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1 | package Attribute::Handlers; |
2 | use 5.006; |
3 | use Carp; |
4 | use warnings; |
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5 | $VERSION = '0.78_01'; |
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6 | # $DB::single=1; |
7 | |
8 | my %symcache; |
9 | sub findsym { |
10 | my ($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} == $ref; |
17 | } |
18 | } |
19 | |
20 | my %validtype = ( |
21 | VAR => [qw[SCALAR ARRAY HASH]], |
22 | ANY => [qw[SCALAR ARRAY HASH CODE]], |
23 | "" => [qw[SCALAR ARRAY HASH CODE]], |
24 | SCALAR => [qw[SCALAR]], |
25 | ARRAY => [qw[ARRAY]], |
26 | HASH => [qw[HASH]], |
27 | CODE => [qw[CODE]], |
28 | ); |
29 | my %lastattr; |
30 | my @declarations; |
31 | my %raw; |
32 | my %phase; |
33 | my %sigil = (SCALAR=>'$', ARRAY=>'@', HASH=>'%'); |
34 | my $global_phase = 0; |
35 | my %global_phases = ( |
36 | BEGIN => 0, |
37 | CHECK => 1, |
38 | INIT => 2, |
39 | END => 3, |
40 | ); |
41 | my @global_phases = qw(BEGIN CHECK INIT END); |
42 | |
43 | sub _usage_AH_ { |
44 | croak "Usage: use $_[0] autotie => {AttrName => TieClassName,...}"; |
45 | } |
46 | |
47 | my $qual_id = qr/^[_a-z]\w*(::[_a-z]\w*)*$/i; |
48 | |
49 | sub 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 | } |
89 | sub _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}"} = $lastattr{ref}; |
98 | } |
99 | %lastattr = (); |
100 | } |
101 | |
102 | sub AUTOLOAD { |
103 | my ($class) = $AUTOLOAD =~ m/(.*)::/g; |
104 | $AUTOLOAD =~ m/_ATTR_(.*?)_(.*)/ or |
105 | croak "Can't locate class method '$AUTOLOAD' via package '$class'"; |
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106 | croak "Attribute handler '$2' doesn't handle $1 attributes"; |
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107 | } |
108 | |
109 | sub DESTROY {} |
110 | |
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111 | my $builtin = qr/lvalue|method|locked|unique|shared/; |
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112 | |
113 | sub _gen_handler_AH_() { |
114 | return sub { |
115 | _resolve_lastattr; |
116 | my ($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 { |
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140 | my $type = ref $ref; |
141 | my $handler = $pkg->can("_ATTR_${type}_${attr}"); |
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142 | next unless $handler; |
143 | my $decl = [$pkg, $ref, $attr, $data, |
144 | $raw{$handler}, $phase{$handler}]; |
145 | foreach my $gphase (@global_phases) { |
146 | _apply_handler_AH_($decl,$gphase) |
147 | if $global_phases{$gphase} <= $global_phase; |
148 | } |
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149 | if ($global_phase != 0) { |
150 | # if _gen_handler_AH_ is being called after |
151 | # CHECK it's for a lexical, so make sure |
152 | # it didn't want to run anything later |
153 | |
154 | local $Carp::CarpLevel = 2; |
155 | carp "Won't be able to apply END handler" |
156 | if $phase{$handler}{END}; |
157 | } |
158 | else { |
159 | push @declarations, $decl |
160 | } |
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161 | } |
162 | $_ = undef; |
163 | } |
164 | return grep {defined && !/$builtin/} @attrs; |
165 | } |
166 | } |
167 | |
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168 | *{"Attribute::Handlers::UNIVERSAL::MODIFY_${_}_ATTRIBUTES"} = |
169 | _gen_handler_AH_ foreach @{$validtype{ANY}}; |
170 | push @UNIVERSAL::ISA, 'Attribute::Handlers::UNIVERSAL' |
171 | unless grep /^Attribute::Handlers::UNIVERSAL$/, @UNIVERSAL::ISA; |
