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 "locked" attribute has no effect in
244 5.10.0 and later. It was used as part
245 of the now-removed "Perl 5.005 threads".
249 =head2 Available Subroutines
251 The following subroutines are available for general use once this module
258 This routine expects a single parameter--a reference to a
259 subroutine or variable. It returns a list of attributes, which may be
260 empty. If passed invalid arguments, it uses die() (via L<Carp::croak|Carp>)
261 to raise a fatal exception. If it can find an appropriate package name
262 for a class method lookup, it will include the results from a
263 C<FETCH_I<type>_ATTRIBUTES> call in its return list, as described in
264 L<"Package-specific Attribute Handling"> below.
265 Otherwise, only L<built-in attributes|"Built-in Attributes"> will be returned.
269 This routine expects a single parameter--a reference to a subroutine or
270 variable. It returns the built-in type of the referenced variable,
271 ignoring any package into which it might have been blessed.
272 This can be useful for determining the I<type> value which forms part of
273 the method names described in L<"Package-specific Attribute Handling"> below.
277 Note that these routines are I<not> exported by default.
279 =head2 Package-specific Attribute Handling
281 B<WARNING>: the mechanisms described here are still experimental. Do not
282 rely on the current implementation. In particular, there is no provision
283 for applying package attributes to 'cloned' copies of subroutines used as
284 closures. (See L<perlref/"Making References"> for information on closures.)
285 Package-specific attribute handling may change incompatibly in a future
288 When an attribute list is present in a declaration, a check is made to see
289 whether an attribute 'modify' handler is present in the appropriate package
290 (or its @ISA inheritance tree). Similarly, when C<attributes::get> is
291 called on a valid reference, a check is made for an appropriate attribute
292 'fetch' handler. See L<"EXAMPLES"> to see how the "appropriate package"
295 The handler names are based on the underlying type of the variable being
296 declared or of the reference passed. Because these attributes are
297 associated with subroutine or variable declarations, this deliberately
298 ignores any possibility of being blessed into some package. Thus, a
299 subroutine declaration uses "CODE" as its I<type>, and even a blessed
300 hash reference uses "HASH" as its I<type>.
302 The class methods invoked for modifying and fetching are these:
306 =item FETCH_I<type>_ATTRIBUTES
308 This method is called with two arguments: the relevant package name,
309 and a reference to a variable or subroutine for which package-defined
310 attributes are desired. The expected return value is a list of
311 associated attributes. This list may be empty.
313 =item MODIFY_I<type>_ATTRIBUTES
315 This method is called with two fixed arguments, followed by the list of
316 attributes from the relevant declaration. The two fixed arguments are
317 the relevant package name and a reference to the declared subroutine or
318 variable. The expected return value is a list of attributes which were
319 not recognized by this handler. Note that this allows for a derived class
320 to delegate a call to its base class, and then only examine the attributes
321 which the base class didn't already handle for it.
323 The call to this method is currently made I<during> the processing of the
324 declaration. In particular, this means that a subroutine reference will
325 probably be for an undefined subroutine, even if this declaration is
326 actually part of the definition.
330 Calling C<attributes::get()> from within the scope of a null package
331 declaration C<package ;> for an unblessed variable reference will
332 not provide any starting package name for the 'fetch' method lookup.
333 Thus, this circumstance will not result in a method call for package-defined
334 attributes. A named subroutine knows to which symbol table entry it belongs
335 (or originally belonged), and it will use the corresponding package.
336 An anonymous subroutine knows the package name into which it was compiled
337 (unless it was also compiled with a null package declaration), and so it
338 will use that package name.
340 =head2 Syntax of Attribute Lists
342 An attribute list is a sequence of attribute specifications, separated by
343 whitespace or a colon (with optional whitespace).
344 Each attribute specification is a simple
345 name, optionally followed by a parenthesised parameter list.
346 If such a parameter list is present, it is scanned past as for the rules
347 for the C<q()> operator. (See L<perlop/"Quote and Quote-like Operators">.)
348 The parameter list is passed as it was found, however, and not as per C<q()>.
350 Some examples of syntactically valid attribute lists:
352 switch(10,foo(7,3)) : expensive
357 Some examples of syntactically invalid attribute lists (with annotation):
359 switch(10,foo() # ()-string not balanced
360 Ugly('(') # ()-string not balanced
361 5x5 # "5x5" not a valid identifier
362 Y2::north # "Y2::north" not a simple identifier
363 foo + bar # "+" neither a colon nor whitespace
367 =head2 Default exports
371 =head2 Available exports
373 The routines C<get> and C<reftype> are exportable.
375 =head2 Export tags defined
377 The C<:ALL> tag will get all of the above exports.
381 Here are some samples of syntactically valid declarations, with annotation
382 as to how they resolve internally into C<use attributes> invocations by
383 perl. These examples are primarily useful to see how the "appropriate
384 package" is found for the possible method lookups for package-defined
395 my Canine $spot : Watchful ;
400 attributes::->import(Canine => \$spot, "Watchful");
412 attributes::->import(Felis => \$cat, "Nervous");
423 use attributes X => \&foo, "lvalue";
430 sub Y::x : lvalue { 1 }
434 use attributes Y => \&Y::x, "lvalue";
444 BEGIN { *bar = \&X::foo; }
447 sub Y::bar : lvalue ;
451 use attributes X => \&X::foo, "lvalue";
455 This last example is purely for purposes of completeness. You should not
456 be trying to mess with the attributes of something in a package that's
465 sub MODIFY_CODE_ATTRIBUTES {
466 my ($class,$code,@attrs) = @_;
468 my $allowed = 'MyAttribute';
469 my @bad = grep { $_ ne $allowed } @attrs;
474 sub foo : MyAttribute {
478 This example runs. At compile time
479 C<MODIFY_CODE_ATTRIBUTES> is called. In that
480 subroutine, we check if any attribute is disallowed and we return a list of
481 these "bad attributes".
483 As we return an empty list, everything is fine.
487 sub MODIFY_CODE_ATTRIBUTES {
488 my ($class,$code,@attrs) = @_;
490 my $allowed = 'MyAttribute';
491 my @bad = grep{ $_ ne $allowed }@attrs;
496 sub foo : MyAttribute Test {
500 This example is aborted at compile time as we use the attribute "Test" which
501 isn't allowed. C<MODIFY_CODE_ATTRIBUTES>
502 returns a list that contains a single
509 L<perlsub/"Private Variables via my()"> and
510 L<perlsub/"Subroutine Attributes"> for details on the basic declarations;
511 L<perlfunc/use> for details on the normal invocation mechanism.