5 @EXPORT_OK = qw(get reftype);
7 %EXPORT_TAGS = (ALL => [@EXPORT, @EXPORT_OK]);
22 @_ > 2 && ref $_[2] or do {
24 goto &Exporter::import;
26 my (undef,$home_stash,$svref,@attrs) = @_;
28 my $svtype = uc reftype($svref);
30 $pkgmeth = UNIVERSAL::can($home_stash, "MODIFY_${svtype}_ATTRIBUTES")
31 if defined $home_stash && $home_stash ne '';
34 my @pkgattrs = _modify_attrs($svref, @attrs);
35 @badattrs = $pkgmeth->($home_stash, $svref, @pkgattrs);
36 if (!@badattrs && @pkgattrs) {
38 return unless warnings::enabled('reserved');
39 @pkgattrs = grep { m/\A[[:lower:]]+(?:\z|\()/ } @pkgattrs;
41 for my $attr (@pkgattrs) {
44 my $s = ((@pkgattrs == 1) ? '' : 's');
45 carp "$svtype package attribute$s " .
46 "may clash with future reserved word$s: " .
47 join(' : ' , @pkgattrs);
52 @badattrs = _modify_attrs($svref, @attrs);
55 croak "Invalid $svtype attribute" .
56 (( @badattrs == 1 ) ? '' : 's') .
58 join(' : ', @badattrs);
63 @_ == 1 && ref $_[0] or
64 croak 'Usage: '.__PACKAGE__.'::get $ref';
66 my $svtype = uc reftype($svref);
67 my $stash = _guess_stash($svref);
68 $stash = caller unless defined $stash;
70 $pkgmeth = UNIVERSAL::can($stash, "FETCH_${svtype}_ATTRIBUTES")
71 if defined $stash && $stash ne '';
73 (_fetch_attrs($svref), $pkgmeth->($stash, $svref)) :
74 (_fetch_attrs($svref))
78 sub require_version { goto &UNIVERSAL::VERSION }
81 XSLoader::load('attributes', $VERSION);
89 attributes - get/set subroutine or variable attributes
94 my ($x,@y,%z) : Bent = 1;
95 my $s = sub : method { ... };
97 use attributes (); # optional, to get subroutine declarations
98 my @attrlist = attributes::get(\&foo);
100 use attributes 'get'; # import the attributes::get subroutine
101 my @attrlist = get \&foo;
105 Subroutine declarations and definitions may optionally have attribute lists
106 associated with them. (Variable C<my> declarations also may, but see the
107 warning below.) Perl handles these declarations by passing some information
108 about the call site and the thing being declared along with the attribute
109 list to this module. In particular, the first example above is equivalent to
112 use attributes __PACKAGE__, \&foo, 'method';
114 The second example in the synopsis does something equivalent to this:
118 attributes::->import(__PACKAGE__, \$x, 'Bent');
119 attributes::->import(__PACKAGE__, \@y, 'Bent');
120 attributes::->import(__PACKAGE__, \%z, 'Bent');
123 Yes, that's a lot of expansion.
125 B<WARNING>: attribute declarations for variables are still evolving.
126 The semantics and interfaces of such declarations could change in
127 future versions. They are present for purposes of experimentation
128 with what the semantics ought to be. Do not rely on the current
129 implementation of this feature.
131 There are only a few attributes currently handled by Perl itself (or
132 directly by this module, depending on how you look at it.) However,
133 package-specific attributes are allowed by an extension mechanism.
134 (See L<"Package-specific Attribute Handling"> below.)
136 The setting of subroutine attributes happens at compile time.
137 Variable attributes in C<our> declarations are also applied at compile time.
138 However, C<my> variables get their attributes applied at run-time.
139 This means that you have to I<reach> the run-time component of the C<my>
140 before those attributes will get applied. For example:
142 my $x : Bent = 42 if 0;
144 will neither assign 42 to $x I<nor> will it apply the C<Bent> attribute
147 An attempt to set an unrecognized attribute is a fatal error. (The
148 error is trappable, but it still stops the compilation within that
149 C<eval>.) Setting an attribute with a name that's all lowercase
150 letters that's not a built-in attribute (such as "foo") will result in
151 a warning with B<-w> or C<use warnings 'reserved'>.