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172 | |
173 | sub _apply_handler_AH_ { |
174 | my ($declaration, $phase) = @_; |
175 | my ($pkg, $ref, $attr, $data, $raw, $handlerphase) = @$declaration; |
176 | return unless $handlerphase->{$phase}; |
177 | # print STDERR "Handling $attr on $ref in $phase with [$data]\n"; |
178 | my $type = ref $ref; |
179 | my $handler = "_ATTR_${type}_${attr}"; |
180 | my $sym = findsym($pkg, $ref); |
181 | $sym ||= $type eq 'CODE' ? 'ANON' : 'LEXICAL'; |
182 | no warnings; |
183 | my $evaled = !$raw && eval("package $pkg; no warnings; |
184 | local \$SIG{__WARN__}=sub{die}; [$data]"); |
185 | $data = ($evaled && $data =~ /^\s*\[/) ? [$evaled] |
186 | : ($evaled) ? $evaled |
187 | : [$data]; |
188 | $pkg->$handler($sym, |
189 | (ref $sym eq 'GLOB' ? *{$sym}{ref $ref}||$ref : $ref), |
190 | $attr, |
191 | (@$data>1? $data : $data->[0]), |
192 | $phase, |
193 | ); |
194 | return 1; |
195 | } |
196 | |
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197 | { |
198 | no warnings 'void'; |
199 | CHECK { |
200 | $global_phase++; |
201 | _resolve_lastattr; |
202 | _apply_handler_AH_($_,'CHECK') foreach @declarations; |
203 | } |
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204 | |
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205 | INIT { |
206 | $global_phase++; |
207 | _apply_handler_AH_($_,'INIT') foreach @declarations |
208 | } |
209 | } |
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210 | |
211 | END { $global_phase++; _apply_handler_AH_($_,'END') foreach @declarations } |
212 | |
213 | 1; |
214 | __END__ |
215 | |
216 | =head1 NAME |
217 | |
218 | Attribute::Handlers - Simpler definition of attribute handlers |
219 | |
220 | =head1 VERSION |
221 | |
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222 | This document describes version 0.78 of Attribute::Handlers, |
223 | released October 5, 2002. |
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224 | |
225 | =head1 SYNOPSIS |
226 | |
227 | package MyClass; |
228 | require v5.6.0; |
229 | use Attribute::Handlers; |
230 | no warnings 'redefine'; |
231 | |
232 | |
233 | sub Good : ATTR(SCALAR) { |
234 | my ($package, $symbol, $referent, $attr, $data) = @_; |
235 | |
236 | # Invoked for any scalar variable with a :Good attribute, |
237 | # provided the variable was declared in MyClass (or |
238 | # a derived class) or typed to MyClass. |
239 | |
240 | # Do whatever to $referent here (executed in CHECK phase). |
241 | ... |
242 | } |
243 | |
244 | sub Bad : ATTR(SCALAR) { |
245 | # Invoked for any scalar variable with a :Bad attribute, |
246 | # provided the variable was declared in MyClass (or |
247 | # a derived class) or typed to MyClass. |
248 | ... |
249 | } |
250 | |
251 | sub Good : ATTR(ARRAY) { |
252 | # Invoked for any array variable with a :Good attribute, |
253 | # provided the variable was declared in MyClass (or |
254 | # a derived class) or typed to MyClass. |
255 | ... |
256 | } |
257 | |
258 | sub Good : ATTR(HASH) { |
259 | # Invoked for any hash variable with a :Good attribute, |
260 | # provided the variable was declared in MyClass (or |
261 | # a derived class) or typed to MyClass. |
262 | ... |
263 | } |
264 | |
265 | sub Ugly : ATTR(CODE) { |
266 | # Invoked for any subroutine declared in MyClass (or a |
267 | # derived class) with an :Ugly attribute. |
268 | ... |
269 | } |
270 | |
271 | sub Omni : ATTR { |
272 | # Invoked for any scalar, array, hash, or subroutine |
