1MooseX::AttributeShortcUustesr(3C)ontributed Perl DocumeMnotoasteiXo:n:AttributeShortcuts(3)
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NAME

6       MooseX::AttributeShortcuts - Shorthand for common attribute options
7

VERSION

9       This document describes version 0.037 of MooseX::AttributeShortcuts -
10       released November 20, 2017 as part of MooseX-AttributeShortcuts.
11

SYNOPSIS

13           package Some::Class;
14
15           use Moose;
16           use MooseX::AttributeShortcuts;
17
18           # same as:
19           #   is => 'ro', lazy => 1, builder => '_build_foo'
20           has foo => (is => 'lazy');
21
22           # same as: is => 'ro', writer => '_set_foo'
23           has foo => (is => 'rwp');
24
25           # same as: is => 'ro', builder => '_build_bar'
26           has bar => (is => 'ro', builder => 1);
27
28           # same as: is => 'ro', clearer => 'clear_bar'
29           has bar => (is => 'ro', clearer => 1);
30
31           # same as: is => 'ro', predicate => 'has_bar'
32           has bar => (is => 'ro', predicate => 1);
33
34           # works as you'd expect for "private": predicate => '_has_bar'
35           has _bar => (is => 'ro', predicate => 1);
36
37           # extending? Use the "Shortcuts" trait alias
38           extends 'Some::OtherClass';
39           has '+bar' => (traits => [Shortcuts], builder => 1, ...);
40

DESCRIPTION

42       Ever find yourself repeatedly specifying writers and builders, because
43       there's no good shortcut to specifying them?  Sometimes you want an
44       attribute to have a read-only public interface, but a private writer.
45       And wouldn't it be easier to just say "builder => 1" and have the
46       attribute construct the canonical "_build_$name" builder name for you?
47
48       This package causes an attribute trait to be applied to all attributes
49       defined to the using class.  This trait extends the attribute option
50       processing to handle the above variations.  All attribute options as
51       described in Moose or Class::MOP::Attribute remain usable, just as when
52       this trait is not applied.
53
54   Some Notes On History
55       Moose has long had a lazy_build attribute option.  It was once
56       considered a best practice, but that has, ah, changed.  This trait
57       began as a desire to still leverage bits of "lazy_build" (and a tacit
58       acknowledgment that fat-finger bugs rank among the most embarrassing,
59       right up there with "the TV was unplugged the entire time").
60
61       This author does not recommend you use "lazy_build", unless you know
62       exactly what you're doing (probably) and that it's a good idea
63       (probably not).
64
65       Nonetheless, this "lazy_build" option is why we set certain options the
66       way we do below; while "lazy_build" in its entirety is not optimal, it
67       had the right idea: regular, predictable accessor names for regular,
68       predictable attribute options.
69
70       As an example, just looking at the below it doesn't seem logical that:
71
72           has _foo => (is => 'ro', clearer => 1);
73
74       ...becomes:
75
76           has _foo => (is => 'ro', clearer => '_clear_foo');
77
78       After reading the lazy_build attribute option, however, we see that the
79       choice had already been made for us.
80

USAGE

82       This package automatically applies an attribute metaclass trait.
83       Simply using this package causes the trait to be applied by default to
84       your attribute's metaclasses.
85

EXTENDING A CLASS

87       If you're extending a class and trying to extend its attributes as
88       well, you'll find out that the trait is only applied to attributes
89       defined locally in the class.  This package exports a trait shortcut
90       function "Shortcuts" that will help you apply this to the extended
91       attribute:
92
93           has '+something' => (traits => [Shortcuts], ...);
94

