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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_04'; |
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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) = @_; |
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117 | my (undef, $filename, $linenum) = caller 2; |
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118 | foreach (@attrs) { |
119 | my ($attr, $data) = /^([a-z_]\w*)(?:[(](.*)[)])?$/is or next; |
120 | if ($attr eq 'ATTR') { |
121 | $data ||= "ANY"; |
122 | $raw{$ref} = $data =~ s/\s*,?\s*RAWDATA\s*,?\s*//; |
123 | $phase{$ref}{BEGIN} = 1 |
124 | if $data =~ s/\s*,?\s*(BEGIN)\s*,?\s*//; |
125 | $phase{$ref}{INIT} = 1 |
126 | if $data =~ s/\s*,?\s*(INIT)\s*,?\s*//; |
127 | $phase{$ref}{END} = 1 |
128 | if $data =~ s/\s*,?\s*(END)\s*,?\s*//; |
129 | $phase{$ref}{CHECK} = 1 |
130 | if $data =~ s/\s*,?\s*(CHECK)\s*,?\s*// |
131 | || ! keys %{$phase{$ref}}; |
132 | # Added for cleanup to not pollute next call. |
133 | (%lastattr = ()), |
134 | croak "Can't have two ATTR specifiers on one subroutine" |
135 | if keys %lastattr; |
136 | croak "Bad attribute type: ATTR($data)" |
137 | unless $validtype{$data}; |
138 | %lastattr=(pkg=>$pkg,ref=>$ref,type=>$data); |
139 | } |
140 | else { |
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141 | my $type = ref $ref; |
142 | my $handler = $pkg->can("_ATTR_${type}_${attr}"); |
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143 | next unless $handler; |
144 | my $decl = [$pkg, $ref, $attr, $data, |
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145 | $raw{$handler}, $phase{$handler}, $filename, $linenum]; |
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146 | foreach my $gphase (@global_phases) { |
147 | _apply_handler_AH_($decl,$gphase) |
148 | if $global_phases{$gphase} <= $global_phase; |
149 | } |
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150 | if ($global_phase != 0) { |
151 | # if _gen_handler_AH_ is being called after |
152 | # CHECK it's for a lexical, so make sure |
153 | # it didn't want to run anything later |
154 | |
155 | local $Carp::CarpLevel = 2; |
156 | carp "Won't be able to apply END handler" |
157 | if $phase{$handler}{END}; |
158 | } |
159 | else { |
160 | push @declarations, $decl |
161 | } |
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162 | } |
163 | $_ = undef; |
164 | } |
165 | return grep {defined && !/$builtin/} @attrs; |
166 | } |
167 | } |
168 | |
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169 | *{"Attribute::Handlers::UNIVERSAL::MODIFY_${_}_ATTRIBUTES"} = |
170 | _gen_handler_AH_ foreach @{$validtype{ANY}}; |
171 | push @UNIVERSAL::ISA, 'Attribute::Handlers::UNIVERSAL' |
172 | unless grep /^Attribute::Handlers::UNIVERSAL$/, @UNIVERSAL::ISA; |
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173 | |
174 | sub _apply_handler_AH_ { |
175 | my ($declaration, $phase) = @_; |
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176 | my ($pkg, $ref, $attr, $data, $raw, $handlerphase, $filename, $linenum) = @$declaration; |
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177 | return unless $handlerphase->{$phase}; |
178 | # print STDERR "Handling $attr on $ref in $phase with [$data]\n"; |
179 | my $type = ref $ref; |
180 | my $handler = "_ATTR_${type}_${attr}"; |
181 | my $sym = findsym($pkg, $ref); |
182 | $sym ||= $type eq 'CODE' ? 'ANON' : 'LEXICAL'; |
183 | no warnings; |
184 | my $evaled = !$raw && eval("package $pkg; no warnings; |
185 | local \$SIG{__WARN__}=sub{die}; [$data]"); |
186 | $data = ($evaled && $data =~ /^\s*\[/) ? [$evaled] |