273 | # with an :Omni attribute, provided the variable or |
274 | # subroutine was declared in MyClass (or a derived class) |
275 | # or the variable was typed to MyClass. |
276 | # Use ref($_[2]) to determine what kind of referent it was. |
277 | ... |
278 | } |
279 | |
280 | |
281 | use Attribute::Handlers autotie => { Cycle => Tie::Cycle }; |
282 | |
283 | my $next : Cycle(['A'..'Z']); |
284 | |
285 | |
286 | =head1 DESCRIPTION |
287 | |
288 | This module, when inherited by a package, allows that package's class to |
289 | define attribute handler subroutines for specific attributes. Variables |
290 | and subroutines subsequently defined in that package, or in packages |
291 | derived from that package may be given attributes with the same names as |
292 | the attribute handler subroutines, which will then be called in one of |
293 | the compilation phases (i.e. in a C<BEGIN>, C<CHECK>, C<INIT>, or C<END> |
294 | block). |
295 | |
296 | To create a handler, define it as a subroutine with the same name as |
297 | the desired attribute, and declare the subroutine itself with the |
298 | attribute C<:ATTR>. For example: |
299 | |
300 | package LoudDecl; |
301 | use Attribute::Handlers; |
302 | |
303 | sub Loud :ATTR { |
304 | my ($package, $symbol, $referent, $attr, $data, $phase) = @_; |
305 | print STDERR |
306 | ref($referent), " ", |
307 | *{$symbol}{NAME}, " ", |
308 | "($referent) ", "was just declared ", |
309 | "and ascribed the ${attr} attribute ", |
310 | "with data ($data)\n", |
311 | "in phase $phase\n"; |
312 | } |
313 | |
314 | This creates a handler for the attribute C<:Loud> in the class LoudDecl. |
315 | Thereafter, any subroutine declared with a C<:Loud> attribute in the class |
316 | LoudDecl: |
317 | |
318 | package LoudDecl; |
319 | |
320 | sub foo: Loud {...} |
321 | |
322 | causes the above handler to be invoked, and passed: |
323 | |
324 | =over |
325 | |
326 | =item [0] |
327 | |
328 | the name of the package into which it was declared; |
329 | |
330 | =item [1] |
331 | |
332 | a reference to the symbol table entry (typeglob) containing the subroutine; |
333 | |
334 | =item [2] |
335 | |
336 | a reference to the subroutine; |
337 | |
338 | =item [3] |
339 | |
340 | the name of the attribute; |
341 | |
342 | =item [4] |
343 | |
344 | any data associated with that attribute; |
345 | |
346 | =item [5] |
347 | |
348 | the name of the phase in which the handler is being invoked. |
349 | |
350 | =back |
351 | |
352 | Likewise, declaring any variables with the C<:Loud> attribute within the |
353 | package: |
354 | |
355 | package LoudDecl; |
356 | |
357 | my $foo :Loud; |
358 | my @foo :Loud; |
359 | my %foo :Loud; |
360 | |
361 | will cause the handler to be called with a similar argument list (except, |
362 | of course, that C<$_[2]> will be a reference to the variable). |
363 | |
364 | The package name argument will typically be the name of the class into |
365 | which the subroutine was declared, but it may also be the name of a derived |
366 | class (since handlers are inherited). |
367 | |
368 | If a lexical variable is given an attribute, there is no symbol table to |
369 | which it belongs, so the symbol table argument (C<$_[1]>) is set to the |
370 | string C<'LEXICAL'> in that case. Likewise, ascribing an attribute to |
371 | an anonymous subroutine results in a symbol table argument of C<'ANON'>. |
372 | |
373 | The data argument passes in the value (if any) associated with the |
374 | attribute. For example, if C<&foo> had been declared: |
