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1 | =pod |
2 | |
3 | =head1 NAME |
4 | |
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5 | Moose::Manual::Types - Moose's type system |
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6 | |
7 | =head1 TYPES IN PERL? |
8 | |
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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 |
11 | module. |
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12 | |
13 | Moose's type system is based on a combination of Perl 5's own |
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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 |
16 | sort of validation. |
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17 | |
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18 | Types have names, and you can re-use them by name, making it easy to |
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19 | share types throughout a large application. |
20 | |
21 | Let us be clear that is not a "real" type system. Moose does not |
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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. |
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25 | |
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. |
30 | |
31 | =head1 THE TYPES |
32 | |
33 | The basic Moose type hierarchy looks like this |
34 | |
35 | Any |
36 | Item |
37 | Bool |
38 | Maybe[`a] |
39 | Undef |
40 | Defined |
41 | Value |
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42 | Str |
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43 | Num |
44 | Int |
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45 | ClassName |
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46 | RoleName |
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47 | Ref |
48 | ScalarRef |
49 | ArrayRef[`a] |
50 | HashRef[`a] |
51 | CodeRef |
52 | RegexpRef |
53 | GlobRef |
54 | FileHandle |
55 | Object |
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56 | |
57 | In practice, the only difference between C<Any> and C<Item> is |
58 | conceptual. C<Item> is used as the top-level type in the hierarchy. |
59 | |
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60 | The rest of these types correspond to existing Perl concepts. |
61 | In particular: |
62 | |
63 | =over 4 |
64 | |
65 | =item C<Bool> accepts C<1> for true, and any value that perl treats as false for false. |
66 | |
67 | =item C<Maybe[`a]> accepts either C<`a> or C<undef>. |
68 | |
69 | =item C<Num> accepts anything that perl thinks looks like a number (see L<Scalar::Util/looks_like_number>). |
70 | |
71 | =item C<ClassName> and C<RoleName> accept strings that are either a the name of a class or the name of a role. The class/role must be loaded beforehand for this to succeed. |
72 | |
73 | =item C<FileHandle> accepts either an object of type L<IO::Handle> or a builtin perl filehandle (see L<Scalar::Util/openhandle>). |
74 | |
75 | =item C<Object> accepts any blessed reference. |
76 | |
77 | =back |
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78 | |
79 | The types followed by "[`a]" can be parameterized. So instead of just |
80 | plain C<ArrayRef> we can say that we want C<ArrayRef[Int]> instead. We |
81 | can even do something like C<HashRef[ArrayRef[Str]]>. |
82 | |
83 | The C<Maybe[`a]> type deserves a special mention. Used by itself, it |
84 | doesn't really mean anything (and is equivalent to C<Item>). When it |
85 | is parameterized, it means that the value is either C<undef> or the |
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86 | parameterized type. So C<Maybe[Int]> means an integer or C<undef>. |
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87 | |
88 | For more details on the type hierarchy, see |
89 | L<Moose::Util::TypeConstraints>. |
90 | |
91 | =head1 WHAT IS A TYPE? |
92 | |
93 | It's important to realize that types are not classes (or |
94 | packages). Types are just objects (L<Moose::Meta::TypeConstraint> |
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95 | objects, to be exact) with a name and a constraint. Moose maintains a |
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96 | global type registry that lets it convert names like C<Num> into the |
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97 | appropriate object. |
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98 | |
99 | However, class names I<can be> type names. When you define a new class |
100 | using Moose, it defines an associated type name behind the scenes: |
101 | |
102 | package MyApp::User; |
103 | |
104 | use Moose; |
105 | |
106 | Now you can use C<'MyApp::User'> as a type name: |
107 | |
108 | has creator => ( |
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109 | is => 'ro', |
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110 | isa => 'MyApp::User', |
111 | ); |
112 | |
113 | However, for non-Moose classes there's no magic. You may have to |
114 | explicitly declare the class type. This is a bit muddled because Moose |
115 | assumes that any unknown type name passed as the C<isa> value for an |
116 | attribute is a class. So this works: |
117 | |
118 | has 'birth_date' => ( |
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119 | is => 'ro', |
