Commit | Line | Data |
---|---|---|
09bef843 SB |
1 | package attributes; |
2 | ||
0120eecf | 3 | $VERSION = 0.03; |
09bef843 | 4 | |
26f2972e GS |
5 | @EXPORT_OK = qw(get reftype); |
6 | @EXPORT = (); | |
7 | %EXPORT_TAGS = (ALL => [@EXPORT, @EXPORT_OK]); | |
09bef843 SB |
8 | |
9 | use strict; | |
10 | ||
11 | sub croak { | |
12 | require Carp; | |
13 | goto &Carp::croak; | |
14 | } | |
15 | ||
16 | sub carp { | |
17 | require Carp; | |
18 | goto &Carp::carp; | |
19 | } | |
20 | ||
21 | ## forward declaration(s) rather than wrapping the bootstrap call in BEGIN{} | |
22 | #sub reftype ($) ; | |
23 | #sub _fetch_attrs ($) ; | |
24 | #sub _guess_stash ($) ; | |
25 | #sub _modify_attrs ; | |
26 | #sub _warn_reserved () ; | |
27 | # | |
28 | # The extra trips through newATTRSUB in the interpreter wipe out any savings | |
29 | # from avoiding the BEGIN block. Just do the bootstrap now. | |
30 | BEGIN { bootstrap } | |
31 | ||
32 | sub import { | |
26f2972e GS |
33 | @_ > 2 && ref $_[2] or do { |
34 | require Exporter; | |
35 | goto &Exporter::import; | |
c0c5a66b | 36 | }; |
09bef843 SB |
37 | my (undef,$home_stash,$svref,@attrs) = @_; |
38 | ||
39 | my $svtype = uc reftype($svref); | |
40 | my $pkgmeth; | |
41 | $pkgmeth = UNIVERSAL::can($home_stash, "MODIFY_${svtype}_ATTRIBUTES") | |
42 | if defined $home_stash && $home_stash ne ''; | |
43 | my @badattrs; | |
44 | if ($pkgmeth) { | |
45 | my @pkgattrs = _modify_attrs($svref, @attrs); | |
46 | @badattrs = $pkgmeth->($home_stash, $svref, @attrs); | |
47 | if (!@badattrs && @pkgattrs) { | |
48 | return unless _warn_reserved; | |
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 ; | |
101 | my ($x,@y,%z) : Bent ; | |
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 | ||
123 | use attributes __PACKAGE__, \$x, 'Bent'; | |
124 | use attributes __PACKAGE__, \@y, 'Bent'; | |
125 | use attributes __PACKAGE__, \%z, 'Bent'; | |
126 | ||
127 | Yes, that's three invocations. | |
128 | ||
129 | B<WARNING>: attribute declarations for variables are an I<experimental> | |
130 | feature. The semantics of such declarations could change or be removed | |
131 | in future versions. They are present for purposes of experimentation | |
132 | with what the semantics ought to be. Do not rely on the current | |
133 | implementation of this feature. | |
134 | ||
135 | There are only a few attributes currently handled by Perl itself (or | |
136 | directly by this module, depending on how you look at it.) However, | |
137 | package-specific attributes are allowed by an extension mechanism. | |
138 | (See L<"Package-specific Attribute Handling"> below.) | |
139 | ||
140 | The setting of attributes happens at compile time. An attempt to set | |
141 | an unrecognized attribute is a fatal error. (The error is trappable, but | |
142 | it still stops the compilation within that C<eval>.) Setting an attribute | |
143 | with a name that's all lowercase letters that's not a built-in attribute | |
144 | (such as "foo") | |
145 | will result in a warning with B<-w> or C<use warnings 'reserved'>. | |
146 | ||
147 | =head2 Built-in Attributes | |
148 | ||
149 | The following are the built-in attributes for subroutines: | |
150 | ||
151 | =over 4 | |
152 | ||
153 | =item locked | |
154 | ||
155 | Setting this attribute is only meaningful when the subroutine or | |
156 | method is to be called by multiple threads. When set on a method | |
157 | subroutine (i.e., one marked with the B<method> attribute below), | |
158 | Perl ensures that any invocation of it implicitly locks its first | |
159 | argument before execution. When set on a non-method subroutine, | |
160 | Perl ensures that a lock is taken on the subroutine itself before | |
161 | execution. The semantics of the lock are exactly those of one | |
162 | explicitly taken with the C<lock> operator immediately after the | |
163 | subroutine is entered. | |
164 | ||
165 | =item method | |
166 | ||
167 | Indicates that the referenced subroutine is a method. | |
168 | This has a meaning when taken together with the B<locked> attribute, | |
169 | as described there. It also means that a subroutine so marked | |
170 | will not trigger the "Ambiguous call resolved as CORE::%s" warning. | |
171 | ||
89752b9c GS |
172 | =item lvalue |
173 | ||
174 | Indicates that the referenced subroutine is a valid lvalue and can | |
175 | be assigned to. The subroutine must return a modifiable value such | |