375 | |
376 | sub foo :Loud("turn it up to 11, man!") {...} |
377 | |
378 | then the string C<"turn it up to 11, man!"> would be passed as the |
379 | last argument. |
380 | |
381 | Attribute::Handlers makes strenuous efforts to convert |
382 | the data argument (C<$_[4]>) to a useable form before passing it to |
383 | the handler (but see L<"Non-interpretive attribute handlers">). |
384 | For example, all of these: |
385 | |
386 | sub foo :Loud(till=>ears=>are=>bleeding) {...} |
387 | sub foo :Loud(['till','ears','are','bleeding']) {...} |
388 | sub foo :Loud(qw/till ears are bleeding/) {...} |
389 | sub foo :Loud(qw/my, ears, are, bleeding/) {...} |
390 | sub foo :Loud(till,ears,are,bleeding) {...} |
391 | |
392 | causes it to pass C<['till','ears','are','bleeding']> as the handler's |
393 | data argument. However, if the data can't be parsed as valid Perl, then |
394 | it is passed as an uninterpreted string. For example: |
395 | |
396 | sub foo :Loud(my,ears,are,bleeding) {...} |
397 | sub foo :Loud(qw/my ears are bleeding) {...} |
398 | |
399 | cause the strings C<'my,ears,are,bleeding'> and C<'qw/my ears are bleeding'> |
400 | respectively to be passed as the data argument. |
401 | |
402 | If the attribute has only a single associated scalar data value, that value is |
403 | passed as a scalar. If multiple values are associated, they are passed as an |
404 | array reference. If no value is associated with the attribute, C<undef> is |
405 | passed. |
406 | |
407 | |
408 | =head2 Typed lexicals |
409 | |
410 | Regardless of the package in which it is declared, if a lexical variable is |
411 | ascribed an attribute, the handler that is invoked is the one belonging to |
412 | the package to which it is typed. For example, the following declarations: |
413 | |
414 | package OtherClass; |
415 | |
416 | my LoudDecl $loudobj : Loud; |
417 | my LoudDecl @loudobjs : Loud; |
418 | my LoudDecl %loudobjex : Loud; |
419 | |
420 | causes the LoudDecl::Loud handler to be invoked (even if OtherClass also |
421 | defines a handler for C<:Loud> attributes). |
422 | |
423 | |
424 | =head2 Type-specific attribute handlers |
425 | |
426 | If an attribute handler is declared and the C<:ATTR> specifier is |
427 | given the name of a built-in type (C<SCALAR>, C<ARRAY>, C<HASH>, or C<CODE>), |
428 | the handler is only applied to declarations of that type. For example, |
429 | the following definition: |
430 | |
431 | package LoudDecl; |
432 | |
433 | sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" } |
434 | |
435 | creates an attribute handler that applies only to scalars: |
436 | |
437 | |
438 | package Painful; |
439 | use base LoudDecl; |
440 | |
441 | my $metal : RealLoud; # invokes &LoudDecl::RealLoud |
442 | my @metal : RealLoud; # error: unknown attribute |
443 | my %metal : RealLoud; # error: unknown attribute |
444 | sub metal : RealLoud {...} # error: unknown attribute |
445 | |
446 | You can, of course, declare separate handlers for these types as well |
447 | (but you'll need to specify C<no warnings 'redefine'> to do it quietly): |
448 | |
449 | package LoudDecl; |
450 | use Attribute::Handlers; |
451 | no warnings 'redefine'; |
452 | |
453 | sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" } |
454 | sub RealLoud :ATTR(ARRAY) { print "Urrrrrrrrrr!" } |
455 | sub RealLoud :ATTR(HASH) { print "Arrrrrgggghhhhhh!" } |
456 | sub RealLoud :ATTR(CODE) { croak "Real loud sub torpedoed" } |
457 | |
458 | You can also explicitly indicate that a single handler is meant to be |