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120 | isa => 'DateTime', |
121 | ); |
122 | |
123 | In general, when Moose is presented with an unknown name, it assumes |
124 | that the name is a class: |
125 | |
126 | subtype 'ModernDateTime' |
127 | => as 'DateTime' |
128 | => where { $_->year() >= 1980 } |
129 | => message { 'The date you provided is not modern enough' }; |
130 | |
131 | has 'valid_dates' => ( |
132 | is => 'ro', |
133 | isa => 'ArrayRef[DateTime]', |
134 | ); |
135 | |
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136 | Moose will assume that C<DateTime> is a class name in both of these |
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137 | instances. |
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138 | |
139 | =head1 SUBTYPES |
140 | |
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141 | Moose uses subtypes in its built-in hierarchy. For example, C<Int> is |
142 | a child of C<Num>. |
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143 | |
144 | A subtype is defined in terms of a parent type and a constraint. Any |
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145 | constraints defined by the parent(s) will be checked first, followed by |
146 | constraints defined by the subtype. A value must pass I<all> of these |
147 | checks to be valid for the subtype. |
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148 | |
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149 | Typically, a subtype takes the parent's constraint and makes it more |
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150 | specific. |
151 | |
152 | A subtype can also define its own constraint failure message. This |
153 | lets you do things like have an error "The value you provided (20), |
154 | was not a valid rating, which must be a number from 1-10." This is |
155 | much friendlier than the default error, which just says that the value |
156 | failed a validation check for the type. |
157 | |
158 | Here's a simple (and useful) subtype example: |
159 | |
160 | subtype 'PositiveInt' |
161 | => as 'Int' |
162 | => where { $_ > 0 } |
163 | => message { "The number you provided, $_, was not a positive number" } |
164 | |
165 | Note that the sugar functions for working with types are all exported |
166 | by L<Moose::Util::TypeConstraints>. |
167 | |
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168 | =head2 Creating a new type (that isn't a subtype) |
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169 | |
170 | You can also create new top-level types: |
171 | |
172 | type 'FourCharacters' => where { defined $_ && length $_ == 4 }; |
173 | |
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174 | In practice, this example is more or less the same as subtyping |
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175 | C<Str>, except you have to check definedness yourself. |
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176 | |
177 | It's hard to find a case where you wouldn't want to subtype a very |
178 | broad type like C<Defined>, C<Ref> or C<Object>. |
179 | |
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180 | Defining a new top-level type is conceptually the same as subtyping |
181 | C<Item>. |
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182 | |
183 | =head1 TYPE NAMES |
184 | |
185 | Type names are global throughout the current Perl |
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186 | interpreter. Internally, Moose maps names to type objects via a |
187 | L<registry|Moose::Meta::TypeConstraint::Registry>. |
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188 | |
189 | If you have multiple apps or libraries all using Moose in the same |
190 | process, you could have problems with collisions. We recommend that |
191 | you prefix names with some sort of namespace indicator to prevent |
192 | these sorts of collisions. |
193 | |
194 | For example, instead of calling a type "PositiveInt", call it |
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195 | "MyApp::Type::PositiveInt" or "MyApp::Types::PositiveInt". We |
196 | recommend that you centralize all of these definitions in a single |
197 | package, C<MyApp::Types>, which can be loaded by other classes in your |
198 | application. |
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199 | |
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200 | Once you're doing this, you should almost certainly look at the |
201 | L<MooseX::Types> extension which allows easy declaration of type libraries |
202 | and can export your types as perl constants so that you can refer to them |
203 | as just |
204 | |
205 | has 'counter' => (is => 'rw', isa => PositiveInt); |
206 | |
207 | rather than needing to fully qualify them everywhere. It also allows |
208 | |
209 | has 'counts' => (is => 'ro', isa => HashRef[PositiveInt]); |
210 | |
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211 | and similarly for the union and other syntax discussed below, which |
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212 | will compile time check your use of names and is generally more robust |
213 | than the string type parsing for complex cases. |
214 | |
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215 | =head1 COERCION |
