1Spiffy(3) User Contributed Perl Documentation Spiffy(3)
2
6 Spiffy - Spiffy Perl Interface Framework For You
7
9 package Keen;
10 use Spiffy -Base;
11 field 'mirth';
12 const mood => ':-)';
13 sub happy {
15 if ($self->mood eq ':-(') {
16 $self->mirth(-1);
17 print "Cheer up!";
18 }
19 super;
20 }
21
23 "Spiffy" is a framework and methodology for doing object oriented (OO)
24 programming in Perl. Spiffy combines the best parts of Exporter.pm,
25 base.pm, mixin.pm and SUPER.pm into one magic foundation class. It
26 attempts to fix all the nits and warts of traditional Perl OO, in a
27 clean, straightforward and (perhaps someday) standard way.
28 Spiffy borrows ideas from other OO languages like Python, Ruby, Java
30 and Perl 6. It also adds a few tricks of its own.
31 If you take a look on CPAN, there are a ton of OO related modules. When
33 starting a new project, you need to pick the set of modules that makes
34 most sense, and then you need to use those modules in each of your
35 classes. Spiffy, on the other hand, has everything you'll probably need
36 in one module, and you only need to use it once in one of your classes.
37 If you make Spiffy.pm the base class of the basest class in your
38 project, Spiffy will automatically pass all of its magic to all of your
39 subclasses. You may eventually forget that you're even using it!
40 The most striking difference between Spiffy and other Perl object
42 oriented base classes, is that it has the ability to export things. If
43 you create a subclass of Spiffy, all the things that Spiffy exports
44 will automatically be exported by your subclass, in addition to any
45 more things that you want to export. And if someone creates a subclass
46 of your subclass, all of those things will be exported automatically,
47 and so on. Think of it as "Inherited Exportation", and it uses the
48 familiar Exporter.pm specification syntax.
49 To use Spiffy or any subclass of Spiffy as a base class of your class,
51 you specify the "-base" argument to the "use" command.
52 use MySpiffyBaseModule -base;
54 You can also use the traditional "use base 'MySpiffyBaseModule';"
56 syntax and everything will work exactly the same. The only caveat is
57 that Spiffy.pm must already be loaded. That's because Spiffy rewires
58 base.pm on the fly to do all the Spiffy magics.
59 Spiffy has support for Ruby-like mixins with Perl6-like roles. Just
61 like "base" you can use either of the following invocations:
62 use mixin 'MySpiffyBaseModule';
64 use MySpiffyBaseModule -mixin;
65 The second version will only work if the class being mixed in is a
67 subclass of Spiffy. The first version will work in all cases, as long
68 as Spiffy has already been loaded.
69 To limit the methods that get mixed in, use roles. (Hint: they work
71 just like an Exporter list):
72 use MySpiffyBaseModule -mixin => qw(:basics x y !foo);
74 In object oriented Perl almost every subroutine is a method. Each
76 method gets the object passed to it as its first argument. That means
77 practically every subroutine starts with the line:
78 my $self = shift;
80 Spiffy provides a simple, optional filter mechanism to insert that line
82 for you, resulting in cleaner code. If you figure an average method has
83 10 lines of code, that's 10% of your code! To turn this option on, you
84 just use the "-Base" option instead of the "-base" option, or add the
85 "-selfless" option. If source filtering makes you queazy, don't use the
86 feature. I personally find it addictive in my quest for writing squeaky
87 clean, maintainable code.
88 A useful feature of Spiffy is that it exports two functions: "field"
90 and "const" that can be used to declare the attributes of your class,
91 and automatically generate accessor methods for them. The only
92 difference between the two functions is that "const" attributes can not
93 be modified; thus the accessor is much faster.
94 One interesting aspect of OO programming is when a method calls the
96 same method from a parent class. This is generally known as calling a
97 super method. Perl's facility for doing this is butt ugly:
98 sub cleanup {
100 my $self = shift;
101 $self->scrub;
102 $self->SUPER::cleanup(@_);
103 }
104 Spiffy makes it, er, super easy to call super methods. You just use the
106 "super" function. You don't need to pass it any arguments because it
107 automatically passes them on for you. Here's the same function with
108 Spiffy:
109 sub cleanup {
111 $self->scrub;
112 super;
113 }
114 Spiffy has a special method for parsing arguments called
116 "parse_arguments", that it also uses for parsing its own arguments. You
117 declare which arguments are boolean (singletons) and which ones are
118 paired, with two special methods called "boolean_arguments" and
119 "paired_arguments". Parse arguments pulls out the booleans and pairs
120 and returns them in an anonymous hash, followed by a list of the
121 unmatched arguments.