187 | : ($evaled) ? $evaled |
188 | : [$data]; |
189 | $pkg->$handler($sym, |
190 | (ref $sym eq 'GLOB' ? *{$sym}{ref $ref}||$ref : $ref), |
191 | $attr, |
192 | (@$data>1? $data : $data->[0]), |
193 | $phase, |
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194 | $filename, |
195 | $linenum, |
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196 | ); |
197 | return 1; |
198 | } |
199 | |
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200 | { |
201 | no warnings 'void'; |
202 | CHECK { |
203 | $global_phase++; |
204 | _resolve_lastattr; |
205 | _apply_handler_AH_($_,'CHECK') foreach @declarations; |
206 | } |
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207 | |
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208 | INIT { |
209 | $global_phase++; |
210 | _apply_handler_AH_($_,'INIT') foreach @declarations |
211 | } |
212 | } |
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213 | |
214 | END { $global_phase++; _apply_handler_AH_($_,'END') foreach @declarations } |
215 | |
216 | 1; |
217 | __END__ |
218 | |
219 | =head1 NAME |
220 | |
221 | Attribute::Handlers - Simpler definition of attribute handlers |
222 | |
223 | =head1 VERSION |
224 | |
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225 | This document describes version 0.78 of Attribute::Handlers, |
226 | released October 5, 2002. |
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227 | |
228 | =head1 SYNOPSIS |
229 | |
230 | package MyClass; |
231 | require v5.6.0; |
232 | use Attribute::Handlers; |
233 | no warnings 'redefine'; |
234 | |
235 | |
236 | sub Good : ATTR(SCALAR) { |
237 | my ($package, $symbol, $referent, $attr, $data) = @_; |
238 | |
239 | # Invoked for any scalar variable with a :Good attribute, |
240 | # provided the variable was declared in MyClass (or |
241 | # a derived class) or typed to MyClass. |
242 | |
243 | # Do whatever to $referent here (executed in CHECK phase). |
244 | ... |
245 | } |
246 | |
247 | sub Bad : ATTR(SCALAR) { |
248 | # Invoked for any scalar variable with a :Bad attribute, |
249 | # provided the variable was declared in MyClass (or |
250 | # a derived class) or typed to MyClass. |
251 | ... |
252 | } |
253 | |
254 | sub Good : ATTR(ARRAY) { |
255 | # Invoked for any array variable with a :Good attribute, |
256 | # provided the variable was declared in MyClass (or |
257 | # a derived class) or typed to MyClass. |
258 | ... |
259 | } |
260 | |
261 | sub Good : ATTR(HASH) { |
262 | # Invoked for any hash variable with a :Good attribute, |
263 | # provided the variable was declared in MyClass (or |
264 | # a derived class) or typed to MyClass. |
265 | ... |
266 | } |
267 | |
268 | sub Ugly : ATTR(CODE) { |
269 | # Invoked for any subroutine declared in MyClass (or a |
270 | # derived class) with an :Ugly attribute. |
271 | ... |
272 | } |
273 | |
274 | sub Omni : ATTR { |
275 | # Invoked for any scalar, array, hash, or subroutine |
276 | # with an :Omni attribute, provided the variable or |
277 | # subroutine was declared in MyClass (or a derived class) |
278 | # or the variable was typed to MyClass. |
279 | # Use ref($_[2]) to determine what kind of referent it was. |
280 | ... |
281 | } |
282 | |
283 | |
284 | use Attribute::Handlers autotie => { Cycle => Tie::Cycle }; |
285 | |
286 | my $next : Cycle(['A'..'Z']); |
287 | |
288 | |
289 | =head1 DESCRIPTION |
290 | |
291 | This module, when inherited by a package, allows that package's class to |
292 | define attribute handler subroutines for specific attributes. Variables |