216 | |
217 | One of the most powerful features of Moose's type system is its |
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218 | coercions. A coercion is a way to convert from one type to another. |
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219 | |
220 | subtype 'ArrayRefOfInts' |
221 | => as 'ArrayRef[Int]'; |
222 | |
223 | coerce 'ArrayRefOfInts' |
224 | => from 'Int' |
225 | => via { [ $_ ] }; |
226 | |
227 | You'll note that we had to create a subtype rather than coercing |
228 | C<ArrayRef[Int]> directly. This is just a quirk of how Moose |
229 | works. |
230 | |
231 | Coercions, like type names, are global. This is I<another> reason why |
232 | it is good to namespace your types. Moose will I<never> try to coerce |
233 | a value unless you explicitly ask for it. This is done by setting the |
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234 | C<coerce> attribute option to a true value: |
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235 | |
236 | package Foo; |
237 | |
238 | has 'sizes' => ( |
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239 | is => 'ro', |
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240 | isa => 'ArrayRefOfInts', |
241 | coerce => 1, |
242 | ); |
243 | |
244 | Foo->new( sizes => 42 ); |
245 | |
246 | This code example will do the right thing, and the newly created |
247 | object will have C<[ 42 ]> as its C<sizes> attribute. |
248 | |
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249 | =head2 Deep coercion |
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250 | |
251 | Deep coercion is the coercion of type parameters for parameterized |
252 | types. Let's take these types as an example: |
253 | |
254 | subtype 'HexNum' |
255 | => as 'Str' |
256 | => where { /[a-f0-9]/i }; |
257 | |
258 | coerce 'Int' |
259 | => from 'HexNum' |
260 | => via { hex $_ }; |
261 | |
262 | has 'sizes' => ( |
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263 | is => 'ro', |
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264 | isa => 'ArrayRef[Int]', |
265 | coerce => 1, |
266 | ); |
267 | |
268 | If we try passing an array reference of hex numbers for the C<sizes> |
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269 | attribute, Moose will not do any coercion. |
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270 | |
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271 | However, you can define a set of subtypes to enable coercion between |
272 | two parameterized types. |
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273 | |
274 | subtype 'ArrayRefOfHexNums' |
275 | => as 'ArrayRef[HexNum]'; |
276 | |
277 | subtype 'ArrayRefOfInts' |
278 | => as 'ArrayRef[Int]'; |
279 | |
280 | coerce 'ArrayRefOfInts' |
281 | => from 'ArrayRefOfHexNums' |
282 | => via { [ map { hex } @{$_} ] }; |
283 | |
284 | Foo->new( sizes => [ 'a1', 'ff', '22' ] ); |
285 | |
286 | Now Moose will coerce the hex numbers to integers. |
287 | |
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288 | However, Moose does not attempt to chain coercions, so it will not |
289 | coerce a single hex number. To do that, we need to define a separate |
290 | coercion: |
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291 | |
292 | coerce 'ArrayRefOfInts' |
293 | => from 'HexNum' |
294 | => via { [ hex $_ ] }; |
295 | |
296 | Yes, this can all get verbose, but coercion is tricky magic, and we |
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297 | think it's best to make it explicit. |
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298 | |
299 | =head1 TYPE UNIONS |
300 | |
301 | Moose allows you to say that an attribute can be of two or more |
302 | disparate types. For example, we might allow an C<Object> or |
303 | C<FileHandle>: |
304 | |
305 | has 'output' => ( |
306 | is => 'rw', |
307 | isa => 'Object | FileHandle', |
308 | ); |
309 | |
310 | Moose actually parses that string and recognizes that you are creating |
311 | a type union. The C<output> attribute will accept any sort of object, |
312 | as well as an unblessed file handle. It is up to you to do the right |
313 | thing for each of them in your code. |
314 | |
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315 | Whenever you use a type union, you should consider whether or not |
316 | coercion might be a better answer. |
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317 | |
318 | For our example above, we might want to be more specific, and insist |
319 | that output be an object with a C<print> method: |
320 | |
321 | subtype 'CanPrint' |
322 | => as 'Object' |
323 | => where { $_->can('print') }; |
324 | |
325 | We can coerce file handles to an object that satisfies this condition |
326 | with a simple wrapper class: |
327 | |
328 | package FHWrapper; |
329 | |
330 | use Moose; |
331 | |
332 | has 'handle' => ( |
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333 | is => 'rw', |
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334 | isa => 'FileHandle', |
335 | ); |
336 | |
337 | sub print { |
338 | my $self = shift; |
339 | my $fh = $self->handle(); |
340 | |
341 | print $fh @_; |
342 | } |
343 | |
344 | Now we can define a coercion from C<FileHandle> to our wrapper class: |
345 | |
