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dc6b6eef JH |
1 | package Attribute::Handlers; |
2 | use 5.006; | |
3 | use Carp; | |
4 | use warnings; | |
9df0c874 | 5 | $VERSION = '0.70'; |
dc6b6eef JH |
6 | $DB::single=1; |
7 | ||
9df0c874 | 8 | my %symcache; |
dc6b6eef JH |
9 | sub findsym { |
10 | my ($pkg, $ref, $type) = @_; | |
9df0c874 | 11 | return $symcache{$pkg,$ref} if $symcache{$pkg,$ref}; |
dc6b6eef | 12 | $type ||= ref($ref); |
9df0c874 | 13 | my $found; |
dc6b6eef | 14 | foreach my $sym ( values %{$pkg."::"} ) { |
9df0c874 JH |
15 | return $symcache{$pkg,$ref} = \$sym |
16 | if *{$sym}{$type} && *{$sym}{$type} == $ref; | |
dc6b6eef JH |
17 | } |
18 | } | |
19 | ||
20 | my %validtype = ( | |
21 | VAR => [qw[SCALAR ARRAY HASH]], | |
22 | ANY => [qw[SCALAR ARRAY HASH CODE]], | |
23 | "" => [qw[SCALAR ARRAY HASH CODE]], | |
24 | SCALAR => [qw[SCALAR]], | |
25 | ARRAY => [qw[ARRAY]], | |
26 | HASH => [qw[HASH]], | |
27 | CODE => [qw[CODE]], | |
28 | ); | |
29 | my %lastattr; | |
30 | my @declarations; | |
31 | my %raw; | |
9df0c874 | 32 | my %phase; |
dc6b6eef JH |
33 | my %sigil = (SCALAR=>'$', ARRAY=>'@', HASH=>'%'); |
34 | ||
9df0c874 JH |
35 | sub _usage_AH_ { |
36 | croak "Usage: use $_[0] autotie => {AttrName => TieClassName,...}"; | |
37 | } | |
dc6b6eef JH |
38 | |
39 | sub import { | |
40 | my $class = shift @_; | |
9df0c874 | 41 | return unless $class eq "Attribute::Handlers"; |
dc6b6eef JH |
42 | while (@_) { |
43 | my $cmd = shift; | |
44 | if ($cmd eq 'autotie') { | |
45 | my $mapping = shift; | |
9df0c874 | 46 | _usage_AH_ $class unless ref($mapping) eq 'HASH'; |
dc6b6eef | 47 | while (my($attr, $tieclass) = each %$mapping) { |
9df0c874 JH |
48 | $tieclass =~ s/^([_a-z]\w*(::[_a-z]\w*))(.*)/$1/is; |
49 | my $args = $3||'()'; | |
50 | usage $class unless $attr =~ m/^[_a-z]\w*(::[_a-z]\w*)*$/i | |
51 | && $tieclass =~ m/^[_a-z]\w*(::[_a-z]\w*)/i | |
dc6b6eef | 52 | && eval "use base $tieclass; 1"; |
9df0c874 JH |
53 | if ($tieclass->isa('Exporter')) { |
54 | local $Exporter::ExportLevel = 2; | |
55 | $tieclass->import(eval $args); | |
56 | } | |
57 | $attr =~ s/__CALLER__/caller(1)/e; | |
58 | $attr = caller()."::".$attr unless $attr =~ /::/; | |
dc6b6eef JH |
59 | eval qq{ |
60 | sub $attr : ATTR(VAR) { | |
61 | my (\$ref, \$data) = \@_[2,4]; | |
62 | \$data = [ \$data ] unless ref \$data eq 'ARRAY'; | |
9df0c874 JH |
63 | # print \$ref, ": "; |
64 | # use Data::Dumper 'Dumper'; | |
65 | # print Dumper [ [\$ref, \$data] ]; | |
66 | my \$type = ref(\$ref)||"value (".(\$ref||"<undef>").")"; | |
dc6b6eef JH |
67 | (\$type eq 'SCALAR')? tie \$\$ref,'$tieclass',\@\$data |
68 | :(\$type eq 'ARRAY') ? tie \@\$ref,'$tieclass',\@\$data | |
69 | :(\$type eq 'HASH') ? tie \%\$ref,'$tieclass',\@\$data | |
9df0c874 | 70 | : die "Can't autotie a \$type\n" |
dc6b6eef JH |
71 | } 1 |
72 | } or die "Internal error: $@"; | |
73 | } | |
74 | } | |
75 | else { | |
76 | croak "Can't understand $_"; | |
77 | } | |
78 | } | |
79 | } | |
9df0c874 | 80 | sub _resolve_lastattr { |
dc6b6eef JH |
81 | return unless $lastattr{ref}; |
82 | my $sym = findsym @lastattr{'pkg','ref'} | |
83 | or die "Internal error: $lastattr{pkg} symbol went missing"; | |
84 | my $name = *{$sym}{NAME}; | |
85 | warn "Declaration of $name attribute in package $lastattr{pkg} may clash with future reserved word\n" | |
86 | if $^W and $name !~ /[A-Z]/; | |
87 | foreach ( @{$validtype{$lastattr{type}}} ) { | |
88 | *{"$lastattr{pkg}::_ATTR_${_}_${name}"} = $lastattr{ref}; | |
89 | } | |
90 | %lastattr = (); | |
91 | } | |
92 | ||
93 | sub AUTOLOAD { | |
94 | my ($class) = @_; | |
95 | $AUTOLOAD =~ /_ATTR_(.*?)_(.*)/ or | |
