5 #@EXPORT_OK = qw(get reftype);
20 ## forward declaration(s) rather than wrapping the bootstrap call in BEGIN{}
22 #sub _fetch_attrs ($) ;
23 #sub _guess_stash ($) ;
25 #sub _warn_reserved () ;
27 # The extra trips through newATTRSUB in the interpreter wipe out any savings
28 # from avoiding the BEGIN block. Just do the bootstrap now.
32 @_ > 2 && ref $_[2] or
33 croak 'Usage: use '.__PACKAGE__.' $home_stash, $ref, @attrlist';
34 my (undef,$home_stash,$svref,@attrs) = @_;
36 my $svtype = uc reftype($svref);
38 $pkgmeth = UNIVERSAL::can($home_stash, "MODIFY_${svtype}_ATTRIBUTES")
39 if defined $home_stash && $home_stash ne '';
42 my @pkgattrs = _modify_attrs($svref, @attrs);
43 @badattrs = $pkgmeth->($home_stash, $svref, @attrs);
44 if (!@badattrs && @pkgattrs) {
45 return unless _warn_reserved;
46 @pkgattrs = grep { m/\A[[:lower:]]+(?:\z|\()/ } @pkgattrs;
48 for my $attr (@pkgattrs) {
51 my $s = ((@pkgattrs == 1) ? '' : 's');
52 carp "$svtype package attribute$s " .
53 "may clash with future reserved word$s: " .
54 join(' , ' , @pkgattrs);
59 @badattrs = _modify_attrs($svref, @attrs);
62 croak "Invalid $svtype attribute" .
63 (( @badattrs == 1 ) ? '' : 's') .
65 join(' , ', @badattrs);
70 @_ == 1 && ref $_[0] or
71 croak 'Usage: '.__PACKAGE__.'::get $ref';
73 my $svtype = uc reftype $svref;
74 my $stash = _guess_stash $svref;
75 $stash = caller unless defined $stash;
77 $pkgmeth = UNIVERSAL::can($stash, "FETCH_${svtype}_ATTRIBUTES")
78 if defined $stash && $stash ne '';
80 (_fetch_attrs($svref), $pkgmeth->($stash, $svref)) :
81 (_fetch_attrs($svref))
87 # goto &Exporter::import;
90 #sub require_version { goto &UNIVERSAL::VERSION }
98 attributes - get/set subroutine or variable attributes
103 my ($x,@y,%z) : Bent ;
104 my $s = sub : method { ... };
106 use attributes (); # optional, to get subroutine declarations
107 my @attrlist = attributes::get(\&foo);
111 Subroutine declarations and definitions may optionally have attribute lists
112 associated with them. (Variable C<my> declarations also may, but see the
113 warning below.) Perl handles these declarations by passing some information
114 about the call site and the thing being declared along with the attribute
115 list to this module. In particular, first example above is equivalent to
118 use attributes __PACKAGE__, \&foo, 'method';
120 The second example in the synopsis does something equivalent to this:
122 use attributes __PACKAGE__, \$x, 'Bent';
123 use attributes __PACKAGE__, \@y, 'Bent';
124 use attributes __PACKAGE__, \%z, 'Bent';
126 Yes, that's three invocations.
128 B<WARNING>: attribute declarations for variables are an I<experimental>
129 feature. The semantics of such declarations could change or be removed
130 in future versions. They are present for purposes of experimentation
131 with what the semantics ought to be. Do not rely on the current
132 implementation of this feature.
134 There are only a few attributes currently handled by Perl itself (or
135 directly by this module, depending on how you look at it.) However,
136 package-specific attributes are allowed by an extension mechanism.
137 (See L<"Package-specific Attribute Handling"> below.)
139 The setting of attributes happens at compile time. An attempt to set
140 an unrecognized attribute is a fatal error. (The error is trappable, but
141 it still stops the compilation within that C<eval>.) Setting an attribute
142 with a name that's all lowercase letters that's not a built-in attribute
144 will result in a warning with B<-w> or C<use warnings 'reserved'>.
146 =head2 Built-in Attributes
148 The following are the built-in attributes for subroutines:
154 Setting this attribute is only meaningful when the subroutine or
155 method is to be called by multiple threads. When set on a method
156 subroutine (i.e., one marked with the B<method> attribute below),
157 Perl ensures that any invocation of it implicitly locks its first
158 argument before execution. When set on a non-method subroutine,
159 Perl ensures that a lock is taken on the subroutine itself before
160 execution. The semantics of the lock are exactly those of one
161 explicitly taken with the C<lock> operator immediately after the
162 subroutine is entered.