293 | and subroutines subsequently defined in that package, or in packages |
294 | derived from that package may be given attributes with the same names as |
295 | the attribute handler subroutines, which will then be called in one of |
296 | the compilation phases (i.e. in a C<BEGIN>, C<CHECK>, C<INIT>, or C<END> |
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297 | block). (C<UNITCHECK> blocks don't correspond to a global compilation |
298 | phase, so they can't be specified here.) |
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299 | |
300 | To create a handler, define it as a subroutine with the same name as |
301 | the desired attribute, and declare the subroutine itself with the |
302 | attribute C<:ATTR>. For example: |
303 | |
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304 | package LoudDecl; |
305 | use Attribute::Handlers; |
306 | |
307 | sub Loud :ATTR { |
308 | my ($package, $symbol, $referent, $attr, $data, $phase, $filename, $linenum) = @_; |
309 | print STDERR |
310 | ref($referent), " ", |
311 | *{$symbol}{NAME}, " ", |
312 | "($referent) ", "was just declared ", |
313 | "and ascribed the ${attr} attribute ", |
314 | "with data ($data)\n", |
315 | "in phase $phase\n", |
316 | "in file $filename at line $linenum\n"; |
317 | } |
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318 | |
319 | This creates a handler for the attribute C<:Loud> in the class LoudDecl. |
320 | Thereafter, any subroutine declared with a C<:Loud> attribute in the class |
321 | LoudDecl: |
322 | |
323 | package LoudDecl; |
324 | |
325 | sub foo: Loud {...} |
326 | |
327 | causes the above handler to be invoked, and passed: |
328 | |
329 | =over |
330 | |
331 | =item [0] |
332 | |
333 | the name of the package into which it was declared; |
334 | |
335 | =item [1] |
336 | |
337 | a reference to the symbol table entry (typeglob) containing the subroutine; |
338 | |
339 | =item [2] |
340 | |
341 | a reference to the subroutine; |
342 | |
343 | =item [3] |
344 | |
345 | the name of the attribute; |
346 | |
347 | =item [4] |
348 | |
349 | any data associated with that attribute; |
350 | |
351 | =item [5] |
352 | |
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353 | the name of the phase in which the handler is being invoked; |
354 | |
355 | =item [6] |
356 | |
357 | the filename in which the handler is being invoked; |
358 | |
359 | =item [7] |
360 | |
361 | the line number in this file. |
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362 | |
363 | =back |
364 | |
365 | Likewise, declaring any variables with the C<:Loud> attribute within the |
366 | package: |
367 | |
368 | package LoudDecl; |
369 | |
370 | my $foo :Loud; |
371 | my @foo :Loud; |
372 | my %foo :Loud; |
373 | |
374 | will cause the handler to be called with a similar argument list (except, |
375 | of course, that C<$_[2]> will be a reference to the variable). |
376 | |
377 | The package name argument will typically be the name of the class into |
378 | which the subroutine was declared, but it may also be the name of a derived |
379 | class (since handlers are inherited). |
380 | |
381 | If a lexical variable is given an attribute, there is no symbol table to |
382 | which it belongs, so the symbol table argument (C<$_[1]>) is set to the |
383 | string C<'LEXICAL'> in that case. Likewise, ascribing an attribute to |
384 | an anonymous subroutine results in a symbol table argument of C<'ANON'>. |
385 | |
386 | The data argument passes in the value (if any) associated with the |
387 | attribute. For example, if C<&foo> had been declared: |
388 | |