122 Finally, Spiffy can export a few debugging functions "WWW", "XXX",
124 "YYY" and "ZZZ". Each of them produces a YAML dump of its arguments.
125 WWW warns the output, XXX dies with the output, YYY prints the output,
126 and ZZZ confesses the output. If YAML doesn't suit your needs, you can
127 switch all the dumps to Data::Dumper format with the "-dumper" option.
128 That's Spiffy!
130
132 Spiffy implements a completely new idea in Perl. Modules that act both
133 as object oriented classes and that also export functions. But it takes
134 the concept of Exporter.pm one step further; it walks the entire @ISA
135 path of a class and honors the export specifications of each module.
136 Since Spiffy calls on the Exporter module to do this, you can use all
137 the fancy interface features that Exporter has, including tags and
138 negation.
139 Spiffy considers all the arguments that don't begin with a dash to
141 comprise the export specification.
142 package Vehicle;
144 use Spiffy -base;
145 our $SERIAL_NUMBER = 0;
146 our @EXPORT = qw($SERIAL_NUMBER);
147 our @EXPORT_BASE = qw(tire horn);
148 package Bicycle;
150 use Vehicle -base, '!field';
151 $self->inflate(tire);
152 In this case, "Bicycle-"isa('Vehicle')> and also all the things that
154 "Vehicle" and "Spiffy" export, will go into "Bicycle", except "field".
155 Exporting can be very helpful when you've designed a system with
157 hundreds of classes, and you want them all to have access to some
158 functions or constants or variables. Just export them in your main base
159 class and every subclass will get the functions they need.
160 You can do almost everything that Exporter does because Spiffy
162 delegates the job to Exporter (after adding some Spiffy magic). Spiffy
163 offers a @EXPORT_BASE variable which is like @EXPORT, but only for
164 usages that use "-base".
165
167 If you've done much OO programming in Perl you've probably used
168 Multiple Inheritance (MI), and if you've done much MI you've probably
169 run into weird problems and headaches. Some languages like Ruby,
170 attempt to resolve MI issues using a technique called mixins.
171 Basically, all Ruby classes use only Single Inheritance (SI), and then
172 mixin functionality from other modules if they need to.
173 Mixins can be thought of at a simplistic level as importing the methods
175 of another class into your subclass. But from an implementation
176 standpoint that's not the best way to do it. Spiffy does what Ruby
177 does. It creates an empty anonymous class, imports everything into that
178 class, and then chains the new class into your SI ISA path. In other
179 words, if you say:
180 package A;
182 use B -base;
183 use C -mixin;
184 use D -mixin;
185 You end up with a single inheritance chain of classes like this:
187 A << A-D << A-C << B;
189 "A-D" and "A-C" are the actual package names of the generated classes.
191 The nice thing about this style is that mixing in C doesn't clobber any
192 methods in A, and D doesn't conflict with A or C either. If you mixed
193 in a method in C that was also in A, you can still get to it by using
194 "super".
195 When Spiffy mixes in C, it pulls in all the methods in C that do not
197 begin with an underscore. Actually it goes farther than that. If C is a
198 subclass it will pull in every method that C "can" do through
199 inheritance. This is very powerful, maybe too powerful.
200 To limit what you mixin, Spiffy borrows the concept of Roles from
202 Perl6. The term role is used more loosely in Spiffy though. It's much
203 like an import list that the Exporter module uses, and you can use
204 groups (tags) and negation. If the first element of your list uses
205 negation, Spiffy will start with all the methods that your mixin class
206 can do.
207 use E -mixin => qw(:tools walk !run !:sharp_tools);
209 In this example, "walk" and "run" are methods that E can do, and
211 "tools" and "sharp_tools" are roles of class E. How does class E define
212 these roles? It very simply defines methods called "_role_tools" and
213 "_role_sharp_tools" which return lists of more methods. (And possibly
214 other roles!) The neat thing here is that since roles are just methods,
215 they too can be inherited. Take that Perl6!
