Commit | Line | Data |
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09bef843 SB |
1 | package attributes; |
2 | ||
c32124fe | 3 | our $VERSION = 0.12; |
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 | ||
f1a3ce43 NC |
21 | my %deprecated; |
22 | $deprecated{CODE} = qr/\A-?(locked)\z/; | |
23 | $deprecated{ARRAY} = $deprecated{HASH} = $deprecated{SCALAR} | |
24 | = qr/\A-?(unique)\z/; | |
25 | ||
c32124fe NC |
26 | sub _modify_attrs_and_deprecate { |
27 | my $svtype = shift; | |
28 | # Now that we've removed handling of locked from the XS code, we need to | |
29 | # remove it here, else it ends up in @badattrs. (If we do the deprecation in | |
30 | # XS, we can't control the warning based on *our* caller's lexical settings, | |
31 | # and the warned line is in this package) | |
32 | grep { | |
f1a3ce43 | 33 | $deprecated{$svtype} && /$deprecated{$svtype}/ ? do { |
c32124fe | 34 | require warnings; |
f1a3ce43 | 35 | warnings::warnif('deprecated', "Attribute \"$1\" is deprecated"); |
c32124fe NC |
36 | 0; |
37 | } : 1 | |
38 | } _modify_attrs(@_); | |
39 | } | |
40 | ||
09bef843 | 41 | sub import { |
26f2972e GS |
42 | @_ > 2 && ref $_[2] or do { |
43 | require Exporter; | |
44 | goto &Exporter::import; | |
c0c5a66b | 45 | }; |
09bef843 SB |
46 | my (undef,$home_stash,$svref,@attrs) = @_; |
47 | ||
48 | my $svtype = uc reftype($svref); | |
49 | my $pkgmeth; | |
50 | $pkgmeth = UNIVERSAL::can($home_stash, "MODIFY_${svtype}_ATTRIBUTES") | |
51 | if defined $home_stash && $home_stash ne ''; | |
52 | my @badattrs; | |
53 | if ($pkgmeth) { | |
c32124fe | 54 | my @pkgattrs = _modify_attrs_and_deprecate($svtype, $svref, @attrs); |
d5adc3a1 | 55 | @badattrs = $pkgmeth->($home_stash, $svref, @pkgattrs); |
09bef843 | 56 | if (!@badattrs && @pkgattrs) { |
20f4e289 JH |
57 | require warnings; |
58 | return unless warnings::enabled('reserved'); | |
09bef843 SB |
59 | @pkgattrs = grep { m/\A[[:lower:]]+(?:\z|\()/ } @pkgattrs; |
60 | if (@pkgattrs) { | |
61 | for my $attr (@pkgattrs) { | |
62 | $attr =~ s/\(.+\z//s; | |
63 | } | |
64 | my $s = ((@pkgattrs == 1) ? '' : 's'); | |
65 | carp "$svtype package attribute$s " . | |
66 | "may clash with future reserved word$s: " . | |
0120eecf | 67 | join(' : ' , @pkgattrs); |
09bef843 SB |
68 | } |
69 | } | |
70 | } | |
71 | else { | |
c32124fe | 72 | @badattrs = _modify_attrs_and_deprecate($svtype, $svref, @attrs); |
09bef843 SB |
73 | } |
74 | if (@badattrs) { | |
75 | croak "Invalid $svtype attribute" . | |
76 | (( @badattrs == 1 ) ? '' : 's') . | |
77 | ": " . | |
0120eecf | 78 | join(' : ', @badattrs); |
09bef843 SB |
79 | } |
80 | } | |
81 | ||
82 | sub get ($) { | |
83 | @_ == 1 && ref $_[0] or | |
84 | croak 'Usage: '.__PACKAGE__.'::get $ref'; | |
85 | my $svref = shift; | |
48462a74 NC |
86 | my $svtype = uc reftype($svref); |
87 | my $stash = _guess_stash($svref); | |
09bef843 SB |
88 | $stash = caller unless defined $stash; |
89 | my $pkgmeth; | |
90 | $pkgmeth = UNIVERSAL::can($stash, "FETCH_${svtype}_ATTRIBUTES") | |
91 | if defined $stash && $stash ne ''; | |
92 | return $pkgmeth ? | |
93 | (_fetch_attrs($svref), $pkgmeth->($stash, $svref)) : | |
94 | (_fetch_attrs($svref)) | |
95 | ; | |
96 | } | |
97 | ||
26f2972e | 98 | sub require_version { goto &UNIVERSAL::VERSION } |
09bef843 | 99 | |
48462a74 NC |
100 | require XSLoader; |
101 | XSLoader::load('attributes', $VERSION); | |
102 | ||
09bef843 SB |
103 | 1; |
104 | __END__ | |
105 | #The POD goes here | |
106 | ||
107 | =head1 NAME | |
108 | ||
109 | attributes - get/set subroutine or variable attributes | |
110 | ||
111 | =head1 SYNOPSIS | |
112 | ||
113 | sub foo : method ; | |
95f0a2f1 | 114 | my ($x,@y,%z) : Bent = 1; |
09bef843 SB |
115 | my $s = sub : method { ... }; |
116 | ||
117 | use attributes (); # optional, to get subroutine declarations | |
118 | my @attrlist = attributes::get(\&foo); | |
