5 @EXPORT_OK = qw(get reftype);
7 %EXPORT_TAGS = (ALL => [@EXPORT, @EXPORT_OK]);
21 ## forward declaration(s) rather than wrapping the bootstrap call in BEGIN{}
23 #sub _fetch_attrs ($) ;
24 #sub _guess_stash ($) ;
26 #sub _warn_reserved () ;
28 # The extra trips through newATTRSUB in the interpreter wipe out any savings
29 # from avoiding the BEGIN block. Just do the bootstrap now.
33 @_ > 2 && ref $_[2] or do {
35 goto &Exporter::import;
37 my (undef,$home_stash,$svref,@attrs) = @_;
39 my $svtype = uc reftype($svref);
41 $pkgmeth = UNIVERSAL::can($home_stash, "MODIFY_${svtype}_ATTRIBUTES")
42 if defined $home_stash && $home_stash ne '';
45 my @pkgattrs = _modify_attrs($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;
51 for my $attr (@pkgattrs) {
54 my $s = ((@pkgattrs == 1) ? '' : 's');
55 carp "$svtype package attribute$s " .
56 "may clash with future reserved word$s: " .
57 join(' , ' , @pkgattrs);
62 @badattrs = _modify_attrs($svref, @attrs);
65 croak "Invalid $svtype attribute" .
66 (( @badattrs == 1 ) ? '' : 's') .
68 join(' , ', @badattrs);
73 @_ == 1 && ref $_[0] or
74 croak 'Usage: '.__PACKAGE__.'::get $ref';
76 my $svtype = uc reftype $svref;
77 my $stash = _guess_stash $svref;
78 $stash = caller unless defined $stash;
80 $pkgmeth = UNIVERSAL::can($stash, "FETCH_${svtype}_ATTRIBUTES")
81 if defined $stash && $stash ne '';
83 (_fetch_attrs($svref), $pkgmeth->($stash, $svref)) :
84 (_fetch_attrs($svref))
88 sub require_version { goto &UNIVERSAL::VERSION }
96 attributes - get/set subroutine or variable attributes
101 my ($x,@y,%z) : Bent ;
102 my $s = sub : method { ... };
104 use attributes (); # optional, to get subroutine declarations
105 my @attrlist = attributes::get(\&foo);
107 use attributes 'get'; # import the attributes::get subroutine
108 my @attrlist = get \&foo;
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
116 list to this module. In particular, the first example above is equivalent to
119 use attributes __PACKAGE__, \&foo, 'method';
121 The second example in the synopsis does something equivalent to this:
123 use attributes __PACKAGE__, \$x, 'Bent';
124 use attributes __PACKAGE__, \@y, 'Bent';
125 use attributes __PACKAGE__, \%z, 'Bent';
127 Yes, that's three invocations.
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.
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.)
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
145 will result in a warning with B<-w> or C<use warnings 'reserved'>.
147 =head2 Built-in Attributes
149 The following are the built-in attributes for subroutines:
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.
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.
174 There are no built-in attributes for anything other than subroutines.
176 =head2 Available Subroutines
178 The following subroutines are available for general use once this module
185 This routine expects a single parameter--a reference to a
186 subroutine or variable. It returns a list of attributes, which may be
187 empty. If passed invalid arguments, it uses die() (via L<Carp::croak|Carp>)
188 to raise a fatal exception. If it can find an appropriate package name
189 for a class method lookup, it will include the results from a
190 C<FETCH_I<type>_ATTRIBUTES> call in its return list, as described in
191 L<"Package-specific Attribute Handling"> below.
192 Otherwise, only L<built-in attributes|"Built-in Attributes"> will be returned.
196 This routine expects a single parameter--a reference to a subroutine or
197 variable. It returns the built-in type of the referenced variable,
198 ignoring any package into which it might have been blessed.
199 This can be useful for determining the I<type> value which forms part of
200 the method names described in L<"Package-specific Attribute Handling"> below.
204 Note that these routines are I<not> exported by default.
206 =head2 Package-specific Attribute Handling
208 B<WARNING>: the mechanisms described here are still experimental. Do not
209 rely on the current implementation. In particular, there is no provision
210 for applying package attributes to 'cloned' copies of subroutines used as
211 closures. (See L<perlref/"Making References"> for information on closures.)