459 | used for all types of referents like so: |
460 | |
461 | package LoudDecl; |
462 | use Attribute::Handlers; |
463 | |
464 | sub SeriousLoud :ATTR(ANY) { warn "Hearing loss imminent" } |
465 | |
466 | (I.e. C<ATTR(ANY)> is a synonym for C<:ATTR>). |
467 | |
468 | |
469 | =head2 Non-interpretive attribute handlers |
470 | |
471 | Occasionally the strenuous efforts Attribute::Handlers makes to convert |
472 | the data argument (C<$_[4]>) to a useable form before passing it to |
473 | the handler get in the way. |
474 | |
475 | You can turn off that eagerness-to-help by declaring |
476 | an attribute handler with the keyword C<RAWDATA>. For example: |
477 | |
478 | sub Raw : ATTR(RAWDATA) {...} |
479 | sub Nekkid : ATTR(SCALAR,RAWDATA) {...} |
480 | sub Au::Naturale : ATTR(RAWDATA,ANY) {...} |
481 | |
482 | Then the handler makes absolutely no attempt to interpret the data it |
483 | receives and simply passes it as a string: |
484 | |
485 | my $power : Raw(1..100); # handlers receives "1..100" |
486 | |
487 | =head2 Phase-specific attribute handlers |
488 | |
489 | By default, attribute handlers are called at the end of the compilation |
490 | phase (in a C<CHECK> block). This seems to be optimal in most cases because |
491 | most things that can be defined are defined by that point but nothing has |
492 | been executed. |
493 | |
494 | However, it is possible to set up attribute handlers that are called at |
495 | other points in the program's compilation or execution, by explicitly |
496 | stating the phase (or phases) in which you wish the attribute handler to |
497 | be called. For example: |
498 | |
499 | sub Early :ATTR(SCALAR,BEGIN) {...} |
500 | sub Normal :ATTR(SCALAR,CHECK) {...} |
501 | sub Late :ATTR(SCALAR,INIT) {...} |
502 | sub Final :ATTR(SCALAR,END) {...} |
503 | sub Bookends :ATTR(SCALAR,BEGIN,END) {...} |
504 | |
505 | As the last example indicates, a handler may be set up to be (re)called in |
506 | two or more phases. The phase name is passed as the handler's final argument. |
507 | |
508 | Note that attribute handlers that are scheduled for the C<BEGIN> phase |
509 | are handled as soon as the attribute is detected (i.e. before any |
510 | subsequently defined C<BEGIN> blocks are executed). |
511 | |
512 | |
513 | =head2 Attributes as C<tie> interfaces |
514 | |
515 | Attributes make an excellent and intuitive interface through which to tie |
516 | variables. For example: |
517 | |
518 | use Attribute::Handlers; |
519 | use Tie::Cycle; |
520 | |
521 | sub UNIVERSAL::Cycle : ATTR(SCALAR) { |
522 | my ($package, $symbol, $referent, $attr, $data, $phase) = @_; |
523 | $data = [ $data ] unless ref $data eq 'ARRAY'; |
524 | tie $$referent, 'Tie::Cycle', $data; |
525 | } |
526 | |
527 | # and thereafter... |
528 | |
529 | package main; |
530 | |
531 | my $next : Cycle('A'..'Z'); # $next is now a tied variable |
532 | |
533 | while (<>) { |
534 | print $next; |
535 | } |
536 | |
537 | Note that, because the C<Cycle> attribute receives its arguments in the |
538 | C<$data> variable, if the attribute is given a list of arguments, C<$data> |
539 | will consist of a single array reference; otherwise, it will consist of the |
540 | single argument directly. Since Tie::Cycle requires its cycling values to |
541 | be passed as an array reference, this means that we need to wrap |
542 | non-array-reference arguments in an array constructor: |
543 | |
544 | $data = [ $data ] unless ref $data eq 'ARRAY'; |
545 | |
