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09bef843 SB |
1 | package attributes; |
2 | ||
6f878116 | 3 | our $VERSION = 0.09; |
09bef843 | 4 | |
26f2972e GS |
5 | @EXPORT_OK = qw(get reftype); |
6 | @EXPORT = (); | |
7 | %EXPORT_TAGS = (ALL => [@EXPORT, @EXPORT_OK]); | |
09bef843 SB |
8 | |
9 | use strict; | |
10 | ||
11 | sub croak { | |
12 | require Carp; | |
13 | goto &Carp::croak; | |
14 | } | |
15 | ||
16 | sub carp { | |
17 | require Carp; | |
18 | goto &Carp::carp; | |
19 | } | |
20 | ||
21 | ## forward declaration(s) rather than wrapping the bootstrap call in BEGIN{} | |
22 | #sub reftype ($) ; | |
23 | #sub _fetch_attrs ($) ; | |
24 | #sub _guess_stash ($) ; | |
25 | #sub _modify_attrs ; | |
09bef843 SB |
26 | # |
27 | # The extra trips through newATTRSUB in the interpreter wipe out any savings | |
28 | # from avoiding the BEGIN block. Just do the bootstrap now. | |
592f5969 | 29 | BEGIN { bootstrap attributes } |
09bef843 SB |
30 | |
31 | sub import { | |
26f2972e GS |
32 | @_ > 2 && ref $_[2] or do { |
33 | require Exporter; | |
34 | goto &Exporter::import; | |
c0c5a66b | 35 | }; |
09bef843 SB |
36 | my (undef,$home_stash,$svref,@attrs) = @_; |
37 | ||
38 | my $svtype = uc reftype($svref); | |
39 | my $pkgmeth; | |
40 | $pkgmeth = UNIVERSAL::can($home_stash, "MODIFY_${svtype}_ATTRIBUTES") | |
41 | if defined $home_stash && $home_stash ne ''; | |
42 | my @badattrs; | |
43 | if ($pkgmeth) { | |
44 | my @pkgattrs = _modify_attrs($svref, @attrs); | |
d5adc3a1 | 45 | @badattrs = $pkgmeth->($home_stash, $svref, @pkgattrs); |
09bef843 | 46 | if (!@badattrs && @pkgattrs) { |
20f4e289 JH |
47 | require warnings; |
48 | return unless warnings::enabled('reserved'); | |
09bef843 SB |
49 | @pkgattrs = grep { m/\A[[:lower:]]+(?:\z|\()/ } @pkgattrs; |
50 | if (@pkgattrs) { | |
51 | for my $attr (@pkgattrs) { | |
52 | $attr =~ s/\(.+\z//s; | |
53 | } | |
54 | my $s = ((@pkgattrs == 1) ? '' : 's'); | |
55 | carp "$svtype package attribute$s " . | |
56 | "may clash with future reserved word$s: " . | |
0120eecf | 57 | join(' : ' , @pkgattrs); |
09bef843 SB |
58 | } |
59 | } | |
60 | } | |
61 | else { | |
62 | @badattrs = _modify_attrs($svref, @attrs); | |
63 | } | |
64 | if (@badattrs) { | |
65 | croak "Invalid $svtype attribute" . | |
66 | (( @badattrs == 1 ) ? '' : 's') . | |
67 | ": " . | |
0120eecf | 68 | join(' : ', @badattrs); |
09bef843 SB |
69 | } |
70 | } | |
71 | ||
72 | sub get ($) { | |
73 | @_ == 1 && ref $_[0] or | |
74 | croak 'Usage: '.__PACKAGE__.'::get $ref'; | |
75 | my $svref = shift; | |
76 | my $svtype = uc reftype $svref; | |
77 | my $stash = _guess_stash $svref; | |
78 | $stash = caller unless defined $stash; | |
79 | my $pkgmeth; | |
80 | $pkgmeth = UNIVERSAL::can($stash, "FETCH_${svtype}_ATTRIBUTES") | |
81 | if defined $stash && $stash ne ''; | |
82 | return $pkgmeth ? | |
83 | (_fetch_attrs($svref), $pkgmeth->($stash, $svref)) : | |
84 | (_fetch_attrs($svref)) | |
85 | ; | |
86 | } | |
87 | ||
26f2972e | 88 | sub require_version { goto &UNIVERSAL::VERSION } |
09bef843 SB |
89 | |
90 | 1; | |
91 | __END__ | |
92 | #The POD goes here | |
93 | ||
94 | =head1 NAME | |
95 | ||
96 | attributes - get/set subroutine or variable attributes | |
97 | ||
98 | =head1 SYNOPSIS | |
99 | ||
100 | sub foo : method ; | |
95f0a2f1 | 101 | my ($x,@y,%z) : Bent = 1; |
09bef843 SB |
102 | my $s = sub : method { ... }; |
103 | ||
104 | use attributes (); # optional, to get subroutine declarations | |
105 | my @attrlist = attributes::get(\&foo); | |
106 | ||
26f2972e GS |
107 | use attributes 'get'; # import the attributes::get subroutine |
108 | my @attrlist = get \&foo; | |
109 | ||
09bef843 SB |
110 | =head1 DESCRIPTION |
111 | ||
112 | Subroutine declarations and definitions may optionally have attribute lists | |
113 | associated with them. (Variable C<my> declarations also may, but see the | |
114 | warning below.) Perl handles these declarations by passing some information | |