216
218 By using the "-Base" flag instead of "-base" you never need to write
219 the line:
220 my $self = shift;
222 This statement is added to every subroutine in your class by using a
224 source filter. The magic is simple and fast, so there is litte
225 performance penalty for creating clean code on par with Ruby and
226 Python.
227 package Example;
229 use Spiffy -Base;
230 sub crazy {
232 $self->nuts;
233 }
234 sub wacky { }
235 sub new() {
236 bless [], shift;
237 }
238 is exactly the same as:
240 package Example;
242 use Spiffy -base;
243 use strict;use warnings;
244 sub crazy {my $self = shift;
245 $self->nuts;
246 }
247 sub wacky {my $self = shift; }
248 sub new {
249 bless [], shift;
250 }
251 ;1;
252 Note that the empty parens after the subroutine "new" keep it from
254 having a $self added. Also note that the extra code is added to
255 existing lines to ensure that line numbers are not altered.
256 "-Base" also turns on the strict and warnings pragmas, and adds that
258 annoying '1;' line to your module.
259
261 Spiffy now has support for private methods when you use the '-Base'
262 filter mechanism. You just declare the subs with the "my" keyword, and
263 call them with a '$' in front. Like this:
264 package Keen;
266 use SomethingSpiffy -Base;
267 # normal public method
269 sub swell {
270 $self->$stinky;
271 }
272 # private lexical method. uncallable from outside this file.
274 my sub stinky {
275 ...
276 }
277
279 The XXX function is very handy for debugging because you can insert it
280 almost anywhere, and it will dump your data in nice clean YAML. Take
281 the following statement:
282 my @stuff = grep { /keen/ } $self->find($a, $b);
284 If you have a problem with this statement, you can debug it in any of
286 the following ways:
287 XXX my @stuff = grep { /keen/ } $self->find($a, $b);
289 my @stuff = XXX grep { /keen/ } $self->find($a, $b);
290 my @stuff = grep { /keen/ } XXX $self->find($a, $b);
291 my @stuff = grep { /keen/ } $self->find(XXX $a, $b);
292 XXX is easy to insert and remove. It is also a tradition to mark
294 uncertain areas of code with XXX. This will make the debugging dumpers
295 easy to spot if you forget to take them out.
296 WWW and YYY are nice because they dump their arguments and then return
298 the arguments. This way you can insert them into many places and still
299 have the code run as before. Use ZZZ when you need to die with both a
300 YAML dump and a full stack trace.
301 The debugging functions are exported by default if you use the "-base"
303 option, but only if you have previously used the "-XXX" option. To
304 export all 4 functions use the export tag:
305 use SomeSpiffyModule ':XXX';
307 To force the debugging functions to use Data::Dumper instead of YAML:
309 use SomeSpiffyModule -dumper;
311
313 This section describes the functions the Spiffy exports. The "field",
314 "const", "stub" and "super" functions are only exported when you use
315 the "-base" or "-Base" options.
316 · field
318 Defines accessor methods for a field of your class:
320 package Example;
322 use Spiffy -Base;
323 field 'foo';
325 field bar => [];
326 sub lalala {
328 $self->foo(42);
329 push @{$self->{bar}}, $self->foo;
330 }
331 The first parameter passed to "field" is the name of the attribute
333 being defined. Accessors can be given an optional default value.
334 This value will be returned if no value for the field has been set
335 in the object.
336 · const
338 const bar => 42;
340 The "const" function is similar to <field> except that it is
342 immutable. It also does not store data in the object. You probably
343 always want to give a "const" a default value, otherwise the
344 generated method will be somewhat useless.
345 · stub
347 stub 'cigar';
349 The "stub" function generates a method that will die with an
351 appropriate message. The idea is that subclasses must implement
352 these methods so that the stub methods don't get called.
353 · super
355 If this function is called without any arguments, it will call the
357 same method that it is in, higher up in the ISA tree, passing it
358 all the same arguments. If it is called with arguments, it will use
359 those arguments with $self in the front. In other words, it just
360 works like you'd expect.
361 sub foo {
363 super; # Same as $self->SUPER::foo(@_);
364 super('hello'); # Same as $self->SUPER::foo('hello');
365 $self->bar(42);
366 }
367 sub new() {
369 my $self = super;
370 $self->init;
371 return $self;
372 }
373 "super" will simply do nothing if there is no super method.