546 | Typically, however, things are the other way around: the tieable class expects |
547 | its arguments as a flattened list, so the attribute looks like: |
548 | |
549 | sub UNIVERSAL::Cycle : ATTR(SCALAR) { |
550 | my ($package, $symbol, $referent, $attr, $data, $phase) = @_; |
551 | my @data = ref $data eq 'ARRAY' ? @$data : $data; |
552 | tie $$referent, 'Tie::Whatever', @data; |
553 | } |
554 | |
555 | |
556 | This software pattern is so widely applicable that Attribute::Handlers |
557 | provides a way to automate it: specifying C<'autotie'> in the |
558 | C<use Attribute::Handlers> statement. So, the cycling example, |
559 | could also be written: |
560 | |
561 | use Attribute::Handlers autotie => { Cycle => 'Tie::Cycle' }; |
562 | |
563 | # and thereafter... |
564 | |
565 | package main; |
566 | |
567 | my $next : Cycle(['A'..'Z']); # $next is now a tied variable |
568 | |
569 | while (<>) { |
570 | print $next; |
571 | |
572 | Note that we now have to pass the cycling values as an array reference, |
573 | since the C<autotie> mechanism passes C<tie> a list of arguments as a list |
574 | (as in the Tie::Whatever example), I<not> as an array reference (as in |
575 | the original Tie::Cycle example at the start of this section). |
576 | |
577 | The argument after C<'autotie'> is a reference to a hash in which each key is |
578 | the name of an attribute to be created, and each value is the class to which |
579 | variables ascribed that attribute should be tied. |
580 | |
581 | Note that there is no longer any need to import the Tie::Cycle module -- |
582 | Attribute::Handlers takes care of that automagically. You can even pass |
583 | arguments to the module's C<import> subroutine, by appending them to the |
584 | class name. For example: |
585 | |
586 | use Attribute::Handlers |
587 | autotie => { Dir => 'Tie::Dir qw(DIR_UNLINK)' }; |
588 | |
589 | If the attribute name is unqualified, the attribute is installed in the |
590 | current package. Otherwise it is installed in the qualifier's package: |
591 | |
592 | package Here; |
593 | |
594 | use Attribute::Handlers autotie => { |
595 | Other::Good => Tie::SecureHash, # tie attr installed in Other:: |
596 | Bad => Tie::Taxes, # tie attr installed in Here:: |
597 | UNIVERSAL::Ugly => Software::Patent # tie attr installed everywhere |
598 | }; |
599 | |
600 | Autoties are most commonly used in the module to which they actually tie, |
601 | and need to export their attributes to any module that calls them. To |
602 | facilitiate this, Attribute::Handlers recognizes a special "pseudo-class" -- |
603 | C<__CALLER__>, which may be specified as the qualifier of an attribute: |
604 | |
605 | package Tie::Me::Kangaroo:Down::Sport; |
606 | |
f903cfef |
607 | use Attribute::Handlers autotie => { '__CALLER__::Roo' => __PACKAGE__ }; |
0e9b9e0c |
608 | |
609 | This causes Attribute::Handlers to define the C<Roo> attribute in the package |
610 | that imports the Tie::Me::Kangaroo:Down::Sport module. |
611 | |
f903cfef |
612 | Note that it is important to quote the __CALLER__::Roo identifier because |
613 | a bug in perl 5.8 will refuse to parse it and cause an unknown error. |
614 | |
0e9b9e0c |
615 | =head3 Passing the tied object to C<tie> |
616 | |
617 | Occasionally it is important to pass a reference to the object being tied |
618 | to the TIESCALAR, TIEHASH, etc. that ties it. |
619 | |
620 | The C<autotie> mechanism supports this too. The following code: |
621 | |
622 | use Attribute::Handlers autotieref => { Selfish => Tie::Selfish }; |