115 | about the call site and the thing being declared along with the attribute | |
26f2972e | 116 | list to this module. In particular, the first example above is equivalent to |
09bef843 SB |
117 | the following: |
118 | ||
119 | use attributes __PACKAGE__, \&foo, 'method'; | |
120 | ||
121 | The second example in the synopsis does something equivalent to this: | |
122 | ||
95f0a2f1 SB |
123 | use attributes (); |
124 | my ($x,@y,%z); | |
125 | attributes::->import(__PACKAGE__, \$x, 'Bent'); | |
126 | attributes::->import(__PACKAGE__, \@y, 'Bent'); | |
127 | attributes::->import(__PACKAGE__, \%z, 'Bent'); | |
128 | ($x,@y,%z) = 1; | |
09bef843 | 129 | |
95f0a2f1 | 130 | Yes, that's a lot of expansion. |
09bef843 | 131 | |
1d2de774 JH |
132 | B<WARNING>: attribute declarations for variables are still evolving. |
133 | The semantics and interfaces of such declarations could change in | |
134 | future versions. They are present for purposes of experimentation | |
09bef843 | 135 | with what the semantics ought to be. Do not rely on the current |
95f0a2f1 | 136 | implementation of this feature. |
09bef843 SB |
137 | |
138 | There are only a few attributes currently handled by Perl itself (or | |
139 | directly by this module, depending on how you look at it.) However, | |
140 | package-specific attributes are allowed by an extension mechanism. | |
141 | (See L<"Package-specific Attribute Handling"> below.) | |
142 | ||
95f0a2f1 SB |
143 | The setting of subroutine attributes happens at compile time. |
144 | Variable attributes in C<our> declarations are also applied at compile time. | |
145 | However, C<my> variables get their attributes applied at run-time. | |
146 | This means that you have to I<reach> the run-time component of the C<my> | |
147 | before those attributes will get applied. For example: | |
148 | ||
149 | my $x : Bent = 42 if 0; | |
150 | ||
151 | will neither assign 42 to $x I<nor> will it apply the C<Bent> attribute | |
152 | to the variable. | |
153 | ||
1d2de774 JH |
154 | An attempt to set an unrecognized attribute is a fatal error. (The |
155 | error is trappable, but it still stops the compilation within that | |
156 | C<eval>.) Setting an attribute with a name that's all lowercase | |
157 | letters that's not a built-in attribute (such as "foo") will result in | |
158 | a warning with B<-w> or C<use warnings 'reserved'>. | |
09bef843 | 159 | |
a911a0f8 RB |
160 | =head2 What C<import> does |
161 | ||
162 | In the description it is mentioned that | |
163 | ||
164 | sub foo : method; | |
165 | ||
166 | is equivalent to | |
167 | ||
168 | use attributes __PACKAGE__, \&foo, 'method'; | |
169 | ||
170 | As you might know this calls the C<import> function of C<attributes> at compile | |
171 | time with these parameters: 'attributes', the caller's package name, the reference | |
172 | to the code and 'method'. | |
173 | ||
174 | attributes->import( __PACKAGE__, \&foo, 'method' ); | |
175 | ||
176 | So you want to know what C<import> actually does? | |
177 | ||
178 | First of all C<import> gets the type of the third parameter ('CODE' in this case). | |
179 | C<attributes.pm> checks if there is a subroutine called C<< MODIFY_<reftype>_ATTRIBUTES >> | |
180 | in the caller's namespace (here: 'main'). In this case a subroutine C<MODIFY_CODE_ATTRIBUTES> is | |
181 | required. Then this method is called to check if you have used a "bad attribute". | |
182 | The subroutine call in this example would look like | |
183 | ||
184 | MODIFY_CODE_ATTRIBUTES( 'main', \&foo, 'method' ); | |
185 | ||
186 | C<< MODIFY_<reftype>_ATTRIBUTES >> has to return a list of all "bad attributes". | |
187 | If there are any bad attributes C<import> croaks. | |
188 | ||
189 | (See L<"Package-specific Attribute Handling"> below.) | |
190 | ||
09bef843 SB |
191 | =head2 Built-in Attributes |
192 | ||
193 | The following are the built-in attributes for subroutines: | |
194 | ||
195 | =over 4 | |