119 | ||
26f2972e GS |
120 | use attributes 'get'; # import the attributes::get subroutine |
121 | my @attrlist = get \&foo; | |
122 | ||
09bef843 SB |
123 | =head1 DESCRIPTION |
124 | ||
125 | Subroutine declarations and definitions may optionally have attribute lists | |
126 | associated with them. (Variable C<my> declarations also may, but see the | |
127 | warning below.) Perl handles these declarations by passing some information | |
128 | about the call site and the thing being declared along with the attribute | |
26f2972e | 129 | list to this module. In particular, the first example above is equivalent to |
09bef843 SB |
130 | the following: |
131 | ||
132 | use attributes __PACKAGE__, \&foo, 'method'; | |
133 | ||
134 | The second example in the synopsis does something equivalent to this: | |
135 | ||
95f0a2f1 SB |
136 | use attributes (); |
137 | my ($x,@y,%z); | |
138 | attributes::->import(__PACKAGE__, \$x, 'Bent'); | |
139 | attributes::->import(__PACKAGE__, \@y, 'Bent'); | |
140 | attributes::->import(__PACKAGE__, \%z, 'Bent'); | |
141 | ($x,@y,%z) = 1; | |
09bef843 | 142 | |
95f0a2f1 | 143 | Yes, that's a lot of expansion. |
09bef843 | 144 | |
1d2de774 JH |
145 | B<WARNING>: attribute declarations for variables are still evolving. |
146 | The semantics and interfaces of such declarations could change in | |
147 | future versions. They are present for purposes of experimentation | |
09bef843 | 148 | with what the semantics ought to be. Do not rely on the current |
95f0a2f1 | 149 | implementation of this feature. |
09bef843 SB |
150 | |
151 | There are only a few attributes currently handled by Perl itself (or | |
152 | directly by this module, depending on how you look at it.) However, | |
153 | package-specific attributes are allowed by an extension mechanism. | |
154 | (See L<"Package-specific Attribute Handling"> below.) | |
155 | ||
95f0a2f1 SB |
156 | The setting of subroutine attributes happens at compile time. |
157 | Variable attributes in C<our> declarations are also applied at compile time. | |
158 | However, C<my> variables get their attributes applied at run-time. | |
159 | This means that you have to I<reach> the run-time component of the C<my> | |
160 | before those attributes will get applied. For example: | |
161 | ||
162 | my $x : Bent = 42 if 0; | |
163 | ||
164 | will neither assign 42 to $x I<nor> will it apply the C<Bent> attribute | |
165 | to the variable. | |
166 | ||
1d2de774 JH |
167 | An attempt to set an unrecognized attribute is a fatal error. (The |
168 | error is trappable, but it still stops the compilation within that | |
169 | C<eval>.) Setting an attribute with a name that's all lowercase | |
170 | letters that's not a built-in attribute (such as "foo") will result in | |
171 | a warning with B<-w> or C<use warnings 'reserved'>. | |
09bef843 | 172 | |
a911a0f8 RB |
173 | =head2 What C<import> does |
174 | ||
175 | In the description it is mentioned that | |
176 | ||
177 | sub foo : method; | |
178 | ||
179 | is equivalent to | |
180 | ||
181 | use attributes __PACKAGE__, \&foo, 'method'; | |
182 | ||
183 | As you might know this calls the C<import> function of C<attributes> at compile | |
184 | time with these parameters: 'attributes', the caller's package name, the reference | |
185 | to the code and 'method'. | |
186 | ||
187 | attributes->import( __PACKAGE__, \&foo, 'method' ); | |
188 | ||
189 | So you want to know what C<import> actually does? | |
190 | ||
191 | First of all C<import> gets the type of the third parameter ('CODE' in this case). | |
192 | C<attributes.pm> checks if there is a subroutine called C<< MODIFY_<reftype>_ATTRIBUTES >> | |
193 | in the caller's namespace (here: 'main'). In this case a subroutine C<MODIFY_CODE_ATTRIBUTES> is | |
194 | required. Then this method is called to check if you have used a "bad attribute". | |