96 | croak "Can't locate class method '$AUTOLOAD' via package '$class'"; | |
97 | croak "Attribute handler '$2' doesn't handle $1 attributes"; | |
98 | } | |
99 | ||
100 | sub DESTROY {} | |
101 | ||
102 | my $builtin = qr/lvalue|method|locked/; | |
103 | ||
9df0c874 | 104 | sub _gen_handler_AH_() { |
dc6b6eef | 105 | return sub { |
9df0c874 | 106 | _resolve_lastattr; |
dc6b6eef JH |
107 | my ($pkg, $ref, @attrs) = @_; |
108 | foreach (@attrs) { | |
109 | my ($attr, $data) = /^([a-z_]\w*)(?:[(](.*)[)])?$/i or next; | |
110 | if ($attr eq 'ATTR') { | |
111 | $data ||= "ANY"; | |
112 | $raw{$ref} = $data =~ s/\s*,?\s*RAWDATA\s*,?\s*//; | |
9df0c874 JH |
113 | $phase{$ref}{BEGIN} = 1 |
114 | if $data =~ s/\s*,?\s*(BEGIN)\s*,?\s*//; | |
115 | $phase{$ref}{INIT} = 1 | |
116 | if $data =~ s/\s*,?\s*(INIT)\s*,?\s*//; | |
117 | $phase{$ref}{END} = 1 | |
118 | if $data =~ s/\s*,?\s*(END)\s*,?\s*//; | |
119 | $phase{$ref}{CHECK} = 1 | |
120 | if $data =~ s/\s*,?\s*(CHECK)\s*,?\s*// | |
121 | || ! keys %{$phase{$ref}}; | |
122 | croak "Can't have two ATTR specifiers on one subroutine" | |
123 | if keys %lastattr; | |
dc6b6eef JH |
124 | croak "Bad attribute type: ATTR($data)" |
125 | unless $validtype{$data}; | |
126 | %lastattr=(pkg=>$pkg,ref=>$ref,type=>$data); | |
127 | } | |
128 | else { | |
129 | my $handler = $pkg->can($attr); | |
130 | next unless $handler; | |
9df0c874 JH |
131 | my $decl = [$pkg, $ref, $attr, $data, |
132 | $raw{$handler}, $phase{$handler}]; | |
133 | _apply_handler_AH_($decl,'BEGIN'); | |
134 | push @declarations, $decl; | |
dc6b6eef JH |
135 | } |
136 | $_ = undef; | |
137 | } | |
138 | return grep {defined && !/$builtin/} @attrs; | |
139 | } | |
140 | } | |
141 | ||
9df0c874 | 142 | *{"MODIFY_${_}_ATTRIBUTES"} = _gen_handler_AH_ foreach @{$validtype{ANY}}; |
dc6b6eef JH |
143 | push @UNIVERSAL::ISA, 'Attribute::Handlers' |
144 | unless grep /^Attribute::Handlers$/, @UNIVERSAL::ISA; | |
145 | ||
9df0c874 JH |
146 | sub _apply_handler_AH_ { |
147 | my ($declaration, $phase) = @_; | |
148 | my ($pkg, $ref, $attr, $data, $raw, $handlerphase) = @$declaration; | |
149 | return unless $handlerphase->{$phase}; | |
150 | # print STDERR "Handling $attr on $ref in $phase with [$data]\n"; | |
151 | my $type = ref $ref; | |
152 | my $handler = "_ATTR_${type}_${attr}"; | |
153 | my $sym = findsym($pkg, $ref); | |
154 | $sym ||= $type eq 'CODE' ? 'ANON' : 'LEXICAL'; | |
155 | no warnings; | |
156 | my $evaled = !$raw && eval("package $pkg; no warnings; | |
157 | local \$SIG{__WARN__}=sub{die}; [$data]"); | |
158 | $data = ($evaled && $data =~ /^\s*\[/) ? [$evaled] | |
159 | : ($evaled) ? $evaled | |
160 | : [$data]; | |
161 | $pkg->$handler($sym, | |
162 | (ref $sym eq 'GLOB' ? *{$sym}{ref $ref}||$ref : $ref), | |
163 | $attr, | |
164 | (@$data>1? $data : $data->[0]), | |
165 | $phase, | |
166 | ); | |
167 | return 1; | |
168 | } | |
169 | ||
dc6b6eef | 170 | CHECK { |
9df0c874 JH |
171 | _resolve_lastattr; |
172 | _apply_handler_AH_($_,'CHECK') foreach @declarations; | |
dc6b6eef JH |
173 | } |
174 | ||
9df0c874 JH |
175 | INIT { _apply_handler_AH_($_,'INIT') foreach @declarations } |
176 | ||
177 | END { _apply_handler_AH_($_,'END') foreach @declarations } | |
178 | ||
dc6b6eef JH |
179 | 1; |
180 | __END__ | |
181 | ||
182 | =head1 NAME | |
183 | ||
184 | Attribute::Handlers - Simpler definition of attribute handlers | |
185 | ||
186 | =head1 VERSION | |
187 | ||
9df0c874 JH |
188 | This document describes version 0.70 of Attribute::Handlers, |
189 | released June 3, 2001. | |
dc6b6eef JH |
190 | |
191 | =head1 SYNOPSIS | |
192 | ||
193 | package MyClass; | |
194 | require v5.6.0; | |
195 | use Attribute::Handlers; | |
