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Reintroduce Attribute::Handlers with Spider's fixes.
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1package Attribute::Handlers;
2use 5.006;
3use Carp;
4use warnings;
5$VERSION = '0.76';
6# $DB::single=1;
7
8my %symcache;
9sub findsym {
10 my ($pkg, $ref, $type) = @_;
11 return $symcache{$pkg,$ref} if $symcache{$pkg,$ref};
12 $type ||= ref($ref);
13 my $found;
14 foreach my $sym ( values %{$pkg."::"} ) {
15 return $symcache{$pkg,$ref} = \$sym
16 if *{$sym}{$type} && *{$sym}{$type} == $ref;
17 }
18}
19
20my %validtype = (
21 VAR => [qw[SCALAR ARRAY HASH]],
22 ANY => [qw[SCALAR ARRAY HASH CODE]],
23 "" => [qw[SCALAR ARRAY HASH CODE]],
24 SCALAR => [qw[SCALAR]],
25 ARRAY => [qw[ARRAY]],
26 HASH => [qw[HASH]],
27 CODE => [qw[CODE]],
28);
29my %lastattr;
30my @declarations;
31my %raw;
32my %phase;
33my %sigil = (SCALAR=>'$', ARRAY=>'@', HASH=>'%');
34my $global_phase = 0;
35my %global_phases = (
36 BEGIN => 0,
37 CHECK => 1,
38 INIT => 2,
39 END => 3,
40);
41my @global_phases = qw(BEGIN CHECK INIT END);
42
43sub _usage_AH_ {
44 croak "Usage: use $_[0] autotie => {AttrName => TieClassName,...}";
45}
46
47my $qual_id = qr/^[_a-z]\w*(::[_a-z]\w*)*$/i;
48
49sub import {
50 my $class = shift @_;
51 return unless $class eq "Attribute::Handlers";
52 while (@_) {
53 my $cmd = shift;
54 if ($cmd =~ /^autotie((?:ref)?)$/) {
55 my $tiedata = ($1 ? '$ref, ' : '') . '@$data';
56 my $mapping = shift;
57 _usage_AH_ $class unless ref($mapping) eq 'HASH';
58 while (my($attr, $tieclass) = each %$mapping) {
59 $tieclass =~ s/^([_a-z]\w*(::[_a-z]\w*)*)(.*)/$1/is;
60 my $args = $3||'()';
61 _usage_AH_ $class unless $attr =~ $qual_id
62 && $tieclass =~ $qual_id
63 && eval "use base $tieclass; 1";
64 if ($tieclass->isa('Exporter')) {
65 local $Exporter::ExportLevel = 2;
66 $tieclass->import(eval $args);
67 }
68 $attr =~ s/__CALLER__/caller(1)/e;
69 $attr = caller()."::".$attr unless $attr =~ /::/;
70 eval qq{
71 sub $attr : ATTR(VAR) {
72 my (\$ref, \$data) = \@_[2,4];
73 my \$was_arrayref = ref \$data eq 'ARRAY';
74 \$data = [ \$data ] unless \$was_arrayref;
75 my \$type = ref(\$ref)||"value (".(\$ref||"<undef>").")";
76 (\$type eq 'SCALAR')? tie \$\$ref,'$tieclass',$tiedata
77 :(\$type eq 'ARRAY') ? tie \@\$ref,'$tieclass',$tiedata
78 :(\$type eq 'HASH') ? tie \%\$ref,'$tieclass',$tiedata
79 : die "Can't autotie a \$type\n"
80 } 1
81 } or die "Internal error: $@";
82 }
83 }
84 else {
85 croak "Can't understand $_";
86 }
87 }
88}
89sub _resolve_lastattr {
90 return unless $lastattr{ref};
91 my $sym = findsym @lastattr{'pkg','ref'}
92 or die "Internal error: $lastattr{pkg} symbol went missing";
93 my $name = *{$sym}{NAME};
94 warn "Declaration of $name attribute in package $lastattr{pkg} may clash with future reserved word\n"
95 if $^W and $name !~ /[A-Z]/;
96 foreach ( @{$validtype{$lastattr{type}}} ) {
97 *{"$lastattr{pkg}::_ATTR_${_}_${name}"} = $lastattr{ref};
98 }
99 %lastattr = ();
100}
101
102sub AUTOLOAD {
103 my ($class) = $AUTOLOAD =~ m/(.*)::/g;
