5 @EXPORT_OK = qw(get reftype);
7 %EXPORT_TAGS = (ALL => [@EXPORT, @EXPORT_OK]);
22 $deprecated{CODE} = qr/\A-?(locked)\z/;
23 $deprecated{ARRAY} = $deprecated{HASH} = $deprecated{SCALAR}
26 sub _modify_attrs_and_deprecate {
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)
33 $deprecated{$svtype} && /$deprecated{$svtype}/ ? do {
35 warnings::warnif('deprecated', "Attribute \"$1\" is deprecated");
37 } : $svtype eq 'CODE' && /^-?lvalue\z/ ? do {
42 . (/^-/ ? "removed from" : "applied to")
43 . " already-defined subroutine"
51 @_ > 2 && ref $_[2] or do {
53 goto &Exporter::import;
55 my (undef,$home_stash,$svref,@attrs) = @_;
57 my $svtype = uc reftype($svref);
59 $pkgmeth = UNIVERSAL::can($home_stash, "MODIFY_${svtype}_ATTRIBUTES")
60 if defined $home_stash && $home_stash ne '';
63 my @pkgattrs = _modify_attrs_and_deprecate($svtype, $svref, @attrs);
64 @badattrs = $pkgmeth->($home_stash, $svref, @pkgattrs);
65 if (!@badattrs && @pkgattrs) {
67 return unless warnings::enabled('reserved');
68 @pkgattrs = grep { m/\A[[:lower:]]+(?:\z|\()/ } @pkgattrs;
70 for my $attr (@pkgattrs) {
73 my $s = ((@pkgattrs == 1) ? '' : 's');
74 carp "$svtype package attribute$s " .
75 "may clash with future reserved word$s: " .
76 join(' : ' , @pkgattrs);
81 @badattrs = _modify_attrs_and_deprecate($svtype, $svref, @attrs);
84 croak "Invalid $svtype attribute" .
85 (( @badattrs == 1 ) ? '' : 's') .
87 join(' : ', @badattrs);
92 @_ == 1 && ref $_[0] or
93 croak 'Usage: '.__PACKAGE__.'::get $ref';
95 my $svtype = uc reftype($svref);
96 my $stash = _guess_stash($svref);
97 $stash = caller unless defined $stash;
99 $pkgmeth = UNIVERSAL::can($stash, "FETCH_${svtype}_ATTRIBUTES")
100 if defined $stash && $stash ne '';
102 (_fetch_attrs($svref), $pkgmeth->($stash, $svref)) :
103 (_fetch_attrs($svref))
107 sub require_version { goto &UNIVERSAL::VERSION }
118 attributes - get/set subroutine or variable attributes
123 my ($x,@y,%z) : Bent = 1;
124 my $s = sub : method { ... };
126 use attributes (); # optional, to get subroutine declarations
127 my @attrlist = attributes::get(\&foo);
129 use attributes 'get'; # import the attributes::get subroutine
130 my @attrlist = get \&foo;
134 Subroutine declarations and definitions may optionally have attribute lists
135 associated with them. (Variable C<my> declarations also may, but see the
136 warning below.) Perl handles these declarations by passing some information
137 about the call site and the thing being declared along with the attribute
138 list to this module. In particular, the first example above is equivalent to
141 use attributes __PACKAGE__, \&foo, 'method';
143 The second example in the synopsis does something equivalent to this:
147 attributes::->import(__PACKAGE__, \$x, 'Bent');
148 attributes::->import(__PACKAGE__, \@y, 'Bent');
149 attributes::->import(__PACKAGE__, \%z, 'Bent');
152 Yes, that's a lot of expansion.
154 B<WARNING>: attribute declarations for variables are still evolving.
155 The semantics and interfaces of such declarations could change in
156 future versions. They are present for purposes of experimentation
157 with what the semantics ought to be. Do not rely on the current
158 implementation of this feature.
160 There are only a few attributes currently handled by Perl itself (or
161 directly by this module, depending on how you look at it.) However,
162 package-specific attributes are allowed by an extension mechanism.
163 (See L<"Package-specific Attribute Handling"> below.)
165 The setting of subroutine attributes happens at compile time.
166 Variable attributes in C<our> declarations are also applied at compile time.
167 However, C<my> variables get their attributes applied at run-time.
168 This means that you have to I<reach> the run-time component of the C<my>
169 before those attributes will get applied. For example:
171 my $x : Bent = 42 if 0;
173 will neither assign 42 to $x I<nor> will it apply the C<Bent> attribute
176 An attempt to set an unrecognized attribute is a fatal error. (The
177 error is trappable, but it still stops the compilation within that
178 C<eval>.) Setting an attribute with a name that's all lowercase
179 letters that's not a built-in attribute (such as "foo") will result in
180 a warning with B<-w> or C<use warnings 'reserved'>.
