Class::MakeMethods::Template(3pm)

1MakeMethods::Template(3U)ser Contributed Perl DocumentatiMoankeMethods::Template(3)
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NAME

6       Class::MakeMethods::Template - Extensible code templates
7

SYNOPSIS

9         package MyObject;
10         use Class::MakeMethods::Template::Hash (
11           'new'       => 'new',
12           'string'    => 'foo',
13           'number'    => 'bar',
14         );
15
16         my $obj = MyObject->new( foo => "Foozle", bar => 23 );
17         print $obj->foo();
18         $obj->bar(42);
19

MOTIVATION

21       If you compare the source code of some of the closure-generating
22       methods provided by other subclasses of Class::MakeMethods, such as the
23       "hash" accessors provided by the various Standard::* subclasses, you
24       will notice a fair amount of duplication. This module provides a way of
25       assembling common pieces of code to facilitate support the maintenance
26       of much larger libraries of generated methods.
27

DESCRIPTION

29       This module extends the Class::MakeMethods framework by providing an
30       abstract superclass for extensible code-templating method generators.
31
32       Common types of methods are generalized into template definitions.  For
33       example, "Template::Generic"'s "new" provides a template for methods
34       that create object instances, while "Template::Generic"'s "scalar" is a
35       template for methods that allow you to get and set individual scalar
36       values.
37
38       Thse definitions are then re-used and modified by various template
39       subclasses. For example, the "Template::Hash" subclass supports
40       blessed-hash objects, while the "Template::Global" subclass supports
41       shared data; each of them includes an appropriate version of the
42       "scalar" accessor template for those object types.
43
44       Each template defines one or more behaviors, individual methods which
45       can be installed in a calling package, and interfaces, which select
46       from those behaviours and indicate the names to install the methods
47       under.
48
49       Each individual meta-method defined by a calling package requires a
50       method name, and may optionally include other key-value parameters,
51       which can control the operation of some meta-methods.
52

USAGE

54   Class::MakeMethods Calling Conventions
55       When you "use" this package, the method declarations you provide as
56       arguments cause subroutines to be generated and installed in your
57       module.
58
59       You can also omit the arguments to "use" and instead make methods at
60       runtime by passing the declarations to a subsequent call to "make()".
61
62       You may include any number of declarations in each call to "use" or
63       "make()". If methods with the same name already exist, earlier calls to
64       "use" or "make()" win over later ones, but within each call, later
65       declarations superceed earlier ones.
66
67       You can install methods in a different package by passing "-TargetClass
68       => package" as your first arguments to "use" or "make".
69
70       See Class::MakeMethods for more details.
71
72   Passing Parameters
73       The following types of Basic declarations are supported:
74
75       •   generator_type => "method_name"
76
77       •   generator_type => "name_1 name_2..."
78
79       •   generator_type => [ "name_1", "name_2", ...]
80
81       See "TEMPLATE CLASSES" in Class::MakeMethods::Docs::Catalog for a list
82       of the supported values of generator_type.
83
84       For each method name you provide, a subroutine of the indicated type
85       will be generated and installed under that name in your module.
86
87       Method names should start with a letter, followed by zero or more
88       letters, numbers, or underscores.
89
90   Standard Declaration Syntax
91       The Standard syntax provides several ways to optionally associate a
92       hash of additional parameters with a given method name.
93
94       •   generator_type => [ "name_1" => { param=>value... }, ... ]
95
96           A hash of parameters to use just for this method name.
97
98           (Note: to prevent confusion with self-contained definition hashes,
99           described below, parameter hashes following a method name must not
100           contain the key 'name'.)
101
102       •   generator_type => [ [ "name_1", "name_2", ... ] => {
103           param=>value... } ]
104
105           Each of these method names gets a copy of the same set of
106           parameters.
107
108       •   generator_type => [ { "name"=>"name_1", param=>value... }, ... ]
109
110           By including the reserved parameter "name", you create a self
111           contained declaration with that name and any associated hash
112           values.
113
114       Basic declarations, as described above, are treated as having an empty
115       parameter hash.
116
117   Default Parameters
118       A set of default parameters to be used for several declarations may be
119       specified using any of the following types of arguments to a Template
120       method generator call:
121
122       •   '-param' => 'value'
123
124           Set a default value for the specified parameter.
125
126       •   '--' => { 'param' => 'value', ... }
127
128           Set default values for one or more parameters. Equivalent to a
129           series of '-param' => 'value' pairs for each pair in the referenced
130           hash.
131
132       •   '--special_param_value'
133
134           Specifies a value for special parameter; the two supported
135           parameter types are:
136
137           -   '--interface_name'
138
139               Select a predefined interface; equivalent to '-interface'=>
140               'interface_name'.
141
142               For more information about interfaces, see "Selecting
143               Interfaces" below.
144
145           -   '--modifier_name'
146
147               Select a global behavior modifier, such as '--private' or
148               '--protected'.
149
150               For more information about modifiers, see "Selecting Modifiers"
151               below.
152
153       Parameters set in these ways are passed to each declaration that
154       follows it until the end of the method-generator argument array, or
155       until overridden by another declaration. Parameters specified in a hash
156       for a specific method name, as discussed above, will override the
157       defaults of the same name for that particular method.
158