623 | my $var : Selfish(@args); |
624 | |
625 | has the same effect as: |
626 | |
627 | tie my $var, 'Tie::Selfish', @args; |
628 | |
629 | But when C<"autotieref"> is used instead of C<"autotie">: |
630 | |
631 | use Attribute::Handlers autotieref => { Selfish => Tie::Selfish }; |
632 | my $var : Selfish(@args); |
633 | |
634 | the effect is to pass the C<tie> call an extra reference to the variable |
635 | being tied: |
636 | |
637 | tie my $var, 'Tie::Selfish', \$var, @args; |
638 | |
639 | |
640 | |
641 | =head1 EXAMPLES |
642 | |
643 | If the class shown in L<SYNOPSIS> were placed in the MyClass.pm |
644 | module, then the following code: |
645 | |
646 | package main; |
647 | use MyClass; |
648 | |
649 | my MyClass $slr :Good :Bad(1**1-1) :Omni(-vorous); |
650 | |
651 | package SomeOtherClass; |
652 | use base MyClass; |
653 | |
654 | sub tent { 'acle' } |
655 | |
656 | sub fn :Ugly(sister) :Omni('po',tent()) {...} |
657 | my @arr :Good :Omni(s/cie/nt/); |
658 | my %hsh :Good(q/bye) :Omni(q/bus/); |
659 | |
660 | |
661 | would cause the following handlers to be invoked: |
662 | |
663 | # my MyClass $slr :Good :Bad(1**1-1) :Omni(-vorous); |
664 | |
665 | MyClass::Good:ATTR(SCALAR)( 'MyClass', # class |
666 | 'LEXICAL', # no typeglob |
667 | \$slr, # referent |
668 | 'Good', # attr name |
669 | undef # no attr data |
670 | 'CHECK', # compiler phase |
671 | ); |
672 | |
673 | MyClass::Bad:ATTR(SCALAR)( 'MyClass', # class |
674 | 'LEXICAL', # no typeglob |
675 | \$slr, # referent |
676 | 'Bad', # attr name |
677 | 0 # eval'd attr data |
678 | 'CHECK', # compiler phase |
679 | ); |
680 | |
681 | MyClass::Omni:ATTR(SCALAR)( 'MyClass', # class |
682 | 'LEXICAL', # no typeglob |
683 | \$slr, # referent |
684 | 'Omni', # attr name |
685 | '-vorous' # eval'd attr data |
686 | 'CHECK', # compiler phase |
687 | ); |
688 | |
689 | |
690 | # sub fn :Ugly(sister) :Omni('po',tent()) {...} |
691 | |
692 | MyClass::UGLY:ATTR(CODE)( 'SomeOtherClass', # class |
693 | \*SomeOtherClass::fn, # typeglob |
694 | \&SomeOtherClass::fn, # referent |
695 | 'Ugly', # attr name |
696 | 'sister' # eval'd attr data |
697 | 'CHECK', # compiler phase |
698 | ); |
699 | |
700 | MyClass::Omni:ATTR(CODE)( 'SomeOtherClass', # class |
701 | \*SomeOtherClass::fn, # typeglob |
702 | \&SomeOtherClass::fn, # referent |
703 | 'Omni', # attr name |
704 | ['po','acle'] # eval'd attr data |
705 | 'CHECK', # compiler phase |
706 | ); |
707 | |
708 | |
709 | # my @arr :Good :Omni(s/cie/nt/); |
710 | |
711 | MyClass::Good:ATTR(ARRAY)( 'SomeOtherClass', # class |
712 | 'LEXICAL', # no typeglob |
713 | \@arr, # referent |
714 | 'Good', # attr name |
715 | undef # no attr data |
716 | 'CHECK', # compiler phase |
717 | ); |
718 | |
719 | MyClass::Omni:ATTR(ARRAY)( 'SomeOtherClass', # class |
720 | 'LEXICAL', # no typeglob |
721 | \@arr, # referent |
722 | 'Omni', # attr name |
723 | "" # eval'd attr data |
724 | 'CHECK', # compiler phase |
725 | ); |
726 | |
727 | |
728 | # my %hsh :Good(q/bye) :Omni(q/bus/); |
729 | |
730 | MyClass::Good:ATTR(HASH)( 'SomeOtherClass', # class |
731 | 'LEXICAL', # no typeglob |
732 | \%hsh, # referent |
733 | 'Good', # attr name |
734 | 'q/bye' # raw attr data |
735 | 'CHECK', # compiler phase |
736 | ); |
737 | |
738 | MyClass::Omni:ATTR(HASH)( 'SomeOtherClass', # class |
739 | 'LEXICAL', # no typeglob |
740 | \%hsh, # referent |
741 | 'Omni', # attr name |
742 | 'bus' # eval'd attr data |
743 | 'CHECK', # compiler phase |
744 | ); |
745 | |
746 | |