104 $AUTOLOAD =~ m/_ATTR_(.*?)_(.*)/ or
105 croak "Can't locate class method '$AUTOLOAD' via package '$class'";
106 croak "Attribute handler '$3' doesn't handle $2 attributes";
107}
108
109sub DESTROY {}
110
111my $builtin = qr/lvalue|method|locked/;
112
113sub _gen_handler_AH_() {
114 return sub {
115 _resolve_lastattr;
116 my ($pkg, $ref, @attrs) = @_;
117 foreach (@attrs) {
118 my ($attr, $data) = /^([a-z_]\w*)(?:[(](.*)[)])?$/is or next;
119 if ($attr eq 'ATTR') {
120 $data ||= "ANY";
121 $raw{$ref} = $data =~ s/\s*,?\s*RAWDATA\s*,?\s*//;
122 $phase{$ref}{BEGIN} = 1
123 if $data =~ s/\s*,?\s*(BEGIN)\s*,?\s*//;
124 $phase{$ref}{INIT} = 1
125 if $data =~ s/\s*,?\s*(INIT)\s*,?\s*//;
126 $phase{$ref}{END} = 1
127 if $data =~ s/\s*,?\s*(END)\s*,?\s*//;
128 $phase{$ref}{CHECK} = 1
129 if $data =~ s/\s*,?\s*(CHECK)\s*,?\s*//
130 || ! keys %{$phase{$ref}};
131 # Added for cleanup to not pollute next call.
132 (%lastattr = ()),
133 croak "Can't have two ATTR specifiers on one subroutine"
134 if keys %lastattr;
135 croak "Bad attribute type: ATTR($data)"
136 unless $validtype{$data};
137 %lastattr=(pkg=>$pkg,ref=>$ref,type=>$data);
138 }
139 else {
140 my $handler = $pkg->can($attr);
141 next unless $handler;
142 my $decl = [$pkg, $ref, $attr, $data,
143 $raw{$handler}, $phase{$handler}];
144 foreach my $gphase (@global_phases) {
145 _apply_handler_AH_($decl,$gphase)
146 if $global_phases{$gphase} <= $global_phase;
147 }
148 push @declarations, $decl;
149 }
150 $_ = undef;
151 }
152 return grep {defined && !/$builtin/} @attrs;
153 }
154}
155
156*{"MODIFY_${_}_ATTRIBUTES"} = _gen_handler_AH_ foreach @{$validtype{ANY}};
157push @UNIVERSAL::ISA, 'Attribute::Handlers'
158 unless grep /^Attribute::Handlers$/, @UNIVERSAL::ISA;
159
160sub _apply_handler_AH_ {
161 my ($declaration, $phase) = @_;
162 my ($pkg, $ref, $attr, $data, $raw, $handlerphase) = @$declaration;
163 return unless $handlerphase->{$phase};
164 # print STDERR "Handling $attr on $ref in $phase with [$data]\n";
165 my $type = ref $ref;
166 my $handler = "_ATTR_${type}_${attr}";
167 my $sym = findsym($pkg, $ref);
168 $sym ||= $type eq 'CODE' ? 'ANON' : 'LEXICAL';
169 no warnings;
170 my $evaled = !$raw && eval("package $pkg; no warnings;
171 local \$SIG{__WARN__}=sub{die}; [$data]");
172 $data = ($evaled && $data =~ /^\s*\[/) ? [$evaled]
173 : ($evaled) ? $evaled
174 : [$data];
175 $pkg->$handler($sym,
176 (ref $sym eq 'GLOB' ? *{$sym}{ref $ref}||$ref : $ref),
177 $attr,
178 (@$data>1? $data : $data->[0]),
179 $phase,
180 );
181 return 1;
182}
183
184CHECK {
185 $global_phase++;
186 _resolve_lastattr;
187 _apply_handler_AH_($_,'CHECK') foreach @declarations;
188}
189
190INIT { $global_phase++; _apply_handler_AH_($_,'INIT') foreach @declarations }
191
192END { $global_phase++; _apply_handler_AH_($_,'END') foreach @declarations }
193
1941;
195__END__
196
197=head1 NAME
198
199Attribute::Handlers - Simpler definition of attribute handlers
200
201=head1 VERSION
202
203This document describes version 0.76 of Attribute::Handlers,
204released November 15, 2001.