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346 | coerce 'CanPrint' |
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347 | => from 'FileHandle' |
348 | => via { FHWrapper->new( handle => $_ ) }; |
349 | |
350 | has 'output' => ( |
351 | is => 'rw', |
352 | isa => 'CanPrint', |
353 | coerce => 1, |
354 | ); |
355 | |
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356 | This pattern of using a coercion instead of a type union will help |
357 | make your class internals simpler. |
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358 | |
359 | =head1 TYPE CREATION HELPERS |
360 | |
361 | The L<Moose::Util::TypeConstraints> module exports a number of helper |
362 | functions for creating specific kinds of types. These include |
363 | C<class_type>, C<role_type>, and C<maybe_type>. See the docs for |
364 | details. |
365 | |
366 | One helper worth noting is C<enum>, which allows you to create a |
367 | subtype of C<Str> that only allows the specified values: |
368 | |
369 | enum 'RGB' => qw( red green blue ); |
370 | |
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371 | This creates a type named C<RGB>. |
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372 | |
373 | =head1 ANONYMOUS TYPES |
374 | |
375 | All of the type creation functions return a type object. This type |
376 | object can be used wherever you would use a type name, as a parent |
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377 | type, or as the value for an attribute's C<isa> option: |
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378 | |
379 | has 'size' => ( |
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380 | is => 'ro', |
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381 | isa => subtype('Int' => where { $_ > 0 }), |
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382 | ); |
383 | |
384 | This is handy when you want to create a one-off type and don't want to |
385 | "pollute" the global namespace registry. |
386 | |
387 | =head1 VALIDATING METHOD PARAMETERS |
388 | |
389 | Moose does not provide any means of validating method |
390 | parameters. However, there are several MooseX extensions on CPAN which |
391 | let you do this. |
392 | |
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393 | The simplest and least sugary is L<MooseX::Params::Validate>. This |
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394 | lets you validate a set of named parameters using Moose types: |
395 | |
396 | use Moose; |
397 | use MooseX::Params::Validate; |
398 | |
399 | sub foo { |
400 | my $self = shift; |
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401 | my %params = validated_hash( |
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402 | \@_, |
403 | bar => { isa => 'Str', default => 'Moose' }, |
404 | ); |
405 | ... |
406 | } |
407 | |
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408 | L<MooseX::Params::Validate> also supports coercions. |
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409 | |
410 | There are several more powerful extensions that support method |
411 | parameter validation using Moose types, including |
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412 | L<MooseX::Method::Signatures>, which gives you a full-blown C<method> |
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413 | keyword. |
414 | |
415 | method morning (Str $name) { |
416 | $self->say("Good morning ${name}!"); |
417 | } |
418 | |
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419 | =head1 LOAD ORDER ISSUES |
420 | |
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421 | Because Moose types are defined at runtime, you may run into load |
422 | order problems. In particular, you may want to use a class's type |
423 | constraint before that type has been defined. |
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424 | |
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425 | We have several recommendations for ameliorating this problem. First, |
426 | define I<all> of your custom types in one module, |
427 | C<MyApp::Types>. Second, load this module in all of your other |
428 | modules. |
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429 | |
430 | If you are still having load order problems, you can make use of the |
431 | C<find_type_constraint> function exported by |
432 | L<Moose::Util::TypeConstraints>: |
433 | |
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434 | class_type('MyApp::User') |
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435 | unless find_type_constraint('MyApp::User'); |
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436 | |
437 | This sort of "find or create" logic is simple to write, and will let |
438 | you work around load order issues. |
439 | |
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440 | =head1 AUTHOR |
441 | |
442 | Dave Rolsky E<lt>autarch@urth.orgE<gt> |
443 | |
444 | =head1 COPYRIGHT AND LICENSE |
445 | |
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446 | Copyright 2009 by Infinity Interactive, Inc. |
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447 | |
448 | L<http://www.iinteractive.com> |
449 | |
450 | This library is free software; you can redistribute it and/or modify |
451 | it under the same terms as Perl itself. |
452 | |
453 | =cut |