182 =head2 What C<import> does
184 In the description it is mentioned that
190 use attributes __PACKAGE__, \&foo, 'method';
192 As you might know this calls the C<import> function of C<attributes> at compile
193 time with these parameters: 'attributes', the caller's package name, the reference
194 to the code and 'method'.
196 attributes->import( __PACKAGE__, \&foo, 'method' );
198 So you want to know what C<import> actually does?
200 First of all C<import> gets the type of the third parameter ('CODE' in this case).
201 C<attributes.pm> checks if there is a subroutine called C<< MODIFY_<reftype>_ATTRIBUTES >>
202 in the caller's namespace (here: 'main'). In this case a
203 subroutine C<MODIFY_CODE_ATTRIBUTES> is required. Then this
204 method is called to check if you have used a "bad attribute".
205 The subroutine call in this example would look like
207 MODIFY_CODE_ATTRIBUTES( 'main', \&foo, 'method' );
209 C<< MODIFY_<reftype>_ATTRIBUTES >> has to return a list of all "bad attributes".
210 If there are any bad attributes C<import> croaks.
212 (See L<"Package-specific Attribute Handling"> below.)
214 =head2 Built-in Attributes
216 The following are the built-in attributes for subroutines:
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>.
226 This module allows one to set this attribute on a subroutine that is
227 already defined. For Perl subroutines (XSUBs are fine), it may or may not
228 do what you want, depending on the code inside the subroutine, with details
229 subject to change in future Perl versions. You may run into problems with
230 lvalue context not being propagated properly into the subroutine, or maybe
231 even assertion failures. For this reason, a warning is emitted if warnings
232 are enabled. In other words, you should only do this if you really know
233 what you are doing. You have been warned.
237 Indicates that the referenced subroutine
238 is a method. A subroutine so marked
239 will not trigger the "Ambiguous call resolved as CORE::%s" warning.
243 The "prototype" attribute is an alternate means of specifying a prototype
244 on a sub. The desired prototype is within the parens.
246 The prototype from the attribute is assigned to the sub immediately after
247 the prototype from the sub, which means that if both are declared at the
248 same time, the traditionally defined prototype is ignored. In other words,
249 C<sub foo($$) : prototype(@) {}> is indistinguishable from C<sub foo(@){}>.
251 If illegalproto warnings are enabled, the prototype declared inside this
252 attribute will be sanity checked at compile time.
256 The "locked" attribute is deprecated, and has no effect in 5.10.0 and later.
257 It was used as part of the now-removed "Perl 5.005 threads".
261 The following are the built-in attributes for variables:
267 Indicates that the referenced variable can be shared across different threads
268 when used in conjunction with the L<threads> and L<threads::shared> modules.
272 The "unique" attribute is deprecated, and has no effect in 5.10.0 and later.
273 It used to indicate that a single copy of an C<our> variable was to be used by
274 all interpreters should the program happen to be running in a
275 multi-interpreter environment.
279 =head2 Available Subroutines
281 The following subroutines are available for general use once this module
288 This routine expects a single parameter--a reference to a
289 subroutine or variable. It returns a list of attributes, which may be
290 empty. If passed invalid arguments, it uses die() (via L<Carp::croak|Carp>)
291 to raise a fatal exception. If it can find an appropriate package name
292 for a class method lookup, it will include the results from a
293 C<FETCH_I<type>_ATTRIBUTES> call in its return list, as described in
294 L<"Package-specific Attribute Handling"> below.
295 Otherwise, only L<built-in attributes|"Built-in Attributes"> will be returned.
299 This routine expects a single parameter--a reference to a subroutine or
300 variable. It returns the built-in type of the referenced variable,
301 ignoring any package into which it might have been blessed.
302 This can be useful for determining the I<type> value which forms part of
303 the method names described in L<"Package-specific Attribute Handling"> below.
307 Note that these routines are I<not> exported by default.
309 =head2 Package-specific Attribute Handling
311 B<WARNING>: the mechanisms described here are still experimental. Do not
312 rely on the current implementation. In particular, there is no provision
313 for applying package attributes to 'cloned' copies of subroutines used as
314 closures. (See L<perlref/"Making References"> for information on closures.)
315 Package-specific attribute handling may change incompatibly in a future
318 When an attribute list is present in a declaration, a check is made to see
319 whether an attribute 'modify' handler is present in the appropriate package
320 (or its @ISA inheritance tree). Similarly, when C<attributes::get> is
321 called on a valid reference, a check is made for an appropriate attribute
322 'fetch' handler. See L<"EXAMPLES"> to see how the "appropriate package"
325 The handler names are based on the underlying type of the variable being
326 declared or of the reference passed. Because these attributes are
327 associated with subroutine or variable declarations, this deliberately
328 ignores any possibility of being blessed into some package. Thus, a
329 subroutine declaration uses "CODE" as its I<type>, and even a blessed
330 hash reference uses "HASH" as its I<type>.