205
206=head1 SYNOPSIS
207
208 package MyClass;
209 require v5.6.0;
210 use Attribute::Handlers;
211 no warnings 'redefine';
212
213
214 sub Good : ATTR(SCALAR) {
215 my ($package, $symbol, $referent, $attr, $data) = @_;
216
217 # Invoked for any scalar variable with a :Good attribute,
218 # provided the variable was declared in MyClass (or
219 # a derived class) or typed to MyClass.
220
221 # Do whatever to $referent here (executed in CHECK phase).
222 ...
223 }
224
225 sub Bad : ATTR(SCALAR) {
226 # Invoked for any scalar variable with a :Bad attribute,
227 # provided the variable was declared in MyClass (or
228 # a derived class) or typed to MyClass.
229 ...
230 }
231
232 sub Good : ATTR(ARRAY) {
233 # Invoked for any array variable with a :Good attribute,
234 # provided the variable was declared in MyClass (or
235 # a derived class) or typed to MyClass.
236 ...
237 }
238
239 sub Good : ATTR(HASH) {
240 # Invoked for any hash variable with a :Good attribute,
241 # provided the variable was declared in MyClass (or
242 # a derived class) or typed to MyClass.
243 ...
244 }
245
246 sub Ugly : ATTR(CODE) {
247 # Invoked for any subroutine declared in MyClass (or a
248 # derived class) with an :Ugly attribute.
249 ...
250 }
251
252 sub Omni : ATTR {
253 # Invoked for any scalar, array, hash, or subroutine
254 # with an :Omni attribute, provided the variable or
255 # subroutine was declared in MyClass (or a derived class)
256 # or the variable was typed to MyClass.
257 # Use ref($_[2]) to determine what kind of referent it was.
258 ...
259 }
260
261
262 use Attribute::Handlers autotie => { Cycle => Tie::Cycle };
263
264 my $next : Cycle(['A'..'Z']);
265
266
267=head1 DESCRIPTION
268
269This module, when inherited by a package, allows that package's class to
270define attribute handler subroutines for specific attributes. Variables
271and subroutines subsequently defined in that package, or in packages
272derived from that package may be given attributes with the same names as
273the attribute handler subroutines, which will then be called in one of
274the compilation phases (i.e. in a C<BEGIN>, C<CHECK>, C<INIT>, or C<END>
275block).
276
277To create a handler, define it as a subroutine with the same name as
278the desired attribute, and declare the subroutine itself with the
279attribute C<:ATTR>. For example:
280
281 package LoudDecl;
282 use Attribute::Handlers;
283
284 sub Loud :ATTR {
285 my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
286 print STDERR
287 ref($referent), " ",
288 *{$symbol}{NAME}, " ",
289 "($referent) ", "was just declared ",
290 "and ascribed the ${attr} attribute ",
291 "with data ($data)\n",
292 "in phase $phase\n";
293 }
294
295This creates a handler for the attribute C<:Loud> in the class LoudDecl.
296Thereafter, any subroutine declared with a C<:Loud> attribute in the class
297LoudDecl:
298
299 package LoudDecl;
300
301 sub foo: Loud {...}
302
303causes the above handler to be invoked, and passed:
304
305=over
306
307=item [0]
308
309the name of the package into which it was declared;
310
311=item [1]
312
313a reference to the symbol table entry (typeglob) containing the subroutine;
314
315=item [2]
316
317a reference to the subroutine;
318
319=item [3]
320
321the name of the attribute;
322
323=item [4]
324
325any data associated with that attribute;
326
327=item [5]
328
329the name of the phase in which the handler is being invoked.
330
331=back
332
333Likewise, declaring any variables with the C<:Loud> attribute within the
334package:
335
336 package LoudDecl;
337
338 my $foo :Loud;
339 my @foo :Loud;
340 my %foo :Loud;
341
342will cause the handler to be called with a similar argument list (except,
343of course, that C<$_[2]> will be a reference to the variable).
344
345The package name argument will typically be the name of the class into
346which the subroutine was declared, but it may also be the name of a derived
347class (since handlers are inherited).