196 | no warnings 'redefine'; | |
197 | ||
198 | ||
199 | sub Good : ATTR(SCALAR) { | |
200 | my ($package, $symbol, $referent, $attr, $data) = @_; | |
201 | ||
202 | # Invoked for any scalar variable with a :Good attribute, | |
203 | # provided the variable was declared in MyClass (or | |
204 | # a derived class) or typed to MyClass. | |
205 | ||
206 | # Do whatever to $referent here (executed in CHECK phase). | |
207 | ... | |
208 | } | |
209 | ||
210 | sub Bad : ATTR(SCALAR) { | |
211 | # Invoked for any scalar variable with a :Bad attribute, | |
212 | # provided the variable was declared in MyClass (or | |
213 | # a derived class) or typed to MyClass. | |
214 | ... | |
215 | } | |
216 | ||
217 | sub Good : ATTR(ARRAY) { | |
218 | # Invoked for any array variable with a :Good attribute, | |
219 | # provided the variable was declared in MyClass (or | |
220 | # a derived class) or typed to MyClass. | |
221 | ... | |
222 | } | |
223 | ||
224 | sub Good : ATTR(HASH) { | |
225 | # Invoked for any hash variable with a :Good attribute, | |
226 | # provided the variable was declared in MyClass (or | |
227 | # a derived class) or typed to MyClass. | |
228 | ... | |
229 | } | |
230 | ||
231 | sub Ugly : ATTR(CODE) { | |
232 | # Invoked for any subroutine declared in MyClass (or a | |
233 | # derived class) with an :Ugly attribute. | |
234 | ... | |
235 | } | |
236 | ||
237 | sub Omni : ATTR { | |
238 | # Invoked for any scalar, array, hash, or subroutine | |
239 | # with an :Omni attribute, provided the variable or | |
240 | # subroutine was declared in MyClass (or a derived class) | |
241 | # or the variable was typed to MyClass. | |
242 | # Use ref($_[2]) to determine what kind of referent it was. | |
243 | ... | |
244 | } | |
245 | ||
246 | ||
247 | use Attribute::Handlers autotie => { Cycle => Tie::Cycle }; | |
248 | ||
249 | my $next : Cycle(['A'..'Z']); | |
250 | ||
251 | ||
252 | =head1 DESCRIPTION | |
253 | ||
254 | This module, when inherited by a package, allows that package's class to | |
255 | define attribute handler subroutines for specific attributes. Variables | |
256 | and subroutines subsequently defined in that package, or in packages | |
257 | derived from that package may be given attributes with the same names as | |
9df0c874 JH |
258 | the attribute handler subroutines, which will then be called in one of |
259 | the compilation phases (i.e. in a C<BEGIN>, C<CHECK>, C<INIT>, or C<END> | |
260 | block). | |
dc6b6eef JH |
261 | |
262 | To create a handler, define it as a subroutine with the same name as | |
263 | the desired attribute, and declare the subroutine itself with the | |
264 | attribute C<:ATTR>. For example: | |
265 | ||
266 | package LoudDecl; | |
267 | use Attribute::Handlers; | |
268 | ||
269 | sub Loud :ATTR { | |
9df0c874 | 270 | my ($package, $symbol, $referent, $attr, $data, $phase) = @_; |
dc6b6eef JH |
271 | print STDERR |
272 | ref($referent), " ", | |
273 | *{$symbol}{NAME}, " ", | |
274 | "($referent) ", "was just declared ", | |
275 | "and ascribed the ${attr} attribute ", | |
9df0c874 JH |
276 | "with data ($data)\n", |
277 | "in phase $phase\n"; | |
dc6b6eef JH |
278 | } |
279 | ||
280 | This creates an handler for the attribute C<:Loud> in the class LoudDecl. | |
281 | Thereafter, any subroutine declared with a C<:Loud> attribute in the class | |
282 | LoudDecl: | |
283 | ||
284 | package LoudDecl; | |
285 | ||
286 | sub foo: Loud {...} | |
287 | ||
288 | causes the above handler to be invoked, and passed: | |
289 | ||
290 | =over | |
291 | ||
292 | =item [0] | |
293 | ||
294 | the name of the package into which it was declared; | |
295 | ||
296 | =item [1] | |
297 | ||
