1autobox(3)            User Contributed Perl Documentation           autobox(3)
2
3
4

NAME

6       autobox - call methods on native types
7

SYNOPSIS

9           use autobox;
10
11           # integers
12
13               my $range = 10->to(1); # [ 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 ]
14
15           # floats
16
17               my $error = 3.1415927->minus(22/7)->abs();
18
19           # strings
20
21               my @list = 'SELECT * FROM foo'->list();
22               my $greeting = "Hello, world!"->upper(); # "HELLO, WORLD!"
23
24               $greeting->for_each(\&character_handler);
25
26           # arrays and array refs
27
28               my $schwartzian = @_->map(...)->sort(...)->map(...);
29               my $hash = [ 'SELECT * FROM foo WHERE id IN (?, ?)', 1, 2 ]->hash();
30
31           # hashes and hash refs
32
33               { alpha => 'beta', gamma => 'vlissides' }->for_each(...);
34               %hash->keys();
35
36           # code refs
37
38               my $plus_five = (\&add)->curry()->(5);
39               my $minus_three = sub { $_[0] - $_[1] }->reverse->curry->(3);
40
41           # can, isa, VERSION, import and unimport can be accessed via autobox_class
42
43               42->autobox_class->isa('MyNumber')
44               say []->autobox_class->VERSION
45

DESCRIPTION

47       The autobox pragma allows methods to be called on integers, floats,
48       strings, arrays, hashes, and code references in exactly the same manner
49       as blessed references.
50
51       Autoboxing is transparent: values are not blessed into their (user-
52       defined) implementation class (unless the method elects to bestow such
53       a blessing) - they simply use its methods as though they are.
54
55       The classes (packages) into which the native types are boxed are fully
56       configurable.  By default, a method invoked on a non-object value is
57       assumed to be defined in a class whose name corresponds to the "ref()"
58       type of that value - or SCALAR if the value is a non-reference.
59
60       This mapping can be overridden by passing key/value pairs to the "use
61       autobox" statement, in which the keys represent native types, and the
62       values their associated classes.
63
64       As with regular objects, autoboxed values are passed as the first
65       argument of the specified method.  Consequently, given a vanilla "use
66       autobox":
67
68           "Hello, world!"->upper()
69
70       is invoked as:
71
72           SCALAR::upper("hello, world!")
73
74       while:
75
76           [ 1 .. 10 ]->for_each(sub { ... })
77
78       resolves to:
79
80           ARRAY::for_each([ 1 .. 10 ], sub { ... })
81
82       Values beginning with the array "@" and hash "%" sigils are passed by
83       reference, i.e. under the default bindings:
84
85           @array->join(', ')
86           @{ ... }->length()
87           %hash->keys()
88           %$hash->values()
89
90       are equivalent to:
91
92           ARRAY::join(\@array, ', ')
93           ARRAY::length(\@{ ... })
94           HASH::keys(\%hash)
95           HASH::values(\%$hash)
96
97       Multiple "use autobox" statements can appear in the same scope. These
98       are merged both "horizontally" (i.e.  multiple classes can be
99       associated with a particular type) and "vertically" (i.e. multiple
100       classes can be associated with multiple types).
101
102       Thus:
103
104           use autobox SCALAR => 'Foo';
105           use autobox SCALAR => 'Bar';
106
107       - associates SCALAR types with a synthetic class whose @ISA includes
108       both Foo and Bar (in that order).
109
110       Likewise:
111
112           use autobox SCALAR => 'Foo';
113           use autobox SCALAR => 'Bar';
114           use autobox ARRAY  => 'Baz';
115
116       and
117
118           use autobox SCALAR => [ 'Foo', 'Bar' ];
119           use autobox ARRAY  => 'Baz';
120
121       - bind SCALAR types to the Foo and Bar classes and ARRAY types to Baz.
122
123       autobox is lexically scoped, and bindings for an outer scope can be
124       extended or countermanded in a nested scope:
125
126           {
127               use autobox; # default bindings: autobox all native types
128               ...
129
130               {
131                   # appends 'MyScalar' to the @ISA associated with SCALAR types
132                   use autobox SCALAR => 'MyScalar';
133                   ...
134               }
135
136               # back to the default (no MyScalar)
137               ...
138           }
139
140       Autoboxing can be turned off entirely by using the "no" syntax:
141
142           {
143               use autobox;
144               ...
145               no autobox;
146               ...
147           }
148
149       - or can be selectively disabled by passing arguments to the "no
150       autobox" statement:
151
152           use autobox; # default bindings
153
154           no autobox qw(SCALAR);
155
156           []->foo(); # OK: ARRAY::foo([])
157
158           "Hello, world!"->bar(); # runtime error
159
160       Autoboxing is not performed for barewords i.e.
161
162           my $foo = Foo->new();
163
164       and:
165
166           my $foo = new Foo;
167
168       behave as expected.
169
170       Methods are called on native types by means of the arrow operator. As
171       with regular objects, the right hand side of the operator can either be
172       a bare method name or a variable containing a method name or subroutine
173       reference. Thus the following are all valid:
174
175           sub method1 { ... }
176           my $method2 = 'some_method';
177           my $method3 = sub { ... };
178           my $method4 = \&some_method;
179
180           " ... "->method1();
181           [ ... ]->$method2();
182           { ... }->$method3();
183           sub { ... }->$method4();
184
185       A native type is only associated with a class if the type => class
186       mapping is supplied in the "use autobox" statement. Thus the following
187       will not work:
188
189           use autobox SCALAR => 'MyScalar';
190
191           @array->some_array_method();
192
193       - as no class is specified for the ARRAY type. Note: the result of
194       calling a method on a native type that is not associated with a class
195       is the usual runtime error message:
196
197           Can't call method "some_array_method" on unblessed reference at ...
198
199       As a convenience, there is one exception to this rule. If "use autobox"
200       is invoked with no arguments (ignoring the DEBUG option) the four main
201       native types are associated with classes of the same name.
202
203       Thus:
204
205           use autobox;
206
207       - is equivalent to:
208
209           use autobox {
210               SCALAR => 'SCALAR',
211               ARRAY  => 'ARRAY',
212               HASH   => 'HASH',
213               CODE   => 'CODE',
214           }
215
216       This facilitates one-liners and prototypes:
217
218           use autobox;
219
220           sub SCALAR::split { [ split '', $_[0] ] }
221           sub ARRAY::length { scalar @{$_[0]} }
222
223           print "Hello, world!"->split->length();
224
225       However, using these default bindings is not recommended as there's no
226       guarantee that another piece of code won't trample over the same
227       namespace/methods.
228