389 | sub foo :Loud("turn it up to 11, man!") {...} |
390 | |
391 | then the string C<"turn it up to 11, man!"> would be passed as the |
392 | last argument. |
393 | |
394 | Attribute::Handlers makes strenuous efforts to convert |
395 | the data argument (C<$_[4]>) to a useable form before passing it to |
396 | the handler (but see L<"Non-interpretive attribute handlers">). |
397 | For example, all of these: |
398 | |
399 | sub foo :Loud(till=>ears=>are=>bleeding) {...} |
400 | sub foo :Loud(['till','ears','are','bleeding']) {...} |
401 | sub foo :Loud(qw/till ears are bleeding/) {...} |
402 | sub foo :Loud(qw/my, ears, are, bleeding/) {...} |
403 | sub foo :Loud(till,ears,are,bleeding) {...} |
404 | |
405 | causes it to pass C<['till','ears','are','bleeding']> as the handler's |
406 | data argument. However, if the data can't be parsed as valid Perl, then |
407 | it is passed as an uninterpreted string. For example: |
408 | |
409 | sub foo :Loud(my,ears,are,bleeding) {...} |
410 | sub foo :Loud(qw/my ears are bleeding) {...} |
411 | |
412 | cause the strings C<'my,ears,are,bleeding'> and C<'qw/my ears are bleeding'> |
413 | respectively to be passed as the data argument. |
414 | |
415 | If the attribute has only a single associated scalar data value, that value is |
416 | passed as a scalar. If multiple values are associated, they are passed as an |
417 | array reference. If no value is associated with the attribute, C<undef> is |
418 | passed. |
419 | |
420 | |
421 | =head2 Typed lexicals |
422 | |
423 | Regardless of the package in which it is declared, if a lexical variable is |
424 | ascribed an attribute, the handler that is invoked is the one belonging to |
425 | the package to which it is typed. For example, the following declarations: |
426 | |
427 | package OtherClass; |
428 | |
429 | my LoudDecl $loudobj : Loud; |
430 | my LoudDecl @loudobjs : Loud; |
431 | my LoudDecl %loudobjex : Loud; |
432 | |
433 | causes the LoudDecl::Loud handler to be invoked (even if OtherClass also |
434 | defines a handler for C<:Loud> attributes). |
435 | |
436 | |
437 | =head2 Type-specific attribute handlers |
438 | |
439 | If an attribute handler is declared and the C<:ATTR> specifier is |
440 | given the name of a built-in type (C<SCALAR>, C<ARRAY>, C<HASH>, or C<CODE>), |
441 | the handler is only applied to declarations of that type. For example, |
442 | the following definition: |
443 | |
444 | package LoudDecl; |
445 | |
446 | sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" } |
447 | |
448 | creates an attribute handler that applies only to scalars: |
449 | |
450 | |
451 | package Painful; |
452 | use base LoudDecl; |
453 | |
454 | my $metal : RealLoud; # invokes &LoudDecl::RealLoud |
455 | my @metal : RealLoud; # error: unknown attribute |
456 | my %metal : RealLoud; # error: unknown attribute |
457 | sub metal : RealLoud {...} # error: unknown attribute |
458 | |
459 | You can, of course, declare separate handlers for these types as well |
460 | (but you'll need to specify C<no warnings 'redefine'> to do it quietly): |
461 | |
462 | package LoudDecl; |
463 | use Attribute::Handlers; |
464 | no warnings 'redefine'; |
465 | |
466 | sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" } |
467 | sub RealLoud :ATTR(ARRAY) { print "Urrrrrrrrrr!" } |
468 | sub RealLoud :ATTR(HASH) { print "Arrrrrgggghhhhhh!" } |
469 | sub RealLoud :ATTR(CODE) { croak "Real loud sub torpedoed" } |
470 | |
471 | You can also explicitly indicate that a single handler is meant to be |
472 | used for all types of referents like so: |
473 | |
474 | package LoudDecl; |
