1Type::Coercion(3) User Contributed Perl Documentation Type::Coercion(3)
2
6 Type::Coercion - a set of coercions to a particular target type
7 constraint
8
10 This module is covered by the Type-Tiny stability policy.
11
13 Constructors
14 "new(%attributes)"
15 Moose-style constructor function.
16 "add($c1, $c2)"
18 Create a Type::Coercion from two existing Type::Coercion objects.
19 Attributes
21 Attributes are named values that may be passed to the constructor. For
22 each attribute, there is a corresponding reader method. For example:
23 my $c = Type::Coercion->new( type_constraint => Int );
25 my $t = $c->type_constraint; # Int
26 Important attributes
28 These are the attributes you are likely to be most interested in
30 providing when creating your own type coercions, and most interested in
31 reading when dealing with coercion objects.
32 "type_constraint"
34 Weak reference to the target type constraint (i.e. the type
35 constraint which the output of coercion coderefs is expected to
36 conform to).
37 "type_coercion_map"
39 Arrayref of source-type/code pairs.
40 "frozen"
42 Boolean; default false. A frozen coercion cannot have
43 "add_type_coercions" called upon it.
44 "name"
46 A name for the coercion. These need to conform to certain naming
47 rules (they must begin with an uppercase letter and continue using
48 only letters, digits 0-9 and underscores).
49 Optional; if not supplied will be an anonymous coercion.
51 "display_name"
53 A name to display for the coercion when stringified. These don't
54 have to conform to any naming rules. Optional; a default name will
55 be calculated from the "name".
56 "library"
58 The package name of the type library this coercion is associated
59 with. Optional. Informational only: setting this attribute does
60 not install the coercion into the package.
61 Attributes related to parameterizable and parameterized coercions
63 The following attributes are used for parameterized coercions, but are
65 not fully documented because they may change in the near future:
66 "coercion_generator"
68 "parameters"
69 "parameterized_from"
70 Lazy generated attributes
72 The following attributes should not be usually passed to the
74 constructor; unless you're doing something especially unusual, you
75 should rely on the default lazily-built return values.
76 "compiled_coercion"
78 Coderef to coerce a value ($_[0]).
79 The general point of this attribute is that you should not set it,
81 but rely on the lazily-built default. Type::Coerce will usually
82 generate a pretty fast coderef, inlining all type constraint
83 checks, etc.
84 "moose_coercion"
86 A Moose::Meta::TypeCoercion object equivalent to this one. Don't
87 set this manually; rely on the default built one.
88 Methods
90 Predicate methods
91 These methods return booleans indicating information about the
93 coercion. They are each tightly associated with a particular
94 attribute. (See "Attributes".)
95 "has_type_constraint", "has_library"
97 Simple Moose-style predicate methods indicating the presence or
98 absence of an attribute.
99 "is_anon"
101 Returns true iff the coercion does not have a "name".
102 The following predicates are used for parameterized coercions, but are
104 not fully documented because they may change in the near future:
105 "has_coercion_generator"
107 "has_parameters"
108 "is_parameterizable"
109 "is_parameterized"
110 Coercion
112 The following methods are used for coercing values to a type
114 constraint:
115 "coerce($value)"
117 Coerce the value to the target type.
118 Returns the coerced value, or the original value if no coercion was
120 possible.
121 "assert_coerce($value)"
123 Coerce the value to the target type, and throw an exception if the
124 result does not validate against the target type constraint.
125 Returns the coerced value.
127 Coercion code definition methods
129 These methods all return $self so are suitable for chaining.
131 "add_type_coercions($type1, $code1, ...)"
133 Takes one or more pairs of Type::Tiny constraints and coercion
134 code, creating an ordered list of source types and coercion codes.
135 Coercion codes can be expressed as either a string of Perl code
137 (this includes objects which overload stringification), or a
138 coderef (or object that overloads coderefification). In either
139 case, the value to be coerced is $_.