298 | a reference to the symbol table entry (typeglob) containing the subroutine; | |
299 | ||
300 | =item [2] | |
301 | ||
302 | a reference to the subroutine; | |
303 | ||
304 | =item [3] | |
305 | ||
306 | the name of the attribute; | |
307 | ||
308 | =item [4] | |
309 | ||
9df0c874 JH |
310 | any data associated with that attribute; |
311 | ||
312 | =item [5] | |
313 | ||
314 | the name of the phase in which the handler is being invoked. | |
dc6b6eef JH |
315 | |
316 | =back | |
317 | ||
318 | Likewise, declaring any variables with the C<:Loud> attribute within the | |
319 | package: | |
320 | ||
9df0c874 | 321 | package LoudDecl; |
dc6b6eef | 322 | |
9df0c874 JH |
323 | my $foo :Loud; |
324 | my @foo :Loud; | |
325 | my %foo :Loud; | |
dc6b6eef JH |
326 | |
327 | will cause the handler to be called with a similar argument list (except, | |
328 | of course, that C<$_[2]> will be a reference to the variable). | |
329 | ||
330 | The package name argument will typically be the name of the class into | |
331 | which the subroutine was declared, but it may also be the name of a derived | |
332 | class (since handlers are inherited). | |
333 | ||
334 | If a lexical variable is given an attribute, there is no symbol table to | |
335 | which it belongs, so the symbol table argument (C<$_[1]>) is set to the | |
336 | string C<'LEXICAL'> in that case. Likewise, ascribing an attribute to | |
337 | an anonymous subroutine results in a symbol table argument of C<'ANON'>. | |
338 | ||
339 | The data argument passes in the value (if any) associated with the | |
340 | attribute. For example, if C<&foo> had been declared: | |
341 | ||
9df0c874 | 342 | sub foo :Loud("turn it up to 11, man!") {...} |
dc6b6eef JH |
343 | |
344 | then the string C<"turn it up to 11, man!"> would be passed as the | |
345 | last argument. | |
346 | ||
347 | Attribute::Handlers makes strenuous efforts to convert | |
348 | the data argument (C<$_[4]>) to a useable form before passing it to | |
349 | the handler (but see L<"Non-interpretive attribute handlers">). | |
350 | For example, all of these: | |
351 | ||
9df0c874 JH |
352 | sub foo :Loud(till=>ears=>are=>bleeding) {...} |
353 | sub foo :Loud(['till','ears','are','bleeding']) {...} | |
354 | sub foo :Loud(qw/till ears are bleeding/) {...} | |
355 | sub foo :Loud(qw/my, ears, are, bleeding/) {...} | |
356 | sub foo :Loud(till,ears,are,bleeding) {...} | |
dc6b6eef JH |
357 | |
358 | causes it to pass C<['till','ears','are','bleeding']> as the handler's | |
359 | data argument. However, if the data can't be parsed as valid Perl, then | |
360 | it is passed as an uninterpreted string. For example: | |
361 | ||
9df0c874 JH |
362 | sub foo :Loud(my,ears,are,bleeding) {...} |
363 | sub foo :Loud(qw/my ears are bleeding) {...} | |
dc6b6eef JH |
364 | |
365 | cause the strings C<'my,ears,are,bleeding'> and C<'qw/my ears are bleeding'> | |
366 | respectively to be passed as the data argument. | |
367 | ||
368 | If the attribute has only a single associated scalar data value, that value is | |
369 | passed as a scalar. If multiple values are associated, they are passed as an | |
370 | array reference. If no value is associated with the attribute, C<undef> is | |
371 | passed. | |
372 | ||
373 | ||
374 | =head2 Typed lexicals | |
375 | ||
376 | Regardless of the package in which it is declared, if a lexical variable is | |
377 | ascribed an attribute, the handler that is invoked is the one belonging to | |
378 | the package to which it is typed. For example, the following declarations: | |
379 | ||
9df0c874 | 380 | package OtherClass; |
dc6b6eef | 381 | |
9df0c874 JH |
382 | my LoudDecl $loudobj : Loud; |