PARAMETER REFERENCE

160       Each meta-method is allocated a hash in which to store its parameters
161       and optional information.
162
163       (Note that you can not override parameters on a per-object level.)
164
165   Special Parameters
166       The following parameters are pre-defined or have a special meaning:
167
168       •   name
169
170           The primary name of the meta-method. Note that the subroutines
171           installed into the calling package may be given different names,
172           depending on the rules specified by the interface.
173
174       •   interface
175
176           The name of a predefined interface, or a reference to a custom
177           interface, to use for this meta-method. See "Selecting Interfaces",
178           below.
179
180       •   modifier
181
182           The names of one or more predefined modifier flags. See "Selecting
183           Modifiers", below.
184
185   Informative Parameters
186       The following parameters are set automatically when your meta-method is
187       declared:
188
189       •   target_class
190
191           The class that requested the meta-method, into which its
192           subroutines will be installed.
193
194       •   template_name
195
196           The Class::MakeMethods::Template method used for this declaration.
197
198       •   template_class
199
200           The Class::MakeMethods::Template subclass used for this
201           declaration.
202
203   Other Parameters
204       Specific subclasses and template types provide support for additional
205       parameters.
206
207       Note that you generally should not arbitrarily assign additional
208       parameters to a meta-method unless you know that they do not conflict
209       with any parameters already defined or used by that meta-method.
210
211   Parameter Expansion
212       If a parameter specification contains '*', it is replaced with the
213       primary method name.
214
215       Example: The following defines counter (*, *_incr, *_reset) meta-
216       methods j and k, which use the hash keys j_index and k_index to fetch
217       and store their values.
218
219         use Class::MakeMethods::Template::Hash
220           counter => [ '-hash_key' => '*_index', qw/ j k / ];
221
222       (See Class::MakeMethods::Template::Hash for information about the
223       "hash_key" parameter.)
224
225       If a parameter specification contains '*{param}', it is replaced with
226       the value of that parameter.
227
228       Example: The following defines a Hash scalar meta-method which will
229       store its value in a hash key composed of the defining package's name
230       and individual method name, such as "$self->{MyObject-foo}":
231
232         use Class::MakeMethods::Template::Hash
233           'scalar' => [ '-hash_key' => '*{target_class}-*{name}', qw/ l / ];
234
235   Selecting Interfaces
236       Each template provides one or more predefined interfaces, each of which
237       specifies one or more methods to be installed in your package, and the
238       method names to use. Check the documentation for specific templates for
239       a list of which interfaces they define.
240
241       An interface may be specified for a single method by providing an
242       'interface' parameter:
243
244       •   'interface_name'
245
246           Select a predefined interface.
247
248           Example: Instead of the normal Hash scalar method named x, the
249           following creates methods with "Java-style" names and behaviors,
250           getx and setx.
251
252             use Class::MakeMethods::Template::Hash