348
349If a lexical variable is given an attribute, there is no symbol table to
350which it belongs, so the symbol table argument (C<$_[1]>) is set to the
351string C<'LEXICAL'> in that case. Likewise, ascribing an attribute to
352an anonymous subroutine results in a symbol table argument of C<'ANON'>.
353
354The data argument passes in the value (if any) associated with the
355attribute. For example, if C<&foo> had been declared:
356
357 sub foo :Loud("turn it up to 11, man!") {...}
358
359then the string C<"turn it up to 11, man!"> would be passed as the
360last argument.
361
362Attribute::Handlers makes strenuous efforts to convert
363the data argument (C<$_[4]>) to a useable form before passing it to
364the handler (but see L<"Non-interpretive attribute handlers">).
365For example, all of these:
366
367 sub foo :Loud(till=>ears=>are=>bleeding) {...}
368 sub foo :Loud(['till','ears','are','bleeding']) {...}
369 sub foo :Loud(qw/till ears are bleeding/) {...}
370 sub foo :Loud(qw/my, ears, are, bleeding/) {...}
371 sub foo :Loud(till,ears,are,bleeding) {...}
372
373causes it to pass C<['till','ears','are','bleeding']> as the handler's
374data argument. However, if the data can't be parsed as valid Perl, then
375it is passed as an uninterpreted string. For example:
376
377 sub foo :Loud(my,ears,are,bleeding) {...}
378 sub foo :Loud(qw/my ears are bleeding) {...}
379
380cause the strings C<'my,ears,are,bleeding'> and C<'qw/my ears are bleeding'>
381respectively to be passed as the data argument.
382
383If the attribute has only a single associated scalar data value, that value is
384passed as a scalar. If multiple values are associated, they are passed as an
385array reference. If no value is associated with the attribute, C<undef> is
386passed.
387
388
389=head2 Typed lexicals
390
391Regardless of the package in which it is declared, if a lexical variable is
392ascribed an attribute, the handler that is invoked is the one belonging to
393the package to which it is typed. For example, the following declarations:
394
395 package OtherClass;
396
397 my LoudDecl $loudobj : Loud;
398 my LoudDecl @loudobjs : Loud;
399 my LoudDecl %loudobjex : Loud;
400
401causes the LoudDecl::Loud handler to be invoked (even if OtherClass also
402defines a handler for C<:Loud> attributes).
403
404
405=head2 Type-specific attribute handlers
406
407If an attribute handler is declared and the C<:ATTR> specifier is
408given the name of a built-in type (C<SCALAR>, C<ARRAY>, C<HASH>, or C<CODE>),
409the handler is only applied to declarations of that type. For example,
410the following definition:
411
412 package LoudDecl;
413
414 sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" }
415
416creates an attribute handler that applies only to scalars:
417
418
419 package Painful;
420 use base LoudDecl;
421
422 my $metal : RealLoud; # invokes &LoudDecl::RealLoud
423 my @metal : RealLoud; # error: unknown attribute
424 my %metal : RealLoud; # error: unknown attribute
425 sub metal : RealLoud {...} # error: unknown attribute
426
427You can, of course, declare separate handlers for these types as well
428(but you'll need to specify C<no warnings 'redefine'> to do it quietly):
429
430 package LoudDecl;
431 use Attribute::Handlers;
432 no warnings 'redefine';
433
434 sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" }
435 sub RealLoud :ATTR(ARRAY) { print "Urrrrrrrrrr!" }
436 sub RealLoud :ATTR(HASH) { print "Arrrrrgggghhhhhh!" }
437 sub RealLoud :ATTR(CODE) { croak "Real loud sub torpedoed" }
438
439You can also explicitly indicate that a single handler is meant to be
440used for all types of referents like so:
441
442 package LoudDecl;
443 use Attribute::Handlers;
444
445 sub SeriousLoud :ATTR(ANY) { warn "Hearing loss imminent" }
446
447(I.e. C<ATTR(ANY)> is a synonym for C<:ATTR>).
448
449
450=head2 Non-interpretive attribute handlers
451
452Occasionally the strenuous efforts Attribute::Handlers makes to convert
453the data argument (C<$_[4]>) to a useable form before passing it to
454the handler get in the way.