196 | ||
197 | =item locked | |
198 | ||
cef7f621 EM |
199 | B<5.005 threads only! The use of the "locked" attribute currently |
200 | only makes sense if you are using the deprecated "Perl 5.005 threads" | |
201 | implementation of threads.> | |
202 | ||
09bef843 SB |
203 | Setting this attribute is only meaningful when the subroutine or |
204 | method is to be called by multiple threads. When set on a method | |
205 | subroutine (i.e., one marked with the B<method> attribute below), | |
206 | Perl ensures that any invocation of it implicitly locks its first | |
207 | argument before execution. When set on a non-method subroutine, | |
208 | Perl ensures that a lock is taken on the subroutine itself before | |
209 | execution. The semantics of the lock are exactly those of one | |
210 | explicitly taken with the C<lock> operator immediately after the | |
211 | subroutine is entered. | |
212 | ||
213 | =item method | |
214 | ||
215 | Indicates that the referenced subroutine is a method. | |
216 | This has a meaning when taken together with the B<locked> attribute, | |
217 | as described there. It also means that a subroutine so marked | |
218 | will not trigger the "Ambiguous call resolved as CORE::%s" warning. | |
219 | ||
89752b9c GS |
220 | =item lvalue |
221 | ||
222 | Indicates that the referenced subroutine is a valid lvalue and can | |
223 | be assigned to. The subroutine must return a modifiable value such | |
224 | as a scalar variable, as described in L<perlsub>. | |
225 | ||
09bef843 SB |
226 | =back |
227 | ||
307ea6df | 228 | For global variables there is C<unique> attribute: see L<perlfunc/our>. |
95f0a2f1 | 229 | |
09bef843 SB |
230 | =head2 Available Subroutines |
231 | ||
232 | The following subroutines are available for general use once this module | |
233 | has been loaded: | |
234 | ||
235 | =over 4 | |
236 | ||
237 | =item get | |
238 | ||
239 | This routine expects a single parameter--a reference to a | |
240 | subroutine or variable. It returns a list of attributes, which may be | |
241 | empty. If passed invalid arguments, it uses die() (via L<Carp::croak|Carp>) | |
242 | to raise a fatal exception. If it can find an appropriate package name | |
243 | for a class method lookup, it will include the results from a | |
244 | C<FETCH_I<type>_ATTRIBUTES> call in its return list, as described in | |
26f2972e | 245 | L<"Package-specific Attribute Handling"> below. |
09bef843 SB |
246 | Otherwise, only L<built-in attributes|"Built-in Attributes"> will be returned. |
247 | ||
248 | =item reftype | |
249 | ||
250 | This routine expects a single parameter--a reference to a subroutine or | |
251 | variable. It returns the built-in type of the referenced variable, | |
252 | ignoring any package into which it might have been blessed. | |
253 | This can be useful for determining the I<type> value which forms part of | |
26f2972e | 254 | the method names described in L<"Package-specific Attribute Handling"> below. |
09bef843 SB |
255 | |
256 | =back | |
257 | ||
26f2972e | 258 | Note that these routines are I<not> exported by default. |
09bef843 SB |
259 | |
260 | =head2 Package-specific Attribute Handling | |
261 | ||
262 | B<WARNING>: the mechanisms described here are still experimental. Do not | |
263 | rely on the current implementation. In particular, there is no provision | |
264 | for applying package attributes to 'cloned' copies of subroutines used as | |
265 | closures. (See L<perlref/"Making References"> for information on closures.) | |
266 | Package-specific attribute handling may change incompatibly in a future | |
267 | release. | |
268 | ||
269 | When an attribute list is present in a declaration, a check is made to see | |
270 | whether an attribute 'modify' handler is present in the appropriate package | |
271 | (or its @ISA inheritance tree). Similarly, when C<attributes::get> is | |
272 | called on a valid reference, a check is made for an appropriate attribute | |