253               'scalar' => [ 'x' => { interface=>'java' } ];
254
255           (See "scalar" in Class::MakeMethods::Template::Generic for a
256           description of the "java" interface.)
257
258       •   'behavior_name'
259
260           A simple interface consisting only of the named behavior.
261
262           For example, the below declaration creates a read-only methods
263           named q. (There are no set or clear methods, so any value would
264           have to be placed in the hash by other means.)
265
266             use Class::MakeMethods::Template::Hash (
267               'scalar' => [ 'q' => { interface=>'get' } ]
268             );
269
270       •   {  'subroutine_name_pattern' => 'behavior_name', ... }
271
272           A custom interface consists of a hash-ref that maps subroutine
273           names to the associated behaviors. Any "*" characters in
274           subroutine_name_pattern are replaced with the declared method name.
275
276           For example, the below delcaration creates paired get_w and set_w
277           methods:
278
279             use Class::MakeMethods::Template::Hash (
280               'scalar' => [ 'w' => { interface=> { 'get_*'=>'get', 'set_*'=>'set' } } ]
281             );
282
283       Some interfaces provide very different behaviors than the default
284       interface.
285
286       Example: The following defines a method g, which if called with an
287       argument appends to, rather than overwriting, the current value:
288
289         use Class::MakeMethods::Template::Hash
290           'string' => [ '--get_concat', 'g' ];
291
292       A named interface may also be specified as a default in the argument
293       list with a leading '--' followed by the interface's name.
294
295       Example: Instead of the normal Hash scalar methods (named x and
296       clear_x), the following creates methods with "Java-style" names and
297       behaviors (getx, setx).
298
299         use Class::MakeMethods::Template::Hash
300           'scalar' => [ '--java', 'x'  ];
301
302       An interface set in this way affects all meta-methods that follow it
303       until another interface is selected or the end of the array is reached;
304       to return to the original names request the 'default' interface.
305
306       Example: The below creates "Java-style" methods for e and f, "normal
307       scalar" methods for g, and "Eiffel-style" methods for h.
308
309         use Class::MakeMethods::Template::Hash
310           'scalar' => [
311             '--java'=> 'e', 'f',
312             '--default'=> 'g',
313             '--eiffel'=> 'h',
314           ];
315
316   Selecting Modifiers
317       You may select modifiers, which will affect all behaviors.
318
319         use Class::MakeMethods::Template::Hash
320             'scalar' => [ 'a', '--protected' => 'b', --private' => 'c' ];
321
322       Method b croaks if it's called from outside of the current package or
323       its subclasses.
324
325       Method c croaks if it's called from outside of the current package.
326
327       See the documentation for each template to learn which modifiers it
328       supports.
329
330   Runtime Parameter Access
331       If the meta-method is defined using an interface which includes the
332       attributes method, run-time access to meta-method parameters is
333       available.
334
335       Example: The following defines a counter meta-method named y, and then
336       later changes the 'join' parameter for that method at runtime.
337
338         use Class::MakeMethods ( get_concat => 'y' );
339
340         y_attributes(undef, 'join', "\t" )
341         print y_attributes(undef, 'join')
342

