1Object::InsideOut::MetaUdsaetra(C3o)ntributed Perl DocumOebnjteactti:o:nInsideOut::Metadata(3)
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NAME

6       Object::InsideOut::Metadata - Introspection for Object::InsideOut
7       classes
8

VERSION

10       This document describes Object::InsideOut::Metadata version 4.05
11

SYNOPSIS

13        package My::Class; {
14            use Object::InsideOut;
15            use Object::InsideOut::Metadata;
16
17            my @data :Field :Arg('data') :Get('data') :Set('put_data');
18            my @misc :Field;
19
20            my %init_args :InitArgs = (
21                'INFO' => '',
22            );
23
24            sub _init :Init
25            {
26                my ($self, $args) = @_;
27                if (exists($args->{'INFO'})) {
28                    $misc[$$self] = 'INFO: ' . $args->{'INFO'};
29                }
30            }
31
32            sub misc :lvalue :Method
33            {
34                my $self = shift;
35                $misc[$$self];
36            }
37            add_meta(__PACKAGE__, 'misc', { 'lvalue' => 1 });
38        }
39
40        package main;
41
42        # Obtain a metadata object for a class
43        my $meta = My::Class->meta();
44
45        # ... or obtain a metadata object for an object
46        my $obj = My::Class->new();
47        my $meta = $obj->meta();
48
49        # Obtain the class hierarchy from the metadata object
50        my @classes = $meta->get_classes();
51
52        # Obtain information on the parameters for a class's construction
53        my %args = $meta->get_args();
54
55        # Obtain information on a class's methods
56        my %methods = $meta->get_methods();
57

DESCRIPTION

59       Object::InsideOut provides an introspection API that allows you to
60       obtain metadata on a class's hierarchy, constructor parameters, and
61       methods.  This is done through the use of metadata objects that are
62       generated by this class.
63
64       In addition, developers can specify metadata data for methods they
65       write for their classes.
66

METADATA OBJECT

68       To obtain metadata on an Object::InsideOut class or object, you must
69       first generate a metadata object for that class or object.  Using that
70       metadata object, one can then obtain information on the class
71       hierarchy, constructor parameters, and methods.
72
73       my $meta = My::Class->meta();
74       my $meta = $obj->meta();
75           The "->meta()" method, which is exported by Object::InsideOut to
76           each class, returns an Object::InsideOut::Metadata object which can
77           then be queried for information about the invoking class or
78           invoking object's class.
79

CLASS HIERARCHY

81       Any Object::InsideOut class potentially has four categories of classes
82       associated with it:
83
84       1.  Object::InsideOut
85           While the basis for all Object::InsideOut classes it is not an
86           object class per se because you can create objects from it (i.e.,
87           you can't do "Object::InsideOut-"new()>).  While
88           "My::Class-"isa('Object::InsideOut')> will return true, because
89           Object::InsideOut is not an object class, it is not considered to
90           be part of a class's hierarchy.
91
92       2.  The class itself
93           A class's hierarchy always includes itself.
94
95       3.  Parent classes
96           These are all the Object::InsideOut classes up the inheritance tree
97           that a class is derived from.
98
99       4.  Foreign classes
100           These are non-Object::InsideOut classes that a class inherits from.
101           (See "FOREIGN CLASS INHERITANCE" in Object::InsideOut.)  Because of
102           implementation details, foreign classes do not appear in a class's
103           @ISA array.  However, Object::InsideOut implements a version of
104           "->isa()" that handles foreign classes.
105
106       A class's hierarchy consists of any classes in the latter three
107       categories.
108
109       $meta->get_classes();
110           When called in an array context, returns a list that constitutes
111           the class hierarchy for the class or object used to generate the
112           metadata object.  When called in a scalar context, returns an array
113           ref.
114
115       My::Class->isa();
116       $obj->isa();
117           When called in an array context, calling "->isa()" without any
118           arguments on an Object::InsideOut class or object returns a list of
119           the classes in the class hierarchy for that class or object, and is
120           equivalent to:
121
122            my @classes = $obj->meta()->get_classes();
123
124           When called in a scalar context, it returns an array ref containing
125           the classes.
126

