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
188 One of the most powerful features of Moose's type system is its
189 coercions. A coercion is a way to convert from one type to another.
191 subtype 'ArrayRefOfInts'
192 => as 'ArrayRef[Int]';
194 coerce 'ArrayRefOfInts'
198 You'll note that we had to create a subtype rather than coercing
199 C<ArrayRef[Int]> directly. This is just a quirk of how Moose
202 Coercions, like type names, are global. This is I<another> reason why
203 it is good to namespace your types. Moose will I<never> try to coerce
204 a value unless you explicitly ask for it. This is done by setting the
205 C<coerce> attribute option to a true value:
211 isa => 'ArrayRefOfInts',
215 Foo->new( sizes => 42 );
217 This code example will do the right thing, and the newly created
218 object will have C<[ 42 ]> as its C<sizes> attribute.
222 Deep coercion is the coercion of type parameters for parameterized
223 types. Let's take these types as an example:
227 => where { /[a-f0-9]/i };
235 isa => 'ArrayRef[Int]',
239 If we try passing an array reference of hex numbers for the C<sizes>
240 attribute, Moose will not do any coercion.
242 However, you can define a set of subtypes to enable coercion between
243 two parameterized types.
245 subtype 'ArrayRefOfHexNums'
246 => as 'ArrayRef[HexNum]';
248 subtype 'ArrayRefOfInts'
249 => as 'ArrayRef[Int]';
251 coerce 'ArrayRefOfInts'
252 => from 'ArrayRefOfHexNums'
253 => via { [ map { hex } @{$_} ] };
255 Foo->new( sizes => [ 'a1', 'ff', '22' ] );
257 Now Moose will coerce the hex numbers to integers.
259 However, Moose does not attempt to chain coercions, so it will not
260 coerce a single hex number. To do that, we need to define a separate
263 coerce 'ArrayRefOfInts'
265 => via { [ hex $_ ] };
267 Yes, this can all get verbose, but coercion is tricky magic, and we
268 think it's best to make it explicit.
272 Moose allows you to say that an attribute can be of two or more
273 disparate types. For example, we might allow an C<Object> or
278 isa => 'Object | FileHandle',
281 Moose actually parses that string and recognizes that you are creating
282 a type union. The C<output> attribute will accept any sort of object,
283 as well as an unblessed file handle. It is up to you to do the right
284 thing for each of them in your code.
286 Whenever you use a type union, you should consider whether or not
287 coercion might be a better answer.
289 For our example above, we might want to be more specific, and insist
290 that output be an object with a C<print> method:
294 => where { $_->can('print') };
296 We can coerce file handles to an object that satisfies this condition
297 with a simple wrapper class:
310 my $fh = $self->handle();
315 Now we can define a coercion from C<FileHandle> to our wrapper class:
319 => via { FHWrapper->new( handle => $_ ) };
327 This pattern of using a coercion instead of a type union will help
328 make your class internals simpler.
330 =head1 TYPE CREATION HELPERS
332 The L<Moose::Util::TypeConstraints> module exports a number of helper
333 functions for creating specific kinds of types. These include
334 C<class_type>, C<role_type>, and C<maybe_type>. See the docs for
337 One helper worth noting is C<enum>, which allows you to create a
338 subtype of C<Str> that only allows the specified values:
340 enum 'RGB' => qw( red green blue );
342 This creates a type named C<RGB>.
344 =head1 ANONYMOUS TYPES
346 All of the type creation functions return a type object. This type
347 object can be used wherever you would use a type name, as a parent
348 type, or as the value for an attribute's C<isa> option:
352 isa => subtype 'Int' => where { $_ > 0 },
355 This is handy when you want to create a one-off type and don't want to
356 "pollute" the global namespace registry.
358 =head1 VALIDATING METHOD PARAMETERS
360 Moose does not provide any means of validating method
361 parameters. However, there are several MooseX extensions on CPAN which
364 The simplest and least sugary is L<MooseX::Params::Validate>. This
365 lets you validate a set of named parameters using Moose types:
368 use MooseX::Params::Validate;
372 my %params = validated_hash(
374 bar => { isa => 'Str', default => 'Moose' },
379 L<MooseX::Params::Validate> also supports coercions.
381 There are several more powerful extensions that support method
382 parameter validation using Moose types, including
383 L<MooseX::Method::Signatures>, which gives you a full-blown C<method>
386 method morning (Str $name) {
387 $self->say("Good morning ${name}!");
390 =head1 LOAD ORDER ISSUES
392 Because Moose types are defined at runtime, you may run into load
393 order problems. In particular, you may want to use a class's type
394 constraint before that type has been defined.
396 We have several recommendations for ameliorating this problem. First,
397 define I<all> of your custom types in one module,
398 C<MyApp::Types>. Second, load this module in all of your other
401 If you are still having load order problems, you can make use of the
402 C<find_type_constraint> function exported by
403 L<Moose::Util::TypeConstraints>:
405 class_type('MyApp::User')
406 unless find_type_constraint('MyApp::User');
408 This sort of "find or create" logic is simple to write, and will let
409 you work around load order issues.
413 Dave Rolsky E<lt>autarch@urth.orgE<gt>
415 =head1 COPYRIGHT AND LICENSE
417 Copyright 2009 by Infinity Interactive, Inc.
419 L<http://www.iinteractive.com>
421 This library is free software; you can redistribute it and/or modify
422 it under the same terms as Perl itself.