head1 ANONYMOUS TYPES
361 All of the type creation functions return a type object. This type
362 object can be used wherever you would use a type name, as a parent
363 type, or as the value for an attribute's C<isa> option:
367 isa => subtype 'Int' => where { $_ > 0 },
370 This is handy when you want to create a one-off type and don't want to
371 "pollute" the global namespace registry.
373 =head1 VALIDATING METHOD PARAMETERS
375 Moose does not provide any means of validating method
376 parameters. However, there are several MooseX extensions on CPAN which
379 The simplest and least sugary is L<MooseX::Params::Validate>. This
380 lets you validate a set of named parameters using Moose types:
383 use MooseX::Params::Validate;
387 my %params = validated_hash(
389 bar => { isa => 'Str', default => 'Moose' },
394 L<MooseX::Params::Validate> also supports coercions.
396 There are several more powerful extensions that support method
397 parameter validation using Moose types, including
398 L<MooseX::Method::Signatures>, which gives you a full-blown C<method>
401 method morning (Str $name) {
402 $self->say("Good morning ${name}!");
405 =head1 LOAD ORDER ISSUES
407 Because Moose types are defined at runtime, you may run into load
408 order problems. In particular, you may want to use a class's type
409 constraint before that type has been defined.
411 We have several recommendations for ameliorating this problem. First,
412 define I<all> of your custom types in one module,
413 C<MyApp::Types>. Second, load this module in all of your other
416 If you are still having load order problems, you can make use of the
417 C<find_type_constraint> function exported by
418 L<Moose::Util::TypeConstraints>:
420 class_type('MyApp::User')
421 unless find_type_constraint('MyApp::User');
423 This sort of "find or create" logic is simple to write, and will let
424 you work around load order issues.
428 Dave Rolsky E<lt>autarch@urth.orgE<gt>
430 =head1 COPYRIGHT AND LICENSE
432 Copyright 2009 by Infinity Interactive, Inc.
434 L<http://www.iinteractive.com>
436 This library is free software; you can redistribute it and/or modify
437 it under the same terms as Perl itself.