OPTIONS

230       A mapping from native types to their user-defined classes can be
231       specified by passing a hashref or a list of key/value pairs to the "use
232       autobox" statement.
233
234       The following example shows the range of valid arguments:
235
236           use autobox {
237               SCALAR    => 'MyScalar'                     # class name
238               ARRAY     => 'MyNamespace::',               # class prefix (ending in '::')
239               HASH      => [ 'MyHash', 'MyNamespace::' ], # one or more class names and/or prefixes
240               CODE      => ...,                           # any of the 3 value types above
241               INTEGER   => ...,                           # any of the 3 value types above
242               FLOAT     => ...,                           # any of the 3 value types above
243               NUMBER    => ...,                           # any of the 3 value types above
244               STRING    => ...,                           # any of the 3 value types above
245               UNDEF     => ...,                           # any of the 3 value types above
246               UNIVERSAL => ...,                           # any of the 3 value types above
247               DEFAULT   => ...,                           # any of the 3 value types above
248               DEBUG     => ...                            # boolean or coderef
249           }
250
251       The INTEGER, FLOAT, NUMBER, STRING, SCALAR, ARRAY, HASH, CODE, UNDEF,
252       DEFAULT and UNIVERSAL options can take three different types of value:
253
254       ·   A class name e.g.
255
256               use autobox INTEGER => 'MyInt';
257
258           This binds the specified native type to the specified class. All
259           methods invoked on values of type "key" will be dispatched as
260           methods of the class specified in the corresponding "value".
261
262       ·   A namespace: this is a class prefix (up to and including the final
263           '::') to which the specified type name (INTEGER, FLOAT, STRING &c.)
264           will be appended:
265
266           Thus:
267
268               use autobox ARRAY => 'Prelude::';
269
270           is equivalent to:
271
272               use autobox ARRAY => 'Prelude::ARRAY';
273
274       ·   A reference to an array of class names and/or namespaces. This
275           associates multiple classes with the specified type.
276
277   DEFAULT
278       The "DEFAULT" option specifies bindings for any of the four default
279       types (SCALAR, ARRAY, HASH and CODE) not supplied in the "use autobox"
280       statement. As with the other options, the "value" corresponding to the
281       "DEFAULT" "key" can be a class name, a namespace, or a reference to an
282       array containing one or more class names and/or namespaces.
283
284       Thus:
285
286           use autobox {
287               STRING  => 'MyString',
288               DEFAULT => 'MyDefault',
289           }
290
291       is equivalent to:
292
293           use autobox {
294               STRING  => 'MyString',
295               SCALAR  => 'MyDefault',
296               ARRAY   => 'MyDefault',
297               HASH    => 'MyDefault',
298               CODE    => 'MyDefault',
299           }
300
301       Which in turn is equivalent to:
302
303           use autobox {
304               INTEGER => 'MyDefault',
305               FLOAT   => 'MyDefault',
306               STRING  => [ 'MyString', 'MyDefault' ],
307               ARRAY   => 'MyDefault',
308               HASH    => 'MyDefault',
309               CODE    => 'MyDefault',
310           }
311
312       Namespaces in DEFAULT values have the default type name appended,
313       which, in the case of defaulted SCALAR types, is SCALAR rather than
314       INTEGER, FLOAT &c.
315
316       Thus:
317
318           use autobox {
319               ARRAY   => 'MyArray',
320               HASH    => 'MyHash',
321               CODE    => 'MyCode',
322               DEFAULT => 'MyNamespace::',
323           }
324
325       is equivalent to:
326
327           use autobox {
328               INTEGER => 'MyNamespace::SCALAR',
329               FLOAT   => 'MyNamespace::SCALAR',
330               STRING  => 'MyNamespace::SCALAR',
331               ARRAY   => 'MyArray',
332               HASH    => 'MyArray',
333               CODE    => 'MyCode',
334           }
335
336       Any of the four default types can be exempted from defaulting to the