383 | my LoudDecl @loudobjs : Loud; | |
384 | my LoudDecl %loudobjex : Loud; | |
dc6b6eef JH |
385 | |
386 | causes the LoudDecl::Loud handler to be invoked (even if OtherClass also | |
387 | defines a handler for C<:Loud> attributes). | |
388 | ||
389 | ||
390 | =head2 Type-specific attribute handlers | |
391 | ||
392 | If an attribute handler is declared and the C<:ATTR> specifier is | |
393 | given the name of a built-in type (C<SCALAR>, C<ARRAY>, C<HASH>, or C<CODE>), | |
394 | the handler is only applied to declarations of that type. For example, | |
395 | the following definition: | |
396 | ||
9df0c874 | 397 | package LoudDecl; |
dc6b6eef | 398 | |
9df0c874 | 399 | sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" } |
dc6b6eef JH |
400 | |
401 | creates an attribute handler that applies only to scalars: | |
402 | ||
403 | ||
9df0c874 JH |
404 | package Painful; |
405 | use base LoudDecl; | |
dc6b6eef | 406 | |
9df0c874 JH |
407 | my $metal : RealLoud; # invokes &LoudDecl::RealLoud |
408 | my @metal : RealLoud; # error: unknown attribute | |
409 | my %metal : RealLoud; # error: unknown attribute | |
410 | sub metal : RealLoud {...} # error: unknown attribute | |
dc6b6eef JH |
411 | |
412 | You can, of course, declare separate handlers for these types as well | |
413 | (but you'll need to specify C<no warnings 'redefine'> to do it quietly): | |
414 | ||
9df0c874 JH |
415 | package LoudDecl; |
416 | use Attribute::Handlers; | |
417 | no warnings 'redefine'; | |
dc6b6eef | 418 | |
9df0c874 JH |
419 | sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" } |
420 | sub RealLoud :ATTR(ARRAY) { print "Urrrrrrrrrr!" } | |
421 | sub RealLoud :ATTR(HASH) { print "Arrrrrgggghhhhhh!" } | |
422 | sub RealLoud :ATTR(CODE) { croak "Real loud sub torpedoed" } | |
dc6b6eef JH |
423 | |
424 | You can also explicitly indicate that a single handler is meant to be | |
425 | used for all types of referents like so: | |
426 | ||
9df0c874 JH |
427 | package LoudDecl; |
428 | use Attribute::Handlers; | |
dc6b6eef | 429 | |
9df0c874 | 430 | sub SeriousLoud :ATTR(ANY) { warn "Hearing loss imminent" } |
dc6b6eef JH |
431 | |
432 | (I.e. C<ATTR(ANY)> is a synonym for C<:ATTR>). | |
433 | ||
434 | ||
435 | =head2 Non-interpretive attribute handlers | |
436 | ||
437 | Occasionally the strenuous efforts Attribute::Handlers makes to convert | |
438 | the data argument (C<$_[4]>) to a useable form before passing it to | |
439 | the handler get in the way. | |
440 | ||
441 | You can turn off that eagerness-to-help by declaring | |
442 | an attribute handler with the the keyword C<RAWDATA>. For example: | |
443 | ||
9df0c874 JH |
444 | sub Raw : ATTR(RAWDATA) {...} |
445 | sub Nekkid : ATTR(SCALAR,RAWDATA) {...} | |
446 | sub Au::Naturale : ATTR(RAWDATA,ANY) {...} | |
dc6b6eef JH |
447 | |
448 | Then the handler makes absolutely no attempt to interpret the data it | |
449 | receives and simply passes it as a string: | |
450 | ||
9df0c874 JH |
451 | my $power : Raw(1..100); # handlers receives "1..100" |
452 | ||
453 | =head2 Phase-specific attribute handlers | |
454 | ||
455 | By default, attribute handlers are called at the end of the compilation | |
456 | phase (in a C<CHECK> block). This seems to be optimal in most cases because | |
457 | most things that can be defined are defined by that point but nothing has | |
458 | been executed. | |
459 | ||
460 | However, it is possible to set up attribute handlers that are called at | |
461 | other points in the program's compilation or execution, by explicitly | |
462 | stating the phase (or phases) in which you wish the attribute handler to | |
463 | be called. For example: | |
464 | ||