153 =head2 What C<import> does
155 In the description it is mentioned that
161 use attributes __PACKAGE__, \&foo, 'method';
163 As you might know this calls the C<import> function of C<attributes> at compile
164 time with these parameters: 'attributes', the caller's package name, the reference
165 to the code and 'method'.
167 attributes->import( __PACKAGE__, \&foo, 'method' );
169 So you want to know what C<import> actually does?
171 First of all C<import> gets the type of the third parameter ('CODE' in this case).
172 C<attributes.pm> checks if there is a subroutine called C<< MODIFY_<reftype>_ATTRIBUTES >>
173 in the caller's namespace (here: 'main'). In this case a subroutine C<MODIFY_CODE_ATTRIBUTES> is
174 required. Then this method is called to check if you have used a "bad attribute".
175 The subroutine call in this example would look like
177 MODIFY_CODE_ATTRIBUTES( 'main', \&foo, 'method' );
179 C<< MODIFY_<reftype>_ATTRIBUTES >> has to return a list of all "bad attributes".
180 If there are any bad attributes C<import> croaks.
182 (See L<"Package-specific Attribute Handling"> below.)
184 =head2 Built-in Attributes
186 The following are the built-in attributes for subroutines:
192 Indicates that the referenced subroutine is a valid lvalue and can
193 be assigned to. The subroutine must return a modifiable value such
194 as a scalar variable, as described in L<perlsub>.
198 Indicates that the referenced subroutine is a method. A subroutine so marked
199 will not trigger the "Ambiguous call resolved as CORE::%s" warning.
203 The "locked" attribute has no effect in 5.10.0 and later. It was used as part
204 of the now-removed "Perl 5.005 threads".
208 For global variables there is C<unique> attribute: see L<perlfunc/our>.
210 =head2 Available Subroutines
212 The following subroutines are available for general use once this module
219 This routine expects a single parameter--a reference to a
220 subroutine or variable. It returns a list of attributes, which may be
221 empty. If passed invalid arguments, it uses die() (via L<Carp::croak|Carp>)
222 to raise a fatal exception. If it can find an appropriate package name
223 for a class method lookup, it will include the results from a
224 C<FETCH_I<type>_ATTRIBUTES> call in its return list, as described in
225 L<"Package-specific Attribute Handling"> below.
226 Otherwise, only L<built-in attributes|"Built-in Attributes"> will be returned.
230 This routine expects a single parameter--a reference to a subroutine or
231 variable. It returns the built-in type of the referenced variable,
232 ignoring any package into which it might have been blessed.
233 This can be useful for determining the I<type> value which forms part of
234 the method names described in L<"Package-specific Attribute Handling"> below.
238 Note that these routines are I<not> exported by default.
240 =head2 Package-specific Attribute Handling
242 B<WARNING>: the mechanisms described here are still experimental. Do not
243 rely on the current implementation. In particular, there is no provision
244 for applying package attributes to 'cloned' copies of subroutines used as
245 closures. (See L<perlref/"Making References"> for information on closures.)
246 Package-specific attribute handling may change incompatibly in a future
249 When an attribute list is present in a declaration, a check is made to see
250 whether an attribute 'modify' handler is present in the appropriate package
251 (or its @ISA inheritance tree). Similarly, when C<attributes::get> is
252 called on a valid reference, a check is made for an appropriate attribute
253 'fetch' handler. See L<"EXAMPLES"> to see how the "appropriate package"
256 The handler names are based on the underlying type of the variable being
257 declared or of the reference passed. Because these attributes are
258 associated with subroutine or variable declarations, this deliberately
259 ignores any possibility of being blessed into some package. Thus, a
260 subroutine declaration uses "CODE" as its I<type>, and even a blessed
261 hash reference uses "HASH" as its I<type>.
263 The class methods invoked for modifying and fetching are these:
267 =item FETCH_I<type>_ATTRIBUTES
269 This method is called with two arguments: the relevant package name,
270 and a reference to a variable or subroutine for which package-defined
271 attributes are desired. The expected return value is a list of
272 associated attributes. This list may be empty.