NEW ATTRIBUTE OPTIONS

96       Unless specified here, all options defined by Moose::Meta::Attribute
97       and Class::MOP::Attribute remain unchanged.
98
99       Want to see additional options?  Ask, or better yet, fork on GitHub and
100       send a pull request.  If the shortcuts you're asking for already exist
101       in Moo or Mouse or elsewhere, please note that as it will carry
102       significant weight.
103
104       For the following, $name should be read as the attribute name; and the
105       various prefixes should be read using the defaults.
106
107   is => 'rwp'
108       Specifying "is => 'rwp'" will cause the following options to be set:
109
110           is     => 'ro'
111           writer => "_set_$name"
112
113       rwp can be read as "read + write private".
114
115   is => 'lazy'
116       Specifying "is => 'lazy'" will cause the following options to be set:
117
118           is       => 'ro'
119           builder  => "_build_$name"
120           lazy     => 1
121
122       NOTE: Since 0.009 we no longer set "init_arg => undef" if no "init_arg"
123       is explicitly provided.  This is a change made in parallel with Moo,
124       based on a large number of people surprised that lazy also made one's
125       "init_def" undefined.
126
127   is => 'lazy', default => ...
128       Specifying "is => 'lazy'" and a default will cause the following
129       options to be set:
130
131           is       => 'ro'
132           lazy     => 1
133           default  => ... # as provided
134
135       That is, if you specify "is => 'lazy'" and also provide a "default",
136       then we won't try to set a builder, as well.
137
138   builder => 1
139       Specifying "builder => 1" will cause the following options to be set:
140
141           builder => "_build_$name"
142
143   builder => sub { ... }
144       Passing a coderef to builder will cause that coderef to be installed in
145       the class this attribute is associated with the name you'd expect, and
146       "builder => 1" to be set.
147
148       e.g., in your class (or role),
149
150           has foo => (is => 'ro', builder => sub { 'bar!' });
151
152       ...is effectively the same as...
153
154           has foo => (is => 'ro', builder => '_build_foo');
155           sub _build_foo { 'bar!' }
156
157       The behaviour of this option in roles changed in 0.030, and the builder
158       methods will be installed in the role itself.  This means you can
159       alias/exclude/etc builder methods in roles, just as you can with any
160       other method.
161
162   clearer => 1
163       Specifying "clearer => 1" will cause the following options to be set:
164
165           clearer => "clear_$name"
166
167       or, if your attribute name begins with an underscore:
168
169           clearer => "_clear$name"
170
171       (that is, an attribute named "_foo" would get "_clear_foo")
172
173   predicate => 1
174       Specifying "predicate => 1" will cause the following options to be set:
175
176           predicate => "has_$name"
177
178       or, if your attribute name begins with an underscore:
179
180           predicate => "_has$name"
181
182       (that is, an attribute named "_foo" would get "_has_foo")
183
184   init_arg => 1 / -1
185       This is a somewhat esoteric shortcut; you probably don't want to use
186       this (or even read this section).
187
188       Specifying "init_arg => 1" will cause the following options to be set:
189
190           # attribute: "name"
191           init_arg => 'name'
192
193           # or, attribute: "_name"
194           init_arg => '_name'
195
196       ...while "init_arg => -1" will cause the following options to be set:
197
198           # attribute: "name"
199           init_arg => '_name'
200
201           # or, attribute: "_name"
202           init_arg => 'name'
203
204   trigger => 1
205       Specifying "trigger => 1" will cause the attribute to be created with a
206       trigger that calls a named method in the class with the options passed
207       to the trigger.  By default, the method name the trigger calls is the
208       name of the attribute prefixed with "_trigger_".
209
210       e.g., for an attribute named "foo" this would be equivalent to:
211
212           trigger => sub { shift->_trigger_foo(@_) }
213
214       For an attribute named "_foo":
215
216           trigger => sub { shift->_trigger__foo(@_) }
217
218       This naming scheme, in which the trigger is always private, is the same
219       as the builder naming scheme (just with a different prefix).
220
221   handles => { foo => sub { ... }, ... }
222       Creating a delegation with a coderef will now create a new, "custom
223       accessor" for the attribute.  These coderefs will be installed and
224       called as methods on the associated class (just as readers, writers,
225       and other accessors are), and will have the attribute metaclass
226       available in $_.  Anything the accessor is called with it will have
227       access to in @_, just as you'd expect of a method.
228
229       e.g., the following example creates an attribute named "bar" with a
230       standard reader accessor named "bar" and two custom accessors named
231       "foo" and "foo_too".
232
233           has bar => (
234
235               is      => 'ro',
236               isa     => 'Int',
237               handles => {
238
239                   foo => sub {
240                       my $self = shift @_;
241
242                       return $_->get_value($self) + 1;
243                   },
244
245                   foo_too => sub {
246                       my $self = shift @_;
247
248                       return $self->bar + 1;
249                   },
250
251                   # ...as you'd expect.
252                   bar => 'bar',
253               },
254           );
255
256       ...and later,
257
258       Note that in this example both foo() and foo_too() do effectively the
259       same thing: return the attribute's current value plus 1.  However,
260       foo() accesses the attribute value directly through the metaclass, the
261       pros and cons of which this author leaves as an exercise for the reader
262       to determine.
263
264       You may choose to use the installed accessors to get at the attribute's
265       value, or use the direct metaclass access, your choice.
266