747 | Installing handlers into UNIVERSAL, makes them...err..universal. |
748 | For example: |
749 | |
750 | package Descriptions; |
751 | use Attribute::Handlers; |
752 | |
753 | my %name; |
754 | sub name { return $name{$_[2]}||*{$_[1]}{NAME} } |
755 | |
756 | sub UNIVERSAL::Name :ATTR { |
757 | $name{$_[2]} = $_[4]; |
758 | } |
759 | |
760 | sub UNIVERSAL::Purpose :ATTR { |
761 | print STDERR "Purpose of ", &name, " is $_[4]\n"; |
762 | } |
763 | |
764 | sub UNIVERSAL::Unit :ATTR { |
765 | print STDERR &name, " measured in $_[4]\n"; |
766 | } |
767 | |
768 | Let's you write: |
769 | |
770 | use Descriptions; |
771 | |
772 | my $capacity : Name(capacity) |
773 | : Purpose(to store max storage capacity for files) |
774 | : Unit(Gb); |
775 | |
776 | |
777 | package Other; |
778 | |
779 | sub foo : Purpose(to foo all data before barring it) { } |
780 | |
781 | # etc. |
782 | |
783 | |
784 | =head1 DIAGNOSTICS |
785 | |
786 | =over |
787 | |
788 | =item C<Bad attribute type: ATTR(%s)> |
789 | |
790 | An attribute handler was specified with an C<:ATTR(I<ref_type>)>, but the |
791 | type of referent it was defined to handle wasn't one of the five permitted: |
792 | C<SCALAR>, C<ARRAY>, C<HASH>, C<CODE>, or C<ANY>. |
793 | |
794 | =item C<Attribute handler %s doesn't handle %s attributes> |
795 | |
796 | A handler for attributes of the specified name I<was> defined, but not |
797 | for the specified type of declaration. Typically encountered whe trying |
798 | to apply a C<VAR> attribute handler to a subroutine, or a C<SCALAR> |
799 | attribute handler to some other type of variable. |
800 | |
801 | =item C<Declaration of %s attribute in package %s may clash with future reserved word> |
802 | |
803 | A handler for an attributes with an all-lowercase name was declared. An |
804 | attribute with an all-lowercase name might have a meaning to Perl |
805 | itself some day, even though most don't yet. Use a mixed-case attribute |
806 | name, instead. |
807 | |
808 | =item C<Can't have two ATTR specifiers on one subroutine> |
809 | |
810 | You just can't, okay? |
811 | Instead, put all the specifications together with commas between them |
812 | in a single C<ATTR(I<specification>)>. |
813 | |
814 | =item C<Can't autotie a %s> |
815 | |
816 | You can only declare autoties for types C<"SCALAR">, C<"ARRAY">, and |
817 | C<"HASH">. They're the only things (apart from typeglobs -- which are |
818 | not declarable) that Perl can tie. |
819 | |
820 | =item C<Internal error: %s symbol went missing> |
821 | |
822 | Something is rotten in the state of the program. An attributed |
823 | subroutine ceased to exist between the point it was declared and the point |
824 | at which its attribute handler(s) would have been called. |
825 | |
24952a9c |
826 | =item C<Won't be able to apply END handler> |
827 | |
828 | You have defined an END handler for an attribute that is being applied |
829 | to a lexical variable. Since the variable may not be available during END |
830 | this won't happen. |
831 | |
0e9b9e0c |
832 | =back |
833 | |
834 | =head1 AUTHOR |
835 | |
836 | Damian Conway (damian@conway.org) |
837 | |
838 | =head1 BUGS |
839 | |
840 | There are undoubtedly serious bugs lurking somewhere in code this funky :-) |
841 | Bug reports and other feedback are most welcome. |
842 | |
843 | =head1 COPYRIGHT |
844 | |
845 | Copyright (c) 2001, Damian Conway. All Rights Reserved. |
846 | This module is free software. It may be used, redistributed |
847 | and/or modified under the same terms as Perl itself. |