140 "add_type_coercions($coercion_object)" also works, and can be used
142 to copy coercions from another type constraint:
143 $type->coercion->add_type_coercions($othertype->coercion)->freeze;
145 "freeze"
147 Sets the "frozen" attribute to true. Called automatically by
148 Type::Tiny sometimes.
149 "i_really_want_to_unfreeze"
151 If you really want to unfreeze a coercion, call this method.
152 Don't call this method. It will potentially lead to subtle bugs.
154 This method is considered unstable; future versions of Type::Tiny
156 may alter its behaviour (e.g. to throw an exception if it has been
157 detected that unfreezing this particular coercion will cause bugs).
158 Parameterization
160 The following method is used for parameterized coercions, but is not
162 fully documented because it may change in the near future:
163 "parameterize(@params)"
165 Type coercion introspection methods
167 These methods allow you to determine a coercion's relationship to type
169 constraints:
170 "has_coercion_for_type($source_type)"
172 Returns true iff this coercion has a coercion from the source type.
173 Returns the special string "0 but true" if no coercion should
175 actually be necessary for this type. (For example, if a coercion
176 coerces to a theoretical "Number" type, there is probably no
177 coercion necessary for values that already conform to the "Integer"
178 type.)
179 "has_coercion_for_value($value)"
181 Returns true iff the value could be coerced by this coercion.
182 Returns the special string "0 but true" if no coercion would be
184 actually be necessary for this value (due to it already meeting the
185 target type constraint).
186 The "type_constraint" attribute provides a type constraint object for
188 the target type constraint of the coercion. See "Attributes".
189 Inlining methods
191 The following methods are used to generate strings of Perl code which
193 may be pasted into stringy "eval"uated subs to perform type coercions:
194 "can_be_inlined"
196 Returns true iff the coercion can be inlined.
197 "inline_coercion($varname)"
199 Much like "inline_coerce" from Type::Tiny.
200 Other methods
202 "qualified_name"
204 For non-anonymous coercions that have a library, returns a
205 qualified "MyLib::MyCoercion" sort of name. Otherwise, returns the
206 same as "name".
207 "isa($class)", "can($method)", "AUTOLOAD(@args)"
209 If Moose is loaded, then the combination of these methods is used
210 to mock a Moose::Meta::TypeCoercion.
211 The following methods exist for Moose/Mouse compatibility, but do not
213 do anything useful.
214 "compile_type_coercion"
216 "meta"
217 Overloading
219 · Boolification is overloaded to always return true.
220 · Coderefification is overloaded to call "coerce".
222 · On Perl 5.10.1 and above, smart match is overloaded to call
224 "has_coercion_for_value".
225 Previous versions of Type::Coercion would overload the "+" operator to
227 call "add". Support for this was dropped after 0.040.
228
230 Attempt to add coercion code to a Type::Coercion which has been frozen
231 Type::Tiny type constraints are designed as immutable objects. Once
232 you've created a constraint, rather than modifying it you generally
233 create child constraints to do what you need.
234 Type::Coercion objects, on the other hand, are mutable. Coercion
236 routines can be added at any time during the object's lifetime.
237 Sometimes Type::Tiny needs to freeze a Type::Coercion object to
239 prevent this. In Moose and Mouse code this is likely to happen as
240 soon as you use a type constraint in an attribute.
241 Workarounds:
243 · Define as many of your coercions as possible within type
245 libraries, not within the code that uses the type libraries.
246 The type library will be evaluated relatively early, likely
247 before there is any reason to freeze a coercion.
248 · If you do need to add coercions to a type within application
250 code outside the type library, instead create a subtype and add
251 coercions to that. The "plus_coercions" method provided by
252 Type::Tiny should make this simple.
253
255 Please report any bugs to
256 <http://rt.cpan.org/Dist/Display.html?Queue=Type-Tiny>.
257
259 Type::Tiny::Manual.
260 Type::Tiny, Type::Library, Type::Utils, Types::Standard.
262 Type::Coercion::Union.
264 Moose::Meta::TypeCoercion.
266
268 Toby Inkster <tobyink@cpan.org>.
269
271 This software is copyright (c) 2013-2014, 2017-2019 by Toby Inkster.
272 This is free software; you can redistribute it and/or modify it under
274 the same terms as the Perl 5 programming language system itself.
275
277 THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED
278 WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
279 MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
280perl v5.30.0 2019-07-26 Type::Coercion(3)