176 | as a scalar variable, as described in L<perlsub>. | |
177 | ||
09bef843 SB |
178 | =back |
179 | ||
180 | There are no built-in attributes for anything other than subroutines. | |
181 | ||
182 | =head2 Available Subroutines | |
183 | ||
184 | The following subroutines are available for general use once this module | |
185 | has been loaded: | |
186 | ||
187 | =over 4 | |
188 | ||
189 | =item get | |
190 | ||
191 | This routine expects a single parameter--a reference to a | |
192 | subroutine or variable. It returns a list of attributes, which may be | |
193 | empty. If passed invalid arguments, it uses die() (via L<Carp::croak|Carp>) | |
194 | to raise a fatal exception. If it can find an appropriate package name | |
195 | for a class method lookup, it will include the results from a | |
196 | C<FETCH_I<type>_ATTRIBUTES> call in its return list, as described in | |
26f2972e | 197 | L<"Package-specific Attribute Handling"> below. |
09bef843 SB |
198 | Otherwise, only L<built-in attributes|"Built-in Attributes"> will be returned. |
199 | ||
200 | =item reftype | |
201 | ||
202 | This routine expects a single parameter--a reference to a subroutine or | |
203 | variable. It returns the built-in type of the referenced variable, | |
204 | ignoring any package into which it might have been blessed. | |
205 | This can be useful for determining the I<type> value which forms part of | |
26f2972e | 206 | the method names described in L<"Package-specific Attribute Handling"> below. |
09bef843 SB |
207 | |
208 | =back | |
209 | ||
26f2972e | 210 | Note that these routines are I<not> exported by default. |
09bef843 SB |
211 | |
212 | =head2 Package-specific Attribute Handling | |
213 | ||
214 | B<WARNING>: the mechanisms described here are still experimental. Do not | |
215 | rely on the current implementation. In particular, there is no provision | |
216 | for applying package attributes to 'cloned' copies of subroutines used as | |
217 | closures. (See L<perlref/"Making References"> for information on closures.) | |
218 | Package-specific attribute handling may change incompatibly in a future | |
219 | release. | |
220 | ||
221 | When an attribute list is present in a declaration, a check is made to see | |
222 | whether an attribute 'modify' handler is present in the appropriate package | |
223 | (or its @ISA inheritance tree). Similarly, when C<attributes::get> is | |
224 | called on a valid reference, a check is made for an appropriate attribute | |
225 | 'fetch' handler. See L<"EXAMPLES"> to see how the "appropriate package" | |
226 | determination works. | |
227 | ||
228 | The handler names are based on the underlying type of the variable being | |
229 | declared or of the reference passed. Because these attributes are | |
230 | associated with subroutine or variable declarations, this deliberately | |
231 | ignores any possibility of being blessed into some package. Thus, a | |
232 | subroutine declaration uses "CODE" as its I<type>, and even a blessed | |
233 | hash reference uses "HASH" as its I<type>. | |
234 | ||
235 | The class methods invoked for modifying and fetching are these: | |
236 | ||
237 | =over 4 | |
238 | ||
239 | =item FETCH_I<type>_ATTRIBUTES | |
240 | ||
241 | This method receives a single argument, which is a reference to the | |
242 | variable or subroutine for which package-defined attributes are desired. | |
243 | The expected return value is a list of associated attributes. | |
244 | This list may be empty. | |
245 | ||
246 | =item MODIFY_I<type>_ATTRIBUTES | |
247 | ||
248 | This method is called with two fixed arguments, followed by the list of | |
249 | attributes from the relevant declaration. The two fixed arguments are | |
250 | the relevant package name and a reference to the declared subroutine or | |
251 | variable. The expected return value as a list of attributes which were | |
252 | not recognized by this handler. Note that this allows for a derived class | |
253 | to delegate a call to its base class, and then only examine the attributes | |
254 | which the base class didn't already handle for it. | |
255 | ||
256 | The call to this method is currently made I<during> the processing of the | |
257 | declaration. In particular, this means that a subroutine reference will | |
258 | probably be for an undefined subroutine, even if this declaration is | |
259 | actually part of the definition. | |
260 | ||
261 | =back | |
262 | ||