ANONYMOUS SUBTYPING AND COERCION

268           "Abusus non tollit usum."
269
270       Note that we create new, anonymous subtypes whenever the constraint or
271       coercion options are specified in such a way that the Shortcuts trait
272       (this one) is invoked.  It's fully supported to use both constraint and
273       coerce options at the same time.
274
275       This facility is intended to assist with the creation of one-off type
276       constraints and coercions.  It is not possible to deliberately reuse
277       the subtypes we create, and if you find yourself using a particular isa
278       / constraint / coerce option triplet in more than one place you should
279       really think about creating a type that you can reuse.  MooseX::Types
280       provides the facilities to easily do this, or even a simple constant
281       definition at the package level with an anonymous type stashed away for
282       local use.
283
284   isa => sub { ... }
285           has foo => (
286               is  => 'rw',
287               # $_ == $_[0] == the value to be validated
288               isa => sub { die unless $_[0] == 1 },
289           );
290
291           # passes constraint
292           $thing->foo(1);
293
294           # fails constraint
295           $thing->foo(5);
296
297       Given a coderef, create a type constraint for the attribute.  This
298       constraint will fail if the coderef dies, and pass otherwise.
299
300       Astute users will note that this is the same way Moo constraints work;
301       we use MooseX::Meta::TypeConstraint::Mooish to implement the
302       constraint.
303
304   isa_instance_of => ...
305       Given a package name, this option will create an "isa" type constraint
306       that requires the value of the attribute be an instance of the class
307       (or a descendant class) given.  That is,
308
309           has foo => (is => 'ro', isa_instance_of => 'SomeThing');
310
311       ...is effectively the same as:
312
313           use Moose::TypeConstraints 'class_type';
314           has foo => (
315               is  => 'ro',
316               isa => class_type('SomeThing'),
317           );
318
319       ...but a touch less awkward.
320
321   isa => ..., constraint => sub { ... }
322       Specifying the constraint option with a coderef will cause a new
323       subtype constraint to be created, with the parent type being the type
324       specified in the "isa" option and the constraint being the coderef
325       supplied here.
326
327       For example, only integers greater than 10 will pass this attribute's
328       type constraint:
329
330           # value must be an integer greater than 10 to pass the constraint
331           has thinger => (
332               isa        => 'Int',
333               constraint => sub { $_ > 10 },
334               # ...
335           );
336
337       Note that if you supply a constraint, you must also provide an "isa".
338
339   isa => ..., constraint => sub { ... }, coerce => 1
340       Supplying a constraint and asking for coercion will "Just Work", that
341       is, any coercions that the "isa" type has will still work.
342
343       For example, let's say that you're using the "File" type constraint
344       from MooseX::Types::Path::Class, and you want an additional constraint
345       that the file must exist:
346
347           has thinger => (
348               is         => 'ro',
349               isa        => File,
350               constraint => sub { !! $_->stat },
351               coerce     => 1,
352           );
353
354       "thinger" will correctly coerce the string "/etc/passwd" to a
355       "Path::Class:File", and will only accept the coerced result as a value
356       if the file exists.
357
358   coerce => [ Type => sub { ...coerce... }, ... ]
359       Specifying the coerce option with a hashref will cause a new subtype to
360       be created and used (just as with the constraint option, above), with
361       the specified coercions added to the list.  In the passed hashref, the
362       keys are Moose types (well, strings resolvable to Moose types), and the
363       values are coderefs that will coerce a given type to our type.
364
365           has bar => (
366               is     => 'ro',
367               isa    => 'Str',
368               coerce => [
369                   Int    => sub { "$_"                       },
370                   Object => sub { 'An instance of ' . ref $_ },
371               ],
372           );
373

INTERACTIONS WITH OTHER ATTRIBUTE TRAITS

375       Sometimes attribute traits interact in surprising ways.  This trait is
376       well behaved; if you have discovered any interactions with other traits
377       (good, bad, indifferent, etc), please report this
378       <https://github.com/RsrchBoy/moosex-attributeshortcuts/issues/new> so
379       that it can be worked around, fixed, or documented, as appropriate.
380
381   MooseX::SemiAffordanceAccessor
382       MooseX::SemiAffordanceAccessor changes how the "is => 'rw'" and
383       "accessor => ..." attribute options work.  If our trait detects that an
384       attribute has had the MooseX::SemiAffordanceAccessor attribute trait
385       applied, then we change our behaviour to conform to its expectations:
386
387       •   "is => 'rwp'"
388
389           This:
390
391               has  foo => (is => 'rwp');
392               has _bar => (is => 'rwp');
393
394           ...is now effectively equivalent to:
395
396               has foo  => (is => 'ro', writer => '_set_foo');
397               has _bar => (is => 'ro', writer => '_set_bar')
398
399       •   "-writer_prefix" is ignored
400
401           ...as MooseX::SemiAffordanceAccessor has its own specific ideas as
402           to how writers should look.
403

SEE ALSO

405       Please see those modules/websites for more information related to this
406       module.
407
408       •   Moo
409
410       •   MooseX::Types
411
412       •   MooseX::SemiAffordanceAccessor
413

BUGS

415       Please report any bugs or feature requests on the bugtracker website
416       <https://github.com/RsrchBoy/moosex-attributeshortcuts/issues>
417
418       When submitting a bug or request, please include a test-file or a patch
419       to an existing test-file that illustrates the bug or desired feature.
420

AUTHOR

422       Chris Weyl <cweyl@alumni.drew.edu>
423

CONTRIBUTORS

425       •   David Steinbrunner <dsteinbrunner@pobox.com>
426
427       •   Graham Knop <haarg@haarg.org>
428
429       •   Karen Etheridge <ether@cpan.org>
430
431       •   Olaf Alders <olaf@wundersolutions.com>
432
434       This software is Copyright (c) 2017, 2015, 2014, 2013, 2012, 2011 by
435       Chris Weyl.
436
437       This is free software, licensed under:
438
439         The GNU Lesser General Public License, Version 2.1, February 1999
440
441
442
443perl v5.34.0                      2021-07-22     MooseX::AttributeShortcuts(3)
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