465 | sub Early :ATTR(SCALAR,BEGIN) {...} | |
466 | sub Normal :ATTR(SCALAR,CHECK) {...} | |
467 | sub Late :ATTR(SCALAR,INIT) {...} | |
468 | sub Final :ATTR(SCALAR,END) {...} | |
469 | sub Bookends :ATTR(SCALAR,BEGIN,END) {...} | |
470 | ||
471 | As the last example indicates, a handler may be set up to be (re)called in | |
472 | two or more phases. The phase name is passed as the handler's final argument. | |
473 | ||
474 | Note that attribute handlers that are scheduled for the C<BEGIN> phase | |
475 | are handled as soon as the attribute is detected (i.e. before any | |
476 | subsequently defined C<BEGIN> blocks are executed). | |
dc6b6eef JH |
477 | |
478 | ||
479 | =head2 Attributes as C<tie> interfaces | |
480 | ||
481 | Attributes make an excellent and intuitive interface through which to tie | |
482 | variables. For example: | |
483 | ||
484 | use Attribute::Handlers; | |
485 | use Tie::Cycle; | |
486 | ||
487 | sub UNIVERSAL::Cycle : ATTR(SCALAR) { | |
9df0c874 | 488 | my ($package, $symbol, $referent, $attr, $data, $phase) = @_; |
dc6b6eef JH |
489 | $data = [ $data ] unless ref $data eq 'ARRAY'; |
490 | tie $$referent, 'Tie::Cycle', $data; | |
491 | } | |
492 | ||
493 | # and thereafter... | |
494 | ||
495 | package main; | |
496 | ||
9df0c874 | 497 | my $next : Cycle('A'..'Z'); # $next is now a tied variable |
dc6b6eef JH |
498 | |
499 | while (<>) { | |
500 | print $next; | |
501 | } | |
502 | ||
503 | In fact, this pattern is so widely applicable that Attribute::Handlers | |
504 | provides a way to automate it: specifying C<'autotie'> in the | |
505 | C<use Attribute::Handlers> statement. So, the previous example, | |
506 | could also be written: | |
507 | ||
508 | use Attribute::Handlers autotie => { Cycle => 'Tie::Cycle' }; | |
509 | ||
510 | # and thereafter... | |
511 | ||
512 | package main; | |
513 | ||
9df0c874 | 514 | my $next : Cycle('A'..'Z'); # $next is now a tied variable |
dc6b6eef JH |
515 | |
516 | while (<>) { | |
517 | print $next; | |
518 | ||
519 | The argument after C<'autotie'> is a reference to a hash in which each key is | |
520 | the name of an attribute to be created, and each value is the class to which | |
521 | variables ascribed that attribute should be tied. | |
522 | ||
523 | Note that there is no longer any need to import the Tie::Cycle module -- | |
9df0c874 JH |
524 | Attribute::Handlers takes care of that automagically. You can even pass |
525 | arguments to the module's C<import> subroutine, by appending them to the | |
526 | class name. For example: | |
527 | ||
528 | use Attribute::Handlers | |
529 | autotie => { Dir => 'Tie::Dir qw(DIR_UNLINK)' }; | |
dc6b6eef JH |
530 | |
531 | If the attribute name is unqualified, the attribute is installed in the | |
532 | current package. Otherwise it is installed in the qualifier's package: | |
533 | ||
dc6b6eef JH |
534 | package Here; |
535 | ||
536 | use Attribute::Handlers autotie => { | |
537 | Other::Good => Tie::SecureHash, # tie attr installed in Other:: | |
538 | Bad => Tie::Taxes, # tie attr installed in Here:: | |
539 | UNIVERSAL::Ugly => Software::Patent # tie attr installed everywhere | |
540 | }; | |
541 | ||
9df0c874 JH |
542 | Autoties are most commonly used in the module to which they actually tie, |
543 | and need to export their attributes to any module that calls them. To | |
544 | facilitiate this, Attribute::Handlers recognizes a special "pseudo-class" -- | |
545 | C<__CALLER__>, which may be specified as the qualifier of an attribute: | |
546 | ||
547 | package Tie::Me::Kangaroo:Down::Sport; | |
548 | ||
549 | use Attribute::Handler autotie => { __CALLER__::Roo => __PACKAGE__ }; | |
550 | ||