263 | Calling C<attributes::get()> from within the scope of a null package | |
264 | declaration C<package ;> for an unblessed variable reference will | |
265 | not provide any starting package name for the 'fetch' method lookup. | |
266 | Thus, this circumstance will not result in a method call for package-defined | |
267 | attributes. A named subroutine knows to which symbol table entry it belongs | |
268 | (or originally belonged), and it will use the corresponding package. | |
269 | An anonymous subroutine knows the package name into which it was compiled | |
270 | (unless it was also compiled with a null package declaration), and so it | |
271 | will use that package name. | |
272 | ||
273 | =head2 Syntax of Attribute Lists | |
274 | ||
275 | An attribute list is a sequence of attribute specifications, separated by | |
0120eecf GS |
276 | whitespace or a colon (with optional whitespace). |
277 | Each attribute specification is a simple | |
09bef843 SB |
278 | name, optionally followed by a parenthesised parameter list. |
279 | If such a parameter list is present, it is scanned past as for the rules | |
280 | for the C<q()> operator. (See L<perlop/"Quote and Quote-like Operators">.) | |
281 | The parameter list is passed as it was found, however, and not as per C<q()>. | |
282 | ||
283 | Some examples of syntactically valid attribute lists: | |
284 | ||
0120eecf GS |
285 | switch(10,foo(7,3)) : expensive |
286 | Ugly('\(") :Bad | |
09bef843 SB |
287 | _5x5 |
288 | locked method | |
289 | ||
290 | Some examples of syntactically invalid attribute lists (with annotation): | |
291 | ||
292 | switch(10,foo() # ()-string not balanced | |
293 | Ugly('(') # ()-string not balanced | |
294 | 5x5 # "5x5" not a valid identifier | |
295 | Y2::north # "Y2::north" not a simple identifier | |
0120eecf | 296 | foo + bar # "+" neither a colon nor whitespace |
09bef843 | 297 | |
26f2972e GS |
298 | =head1 EXPORTS |
299 | ||
300 | =head2 Default exports | |
301 | ||
302 | None. | |
303 | ||
304 | =head2 Available exports | |
305 | ||
306 | The routines C<get> and C<reftype> are exportable. | |
307 | ||
308 | =head2 Export tags defined | |
309 | ||
310 | The C<:ALL> tag will get all of the above exports. | |
311 | ||
09bef843 SB |
312 | =head1 EXAMPLES |
313 | ||
314 | Here are some samples of syntactically valid declarations, with annotation | |
315 | as to how they resolve internally into C<use attributes> invocations by | |
316 | perl. These examples are primarily useful to see how the "appropriate | |
317 | package" is found for the possible method lookups for package-defined | |
318 | attributes. | |
319 | ||
320 | =over 4 | |
321 | ||
322 | =item 1. | |
323 | ||
324 | Code: | |
325 | ||
326 | package Canine; | |
327 | package Dog; | |
328 | my Canine $spot : Watchful ; | |
329 | ||
330 | Effect: | |
331 | ||
332 | use attributes Canine => \$spot, "Watchful"; | |
333 | ||
334 | =item 2. | |
335 | ||
336 | Code: | |
337 | ||
338 | package Felis; | |
339 | my $cat : Nervous; | |
340 | ||
341 | Effect: | |
342 | ||
343 | use attributes Felis => \$cat, "Nervous"; | |
344 | ||
345 | =item 3. | |
346 | ||
347 | Code: | |
348 | ||
349 | package X; | |
350 | sub foo : locked ; | |
351 | ||
352 | Effect: | |
353 | ||
354 | use attributes X => \&foo, "locked"; | |
355 | ||
356 | =item 4. | |
357 | ||
358 | Code: | |
359 | ||
360 | package X; | |
361 | sub Y::x : locked { 1 } | |
362 | ||
363 | Effect: | |
364 | ||
365 | use attributes Y => \&Y::x, "locked"; | |
366 | ||
367 | =item 5. | |
368 | ||
369 | Code: | |
370 | ||
371 | package X; | |
372 | sub foo { 1 } | |
373 | ||
374 | package Y; | |
375 | BEGIN { *bar = \&X::foo; } | |
376 | ||
377 | package Z; | |
378 | sub Y::bar : locked ; | |
379 | ||
380 | Effect: | |
381 | ||
382 | use attributes X => \&X::foo, "locked"; | |
383 | ||
384 | =back | |
385 | ||
386 | This last example is purely for purposes of completeness. You should not | |
387 | be trying to mess with the attributes of something in a package that's | |
388 | not your own. | |
389 | ||
390 | =head1 SEE ALSO | |
391 | ||
392 | L<perlsub/"Private Variables via my()"> and | |
393 | L<perlsub/"Subroutine Attributes"> for details on the basic declarations; | |
394 | L<attrs> for the obsolescent form of subroutine attribute specification | |
395 | which this module replaces; | |
396 | L<perlfunc/use> for details on the normal invocation mechanism. | |
397 | ||
398 | =cut | |
399 |