375 Finally, "super" does the right thing in AUTOLOAD subroutines.
376
378 This section lists all of the methods that any subclass of Spiffy
379 automatically inherits.
380 · mixin
382 A method to mixin a class at runtime. Takes the same arguments as
384 "use mixin ...". Makes the target class a mixin of the caller.
385 $self->mixin('SomeClass');
387 $object->mixin('SomeOtherClass' => 'some_method');
388 · parse_arguments
390 This method takes a list of arguments and groups them into pairs.
392 It allows for boolean arguments which may or may not have a value
393 (defaulting to 1). The method returns a hash reference of all the
394 pairs as keys and values in the hash. Any arguments that cannot be
395 paired, are returned as a list. Here is an example:
396 sub boolean_arguments { qw(-has_spots -is_yummy) }
398 sub paired_arguments { qw(-name -size) }
399 my ($pairs, @others) = $self->parse_arguments(
400 'red', 'white',
401 -name => 'Ingy',
402 -has_spots =>
403 -size => 'large',
404 'black',
405 -is_yummy => 0,
406 );
407 After this call, $pairs will contain:
409 {
411 -name => 'Ingy',
412 -has_spots => 1,
413 -size => 'large',
414 -is_yummy => 0,
415 }
416 and @others will contain 'red', 'white', and 'black'.
418 · boolean_arguments
420 Returns the list of arguments that are recognized as being boolean.
422 Override this method to define your own list.
423 · paired_arguments
425 Returns the list of arguments that are recognized as being paired.
427 Override this method to define your own list.
428
430 When you "use" the Spiffy module or a subclass of it, you can pass it a
431 list of arguments. These arguments are parsed using the
432 "parse_arguments" method described above. The special argument "-base",
433 is used to make the current package a subclass of the Spiffy module
434 being used.
435 Any non-paired parameters act like a normal import list; just like
437 those used with the Exporter module.
438
440 The proper way to use a Spiffy module as a base class is with the
441 "-base" parameter to the "use" statement. This differs from typical
442 modules where you would want to "use base".
443 package Something;
445 use Spiffy::Module -base;
446 use base 'NonSpiffy::Module';
447 Now it may be hard to keep track of what's Spiffy and what is not.
449 Therefore Spiffy has actually been made to work with base.pm. You can
450 say:
451 package Something;
453 use base 'Spiffy::Module';
454 use base 'NonSpiffy::Module';
455 "use base" is also very useful when your class is not an actual module
457 (a separate file) but just a package in some file that has already been
458 loaded. "base" will work whether the class is a module or not, while
459 the "-base" syntax cannot work that way, since "use" always tries to
460 load a module.
461 base.pm Caveats
463 To make Spiffy work with base.pm, a dirty trick was played. Spiffy
464 swaps "base::import" with its own version. If the base modules are not
465 Spiffy, Spiffy calls the original base::import. If the base modules are
466 Spiffy, then Spiffy does its own thing.
467 There are two caveats.
469 · Spiffy must be loaded first.
471 If Spiffy is not loaded and "use base" is invoked on a Spiffy
473 module, Spiffy will die with a useful message telling the author to
474 read this documentation. That's because Spiffy needed to do the
475 import swap beforehand.
476 If you get this error, simply put a statement like this up front in
478 your code:
479 use Spiffy ();
481 · No Mixing
483 "base.pm" can take multiple arguments. And this works with Spiffy
485 as long as all the base classes are Spiffy, or they are all non-
486 Spiffy. If they are mixed, Spiffy will die. In this case just use
487 separate "use base" statements.
488
490 Spiffy is a wonderful way to do OO programming in Perl, but it is still
491 a work in progress. New things will be added, and things that don't
492 work well, might be removed.
493
495 Ingy dA~Xt Net <ingy@cpan.org>
496
498 Copyright (c) 2006. Ingy dA~Xt Net. All rights reserved. Copyright (c)
499 2004. Brian Ingerson. All rights reserved.
500 This program is free software; you can redistribute it and/or modify it
502 under the same terms as Perl itself.
503 See <http://www.perl.com/perl/misc/Artistic.html>
505perl v5.10.1 2006-01-29 Spiffy(3)