551 | This causes Attribute::Handlers to define the C<Roo> attribute in the package | |
552 | that imports the Tie::Me::Kangaroo:Down::Sport module. | |
553 | ||
dc6b6eef JH |
554 | |
555 | =head1 EXAMPLES | |
556 | ||
557 | If the class shown in L<SYNOPSIS> were placed in the MyClass.pm | |
558 | module, then the following code: | |
559 | ||
560 | package main; | |
561 | use MyClass; | |
562 | ||
563 | my MyClass $slr :Good :Bad(1**1-1) :Omni(-vorous); | |
564 | ||
565 | package SomeOtherClass; | |
566 | use base MyClass; | |
567 | ||
568 | sub tent { 'acle' } | |
569 | ||
570 | sub fn :Ugly(sister) :Omni('po',tent()) {...} | |
571 | my @arr :Good :Omni(s/cie/nt/); | |
572 | my %hsh :Good(q/bye) :Omni(q/bus/); | |
573 | ||
574 | ||
575 | would cause the following handlers to be invoked: | |
576 | ||
577 | # my MyClass $slr :Good :Bad(1**1-1) :Omni(-vorous); | |
578 | ||
579 | MyClass::Good:ATTR(SCALAR)( 'MyClass', # class | |
580 | 'LEXICAL', # no typeglob | |
581 | \$slr, # referent | |
582 | 'Good', # attr name | |
583 | undef # no attr data | |
9df0c874 | 584 | 'CHECK', # compiler phase |
dc6b6eef JH |
585 | ); |
586 | ||
587 | MyClass::Bad:ATTR(SCALAR)( 'MyClass', # class | |
588 | 'LEXICAL', # no typeglob | |
589 | \$slr, # referent | |
590 | 'Bad', # attr name | |
591 | 0 # eval'd attr data | |
9df0c874 | 592 | 'CHECK', # compiler phase |
dc6b6eef JH |
593 | ); |
594 | ||
595 | MyClass::Omni:ATTR(SCALAR)( 'MyClass', # class | |
596 | 'LEXICAL', # no typeglob | |
597 | \$slr, # referent | |
598 | 'Omni', # attr name | |
599 | '-vorous' # eval'd attr data | |
9df0c874 | 600 | 'CHECK', # compiler phase |
dc6b6eef JH |
601 | ); |
602 | ||
603 | ||
604 | # sub fn :Ugly(sister) :Omni('po',tent()) {...} | |
605 | ||
606 | MyClass::UGLY:ATTR(CODE)( 'SomeOtherClass', # class | |
607 | \*SomeOtherClass::fn, # typeglob | |
608 | \&SomeOtherClass::fn, # referent | |
609 | 'Ugly', # attr name | |
610 | 'sister' # eval'd attr data | |
9df0c874 | 611 | 'CHECK', # compiler phase |
dc6b6eef JH |
612 | ); |
613 | ||
614 | MyClass::Omni:ATTR(CODE)( 'SomeOtherClass', # class | |
615 | \*SomeOtherClass::fn, # typeglob | |
616 | \&SomeOtherClass::fn, # referent | |
617 | 'Omni', # attr name | |
618 | ['po','acle'] # eval'd attr data | |
9df0c874 | 619 | 'CHECK', # compiler phase |
dc6b6eef JH |
620 | ); |
621 | ||
622 | ||
623 | # my @arr :Good :Omni(s/cie/nt/); | |
624 | ||
625 | MyClass::Good:ATTR(ARRAY)( 'SomeOtherClass', # class | |
626 | 'LEXICAL', # no typeglob | |
627 | \@arr, # referent | |
628 | 'Good', # attr name | |
629 | undef # no attr data | |
9df0c874 | 630 | 'CHECK', # compiler phase |
dc6b6eef JH |
631 | ); |
632 | ||
633 | MyClass::Omni:ATTR(ARRAY)( 'SomeOtherClass', # class | |
634 | 'LEXICAL', # no typeglob | |
635 | \@arr, # referent | |
636 | 'Omni', # attr name | |
637 | "" # eval'd attr data | |
9df0c874 | 638 | 'CHECK', # compiler phase |
dc6b6eef JH |
639 | ); |
640 | ||
641 | ||
642 | # my %hsh :Good(q/bye) :Omni(q/bus/); | |
643 | ||
644 | MyClass::Good:ATTR(HASH)( 'SomeOtherClass', # class | |
645 | 'LEXICAL', # no typeglob | |
646 | \%hsh, # referent | |
647 | 'Good', # attr name | |
648 | 'q/bye' # raw attr data | |
9df0c874 | 649 | 'CHECK', # compiler phase |
dc6b6eef JH |
650 | ); |
651 | ||
652 | MyClass::Omni:ATTR(HASH)( 'SomeOtherClass', # class | |
653 | 'LEXICAL', # no typeglob | |
654 | \%hsh, # referent | |
655 | 'Omni', # attr name | |
656 | 'bus' # eval'd attr data | |
9df0c874 | 657 | 'CHECK', # compiler phase |
dc6b6eef JH |
658 | ); |
659 | ||
660 | ||
661 | Installing handlers into UNIVERSAL, makes them...err..universal. | |
662 | For example: | |
663 | ||
9df0c874 JH |
664 | package Descriptions; |