CONSTRUCTOR PARAMETERS

128       Constructor parameters are the arguments given to a class's "->new()"
129       call.
130
131       $meta->get_args();
132           Returns a hash (hash ref in scalar context) containing information
133           on the parameters that can be used to construct an object from the
134           class associated with the metadata object.  Here's an example of
135           such a hash:
136
137            {
138                'My::Class' => {
139                    'data' => {
140                        'field' => 1,
141                        'type' => 'numeric',
142                    },
143                    'misc' => {
144                        'mandatory' => 1,
145                    },
146                },
147                'My::Parent' => {
148                    'info' => {
149                        'default' => '<none>',
150                    },
151                },
152            }
153
154           The keys for this hash are the Object::IsideOut classes in the
155           class hierarchy.  These class keys are paired with hash refs, the
156           keys of which are the names of the parameters for that class (e.g.,
157           'data' and 'misc' for My::Class, and 'info' for My::Parent).  The
158           hashes paired to the parameters contain information about the
159           parameter:
160
161           field
162               The parameter corresponds directly to a class field, and is
163               automatically processed during object creation.  See "Field-
164               Specific Parameters" in Object::InsideOut.
165
166           mandatory
167               The parameter is required for object creation.  See "Mandatory
168               Parameters" in Object::InsideOut.
169
170           default
171               The default value assigned to the parameter if it is not found
172               in the arguments to "->new()".  See "Default Values" in
173               Object::InsideOut.
174
175           preproc
176               The code ref for the subroutine that is used to preprocess a
177               parameter's value.  See "Parameter Preprocessing" in
178               Object::InsideOut
179
180           type
181               The form of type checking performed on the parameter.  See
182               "TYPE CHECKING" in Object::InsideOut for more details.
183
184               'numeric'
185                   Parameter takes a numeric value as recognized by
186                   Scalar::Util::looks_like_number().
187
188               'list'
189               'list(_subtype_)'
190                   Parameter takes a single value (which is then placed in an
191                   array ref) or an array ref.
192
193                   When specified, the contents of the resulting array ref
194                   must be of the specified subtype:
195
196                   'numeric'
197                       Same as for the basic type above.
198
199                   A class name
200                       Same as for the basic type below.
201
202                   A reference type
203                       Any reference type as returned by ref()).
204
205               'ARRAY(_subtype_)'
206                   Parameter takes an array ref with contents of the specified
207                   subtype as per the above.
208
209               A class name
210                   Parameter takes an object of a specified class, or one of
211                   its sub-classes as recognized by "->isa()".
212
213               Other reference type
214                   Parameter takes a reference of the specified type as
215                   returned by ref().
216
217               A code ref
218                   Parameter takes a value that is type-checked by the code
219                   ref paired to the 'type' key.
220