195 | The subroutine call in this example would look like | |
196 | ||
197 | MODIFY_CODE_ATTRIBUTES( 'main', \&foo, 'method' ); | |
198 | ||
199 | C<< MODIFY_<reftype>_ATTRIBUTES >> has to return a list of all "bad attributes". | |
200 | If there are any bad attributes C<import> croaks. | |
201 | ||
202 | (See L<"Package-specific Attribute Handling"> below.) | |
203 | ||
09bef843 SB |
204 | =head2 Built-in Attributes |
205 | ||
206 | The following are the built-in attributes for subroutines: | |
207 | ||
208 | =over 4 | |
209 | ||
0a8c518d | 210 | =item lvalue |
cef7f621 | 211 | |
0a8c518d NC |
212 | Indicates that the referenced subroutine is a valid lvalue and can |
213 | be assigned to. The subroutine must return a modifiable value such | |
214 | as a scalar variable, as described in L<perlsub>. | |
09bef843 SB |
215 | |
216 | =item method | |
217 | ||
0a8c518d | 218 | Indicates that the referenced subroutine is a method. A subroutine so marked |
09bef843 SB |
219 | will not trigger the "Ambiguous call resolved as CORE::%s" warning. |
220 | ||
0a8c518d | 221 | =item locked |
89752b9c | 222 | |
0a8c518d NC |
223 | The "locked" attribute has no effect in 5.10.0 and later. It was used as part |
224 | of the now-removed "Perl 5.005 threads". | |
89752b9c | 225 | |
09bef843 SB |
226 | =back |
227 | ||
09bef843 SB |
228 | =head2 Available Subroutines |
229 | ||
230 | The following subroutines are available for general use once this module | |
231 | has been loaded: | |
232 | ||
233 | =over 4 | |
234 | ||
235 | =item get | |
236 | ||
237 | This routine expects a single parameter--a reference to a | |
238 | subroutine or variable. It returns a list of attributes, which may be | |
239 | empty. If passed invalid arguments, it uses die() (via L<Carp::croak|Carp>) | |
240 | to raise a fatal exception. If it can find an appropriate package name | |
241 | for a class method lookup, it will include the results from a | |
242 | C<FETCH_I<type>_ATTRIBUTES> call in its return list, as described in | |
26f2972e | 243 | L<"Package-specific Attribute Handling"> below. |
09bef843 SB |
244 | Otherwise, only L<built-in attributes|"Built-in Attributes"> will be returned. |
245 | ||
246 | =item reftype | |
247 | ||
248 | This routine expects a single parameter--a reference to a subroutine or | |
249 | variable. It returns the built-in type of the referenced variable, | |
250 | ignoring any package into which it might have been blessed. | |
251 | This can be useful for determining the I<type> value which forms part of | |
26f2972e | 252 | the method names described in L<"Package-specific Attribute Handling"> below. |
09bef843 SB |
253 | |
254 | =back | |
255 | ||
26f2972e | 256 | Note that these routines are I<not> exported by default. |
09bef843 SB |
257 | |
258 | =head2 Package-specific Attribute Handling | |
259 | ||
260 | B<WARNING>: the mechanisms described here are still experimental. Do not | |
261 | rely on the current implementation. In particular, there is no provision | |
262 | for applying package attributes to 'cloned' copies of subroutines used as | |
263 | closures. (See L<perlref/"Making References"> for information on closures.) | |
264 | Package-specific attribute handling may change incompatibly in a future | |
265 | release. | |
266 | ||
267 | When an attribute list is present in a declaration, a check is made to see | |
268 | whether an attribute 'modify' handler is present in the appropriate package | |
269 | (or its @ISA inheritance tree). Similarly, when C<attributes::get> is | |
270 | called on a valid reference, a check is made for an appropriate attribute | |
271 | 'fetch' handler. See L<"EXAMPLES"> to see how the "appropriate package" | |
272 | determination works. | |
273 | ||
274 | The handler names are based on the underlying type of the variable being | |