475 | use Attribute::Handlers; |
476 | |
477 | sub SeriousLoud :ATTR(ANY) { warn "Hearing loss imminent" } |
478 | |
479 | (I.e. C<ATTR(ANY)> is a synonym for C<:ATTR>). |
480 | |
481 | |
482 | =head2 Non-interpretive attribute handlers |
483 | |
484 | Occasionally the strenuous efforts Attribute::Handlers makes to convert |
485 | the data argument (C<$_[4]>) to a useable form before passing it to |
486 | the handler get in the way. |
487 | |
488 | You can turn off that eagerness-to-help by declaring |
489 | an attribute handler with the keyword C<RAWDATA>. For example: |
490 | |
491 | sub Raw : ATTR(RAWDATA) {...} |
492 | sub Nekkid : ATTR(SCALAR,RAWDATA) {...} |
493 | sub Au::Naturale : ATTR(RAWDATA,ANY) {...} |
494 | |
495 | Then the handler makes absolutely no attempt to interpret the data it |
496 | receives and simply passes it as a string: |
497 | |
498 | my $power : Raw(1..100); # handlers receives "1..100" |
499 | |
500 | =head2 Phase-specific attribute handlers |
501 | |
502 | By default, attribute handlers are called at the end of the compilation |
503 | phase (in a C<CHECK> block). This seems to be optimal in most cases because |
504 | most things that can be defined are defined by that point but nothing has |
505 | been executed. |
506 | |
507 | However, it is possible to set up attribute handlers that are called at |
508 | other points in the program's compilation or execution, by explicitly |
509 | stating the phase (or phases) in which you wish the attribute handler to |
510 | be called. For example: |
511 | |
512 | sub Early :ATTR(SCALAR,BEGIN) {...} |
513 | sub Normal :ATTR(SCALAR,CHECK) {...} |
514 | sub Late :ATTR(SCALAR,INIT) {...} |
515 | sub Final :ATTR(SCALAR,END) {...} |
516 | sub Bookends :ATTR(SCALAR,BEGIN,END) {...} |
517 | |
518 | As the last example indicates, a handler may be set up to be (re)called in |
519 | two or more phases. The phase name is passed as the handler's final argument. |
520 | |
521 | Note that attribute handlers that are scheduled for the C<BEGIN> phase |
522 | are handled as soon as the attribute is detected (i.e. before any |
523 | subsequently defined C<BEGIN> blocks are executed). |
524 | |
525 | |
526 | =head2 Attributes as C<tie> interfaces |
527 | |
528 | Attributes make an excellent and intuitive interface through which to tie |
529 | variables. For example: |
530 | |
531 | use Attribute::Handlers; |
532 | use Tie::Cycle; |
533 | |
534 | sub UNIVERSAL::Cycle : ATTR(SCALAR) { |
535 | my ($package, $symbol, $referent, $attr, $data, $phase) = @_; |
536 | $data = [ $data ] unless ref $data eq 'ARRAY'; |
537 | tie $$referent, 'Tie::Cycle', $data; |
538 | } |
539 | |
540 | # and thereafter... |
541 | |
542 | package main; |
543 | |
544 | my $next : Cycle('A'..'Z'); # $next is now a tied variable |
545 | |
546 | while (<>) { |
547 | print $next; |
548 | } |
549 | |
550 | Note that, because the C<Cycle> attribute receives its arguments in the |
551 | C<$data> variable, if the attribute is given a list of arguments, C<$data> |
552 | will consist of a single array reference; otherwise, it will consist of the |
553 | single argument directly. Since Tie::Cycle requires its cycling values to |
554 | be passed as an array reference, this means that we need to wrap |
555 | non-array-reference arguments in an array constructor: |
556 | |
557 | $data = [ $data ] unless ref $data eq 'ARRAY'; |
558 | |
559 | Typically, however, things are the other way around: the tieable class expects |
560 | its arguments as a flattened list, so the attribute looks like: |
561 | |