455
456You can turn off that eagerness-to-help by declaring
457an attribute handler with the keyword C<RAWDATA>. For example:
458
459 sub Raw : ATTR(RAWDATA) {...}
460 sub Nekkid : ATTR(SCALAR,RAWDATA) {...}
461 sub Au::Naturale : ATTR(RAWDATA,ANY) {...}
462
463Then the handler makes absolutely no attempt to interpret the data it
464receives and simply passes it as a string:
465
466 my $power : Raw(1..100); # handlers receives "1..100"
467
468=head2 Phase-specific attribute handlers
469
470By default, attribute handlers are called at the end of the compilation
471phase (in a C<CHECK> block). This seems to be optimal in most cases because
472most things that can be defined are defined by that point but nothing has
473been executed.
474
475However, it is possible to set up attribute handlers that are called at
476other points in the program's compilation or execution, by explicitly
477stating the phase (or phases) in which you wish the attribute handler to
478be called. For example:
479
480 sub Early :ATTR(SCALAR,BEGIN) {...}
481 sub Normal :ATTR(SCALAR,CHECK) {...}
482 sub Late :ATTR(SCALAR,INIT) {...}
483 sub Final :ATTR(SCALAR,END) {...}
484 sub Bookends :ATTR(SCALAR,BEGIN,END) {...}
485
486As the last example indicates, a handler may be set up to be (re)called in
487two or more phases. The phase name is passed as the handler's final argument.
488
489Note that attribute handlers that are scheduled for the C<BEGIN> phase
490are handled as soon as the attribute is detected (i.e. before any
491subsequently defined C<BEGIN> blocks are executed).
492
493
494=head2 Attributes as C<tie> interfaces
495
496Attributes make an excellent and intuitive interface through which to tie
497variables. For example:
498
499 use Attribute::Handlers;
500 use Tie::Cycle;
501
502 sub UNIVERSAL::Cycle : ATTR(SCALAR) {
503 my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
504 $data = [ $data ] unless ref $data eq 'ARRAY';
505 tie $$referent, 'Tie::Cycle', $data;
506 }
507
508 # and thereafter...
509
510 package main;
511
512 my $next : Cycle('A'..'Z'); # $next is now a tied variable
513
514 while (<>) {
515 print $next;
516 }
517
518Note that, because the C<Cycle> attribute receives its arguments in the
519C<$data> variable, if the attribute is given a list of arguments, C<$data>
520will consist of a single array reference; otherwise, it will consist of the
521single argument directly. Since Tie::Cycle requires its cycling values to
522be passed as an array reference, this means that we need to wrap
523non-array-reference arguments in an array constructor:
524
525 $data = [ $data ] unless ref $data eq 'ARRAY';
526
527Typically, however, things are the other way around: the tieable class expects
528its arguments as a flattened list, so the attribute looks like:
529
530 sub UNIVERSAL::Cycle : ATTR(SCALAR) {
531 my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
532 my @data = ref $data eq 'ARRAY' ? @$data : $data;
533 tie $$referent, 'Tie::Whatever', @data;
534 }
535
536
537This software pattern is so widely applicable that Attribute::Handlers
538provides a way to automate it: specifying C<'autotie'> in the
539C<use Attribute::Handlers> statement. So, the cycling example,
540could also be written:
541
542 use Attribute::Handlers autotie => { Cycle => 'Tie::Cycle' };
543
544 # and thereafter...
545
546 package main;
547
548 my $next : Cycle(['A'..'Z']); # $next is now a tied variable
549
550 while (<>) {
551 print $next;
552
553Note that we now have to pass the cycling values as an array reference,
554since the C<autotie> mechanism passes C<tie> a list of arguments as a list
555(as in the Tie::Whatever example), I<not> as an array reference (as in
556the original Tie::Cycle example at the start of this section).
557
558The argument after C<'autotie'> is a reference to a hash in which each key is
559the name of an attribute to be created, and each value is the class to which
560variables ascribed that attribute should be tied.