332 The class methods invoked for modifying and fetching are these:
336 =item FETCH_I<type>_ATTRIBUTES
338 This method is called with two arguments: the relevant package name,
339 and a reference to a variable or subroutine for which package-defined
340 attributes are desired. The expected return value is a list of
341 associated attributes. This list may be empty.
343 =item MODIFY_I<type>_ATTRIBUTES
345 This method is called with two fixed arguments, followed by the list of
346 attributes from the relevant declaration. The two fixed arguments are
347 the relevant package name and a reference to the declared subroutine or
348 variable. The expected return value is a list of attributes which were
349 not recognized by this handler. Note that this allows for a derived class
350 to delegate a call to its base class, and then only examine the attributes
351 which the base class didn't already handle for it.
353 The call to this method is currently made I<during> the processing of the
354 declaration. In particular, this means that a subroutine reference will
355 probably be for an undefined subroutine, even if this declaration is
356 actually part of the definition.
360 Calling C<attributes::get()> from within the scope of a null package
361 declaration C<package ;> for an unblessed variable reference will
362 not provide any starting package name for the 'fetch' method lookup.
363 Thus, this circumstance will not result in a method call for package-defined
364 attributes. A named subroutine knows to which symbol table entry it belongs
365 (or originally belonged), and it will use the corresponding package.
366 An anonymous subroutine knows the package name into which it was compiled
367 (unless it was also compiled with a null package declaration), and so it
368 will use that package name.
370 =head2 Syntax of Attribute Lists
372 An attribute list is a sequence of attribute specifications, separated by
373 whitespace or a colon (with optional whitespace).
374 Each attribute specification is a simple
375 name, optionally followed by a parenthesised parameter list.
376 If such a parameter list is present, it is scanned past as for the rules
377 for the C<q()> operator. (See L<perlop/"Quote and Quote-like Operators">.)
378 The parameter list is passed as it was found, however, and not as per C<q()>.
380 Some examples of syntactically valid attribute lists:
382 switch(10,foo(7,3)) : expensive
387 Some examples of syntactically invalid attribute lists (with annotation):
389 switch(10,foo() # ()-string not balanced
390 Ugly('(') # ()-string not balanced
391 5x5 # "5x5" not a valid identifier
392 Y2::north # "Y2::north" not a simple identifier
393 foo + bar # "+" neither a colon nor whitespace
397 =head2 Default exports
401 =head2 Available exports
403 The routines C<get> and C<reftype> are exportable.
405 =head2 Export tags defined
407 The C<:ALL> tag will get all of the above exports.
411 Here are some samples of syntactically valid declarations, with annotation
412 as to how they resolve internally into C<use attributes> invocations by
413 perl. These examples are primarily useful to see how the "appropriate
414 package" is found for the possible method lookups for package-defined
425 my Canine $spot : Watchful ;
430 attributes::->import(Canine => \$spot, "Watchful");
442 attributes::->import(Felis => \$cat, "Nervous");
453 use attributes X => \&foo, "lvalue";
460 sub Y::x : lvalue { 1 }
464 use attributes Y => \&Y::x, "lvalue";
474 BEGIN { *bar = \&X::foo; }
477 sub Y::bar : lvalue ;
481 use attributes X => \&X::foo, "lvalue";
485 This last example is purely for purposes of completeness. You should not
486 be trying to mess with the attributes of something in a package that's
495 sub MODIFY_CODE_ATTRIBUTES {
496 my ($class,$code,@attrs) = @_;
498 my $allowed = 'MyAttribute';
499 my @bad = grep { $_ ne $allowed } @attrs;
504 sub foo : MyAttribute {
508 This example runs. At compile time
509 C<MODIFY_CODE_ATTRIBUTES> is called. In that
510 subroutine, we check if any attribute is disallowed and we return a list of
511 these "bad attributes".
513 As we return an empty list, everything is fine.
517 sub MODIFY_CODE_ATTRIBUTES {
518 my ($class,$code,@attrs) = @_;
520 my $allowed = 'MyAttribute';
521 my @bad = grep{ $_ ne $allowed }@attrs;
526 sub foo : MyAttribute Test {
530 This example is aborted at compile time as we use the attribute "Test" which
531 isn't allowed. C<MODIFY_CODE_ATTRIBUTES>
532 returns a list that contains a single
539 L<perlsub/"Private Variables via my()"> and
540 L<perlsub/"Subroutine Attributes"> for details on the basic declarations;
541 L<perlfunc/use> for details on the normal invocation mechanism.