EXTENDING

344       You can create your own method-generator templates by following the
345       below outline.
346
347   Mechanisms
348       Dynamic generation of methods in Perl generally depends on one of two
349       approaches: string evals, which can be as flexible as your string-
350       manipulation functions allow, but are run-time resource intensive; or
351       closures, which are limited by the number of subroutine constructors
352       you write ahead of time but which are faster and smaller than evals.
353
354       Class::MakeMethods::Template uses both of these approaches: To generate
355       different types of subroutines, a simple text-substitution mechanism
356       combines bits of Perl to produce the source code for a subroutine, and
357       then evals those to produce code refs. Any differences which can be
358       handled with only data changes are managed at the closure layer; once
359       the subroutines are built, they are repeatedly bound as closures to
360       hashes of parameter data.
361
362   Code Generation
363       A substitution-based "macro language" is used to assemble code strings.
364       This happens only once per specific subclass/template/behavior
365       combination used in your program. (If you have disk-caching enabled,
366       the template interpretation is only done once, and then saved; see
367       below.)
368
369       There are numerous examples of this within the Generic interface and
370       its subclasses; for examples, look at the following methods:
371       Universal:generic, Generic:scalar, Hash:generic, and Hash:scalar.
372
373       See Class::MakeMethods::Template::TextBuilder for more information.
374
375   Template Definitions
376       Template method generators are declared by creating a subroutine that
377       returns a hash-ref of information about the template. When these
378       subroutines are first called, the template information is filled in
379       with imported and derived values, blessed as a
380       Class::MakeMethods::Template object, and cached.
381
382       Each "use" of your subclass, or call to its "make", causes these
383       objects to assemble the requested methods and return them to
384       Class::MakeMethods for installation in the calling package.
385
386       Method generators defined this way will have support for parameters,
387       custom interfaces, and the other features discussed above.
388
389       (Your module may also use the "Aliasing" and "Rewriting" functionality
390       described in "EXTENDING" in Class::MakeMethods.)
391
392       Definition hashes contain several types of named resources in a second
393       level of hash-refs under the following keys:
394
395       •   interface - Naming styles (see "Defining Interfaces", below)
396
397       •   params - Default parameters for meta-methods declared with this
398           template (see "Default Parameters", below)
399
400       •   behavior - Method recipes (see "Defining Behaviors", below)
401
402       •   code_expr - Bits of code used by the behaviors
403
404   Minimum Template Definition
405       You must at least specify one behavior; all other information is
406       optional.
407
408       Class::MakeMethods will automatically fill in the template name and
409       class as 'template_name' and 'template_class' entries in the version of
410       your template definition hash that it caches and uses for future
411       execution.
412
413       For example a simple sub-class that defines a method type
414       upper_case_get_set might look like this:
415
416         package Class::MakeMethods::UpperCase;
417         use Class::MakeMethods '-isasubclass';
418
419         sub uc_scalar {
420           return {
421             'behavior' => {
422               'default' => sub {
423                 my $m_info = $_[0];
424                 return sub {
425                   my $self = shift;
426                   if ( scalar @_ ) {
427                     $self->{ $m_info->{'name'} } = uc( shift )
428                   } else {
429                     $self->{ $m_info->{'name'} };
430                   }
431                 }
432               },
433             }
434           }
435         }
436
437       And a caller could then use it to generate methods in their package by
438       invoking:
439
440         Class::MakeMethods::UpperCase->make( 'uc_scalar' => [ 'foo' ] );
441
442   Default Parameters
443       Each template may include a set of default parameters for all
444       declarations as "params => hash_ref".
445
446       Template-default parameters can be overrridden by interface '-params',
447       described below, and and method-specific parameters, described above.
448
449   Defining Interfaces
450       Template definitions may have one or more interfaces, including the
451       default one, named 'default', which is automatically selected if
452       another interface is not requested. (If no default interface is
453       provided, one is constructed, which simply calls for a behavior named
454       default.)
455
456       Most commonly, an interface is specified as a hash which maps one or
457       more subroutine names to the behavior to use for each. The interface
458       subroutine names generally contain an asterisk character, '*', which
459       will be replaced by the name of each meta-method.
460
461       Example: The below defines methods e_get, e_set, and e_clear.
462
463         use Class::MakeMethods::Template::Hash
464           'scalar' => [
465             -interface=>{ '*_clear'=>clear, '*_get'=>'get', '*_set'=>'set' }, 'e'
466           ];
467
468       If the provided name does not contain an asterisk, it will not be
469       modified for individual meta-methods; for examples, see the bit_fields
470       method generated by Generic bits, and the DESTROY method generated by
471       InsideOut meta-methods.
472
473       In addition to the name-to-behavior correspondences described above,
474       interfaces may also contain additional entries with keys begining with
475       the '-' character which are interpreted as follows:
476
477       •   "-params => hash_ref"
478
479           Interfaces may include a '-params' key and associated reference to