METHODS METADATA

222       The methods returned by a metadata object are those that are currently
223       available at the time of the "->get_methods()" call.
224
225       The presence of ":Automethod" subroutines in an Object::InsideOut
226       class, or "AUTOLOAD" in a foreign class means that the methods
227       supported by the class may not be determinable.  The presence of
228       "AUTOLOAD" in the list of methods for a class should alert the
229       programmer to the fact that more methods may be supported than are
230       listed.
231
232       Methods that are excluded are private and hidden methods (see
233       "PERMISSIONS" in Object::InsideOut), methods that begin with an
234       underscore (which, by convention, means they are private), and
235       subroutines named "CLONE", "CLONE_SKIP", and "DESTROY" (which are not
236       methods).  While technically a method, "import" is also excluded as it
237       is generally not invoked directly (i.e., it's usually called as part of
238       "use").
239
240       $meta->get_methods();
241           Returns a hash (hash ref in scalar context) containing information
242           on the methods for the class associated with the metadata object.
243           The keys in the hash are the method names.  Paired to the names are
244           hash refs containing metadata about the methods.  Here's an
245           example:
246
247            {
248                # Methods exported by Object::InsideOut
249                'new' => {
250                   'class' => 'My::Class',
251                   'kind'  => 'constructor'
252                },
253                'clone' => {
254                    'class' => 'My::Class',
255                    'kind'  => 'object'
256                },
257                'meta'  => {
258                    'class' => 'My::Class'
259                },
260                'set' => {
261                    'class' => 'My::Class',
262                    'kind'  => 'object',
263                    'restricted' => 1
264                },
265                # Methods provided by Object::InsideOut
266                'dump' => {
267                    'class' => 'Object::InsideOut',
268                    'kind'  => 'object'
269                },
270                'pump' => {
271                    'class' => 'Object::InsideOut',
272                    'kind'  => 'class'
273                },
274                'inherit' => {
275                    'class' => 'Object::InsideOut',
276                    'kind'  => 'object',
277                    'restricted' => 1
278                },
279                'heritage' => {
280                    'class' => 'Object::InsideOut',
281                    'kind'  => 'object',
282                    'restricted' => 1
283                },
284                'disinherit' => {
285                    'class' => 'Object::InsideOut',
286                    'kind'  => 'object',
287                    'restricted' => 1
288                },
289                # Methods generated by Object::InsideOut for My::Class
290                'set_data' => {
291                    'class'  => 'My::Class',
292                    'kind'   => 'set',
293                    'type'   => 'ARRAY',
294                    'return' => 'new'
295                },
296                'get_data' => {
297                    'class' => 'My::Class',
298                    'kind'  => 'get'
299                }
300                # Class method provided by My::Class
301                'my_method' => {
302                    'class' => 'My::Class',
303                    'kind'  => 'class'
304                }
305            }
306
307           Here are the method metadata that are provided:
308
309           class
310               The class in whose symbol table the method resides.  The method
311               may reside in the classes code, it may be exported by another
312               class, or it may be generated by Object::InsideOut.
313
314               Methods that are overridden in child classes are represented as
315               being associated with the most junior class for which they
316               appear.
317
318           kind
319               Designation of the characteristic of the method:
320
321               constructor
322                   The "->new()" method, of course.
323
324               get, set or accessor
325                   A get, set, or combined accessor generated by
326                   Object::InsideOut.  See "AcCESSOR GENERATION" in
327                   Object::InsideOut.
328
329               cumulative, or cumulative (bottom up)
330               chained, or chained (bottom up)
331                   A cumulative or chained method.  See "CUMULATIVE METHODS"
332                   in Object::InsideOut, and "CHAINED METHODS" in
333                   Object::InsideOut.  The class associated with these methods
334                   is the most junior class in which they appears.
335
336               class
337                   A method that is callable only on a class (e.g.,
338                   "My::Class->my_method()").
339
340               object
341                   A method that is callable only on a object (e.g.
342                   "$obj->get_data()").
343
344               foreign
345                   A subroutine found in a foreign class's symbol table.
346                   Programmers must check the class's documentation to