561
562Note that there is no longer any need to import the Tie::Cycle module --
563Attribute::Handlers takes care of that automagically. You can even pass
564arguments to the module's C<import> subroutine, by appending them to the
565class name. For example:
566
567 use Attribute::Handlers
568 autotie => { Dir => 'Tie::Dir qw(DIR_UNLINK)' };
569
570If the attribute name is unqualified, the attribute is installed in the
571current package. Otherwise it is installed in the qualifier's package:
572
573 package Here;
574
575 use Attribute::Handlers autotie => {
576 Other::Good => Tie::SecureHash, # tie attr installed in Other::
577 Bad => Tie::Taxes, # tie attr installed in Here::
578 UNIVERSAL::Ugly => Software::Patent # tie attr installed everywhere
579 };
580
581Autoties are most commonly used in the module to which they actually tie,
582and need to export their attributes to any module that calls them. To
583facilitiate this, Attribute::Handlers recognizes a special "pseudo-class" --
584C<__CALLER__>, which may be specified as the qualifier of an attribute:
585
586 package Tie::Me::Kangaroo:Down::Sport;
587
588 use Attribute::Handlers autotie => { __CALLER__::Roo => __PACKAGE__ };
589
590This causes Attribute::Handlers to define the C<Roo> attribute in the package
591that imports the Tie::Me::Kangaroo:Down::Sport module.
592
593=head3 Passing the tied object to C<tie>
594
595Occasionally it is important to pass a reference to the object being tied
596to the TIESCALAR, TIEHASH, etc. that ties it.
597
598The C<autotie> mechanism supports this too. The following code:
599
600 use Attribute::Handlers autotieref => { Selfish => Tie::Selfish };
601 my $var : Selfish(@args);
602
603has the same effect as:
604
605 tie my $var, 'Tie::Selfish', @args;
606
607But when C<"autotieref"> is used instead of C<"autotie">:
608
609 use Attribute::Handlers autotieref => { Selfish => Tie::Selfish };
610 my $var : Selfish(@args);
611
612the effect is to pass the C<tie> call an extra reference to the variable
613being tied:
614
615 tie my $var, 'Tie::Selfish', \$var, @args;
616
617
618
619=head1 EXAMPLES
620
621If the class shown in L<SYNOPSIS> were placed in the MyClass.pm
622module, then the following code:
623
624 package main;
625 use MyClass;
626
627 my MyClass $slr :Good :Bad(1**1-1) :Omni(-vorous);
628
629 package SomeOtherClass;
630 use base MyClass;
631
632 sub tent { 'acle' }
633
634 sub fn :Ugly(sister) :Omni('po',tent()) {...}
635 my @arr :Good :Omni(s/cie/nt/);
636 my %hsh :Good(q/bye) :Omni(q/bus/);
637
638
639would cause the following handlers to be invoked:
640
641 # my MyClass $slr :Good :Bad(1**1-1) :Omni(-vorous);
642
643 MyClass::Good:ATTR(SCALAR)( 'MyClass', # class
644 'LEXICAL', # no typeglob
645 \$slr, # referent
646 'Good', # attr name
647 undef # no attr data
648 'CHECK', # compiler phase
649 );
650
651 MyClass::Bad:ATTR(SCALAR)( 'MyClass', # class
652 'LEXICAL', # no typeglob
653 \$slr, # referent
654 'Bad', # attr name
655 0 # eval'd attr data
656 'CHECK', # compiler phase
657 );
658
659 MyClass::Omni:ATTR(SCALAR)( 'MyClass', # class
660 'LEXICAL', # no typeglob
661 \$slr, # referent
662 'Omni', # attr name
663 '-vorous' # eval'd attr data
664 'CHECK', # compiler phase
665 );
666
667
668 # sub fn :Ugly(sister) :Omni('po',tent()) {...}
669
670 MyClass::UGLY:ATTR(CODE)( 'SomeOtherClass', # class
671 \*SomeOtherClass::fn, # typeglob
672 \&SomeOtherClass::fn, # referent
673 'Ugly', # attr name
674 'sister' # eval'd attr data
675 'CHECK', # compiler phase
676 );
677
678 MyClass::Omni:ATTR(CODE)( 'SomeOtherClass', # class
679 \*SomeOtherClass::fn, # typeglob
680 \&SomeOtherClass::fn, # referent
681 'Omni', # attr name
682 ['po','acle'] # eval'd attr data
683 'CHECK', # compiler phase
684 );
685
686
687 # my @arr :Good :Omni(s/cie/nt/);
688
689 MyClass::Good:ATTR(ARRAY)( 'SomeOtherClass', # class
690 'LEXICAL', # no typeglob
691 \@arr, # referent
692 'Good', # attr name
693 undef # no attr data
694 'CHECK', # compiler phase
695 );
696
697 MyClass::Omni:ATTR(ARRAY)( 'SomeOtherClass', # class
698 'LEXICAL', # no typeglob
699 \@arr, # referent
700 'Omni', # attr name
701 "" # eval'd attr data
702 'CHECK', # compiler phase
703 );
704
705
706 # my %hsh :Good(q/bye) :Omni(q/bus/);
707
708 MyClass::Good:ATTR(HASH)( 'SomeOtherClass', # class
709 'LEXICAL', # no typeglob
710 \%hsh, # referent
711 'Good', # attr name
712 'q/bye' # raw attr data
713 'CHECK', # compiler phase
714 );
715
716 MyClass::Omni:ATTR(HASH)( 'SomeOtherClass', # class
717 'LEXICAL', # no typeglob
718 \%hsh, # referent
719 'Omni', # attr name
720 'bus' # eval'd attr data
721 'CHECK', # compiler phase
722 );
723
724
725Installing handlers into UNIVERSAL, makes them...err..universal.