275 | declared or of the reference passed. Because these attributes are | |
276 | associated with subroutine or variable declarations, this deliberately | |
277 | ignores any possibility of being blessed into some package. Thus, a | |
278 | subroutine declaration uses "CODE" as its I<type>, and even a blessed | |
279 | hash reference uses "HASH" as its I<type>. | |
280 | ||
281 | The class methods invoked for modifying and fetching are these: | |
282 | ||
283 | =over 4 | |
284 | ||
285 | =item FETCH_I<type>_ATTRIBUTES | |
286 | ||
630ad279 JH |
287 | This method is called with two arguments: the relevant package name, |
288 | and a reference to a variable or subroutine for which package-defined | |
289 | attributes are desired. The expected return value is a list of | |
290 | associated attributes. This list may be empty. | |
09bef843 SB |
291 | |
292 | =item MODIFY_I<type>_ATTRIBUTES | |
293 | ||
294 | This method is called with two fixed arguments, followed by the list of | |
295 | attributes from the relevant declaration. The two fixed arguments are | |
296 | the relevant package name and a reference to the declared subroutine or | |
fd40b977 | 297 | variable. The expected return value is a list of attributes which were |
09bef843 SB |
298 | not recognized by this handler. Note that this allows for a derived class |
299 | to delegate a call to its base class, and then only examine the attributes | |
300 | which the base class didn't already handle for it. | |
301 | ||
302 | The call to this method is currently made I<during> the processing of the | |
303 | declaration. In particular, this means that a subroutine reference will | |
304 | probably be for an undefined subroutine, even if this declaration is | |
305 | actually part of the definition. | |
306 | ||
307 | =back | |
308 | ||
309 | Calling C<attributes::get()> from within the scope of a null package | |
310 | declaration C<package ;> for an unblessed variable reference will | |
311 | not provide any starting package name for the 'fetch' method lookup. | |
312 | Thus, this circumstance will not result in a method call for package-defined | |
313 | attributes. A named subroutine knows to which symbol table entry it belongs | |
314 | (or originally belonged), and it will use the corresponding package. | |
315 | An anonymous subroutine knows the package name into which it was compiled | |
316 | (unless it was also compiled with a null package declaration), and so it | |
317 | will use that package name. | |
318 | ||
319 | =head2 Syntax of Attribute Lists | |
320 | ||
321 | An attribute list is a sequence of attribute specifications, separated by | |
0120eecf GS |
322 | whitespace or a colon (with optional whitespace). |
323 | Each attribute specification is a simple | |
09bef843 SB |
324 | name, optionally followed by a parenthesised parameter list. |
325 | If such a parameter list is present, it is scanned past as for the rules | |
326 | for the C<q()> operator. (See L<perlop/"Quote and Quote-like Operators">.) | |
327 | The parameter list is passed as it was found, however, and not as per C<q()>. | |
328 | ||
329 | Some examples of syntactically valid attribute lists: | |
330 | ||
0120eecf GS |
331 | switch(10,foo(7,3)) : expensive |
332 | Ugly('\(") :Bad | |
09bef843 | 333 | _5x5 |
6db6f353 | 334 | lvalue method |
09bef843 SB |
335 | |
336 | Some examples of syntactically invalid attribute lists (with annotation): | |
337 | ||
338 | switch(10,foo() # ()-string not balanced | |
339 | Ugly('(') # ()-string not balanced | |
340 | 5x5 # "5x5" not a valid identifier | |
341 | Y2::north # "Y2::north" not a simple identifier | |
0120eecf | 342 | foo + bar # "+" neither a colon nor whitespace |
09bef843 | 343 | |
26f2972e GS |
344 | =head1 EXPORTS |
345 | ||
346 | =head2 Default exports | |
347 | ||
348 | None. | |
349 | ||
350 | =head2 Available exports | |