274 =item MODIFY_I<type>_ATTRIBUTES
276 This method is called with two fixed arguments, followed by the list of
277 attributes from the relevant declaration. The two fixed arguments are
278 the relevant package name and a reference to the declared subroutine or
279 variable. The expected return value is a list of attributes which were
280 not recognized by this handler. Note that this allows for a derived class
281 to delegate a call to its base class, and then only examine the attributes
282 which the base class didn't already handle for it.
284 The call to this method is currently made I<during> the processing of the
285 declaration. In particular, this means that a subroutine reference will
286 probably be for an undefined subroutine, even if this declaration is
287 actually part of the definition.
291 Calling C<attributes::get()> from within the scope of a null package
292 declaration C<package ;> for an unblessed variable reference will
293 not provide any starting package name for the 'fetch' method lookup.
294 Thus, this circumstance will not result in a method call for package-defined
295 attributes. A named subroutine knows to which symbol table entry it belongs
296 (or originally belonged), and it will use the corresponding package.
297 An anonymous subroutine knows the package name into which it was compiled
298 (unless it was also compiled with a null package declaration), and so it
299 will use that package name.
301 =head2 Syntax of Attribute Lists
303 An attribute list is a sequence of attribute specifications, separated by
304 whitespace or a colon (with optional whitespace).
305 Each attribute specification is a simple
306 name, optionally followed by a parenthesised parameter list.
307 If such a parameter list is present, it is scanned past as for the rules
308 for the C<q()> operator. (See L<perlop/"Quote and Quote-like Operators">.)
309 The parameter list is passed as it was found, however, and not as per C<q()>.
311 Some examples of syntactically valid attribute lists:
313 switch(10,foo(7,3)) : expensive
318 Some examples of syntactically invalid attribute lists (with annotation):
320 switch(10,foo() # ()-string not balanced
321 Ugly('(') # ()-string not balanced
322 5x5 # "5x5" not a valid identifier
323 Y2::north # "Y2::north" not a simple identifier
324 foo + bar # "+" neither a colon nor whitespace
328 =head2 Default exports
332 =head2 Available exports
334 The routines C<get> and C<reftype> are exportable.
336 =head2 Export tags defined
338 The C<:ALL> tag will get all of the above exports.
342 Here are some samples of syntactically valid declarations, with annotation
343 as to how they resolve internally into C<use attributes> invocations by
344 perl. These examples are primarily useful to see how the "appropriate
345 package" is found for the possible method lookups for package-defined
356 my Canine $spot : Watchful ;
361 attributes::->import(Canine => \$spot, "Watchful");
373 attributes::->import(Felis => \$cat, "Nervous");
384 use attributes X => \&foo, "locked";
391 sub Y::x : locked { 1 }
395 use attributes Y => \&Y::x, "locked";
405 BEGIN { *bar = \&X::foo; }
408 sub Y::bar : locked ;
412 use attributes X => \&X::foo, "locked";
416 This last example is purely for purposes of completeness. You should not
417 be trying to mess with the attributes of something in a package that's
426 sub MODIFY_CODE_ATTRIBUTES {
427 my ($class,$code,@attrs) = @_;
429 my $allowed = 'MyAttribute';
430 my @bad = grep { $_ ne $allowed } @attrs;
435 sub foo : MyAttribute {
439 This example runs. At compile time C<MODIFY_CODE_ATTRIBUTES> is called. In that
440 subroutine, we check if any attribute is disallowed and we return a list of
441 these "bad attributes".
443 As we return an empty list, everything is fine.
447 sub MODIFY_CODE_ATTRIBUTES {
448 my ($class,$code,@attrs) = @_;
450 my $allowed = 'MyAttribute';
451 my @bad = grep{ $_ ne $allowed }@attrs;
456 sub foo : MyAttribute Test {
460 This example is aborted at compile time as we use the attribute "Test" which
461 isn't allowed. C<MODIFY_CODE_ATTRIBUTES> returns a list that contains a single
468 L<perlsub/"Private Variables via my()"> and
469 L<perlsub/"Subroutine Attributes"> for details on the basic declarations;
470 L<attrs> for the obsolescent form of subroutine attribute specification
471 which this module replaces;
472 L<perlfunc/use> for details on the normal invocation mechanism.