562 | sub UNIVERSAL::Cycle : ATTR(SCALAR) { |
563 | my ($package, $symbol, $referent, $attr, $data, $phase) = @_; |
564 | my @data = ref $data eq 'ARRAY' ? @$data : $data; |
565 | tie $$referent, 'Tie::Whatever', @data; |
566 | } |
567 | |
568 | |
569 | This software pattern is so widely applicable that Attribute::Handlers |
570 | provides a way to automate it: specifying C<'autotie'> in the |
571 | C<use Attribute::Handlers> statement. So, the cycling example, |
572 | could also be written: |
573 | |
574 | use Attribute::Handlers autotie => { Cycle => 'Tie::Cycle' }; |
575 | |
576 | # and thereafter... |
577 | |
578 | package main; |
579 | |
580 | my $next : Cycle(['A'..'Z']); # $next is now a tied variable |
581 | |
582 | while (<>) { |
583 | print $next; |
584 | |
585 | Note that we now have to pass the cycling values as an array reference, |
586 | since the C<autotie> mechanism passes C<tie> a list of arguments as a list |
587 | (as in the Tie::Whatever example), I<not> as an array reference (as in |
588 | the original Tie::Cycle example at the start of this section). |
589 | |
590 | The argument after C<'autotie'> is a reference to a hash in which each key is |
591 | the name of an attribute to be created, and each value is the class to which |
592 | variables ascribed that attribute should be tied. |
593 | |
594 | Note that there is no longer any need to import the Tie::Cycle module -- |
595 | Attribute::Handlers takes care of that automagically. You can even pass |
596 | arguments to the module's C<import> subroutine, by appending them to the |
597 | class name. For example: |
598 | |
599 | use Attribute::Handlers |
600 | autotie => { Dir => 'Tie::Dir qw(DIR_UNLINK)' }; |
601 | |
602 | If the attribute name is unqualified, the attribute is installed in the |
603 | current package. Otherwise it is installed in the qualifier's package: |
604 | |
605 | package Here; |
606 | |
607 | use Attribute::Handlers autotie => { |
608 | Other::Good => Tie::SecureHash, # tie attr installed in Other:: |
609 | Bad => Tie::Taxes, # tie attr installed in Here:: |
610 | UNIVERSAL::Ugly => Software::Patent # tie attr installed everywhere |
611 | }; |
612 | |
613 | Autoties are most commonly used in the module to which they actually tie, |
614 | and need to export their attributes to any module that calls them. To |
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615 | facilitate this, Attribute::Handlers recognizes a special "pseudo-class" -- |
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616 | C<__CALLER__>, which may be specified as the qualifier of an attribute: |
617 | |
618 | package Tie::Me::Kangaroo:Down::Sport; |
619 | |
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620 | use Attribute::Handlers autotie => { '__CALLER__::Roo' => __PACKAGE__ }; |
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621 | |
622 | This causes Attribute::Handlers to define the C<Roo> attribute in the package |
623 | that imports the Tie::Me::Kangaroo:Down::Sport module. |
624 | |
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625 | Note that it is important to quote the __CALLER__::Roo identifier because |
626 | a bug in perl 5.8 will refuse to parse it and cause an unknown error. |
627 | |
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628 | =head3 Passing the tied object to C<tie> |
629 | |
630 | Occasionally it is important to pass a reference to the object being tied |
631 | to the TIESCALAR, TIEHASH, etc. that ties it. |
632 | |
633 | The C<autotie> mechanism supports this too. The following code: |
634 | |