337       DEFAULT value by supplying a value of undef:
338
339           use autobox {
340               HASH    => undef,
341               DEFAULT => 'MyDefault',
342           }
343
344           42->foo # ok: MyDefault::foo
345           []->bar # ok: MyDefault::bar
346
347           %INC->baz # not ok: runtime error
348
349   UNDEF
350       The pseudotype, UNDEF, can be used to autobox undefined values. These
351       are not autoboxed by default.
352
353       This doesn't work:
354
355           use autobox;
356
357           undef->foo() # runtime error
358
359       This works:
360
361           use autobox UNDEF => 'MyUndef';
362
363           undef->foo(); # ok
364
365       So does this:
366
367           use autobox UNDEF => 'MyNamespace::';
368
369           undef->foo(); # ok
370
371   NUMBER, SCALAR and UNIVERSAL
372       The virtual types NUMBER, SCALAR and UNIVERSAL function as macros or
373       shortcuts which create bindings for their subtypes. The type hierarchy
374       is as follows:
375
376         UNIVERSAL -+
377                    |
378                    +- SCALAR -+
379                    |          |
380                    |          +- NUMBER -+
381                    |          |          |
382                    |          |          +- INTEGER
383                    |          |          |
384                    |          |          +- FLOAT
385                    |          |
386                    |          +- STRING
387                    |
388                    +- ARRAY
389                    |
390                    +- HASH
391                    |
392                    +- CODE
393
394       Thus:
395
396           use autobox NUMBER => 'MyNumber';
397
398       is equivalent to:
399
400           use autobox {
401               INTEGER => 'MyNumber',
402               FLOAT   => 'MyNumber',
403           }
404
405       And:
406
407           use autobox SCALAR => 'MyScalar';
408
409       is equivalent to:
410
411           use autobox {
412               INTEGER => 'MyScalar',
413               FLOAT   => 'MyScalar',
414               STRING  => 'MyScalar',
415           }
416
417       Virtual types can also be passed to "unimport" via the "no autobox"
418       syntax. This disables autoboxing for the corresponding subtypes e.g.
419
420           no autobox qw(NUMBER);
421
422       is equivalent to:
423
424           no autobox qw(INTEGER FLOAT);
425
426       Virtual type bindings can be mixed with ordinary bindings to provide
427       fine-grained control over inheritance and delegation. For instance:
428
429           use autobox {
430               INTEGER => 'MyInteger',
431               NUMBER  => 'MyNumber',
432               SCALAR  => 'MyScalar',
433           }
434
435       would result in the following bindings:
436
437           42->foo              -> [ MyInteger, MyNumber, MyScalar ]
438           3.1415927->bar       -> [ MyNumber, MyScalar ]
439           "Hello, world!"->baz -> [ MyScalar ]
440
441       Note that DEFAULT bindings take precedence over virtual type bindings
442       i.e.
443
444           use autobox {
445               UNIVERSAL => 'MyUniversal',
446               DEFAULT   => 'MyDefault', # default SCALAR, ARRAY, HASH and CODE before UNIVERSAL
447           }
448
449       is equivalent to:
450
451         use autobox {
452             INTEGER => [ 'MyDefault', 'MyUniversal' ],
453             FLOAT   => [ 'MyDefault', 'MyUniversal' ], # ... &c.
454         }
455
456   DEBUG
457       "DEBUG" allows the autobox bindings for the current scope to be
458       inspected, either by dumping them to the console or passing them to a
459       callback function.  This allows the computed bindings to be seen in
460       "longhand".
461
462       The option is ignored if the value corresponding to the "DEBUG" key is
463       false.
464
465       If the value is a CODE ref, it is called with a reference to the hash
466       containing the computed bindings for the current scope.
467
468       Finally, if "DEBUG" is true but not a CODE ref, the bindings are dumped
469       to STDERR.
470
471       Thus:
472
473           use autobox DEBUG => 1, ...
474
475       or
476
477           use autobox DEBUG => sub { ... }, ...
478
479       or
480
481           sub my_callback ($) {
482               my $hashref = shift;
483               ...
484           }
485
486           use autobox DEBUG => \&my_callback, ...
487