212 Package-specific attribute handling may change incompatibly in a future
215 When an attribute list is present in a declaration, a check is made to see
216 whether an attribute 'modify' handler is present in the appropriate package
217 (or its @ISA inheritance tree). Similarly, when C<attributes::get> is
218 called on a valid reference, a check is made for an appropriate attribute
219 'fetch' handler. See L<"EXAMPLES"> to see how the "appropriate package"
222 The handler names are based on the underlying type of the variable being
223 declared or of the reference passed. Because these attributes are
224 associated with subroutine or variable declarations, this deliberately
225 ignores any possibility of being blessed into some package. Thus, a
226 subroutine declaration uses "CODE" as its I<type>, and even a blessed
227 hash reference uses "HASH" as its I<type>.
229 The class methods invoked for modifying and fetching are these:
233 =item FETCH_I<type>_ATTRIBUTES
235 This method receives a single argument, which is a reference to the
236 variable or subroutine for which package-defined attributes are desired.
237 The expected return value is a list of associated attributes.
238 This list may be empty.
240 =item MODIFY_I<type>_ATTRIBUTES
242 This method is called with two fixed arguments, followed by the list of
243 attributes from the relevant declaration. The two fixed arguments are
244 the relevant package name and a reference to the declared subroutine or
245 variable. The expected return value as a list of attributes which were
246 not recognized by this handler. Note that this allows for a derived class
247 to delegate a call to its base class, and then only examine the attributes
248 which the base class didn't already handle for it.
250 The call to this method is currently made I<during> the processing of the
251 declaration. In particular, this means that a subroutine reference will
252 probably be for an undefined subroutine, even if this declaration is
253 actually part of the definition.
257 Calling C<attributes::get()> from within the scope of a null package
258 declaration C<package ;> for an unblessed variable reference will
259 not provide any starting package name for the 'fetch' method lookup.
260 Thus, this circumstance will not result in a method call for package-defined
261 attributes. A named subroutine knows to which symbol table entry it belongs
262 (or originally belonged), and it will use the corresponding package.
263 An anonymous subroutine knows the package name into which it was compiled
264 (unless it was also compiled with a null package declaration), and so it
265 will use that package name.
267 =head2 Syntax of Attribute Lists
269 An attribute list is a sequence of attribute specifications, separated by
270 whitespace, commas, or both. Each attribute specification is a simple
271 name, optionally followed by a parenthesised parameter list.
272 If such a parameter list is present, it is scanned past as for the rules
273 for the C<q()> operator. (See L<perlop/"Quote and Quote-like Operators">.)
274 The parameter list is passed as it was found, however, and not as per C<q()>.
276 Some examples of syntactically valid attribute lists:
278 switch(10,foo(7,3)) , , expensive
283 Some examples of syntactically invalid attribute lists (with annotation):
285 switch(10,foo() # ()-string not balanced
286 Ugly('(') # ()-string not balanced
287 5x5 # "5x5" not a valid identifier
288 Y2::north # "Y2::north" not a simple identifier
289 foo + bar # "+" neither a comma nor whitespace
293 =head2 Default exports
297 =head2 Available exports
299 The routines C<get> and C<reftype> are exportable.
301 =head2 Export tags defined
303 The C<:ALL> tag will get all of the above exports.
307 Here are some samples of syntactically valid declarations, with annotation
308 as to how they resolve internally into C<use attributes> invocations by
309 perl. These examples are primarily useful to see how the "appropriate
310 package" is found for the possible method lookups for package-defined
321 my Canine $spot : Watchful ;
325 use attributes Canine => \$spot, "Watchful";
336 use attributes Felis => \$cat, "Nervous";
347 use attributes X => \&foo, "locked";
354 sub Y::x : locked { 1 }
358 use attributes Y => \&Y::x, "locked";
368 BEGIN { *bar = \&X::foo; }
371 sub Y::bar : locked ;
375 use attributes X => \&X::foo, "locked";
379 This last example is purely for purposes of completeness. You should not
380 be trying to mess with the attributes of something in a package that's
385 L<perlsub/"Private Variables via my()"> and
386 L<perlsub/"Subroutine Attributes"> for details on the basic declarations;
387 L<attrs> for the obsolescent form of subroutine attribute specification
388 which this module replaces;
389 L<perlfunc/use> for details on the normal invocation mechanism.