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");
42 @_ > 2 && ref $_[2] or do {
44 goto &Exporter::import;
46 my (undef,$home_stash,$svref,@attrs) = @_;
48 my $svtype = uc reftype($svref);
50 $pkgmeth = UNIVERSAL::can($home_stash, "MODIFY_${svtype}_ATTRIBUTES")
51 if defined $home_stash && $home_stash ne '';
54 my @pkgattrs = _modify_attrs_and_deprecate($svtype, $svref, @attrs);
55 @badattrs = $pkgmeth->($home_stash, $svref, @pkgattrs);
56 if (!@badattrs && @pkgattrs) {
58 return unless warnings::enabled('reserved');
59 @pkgattrs = grep { m/\A[[:lower:]]+(?:\z|\()/ } @pkgattrs;
61 for my $attr (@pkgattrs) {
64 my $s = ((@pkgattrs == 1) ? '' : 's');
65 carp "$svtype package attribute$s " .
66 "may clash with future reserved word$s: " .
67 join(' : ' , @pkgattrs);
72 @badattrs = _modify_attrs_and_deprecate($svtype, $svref, @attrs);
75 croak "Invalid $svtype attribute" .
76 (( @badattrs == 1 ) ? '' : 's') .
78 join(' : ', @badattrs);
83 @_ == 1 && ref $_[0] or
84 croak 'Usage: '.__PACKAGE__.'::get $ref';
86 my $svtype = uc reftype($svref);
87 my $stash = _guess_stash($svref);
88 $stash = caller unless defined $stash;
90 $pkgmeth = UNIVERSAL::can($stash, "FETCH_${svtype}_ATTRIBUTES")
91 if defined $stash && $stash ne '';
93 (_fetch_attrs($svref), $pkgmeth->($stash, $svref)) :
94 (_fetch_attrs($svref))
98 sub require_version { goto &UNIVERSAL::VERSION }
101 XSLoader::load('attributes', $VERSION);
109 attributes - get/set subroutine or variable attributes
114 my ($x,@y,%z) : Bent = 1;
115 my $s = sub : method { ... };
117 use attributes (); # optional, to get subroutine declarations
118 my @attrlist = attributes::get(\&foo);
120 use attributes 'get'; # import the attributes::get subroutine
121 my @attrlist = get \&foo;
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
129 list to this module. In particular, the first example above is equivalent to
132 use attributes __PACKAGE__, \&foo, 'method';
134 The second example in the synopsis does something equivalent to this:
138 attributes::->import(__PACKAGE__, \$x, 'Bent');
139 attributes::->import(__PACKAGE__, \@y, 'Bent');
140 attributes::->import(__PACKAGE__, \%z, 'Bent');
143 Yes, that's a lot of expansion.
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
148 with what the semantics ought to be. Do not rely on the current
149 implementation of this feature.
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.)
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:
162 my $x : Bent = 42 if 0;
164 will neither assign 42 to $x I<nor> will it apply the C<Bent> attribute
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'>.
173 =head2 What C<import> does
175 In the description it is mentioned that
181 use attributes __PACKAGE__, \&foo, 'method';
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'.
187 attributes->import( __PACKAGE__, \&foo, 'method' );
189 So you want to know what C<import> actually does?
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
197 MODIFY_CODE_ATTRIBUTES( 'main', \&foo, 'method' );
199 C<< MODIFY_<reftype>_ATTRIBUTES >> has to return a list of all "bad attributes".
200 If there are any bad attributes C<import> croaks.
202 (See L<"Package-specific Attribute Handling"> below.)
204 =head2 Built-in Attributes
206 The following are the built-in attributes for subroutines:
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>.
218 Indicates that the referenced subroutine is a method. A subroutine so marked
219 will not trigger the "Ambiguous call resolved as CORE::%s" warning.
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".
228 =head2 Available Subroutines
230 The following subroutines are available for general use once this module
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
243 L<"Package-specific Attribute Handling"> below.
244 Otherwise, only L<built-in attributes|"Built-in Attributes"> will be returned.
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
252 the method names described in L<"Package-specific Attribute Handling"> below.
256 Note that these routines are I<not> exported by default.
258 =head2 Package-specific Attribute Handling
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
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"
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>.
281 The class methods invoked for modifying and fetching are these:
285 =item FETCH_I<type>_ATTRIBUTES
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.
292 =item MODIFY_I<type>_ATTRIBUTES
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
297 variable. The expected return value is a list of attributes which were
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.
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.
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.
319 =head2 Syntax of Attribute Lists
321 An attribute list is a sequence of attribute specifications, separated by
322 whitespace or a colon (with optional whitespace).
323 Each attribute specification is a simple
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()>.
329 Some examples of syntactically valid attribute lists:
331 switch(10,foo(7,3)) : expensive
336 Some examples of syntactically invalid attribute lists (with annotation):
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
342 foo + bar # "+" neither a colon nor whitespace
346 =head2 Default exports
350 =head2 Available exports
352 The routines C<get> and C<reftype> are exportable.
354 =head2 Export tags defined
356 The C<:ALL> tag will get all of the above exports.
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
374 my Canine $spot : Watchful ;
379 attributes::->import(Canine => \$spot, "Watchful");
391 attributes::->import(Felis => \$cat, "Nervous");
402 use attributes X => \&foo, "lvalue";
409 sub Y::x : lvalue { 1 }
413 use attributes Y => \&Y::x, "lvalue";
423 BEGIN { *bar = \&X::foo; }
426 sub Y::bar : lvalue ;
430 use attributes X => \&X::foo, "lvalue";
434 This last example is purely for purposes of completeness. You should not
435 be trying to mess with the attributes of something in a package that's
444 sub MODIFY_CODE_ATTRIBUTES {
445 my ($class,$code,@attrs) = @_;
447 my $allowed = 'MyAttribute';
448 my @bad = grep { $_ ne $allowed } @attrs;
453 sub foo : MyAttribute {
457 This example runs. At compile time C<MODIFY_CODE_ATTRIBUTES> is called. In that
458 subroutine, we check if any attribute is disallowed and we return a list of
459 these "bad attributes".
461 As we return an empty list, everything is fine.
465 sub MODIFY_CODE_ATTRIBUTES {
466 my ($class,$code,@attrs) = @_;
468 my $allowed = 'MyAttribute';
469 my @bad = grep{ $_ ne $allowed }@attrs;
474 sub foo : MyAttribute Test {
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
486 L<perlsub/"Private Variables via my()"> and
487 L<perlsub/"Subroutine Attributes"> for details on the basic declarations;
488 L<perlfunc/use> for details on the normal invocation mechanism.