METHODS

489   import
490       This method sets up autobox bindings for the current lexical scope. It
491       can be used to implement autobox extensions i.e. lexically-scoped
492       modules that provide autobox bindings for one or more native types
493       without requiring calling code to "use autobox".
494
495       This is done by subclassing autobox and overriding "import". This
496       allows extensions to effectively translate "use MyModule" into a
497       bespoke "use autobox" call e.g.:
498
499           package String::Trim;
500
501           use base qw(autobox);
502
503           sub import {
504               my $class = shift;
505
506               $class->SUPER::import(
507                   STRING => 'String::Trim::String'
508               );
509           }
510
511           package String::Trim::String;
512
513           sub trim {
514               my $string = shift;
515               $string =~ s/^\s+//;
516               $string =~ s/\s+$//;
517               $string;
518           }
519
520           1;
521
522       Note that "trim" is defined in an auxiliary class rather than in
523       String::Trim itself to prevent String::Trim's own methods (i.e. the
524       methods it inherits from autobox) being exposed to "STRING" types.
525
526       This module can now be used without a "use autobox" statement to enable
527       the "trim" method in the current lexical scope e.g.:
528
529           #!/usr/bin/env perl
530
531           use String::Trim;
532
533           print "  Hello, world!  "->trim();
534

UNIVERSAL METHODS FOR AUTOBOXED TYPES

536   autobox_class
537       autobox adds a single method to all autoboxed types: "autobox_class".
538       This can be used to call UNIVERSAL methods i.e. "can", "DOES",
539       "import", "isa", "unimport" and "VERSION" e.g.
540
541           if (sub { ... }->autobox_class->can('curry')) ...
542           if (42->autobox_class->isa('SCALAR')) ...
543
544       Note: "autobox_class" must always be used when calling these methods.
545       Calling them directly on native types produces the same results as
546       calling them with autobox disabled e.g.:
547
548           42->isa('NUMBER') # "" (interpeted as "42"->isa("NUMBER"))
549           []->can('push')   # Error: Can't call method "can" on unblessed reference
550