480           a hash of default parameters for that interface.
481
482       •   "-base => interface_name"
483
484           Interfaces can be based on previously existing ones by including a
485           -base specification in the the hash. The base value should contain
486           one or more space-separated names of the interfaces to be included.
487
488           Example: The below defines methods getG, setG, and clearG.
489
490             use Class::MakeMethods::Template::Hash
491               'scalar' => [
492                 -interface => { -base=>'java', 'clear*'=>'clear' }, qw/ G /
493               ];
494
495           If multiple interfaces are included in the -base specification and
496           specify different behaviors for the same subroutine name, the later
497           ones will override the earlier. Names which appear in the base
498           interface can be overridden by providing a new value, or a name can
499           be removed by mapping it to undef or the empty string.
500
501           Example: The following defines a get-set meta-method h, but
502           supresses the clear_h method:
503
504             use Class::MakeMethods::Template::Hash
505               'scalar' => [
506                 -interface => { -base=>'with_clear', 'clear_*'=>'' }, qw/ h /
507               ];
508
509   Defining Behaviors
510       Behaviors can be provided as text which is eval'd to form a closure-
511       generating subroutine when it's first used; $self is automatically
512       defined and assigned the value of the first argument.
513
514             'behavior' => {
515               'default' => q{
516                   if ( scalar @_ ) { $self->{ $m_info->{'name'} } = uc shift }
517                   $self->{ $m_info->{'name'} };
518               },
519             }
520
521       A simple substitution syntax provides for macro interpretation with
522       definition strings. This functionality is currently undocumented; for
523       additional details see the _interpret_text_builder function in
524       Class::MakeMethods, and review the code_expr hashes defined in
525       Class::MakeMethods::Generic.
526
527   Importing
528       You can copy values out of other template definitions by specifying an
529       '-import' key and corresponding hash reference. You can specify an
530       -import for inside any of the template definition sub-hashes.  If no
531       -import is specified for a subhash, and there is a top-level -import
532       value, it is used instead.
533
534       Inside an -import hash, provide "TemplateClass:type" names for each
535       source you wish to copy from, and the values to import, which can be a
536       string, a reference to an array of strings, or '*' to import everything
537       available. (The order of copying is not defined.)
538
539       Example: The below definition creates a new template which is identical
540       to an existing one.
541
542         package Class::MakeMethods::MyMethods;
543         sub scalarama {
544           { -import => { 'Template::Hash:scalar' => '*' } }
545         }
546
547       Values that are already set are not modified, unless they're an array
548       ref, in which case they're added to.
549
550       Example:
551
552         package Class::MakeMethods::MyMethods;
553         sub foo_method {
554           { 'behavior' => {
555             '-init' => [ sub {  warn "Defining foo_method $_[0]->{'name'}" } ],
556             'default' => q{ warn "Calling foo_method behavior" }.
557           } }
558         }
559         sub bar_method {
560           { 'behavior' => {
561             -import => { 'MyMethods:foo_method' => '*' },
562             '-init' => [ sub {  warn "Defining bar_method $_[0]->{'name'}" } ],
563             'default' => q{ warn "Calling bar_method behavior" }.
564           } }
565         }
566
567       In this case, the bar_method ends up with an array of two '-init'
568       subroutines, its own and the imported one, but only its own default
569       behavior.
570
571   Modifying Existing Templates
572       You can over-write information contained in template definitions to
573       alter their subsequent behavior.
574
575       Example: The following extends the Hash:scalar template definition by
576       adding a new interface, and then uses it to create scalar accessor
577       methods named access_p and access_q that get and set values for the
578       hash keys 'p' and 'q':
579
580         Class::MakeMethods::Template::Hash->named_method('scalar')->
581                 {'interface'}{'frozzle'} = { 'access_*'=>'get_set' };
582
583         package My::Object;
584         Class::MakeMethods::Template::Hash->make( 'scalar' => [ --frozzle => qw( p q ) ] );
585
586         $object->access_p('Potato');    # $object->{p} = 'Potato'
587         print $object->access_q();      # print $object->{q}
588
589       Note that this constitutes "action at a distance" and will affect
590       subsequent use by other packages; unless you are "fixing" the current
591       behavior, you are urged to create your own template definition which
592       imports the base behavior of the existing template and overrides the
593       information in question.
594
595       Example: The following safely declares a new version of Hash:scalar
596       with the desired additional interface:
597
598         package My::Methods;
599
600         sub scalar {
601           {
602             -import => { 'Template::Hash:scalar' => '*' } ,
603             interface => { 'frozzle' => { 'access_*'=>'get_set' } },
604           }
605         }
606
607         package My::Object;
608         My::Methods->make( 'scalar' => [ --frozzle => qw( p q ) ] );
609
610   Disk Caching
611       To enable disk caching of generated code, create an empty directory and
612       pass it to the DiskCache package:
613
614         use Class::MakeMethods::Template::DiskCache qw( /my/code/dir );
615
616       This has a mixed effect on performance, but has the notable advantage
617       of letting you view the subroutines that are being generated by your
618       templates.
619
620       See Class::MakeMethods::Template::DiskCache for more information.
621