665 | use Attribute::Handlers; | |
dc6b6eef | 666 | |
9df0c874 JH |
667 | my %name; |
668 | sub name { return $name{$_[2]}||*{$_[1]}{NAME} } | |
dc6b6eef | 669 | |
9df0c874 JH |
670 | sub UNIVERSAL::Name :ATTR { |
671 | $name{$_[2]} = $_[4]; | |
672 | } | |
dc6b6eef | 673 | |
9df0c874 JH |
674 | sub UNIVERSAL::Purpose :ATTR { |
675 | print STDERR "Purpose of ", &name, " is $_[4]\n"; | |
676 | } | |
dc6b6eef | 677 | |
9df0c874 JH |
678 | sub UNIVERSAL::Unit :ATTR { |
679 | print STDERR &name, " measured in $_[4]\n"; | |
680 | } | |
dc6b6eef JH |
681 | |
682 | Let's you write: | |
683 | ||
9df0c874 | 684 | use Descriptions; |
dc6b6eef | 685 | |
9df0c874 JH |
686 | my $capacity : Name(capacity) |
687 | : Purpose(to store max storage capacity for files) | |
688 | : Unit(Gb); | |
dc6b6eef JH |
689 | |
690 | ||
9df0c874 | 691 | package Other; |
dc6b6eef | 692 | |
9df0c874 | 693 | sub foo : Purpose(to foo all data before barring it) { } |
dc6b6eef | 694 | |
9df0c874 | 695 | # etc. |
dc6b6eef JH |
696 | |
697 | ||
698 | =head1 DIAGNOSTICS | |
699 | ||
700 | =over | |
701 | ||
9df0c874 | 702 | =item C<Bad attribute type: ATTR(%s)> |
dc6b6eef JH |
703 | |
704 | An attribute handler was specified with an C<:ATTR(I<ref_type>)>, but the | |
705 | type of referent it was defined to handle wasn't one of the five permitted: | |
706 | C<SCALAR>, C<ARRAY>, C<HASH>, C<CODE>, or C<ANY>. | |
707 | ||
9df0c874 | 708 | =item C<Attribute handler %s doesn't handle %s attributes> |
dc6b6eef JH |
709 | |
710 | A handler for attributes of the specified name I<was> defined, but not | |
711 | for the specified type of declaration. Typically encountered whe trying | |
712 | to apply a C<VAR> attribute handler to a subroutine, or a C<SCALAR> | |
713 | attribute handler to some other type of variable. | |
714 | ||
9df0c874 | 715 | =item C<Declaration of %s attribute in package %s may clash with future reserved word> |
dc6b6eef JH |
716 | |
717 | A handler for an attributes with an all-lowercase name was declared. An | |
718 | attribute with an all-lowercase name might have a meaning to Perl | |
719 | itself some day, even though most don't yet. Use a mixed-case attribute | |
720 | name, instead. | |
721 | ||
9df0c874 JH |
722 | =item C<Can't have two ATTR specifiers on one subroutine> |
723 | ||
724 | You just can't, okay? | |
725 | Instead, put all the specifications together with commas between them | |
726 | in a single C<ATTR(I<specification>)>. | |
727 | ||
728 | =item C<Can't autotie a %s> | |
729 | ||
730 | You can only declare autoties for types C<"SCALAR">, C<"ARRAY">, and | |
731 | C<"SCALAR">. They're the only things (apart from typeglobs -- which are | |
732 | not declarable) that Perl can tie. | |
0addb26a | 733 | |
9df0c874 | 734 | =item C<Internal error: %s symbol went missing> |
dc6b6eef JH |
735 | |
736 | Something is rotten in the state of the program. An attributed | |
9df0c874 JH |
737 | subroutine ceased to exist between the point it was declared and the point |
738 | at which its attribute handler(s) would have been called. | |
dc6b6eef JH |
739 | |
740 | =back | |
741 | ||
742 | =head1 AUTHOR | |
743 | ||
744 | Damian Conway (damian@conway.org) | |
745 | ||
746 | =head1 BUGS | |
747 | ||
748 | There are undoubtedly serious bugs lurking somewhere in code this funky :-) | |
749 | Bug reports and other feedback are most welcome. | |
750 | ||
751 | =head1 COPYRIGHT | |
752 | ||
753 | Copyright (c) 2001, Damian Conway. All Rights Reserved. | |
754 | This module is free software. It may be used, redistributed | |
755 | and/or modified under the terms of the Perl Artistic License | |
756 | (see http://www.perl.com/perl/misc/Artistic.html) |