EXPORTS

552   type
553       autobox includes an additional module, autobox::universal, which
554       exports a single subroutine, "type".
555
556       This sub returns the type of its argument within autobox (which is
557       essentially longhand for the type names used within perl). This value
558       is used by autobox to associate a method invocant with its designated
559       classes e.g.
560
561           use autobox::universal qw(type);
562
563           type("42")  # STRING
564           type(42)    # INTEGER
565           type(42.0)  # FLOAT
566           type(undef) # UNDEF
567
568       autobox::universal is loaded automatically by autobox, and, as its name
569       suggests, can be used to install a universal "type" method for
570       autoboxed values e.g.
571
572           use autobox UNIVERSAL => 'autobox::universal';
573
574           42->type        # INTEGER
575           3.1415927->type # FLOAT
576           %ENV->type      # HASH
577

CAVEATS

579   Performance
580       Calling
581
582           "Hello, world!"->length()
583
584       is slightly slower than the equivalent method call on a string-like
585       object, and significantly slower than
586
587           length("Hello, world!")
588
589   Gotchas
590       Precedence
591
592       Due to Perl's precedence rules, some autoboxed literals may need to be
593       parenthesized:
594
595       For instance, while this works:
596
597           my $curried = sub { ... }->curry();
598
599       this doesn't:
600
601           my $curried = \&foo->curry();
602
603       The solution is to wrap the reference in parentheses:
604
605           my $curried = (\&foo)->curry();
606
607       The same applies for signed integer and float literals:
608
609           # this works
610           my $range = 10->to(1);
611
612           # this doesn't work
613           my $range = -10->to(10);
614
615           # this works
616           my $range = (-10)->to(10);
617
618       print BLOCK
619
620       Perl's special-casing for the "print BLOCK ..." syntax (see perlsub)
621       means that "print { expression() } ..."  (where the curly brackets
622       denote an anonymous HASH ref) may require some further disambiguation:
623
624           # this works
625           print { foo => 'bar' }->foo();
626
627           # and this
628           print { 'foo', 'bar' }->foo();
629
630           # and even this
631           print { 'foo', 'bar', @_ }->foo();
632
633           # but this doesn't
634           print { @_ }->foo() ? 1 : 0
635
636       In the latter case, the solution is to supply something other than a
637       HASH ref literal as the first argument to "print()":
638
639           # e.g.
640           print STDOUT { @_ }->foo() ? 1 : 0;
641
642           # or
643           my $hashref = { @_ };
644           print $hashref->foo() ? 1 : 0;
645
646           # or
647           print '', { @_ }->foo() ? 1 : 0;
648
649           # or
650           print '' . { @_ }->foo() ? 1 : 0;
651
652           # or even
653           { @_ }->print_if_foo(1, 0);
654
655       eval EXPR
656
657       Like most pragmas, autobox performs operations at compile time, and, as
658       a result, runtime string "eval"s are not executed within its scope i.e.
659       this doesn't work:
660
661           use autobox;
662
663           eval "42->foo";
664
665       The workaround is to use autobox within the "eval" e.g.
666
667           eval <<'EOS';
668               use autobox;
669               42->foo();
670           EOS
671
672       Note that the "eval BLOCK" form works as expected:
673
674           use autobox;
675
676           eval { 42->foo() }; # OK
677
678       Operator Overloading
679
680       Operator overloading via the overload pragma doesn't (automatically)
681       work.  autobox works by lexically overriding the arrow operator.  It
682       doesn't bless native types into objects, so overloading - or any other
683       kind of "magic" which depends on values being blessed - doesn't apply.
684

VERSION

686       3.0.1
687

SEE ALSO

689       ·   autobox::Core
690
691       ·   Moose::Autobox
692
693       ·   perl5i
694
695       ·   Scalar::Properties
696

AUTHOR

698       chocolateboy <chocolate@cpan.org>
699
701       Copyright (c) 2003-2018 by chocolateboy.
702
703       This library is free software; you can redistribute it and/or modify it
704       under the terms of the Artistic License 2.0
705       <http://www.opensource.org/licenses/artistic-license-2.0.php>.
706
707
708
709perl v5.28.1                      2018-05-05                        autobox(3)
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