273 | 'fetch' handler. See L<"EXAMPLES"> to see how the "appropriate package" | |
274 | determination works. | |
275 | ||
276 | The handler names are based on the underlying type of the variable being | |
277 | declared or of the reference passed. Because these attributes are | |
278 | associated with subroutine or variable declarations, this deliberately | |
279 | ignores any possibility of being blessed into some package. Thus, a | |
280 | subroutine declaration uses "CODE" as its I<type>, and even a blessed | |
281 | hash reference uses "HASH" as its I<type>. | |
282 | ||
283 | The class methods invoked for modifying and fetching are these: | |
284 | ||
285 | =over 4 | |
286 | ||
287 | =item FETCH_I<type>_ATTRIBUTES | |
288 | ||
630ad279 JH |
289 | This method is called with two arguments: the relevant package name, |
290 | and a reference to a variable or subroutine for which package-defined | |
291 | attributes are desired. The expected return value is a list of | |
292 | associated attributes. This list may be empty. | |
09bef843 SB |
293 | |
294 | =item MODIFY_I<type>_ATTRIBUTES | |
295 | ||
296 | This method is called with two fixed arguments, followed by the list of | |
297 | attributes from the relevant declaration. The two fixed arguments are | |
298 | the relevant package name and a reference to the declared subroutine or | |
fd40b977 | 299 | variable. The expected return value is a list of attributes which were |
09bef843 SB |
300 | not recognized by this handler. Note that this allows for a derived class |
301 | to delegate a call to its base class, and then only examine the attributes | |
302 | which the base class didn't already handle for it. | |
303 | ||
304 | The call to this method is currently made I<during> the processing of the | |
305 | declaration. In particular, this means that a subroutine reference will | |
306 | probably be for an undefined subroutine, even if this declaration is | |
307 | actually part of the definition. | |
308 | ||
309 | =back | |
310 | ||
311 | Calling C<attributes::get()> from within the scope of a null package | |
312 | declaration C<package ;> for an unblessed variable reference will | |
313 | not provide any starting package name for the 'fetch' method lookup. | |
314 | Thus, this circumstance will not result in a method call for package-defined | |
315 | attributes. A named subroutine knows to which symbol table entry it belongs | |
316 | (or originally belonged), and it will use the corresponding package. | |
317 | An anonymous subroutine knows the package name into which it was compiled | |
318 | (unless it was also compiled with a null package declaration), and so it | |
319 | will use that package name. | |
320 | ||
321 | =head2 Syntax of Attribute Lists | |
322 | ||
323 | An attribute list is a sequence of attribute specifications, separated by | |
0120eecf GS |
324 | whitespace or a colon (with optional whitespace). |
325 | Each attribute specification is a simple | |
09bef843 SB |
326 | name, optionally followed by a parenthesised parameter list. |
327 | If such a parameter list is present, it is scanned past as for the rules | |
328 | for the C<q()> operator. (See L<perlop/"Quote and Quote-like Operators">.) | |
329 | The parameter list is passed as it was found, however, and not as per C<q()>. | |
330 | ||
331 | Some examples of syntactically valid attribute lists: | |
332 | ||
0120eecf GS |
333 | switch(10,foo(7,3)) : expensive |
334 | Ugly('\(") :Bad | |
09bef843 SB |
335 | _5x5 |
336 | locked method | |
337 | ||
338 | Some examples of syntactically invalid attribute lists (with annotation): | |
339 | ||
340 | switch(10,foo() # ()-string not balanced | |
341 | Ugly('(') # ()-string not balanced | |
342 | 5x5 # "5x5" not a valid identifier | |
343 | Y2::north # "Y2::north" not a simple identifier | |
0120eecf | 344 | foo + bar # "+" neither a colon nor whitespace |
09bef843 | 345 | |
26f2972e GS |