351 | ||
352 | The routines C<get> and C<reftype> are exportable. | |
353 | ||
354 | =head2 Export tags defined | |
355 | ||
356 | The C<:ALL> tag will get all of the above exports. | |
357 | ||
09bef843 SB |
358 | =head1 EXAMPLES |
359 | ||
360 | Here are some samples of syntactically valid declarations, with annotation | |
361 | as to how they resolve internally into C<use attributes> invocations by | |
362 | perl. These examples are primarily useful to see how the "appropriate | |
363 | package" is found for the possible method lookups for package-defined | |
364 | attributes. | |
365 | ||
366 | =over 4 | |
367 | ||
368 | =item 1. | |
369 | ||
370 | Code: | |
371 | ||
372 | package Canine; | |
373 | package Dog; | |
374 | my Canine $spot : Watchful ; | |
375 | ||
376 | Effect: | |
377 | ||
95f0a2f1 SB |
378 | use attributes (); |
379 | attributes::->import(Canine => \$spot, "Watchful"); | |
09bef843 SB |
380 | |
381 | =item 2. | |
382 | ||
383 | Code: | |
384 | ||
385 | package Felis; | |
386 | my $cat : Nervous; | |
387 | ||
388 | Effect: | |
389 | ||
95f0a2f1 SB |
390 | use attributes (); |
391 | attributes::->import(Felis => \$cat, "Nervous"); | |
09bef843 SB |
392 | |
393 | =item 3. | |
394 | ||
395 | Code: | |
396 | ||
397 | package X; | |
6db6f353 | 398 | sub foo : lvalue ; |
09bef843 SB |
399 | |
400 | Effect: | |
401 | ||
6db6f353 | 402 | use attributes X => \&foo, "lvalue"; |
09bef843 SB |
403 | |
404 | =item 4. | |
405 | ||
406 | Code: | |
407 | ||
408 | package X; | |
6db6f353 | 409 | sub Y::x : lvalue { 1 } |
09bef843 SB |
410 | |
411 | Effect: | |
412 | ||
6db6f353 | 413 | use attributes Y => \&Y::x, "lvalue"; |
09bef843 SB |
414 | |
415 | =item 5. | |
416 | ||
417 | Code: | |
418 | ||
419 | package X; | |
420 | sub foo { 1 } | |
421 | ||
422 | package Y; | |
423 | BEGIN { *bar = \&X::foo; } | |
424 | ||
425 | package Z; | |
6db6f353 | 426 | sub Y::bar : lvalue ; |
09bef843 SB |
427 | |
428 | Effect: | |
429 | ||
6db6f353 | 430 | use attributes X => \&X::foo, "lvalue"; |
09bef843 SB |
431 | |
432 | =back | |
433 | ||
434 | This last example is purely for purposes of completeness. You should not | |
435 | be trying to mess with the attributes of something in a package that's | |
436 | not your own. | |
437 | ||
a911a0f8 RB |
438 | =head1 MORE EXAMPLES |
439 | ||
440 | =over 4 | |
441 | ||
442 | =item 1. | |
443 | ||
444 | sub MODIFY_CODE_ATTRIBUTES { | |
445 | my ($class,$code,@attrs) = @_; | |
446 | ||
447 | my $allowed = 'MyAttribute'; | |
448 | my @bad = grep { $_ ne $allowed } @attrs; | |
449 | ||
450 | return @bad; | |
451 | } | |
452 | ||
453 | sub foo : MyAttribute { | |
454 | print "foo\n"; | |
455 | } | |
456 | ||
457 | This example runs. At compile time C<MODIFY_CODE_ATTRIBUTES> is called. In that | |
458 | subroutine, we check if any attribute is disallowed and we return a list of | |
459 | these "bad attributes". | |
460 | ||
461 | As we return an empty list, everything is fine. | |
462 | ||
463 | =item 2. | |
464 | ||
465 | sub MODIFY_CODE_ATTRIBUTES { | |
466 | my ($class,$code,@attrs) = @_; | |
467 | ||
468 | my $allowed = 'MyAttribute'; | |
469 | my @bad = grep{ $_ ne $allowed }@attrs; | |
470 | ||
471 | return @bad; | |
472 | } | |
473 | ||
474 | sub foo : MyAttribute Test { | |
475 | print "foo\n"; | |
476 | } | |
477 | ||
478 | This example is aborted at compile time as we use the attribute "Test" which | |
479 | isn't allowed. C<MODIFY_CODE_ATTRIBUTES> returns a list that contains a single | |
480 | element ('Test'). | |
481 | ||
482 | =back | |
483 | ||
09bef843 SB |
484 | =head1 SEE ALSO |
485 | ||
486 | L<perlsub/"Private Variables via my()"> and | |
487 | L<perlsub/"Subroutine Attributes"> for details on the basic declarations; | |
09bef843 SB |
488 | L<perlfunc/use> for details on the normal invocation mechanism. |
489 | ||
490 | =cut |