726For example:
727
728 package Descriptions;
729 use Attribute::Handlers;
730
731 my %name;
732 sub name { return $name{$_[2]}||*{$_[1]}{NAME} }
733
734 sub UNIVERSAL::Name :ATTR {
735 $name{$_[2]} = $_[4];
736 }
737
738 sub UNIVERSAL::Purpose :ATTR {
739 print STDERR "Purpose of ", &name, " is $_[4]\n";
740 }
741
742 sub UNIVERSAL::Unit :ATTR {
743 print STDERR &name, " measured in $_[4]\n";
744 }
745
746Let's you write:
747
748 use Descriptions;
749
750 my $capacity : Name(capacity)
751 : Purpose(to store max storage capacity for files)
752 : Unit(Gb);
753
754
755 package Other;
756
757 sub foo : Purpose(to foo all data before barring it) { }
758
759 # etc.
760
761
762=head1 DIAGNOSTICS
763
764=over
765
766=item C<Bad attribute type: ATTR(%s)>
767
768An attribute handler was specified with an C<:ATTR(I<ref_type>)>, but the
769type of referent it was defined to handle wasn't one of the five permitted:
770C<SCALAR>, C<ARRAY>, C<HASH>, C<CODE>, or C<ANY>.
771
772=item C<Attribute handler %s doesn't handle %s attributes>
773
774A handler for attributes of the specified name I<was> defined, but not
775for the specified type of declaration. Typically encountered whe trying
776to apply a C<VAR> attribute handler to a subroutine, or a C<SCALAR>
777attribute handler to some other type of variable.
778
779=item C<Declaration of %s attribute in package %s may clash with future reserved word>
780
781A handler for an attributes with an all-lowercase name was declared. An
782attribute with an all-lowercase name might have a meaning to Perl
783itself some day, even though most don't yet. Use a mixed-case attribute
784name, instead.
785
786=item C<Can't have two ATTR specifiers on one subroutine>
787
788You just can't, okay?
789Instead, put all the specifications together with commas between them
790in a single C<ATTR(I<specification>)>.
791
792=item C<Can't autotie a %s>
793
794You can only declare autoties for types C<"SCALAR">, C<"ARRAY">, and
795C<"HASH">. They're the only things (apart from typeglobs -- which are
796not declarable) that Perl can tie.
797
798=item C<Internal error: %s symbol went missing>
799
800Something is rotten in the state of the program. An attributed
801subroutine ceased to exist between the point it was declared and the point
802at which its attribute handler(s) would have been called.
803
804=back
805
806=head1 AUTHOR
807
808Damian Conway (damian@conway.org)
809
810=head1 BUGS
811
812There are undoubtedly serious bugs lurking somewhere in code this funky :-)
813Bug reports and other feedback are most welcome.
814
815=head1 COPYRIGHT
816
817 Copyright (c) 2001, Damian Conway. All Rights Reserved.
818 This module is free software. It may be used, redistributed
819 and/or modified under the same terms as Perl itself.