635 | use Attribute::Handlers autotieref => { Selfish => Tie::Selfish }; |
636 | my $var : Selfish(@args); |
637 | |
638 | has the same effect as: |
639 | |
640 | tie my $var, 'Tie::Selfish', @args; |
641 | |
642 | But when C<"autotieref"> is used instead of C<"autotie">: |
643 | |
644 | use Attribute::Handlers autotieref => { Selfish => Tie::Selfish }; |
645 | my $var : Selfish(@args); |
646 | |
647 | the effect is to pass the C<tie> call an extra reference to the variable |
648 | being tied: |
649 | |
650 | tie my $var, 'Tie::Selfish', \$var, @args; |
651 | |
652 | |
653 | |
654 | =head1 EXAMPLES |
655 | |
656 | If the class shown in L<SYNOPSIS> were placed in the MyClass.pm |
657 | module, then the following code: |
658 | |
659 | package main; |
660 | use MyClass; |
661 | |
662 | my MyClass $slr :Good :Bad(1**1-1) :Omni(-vorous); |
663 | |
664 | package SomeOtherClass; |
665 | use base MyClass; |
666 | |
667 | sub tent { 'acle' } |
668 | |
669 | sub fn :Ugly(sister) :Omni('po',tent()) {...} |
670 | my @arr :Good :Omni(s/cie/nt/); |
671 | my %hsh :Good(q/bye) :Omni(q/bus/); |
672 | |
673 | |
674 | would cause the following handlers to be invoked: |
675 | |
676 | # my MyClass $slr :Good :Bad(1**1-1) :Omni(-vorous); |
677 | |
678 | MyClass::Good:ATTR(SCALAR)( 'MyClass', # class |
679 | 'LEXICAL', # no typeglob |
680 | \$slr, # referent |
681 | 'Good', # attr name |
682 | undef # no attr data |
683 | 'CHECK', # compiler phase |
684 | ); |
685 | |
686 | MyClass::Bad:ATTR(SCALAR)( 'MyClass', # class |
687 | 'LEXICAL', # no typeglob |
688 | \$slr, # referent |
689 | 'Bad', # attr name |
690 | 0 # eval'd attr data |
691 | 'CHECK', # compiler phase |
692 | ); |
693 | |
694 | MyClass::Omni:ATTR(SCALAR)( 'MyClass', # class |
695 | 'LEXICAL', # no typeglob |
696 | \$slr, # referent |
697 | 'Omni', # attr name |
698 | '-vorous' # eval'd attr data |
699 | 'CHECK', # compiler phase |
700 | ); |
701 | |
702 | |
703 | # sub fn :Ugly(sister) :Omni('po',tent()) {...} |
704 | |
705 | MyClass::UGLY:ATTR(CODE)( 'SomeOtherClass', # class |
706 | \*SomeOtherClass::fn, # typeglob |
707 | \&SomeOtherClass::fn, # referent |
708 | 'Ugly', # attr name |
709 | 'sister' # eval'd attr data |
710 | 'CHECK', # compiler phase |
711 | ); |
712 | |
713 | MyClass::Omni:ATTR(CODE)( 'SomeOtherClass', # class |
714 | \*SomeOtherClass::fn, # typeglob |
715 | \&SomeOtherClass::fn, # referent |
716 | 'Omni', # attr name |
717 | ['po','acle'] # eval'd attr data |
718 | 'CHECK', # compiler phase |
719 | ); |
720 | |
721 | |
722 | # my @arr :Good :Omni(s/cie/nt/); |
723 | |
724 | MyClass::Good:ATTR(ARRAY)( 'SomeOtherClass', # class |
725 | 'LEXICAL', # no typeglob |
726 | \@arr, # referent |
727 | 'Good', # attr name |
728 | undef # no attr data |
729 | 'CHECK', # compiler phase |
730 | ); |
731 | |
732 | MyClass::Omni:ATTR(ARRAY)( 'SomeOtherClass', # class |
733 | 'LEXICAL', # no typeglob |
734 | \@arr, # referent |
735 | 'Omni', # attr name |
736 | "" # eval'd attr data |
737 | 'CHECK', # compiler phase |
738 | ); |
739 | |
740 | |
741 | # my %hsh :Good(q/bye) :Omni(q/bus/); |
742 | |
743 | MyClass::Good:ATTR(HASH)( 'SomeOtherClass', # class |
744 | 'LEXICAL', # no typeglob |
745 | \%hsh, # referent |
746 | 'Good', # attr name |
747 | 'q/bye' # raw attr data |
748 | 'CHECK', # compiler phase |
749 | ); |
750 | |
751 | MyClass::Omni:ATTR(HASH)( 'SomeOtherClass', # class |
752 | 'LEXICAL', # no typeglob |
753 | \%hsh, # referent |
754 | 'Omni', # attr name |
755 | 'bus' # eval'd attr data |
756 | 'CHECK', # compiler phase |
757 | ); |
758 | |
759 | |
760 | Installing handlers into UNIVERSAL, makes them...err..universal. |