347                   determine which are actually methods, and what kinds of
348                   methods they are.
349
350               overload
351                   A subroutine used for object coercion.  These may be called
352                   as methods, but this is not normally how they are used.
353
354               automethod
355                   Associated with an AUTOLOAD method for an Object::InsideOut
356                   class that implements an ":Automethod" subroutine.  See
357                   "AUTOMETHODS" in Object::InsideOut.
358
359           type
360               The type checking that is done on arguments to set/combined
361               accessors generated by Object::InsideOut.  See "TYPE CHECKING"
362               in Object::InsideOut
363
364           return
365               The value returned by a set/combined accessor generated by
366               Object::InsideOut.  See "Set Accessor Return Value" in
367               Object::InsideOut
368
369           lvalue
370               The method is an :lvalue accessor.
371
372           restricted
373               The method is restricted (i.e., callable only from within the
374               class hierarchy; not callable from application code).  See
375               "PERMISSIONS" in Object::InsideOut.
376
377       My::Class->can();
378       $obj->can();
379           When called in an array context, calling "->can()" without any
380           arguments on an Object::InsideOut class or object returns a list of
381           the method names for that class or object, and is equivalent to:
382
383            my %meths = $obj->meta()->get_methods();
384            my @methods = keys(%meths);
385
386           When called in a scalar context, it returns an array ref containing
387           the method names.
388
389   METADATA ATTRIBUTES
390       Class authors may add the ":Method" attribute to subroutines in their
391       classes to specifically designate them as OO-callable methods.  If a
392       method is only a class method or only an object method, this may be
393       added as a parameter to the attribute:
394
395        sub my_method :Method(class)
396        {
397            ...
398
399       The class or object parameter will appear in the metadata for the
400       method when listed using "->get_methods()".
401
402       CAUTION:  Be sure not to use ":method" (all lowercase) except as
403       appropriate (see "ARGUMENT VALIDATION" in Object::InsideOut) as this is
404       a Perl reserved attribute.
405
406       The ":Sub" attribute can be used to designate subroutines that are not
407       OO-callable methods.  These subroutines will not show up as part of the
408       methods listed by "->get_methods()", etc..
409
410       Subroutine names beginning with an underscore are, by convention,
411       considered private, and will not show up as part of the methods listed
412       by "->get_methods()", etc..
413
414   ADDING METADATA
415       Class authors may add additional metadata to their methods using the
416       "add_meta()" subroutine which is exported by this package.  For
417       example, if the class implements it own ":lvalue" method, it should add
418       that metadata so that it is picked up the "->get_methods()":
419
420        package My::Class; {
421            use Object::InsideOut;
422            use Object::InsideOut::Metadata;
423
424            sub my_method :lvalue :Method(object)
425            {
426                ....
427            }
428            add_meta(__PACKAGE__, 'my_method', 'lvalue', 1);
429        }
430
431       The arguments to "add_meta()" are:
432
433       Class name
434           This can usually be designated using the special literal
435           C__PACKAGE__>.
436
437       Method name
438       Metadata name
439           This can be any of the metadata names under "METHODS METADATA", or
440           can be whatever additional name the programmer chooses to
441           implement.
442
443       Metadata value
444
445       When adding multiple metadata for a method, they may be enclosed in a
446       single hash ref:
447
448        add_meta(__PACKAGE__, 'my_method', { 'lvalue' => 1,
449                                             'return' => 'old' });
450
451       If adding metadata for multiple methods, another level of hash may be
452       used:
453
454        add_meta(__PACKAGE__, { 'my_method' => { 'lvalue' => 1,
455                                                 'return' => 'old' },
456                                'get_info'  => { 'my_meta' => 'true' } });
457

TO DO

459       Provide filtering capabilities on the method information returned by
460       "->get_methods()".
461

REQUIREMENTS

463       Perl 5.8.0 or later
464

SEE ALSO

466       Object::InsideOut
467
468       Perl 6 introspection:
469       <http://dev.perl.org/perl6/doc/design/apo/A12.html#Introspection>, and
470       <http://dev.perl.org/perl6/rfc/335.html>
471

AUTHOR

473       Jerry D. Hedden, <jdhedden AT cpan DOT org>
474
476       Copyright 2006 - 2012 Jerry D. Hedden. All rights reserved.
477
478       This program is free software; you can redistribute it and/or modify it
479       under the same terms as Perl itself.
480
481
482
483perl v5.32.1                      2021-01-27    Object::InsideOut::Metadata(3)
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