346 | =head1 EXPORTS |
347 | ||
348 | =head2 Default exports | |
349 | ||
350 | None. | |
351 | ||
352 | =head2 Available exports | |
353 | ||
354 | The routines C<get> and C<reftype> are exportable. | |
355 | ||
356 | =head2 Export tags defined | |
357 | ||
358 | The C<:ALL> tag will get all of the above exports. | |
359 | ||
09bef843 SB |
360 | =head1 EXAMPLES |
361 | ||
362 | Here are some samples of syntactically valid declarations, with annotation | |
363 | as to how they resolve internally into C<use attributes> invocations by | |
364 | perl. These examples are primarily useful to see how the "appropriate | |
365 | package" is found for the possible method lookups for package-defined | |
366 | attributes. | |
367 | ||
368 | =over 4 | |
369 | ||
370 | =item 1. | |
371 | ||
372 | Code: | |
373 | ||
374 | package Canine; | |
375 | package Dog; | |
376 | my Canine $spot : Watchful ; | |
377 | ||
378 | Effect: | |
379 | ||
95f0a2f1 SB |
380 | use attributes (); |
381 | attributes::->import(Canine => \$spot, "Watchful"); | |
09bef843 SB |
382 | |
383 | =item 2. | |
384 | ||
385 | Code: | |
386 | ||
387 | package Felis; | |
388 | my $cat : Nervous; | |
389 | ||
390 | Effect: | |
391 | ||
95f0a2f1 SB |
392 | use attributes (); |
393 | attributes::->import(Felis => \$cat, "Nervous"); | |
09bef843 SB |
394 | |
395 | =item 3. | |
396 | ||
397 | Code: | |
398 | ||
399 | package X; | |
400 | sub foo : locked ; | |
401 | ||
402 | Effect: | |
403 | ||
404 | use attributes X => \&foo, "locked"; | |
405 | ||
406 | =item 4. | |
407 | ||
408 | Code: | |
409 | ||
410 | package X; | |
411 | sub Y::x : locked { 1 } | |
412 | ||
413 | Effect: | |
414 | ||
415 | use attributes Y => \&Y::x, "locked"; | |
416 | ||
417 | =item 5. | |
418 | ||
419 | Code: | |
420 | ||
421 | package X; | |
422 | sub foo { 1 } | |
423 | ||
424 | package Y; | |
425 | BEGIN { *bar = \&X::foo; } | |
426 | ||
427 | package Z; | |
428 | sub Y::bar : locked ; | |
429 | ||
430 | Effect: | |
431 | ||
432 | use attributes X => \&X::foo, "locked"; | |
433 | ||
434 | =back | |
435 | ||
436 | This last example is purely for purposes of completeness. You should not | |
437 | be trying to mess with the attributes of something in a package that's | |
438 | not your own. | |
439 | ||
a911a0f8 RB |
440 | =head1 MORE EXAMPLES |
441 | ||
442 | =over 4 | |
443 | ||
444 | =item 1. | |
445 | ||
446 | sub MODIFY_CODE_ATTRIBUTES { | |
447 | my ($class,$code,@attrs) = @_; | |
448 | ||
449 | my $allowed = 'MyAttribute'; | |
450 | my @bad = grep { $_ ne $allowed } @attrs; | |
451 | ||
452 | return @bad; | |
453 | } | |
454 | ||
455 | sub foo : MyAttribute { | |
456 | print "foo\n"; | |
457 | } | |
458 | ||
459 | This example runs. At compile time C<MODIFY_CODE_ATTRIBUTES> is called. In that | |
460 | subroutine, we check if any attribute is disallowed and we return a list of | |
461 | these "bad attributes". | |
462 | ||
463 | As we return an empty list, everything is fine. | |
464 | ||
465 | =item 2. | |
466 | ||
467 | sub MODIFY_CODE_ATTRIBUTES { | |
468 | my ($class,$code,@attrs) = @_; | |
469 | ||
470 | my $allowed = 'MyAttribute'; | |
471 | my @bad = grep{ $_ ne $allowed }@attrs; | |
472 | ||
473 | return @bad; | |
474 | } | |
475 | ||
476 | sub foo : MyAttribute Test { | |
477 | print "foo\n"; | |
478 | } | |
479 | ||
480 | This example is aborted at compile time as we use the attribute "Test" which | |
481 | isn't allowed. C<MODIFY_CODE_ATTRIBUTES> returns a list that contains a single | |
482 | element ('Test'). | |
483 | ||
484 | =back | |
485 | ||
09bef843 SB |
486 | =head1 SEE ALSO |
487 | ||
488 | L<perlsub/"Private Variables via my()"> and | |
489 | L<perlsub/"Subroutine Attributes"> for details on the basic declarations; | |
490 | L<attrs> for the obsolescent form of subroutine attribute specification | |
491 | which this module replaces; | |
492 | L<perlfunc/use> for details on the normal invocation mechanism. | |
493 | ||
494 | =cut | |
495 |