761 | For example: |
762 | |
763 | package Descriptions; |
764 | use Attribute::Handlers; |
765 | |
766 | my %name; |
767 | sub name { return $name{$_[2]}||*{$_[1]}{NAME} } |
768 | |
769 | sub UNIVERSAL::Name :ATTR { |
770 | $name{$_[2]} = $_[4]; |
771 | } |
772 | |
773 | sub UNIVERSAL::Purpose :ATTR { |
774 | print STDERR "Purpose of ", &name, " is $_[4]\n"; |
775 | } |
776 | |
777 | sub UNIVERSAL::Unit :ATTR { |
778 | print STDERR &name, " measured in $_[4]\n"; |
779 | } |
780 | |
781 | Let's you write: |
782 | |
783 | use Descriptions; |
784 | |
785 | my $capacity : Name(capacity) |
786 | : Purpose(to store max storage capacity for files) |
787 | : Unit(Gb); |
788 | |
789 | |
790 | package Other; |
791 | |
792 | sub foo : Purpose(to foo all data before barring it) { } |
793 | |
794 | # etc. |
795 | |
796 | |
797 | =head1 DIAGNOSTICS |
798 | |
799 | =over |
800 | |
801 | =item C<Bad attribute type: ATTR(%s)> |
802 | |
803 | An attribute handler was specified with an C<:ATTR(I<ref_type>)>, but the |
804 | type of referent it was defined to handle wasn't one of the five permitted: |
805 | C<SCALAR>, C<ARRAY>, C<HASH>, C<CODE>, or C<ANY>. |
806 | |
807 | =item C<Attribute handler %s doesn't handle %s attributes> |
808 | |
809 | A handler for attributes of the specified name I<was> defined, but not |
810 | for the specified type of declaration. Typically encountered whe trying |
811 | to apply a C<VAR> attribute handler to a subroutine, or a C<SCALAR> |
812 | attribute handler to some other type of variable. |
813 | |
814 | =item C<Declaration of %s attribute in package %s may clash with future reserved word> |
815 | |
816 | A handler for an attributes with an all-lowercase name was declared. An |
817 | attribute with an all-lowercase name might have a meaning to Perl |
818 | itself some day, even though most don't yet. Use a mixed-case attribute |
819 | name, instead. |
820 | |
821 | =item C<Can't have two ATTR specifiers on one subroutine> |
822 | |
823 | You just can't, okay? |
824 | Instead, put all the specifications together with commas between them |
825 | in a single C<ATTR(I<specification>)>. |
826 | |
827 | =item C<Can't autotie a %s> |
828 | |
829 | You can only declare autoties for types C<"SCALAR">, C<"ARRAY">, and |
830 | C<"HASH">. They're the only things (apart from typeglobs -- which are |
831 | not declarable) that Perl can tie. |
832 | |
833 | =item C<Internal error: %s symbol went missing> |
834 | |
835 | Something is rotten in the state of the program. An attributed |
836 | subroutine ceased to exist between the point it was declared and the point |
837 | at which its attribute handler(s) would have been called. |
838 | |
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839 | =item C<Won't be able to apply END handler> |
840 | |
841 | You have defined an END handler for an attribute that is being applied |
842 | to a lexical variable. Since the variable may not be available during END |
843 | this won't happen. |
844 | |
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845 | =back |
846 | |
847 | =head1 AUTHOR |
848 | |
849 | Damian Conway (damian@conway.org) |
850 | |
851 | =head1 BUGS |
852 | |
853 | There are undoubtedly serious bugs lurking somewhere in code this funky :-) |
854 | Bug reports and other feedback are most welcome. |
855 | |
856 | =head1 COPYRIGHT |
857 | |
858 | Copyright (c) 2001, Damian Conway. All Rights Reserved. |
859 | This module is free software. It may be used, redistributed |
860 | and/or modified under the same terms as Perl itself. |