166 Indicates that the referenced subroutine is a method.
167 This has a meaning when taken together with the B<locked> attribute,
168 as described there. It also means that a subroutine so marked
169 will not trigger the "Ambiguous call resolved as CORE::%s" warning.
173 There are no built-in attributes for anything other than subroutines.
175 =head2 Available Subroutines
177 The following subroutines are available for general use once this module
184 This routine expects a single parameter--a reference to a
185 subroutine or variable. It returns a list of attributes, which may be
186 empty. If passed invalid arguments, it uses die() (via L<Carp::croak|Carp>)
187 to raise a fatal exception. If it can find an appropriate package name
188 for a class method lookup, it will include the results from a
189 C<FETCH_I<type>_ATTRIBUTES> call in its return list, as described in
190 L"Package-specific Attribute Handling"> below.
191 Otherwise, only L<built-in attributes|"Built-in Attributes"> will be returned.
195 This routine expects a single parameter--a reference to a subroutine or
196 variable. It returns the built-in type of the referenced variable,
197 ignoring any package into which it might have been blessed.
198 This can be useful for determining the I<type> value which forms part of
199 the method names described in L"Package-specific Attribute Handling"> below.
203 Note that these routines are I<not> exported. This is primarily because
204 the C<use> mechanism which would normally import them is already in use
205 by Perl itself to implement the C<sub : attributes> syntax.
207 =head2 Package-specific Attribute Handling
209 B<WARNING>: the mechanisms described here are still experimental. Do not
210 rely on the current implementation. In particular, there is no provision
211 for applying package attributes to 'cloned' copies of subroutines used as
212 closures. (See L<perlref/"Making References"> for information on closures.)
213 Package-specific attribute handling may change incompatibly in a future
216 When an attribute list is present in a declaration, a check is made to see
217 whether an attribute 'modify' handler is present in the appropriate package
218 (or its @ISA inheritance tree). Similarly, when C<attributes::get> is
219 called on a valid reference, a check is made for an appropriate attribute
220 'fetch' handler. See L<"EXAMPLES"> to see how the "appropriate package"
223 The handler names are based on the underlying type of the variable being
224 declared or of the reference passed. Because these attributes are
225 associated with subroutine or variable declarations, this deliberately
226 ignores any possibility of being blessed into some package. Thus, a
227 subroutine declaration uses "CODE" as its I<type>, and even a blessed
228 hash reference uses "HASH" as its I<type>.
230 The class methods invoked for modifying and fetching are these:
234 =item FETCH_I<type>_ATTRIBUTES
236 This method receives a single argument, which is a reference to the
237 variable or subroutine for which package-defined attributes are desired.
238 The expected return value is a list of associated attributes.
239 This list may be empty.
241 =item MODIFY_I<type>_ATTRIBUTES
243 This method is called with two fixed arguments, followed by the list of
244 attributes from the relevant declaration. The two fixed arguments are
245 the relevant package name and a reference to the declared subroutine or
246 variable. The expected return value as a list of attributes which were
247 not recognized by this handler. Note that this allows for a derived class
248 to delegate a call to its base class, and then only examine the attributes
249 which the base class didn't already handle for it.
251 The call to this method is currently made I<during> the processing of the
252 declaration. In particular, this means that a subroutine reference will
253 probably be for an undefined subroutine, even if this declaration is
254 actually part of the definition.
258 Calling C<attributes::get()> from within the scope of a null package
259 declaration C<package ;> for an unblessed variable reference will
260 not provide any starting package name for the 'fetch' method lookup.
261 Thus, this circumstance will not result in a method call for package-defined
262 attributes. A named subroutine knows to which symbol table entry it belongs
263 (or originally belonged), and it will use the corresponding package.
264 An anonymous subroutine knows the package name into which it was compiled
265 (unless it was also compiled with a null package declaration), and so it
266 will use that package name.
268 =head2 Syntax of Attribute Lists
270 An attribute list is a sequence of attribute specifications, separated by
271 whitespace, commas, or both. Each attribute specification is a simple
272 name, optionally followed by a parenthesised parameter list.
273 If such a parameter list is present, it is scanned past as for the rules
274 for the C<q()> operator. (See L<perlop/"Quote and Quote-like Operators">.)
275 The parameter list is passed as it was found, however, and not as per C<q()>.
277 Some examples of syntactically valid attribute lists:
279 switch(10,foo(7,3)) , , expensive
284 Some examples of syntactically invalid attribute lists (with annotation):
286 switch(10,foo() # ()-string not balanced
287 Ugly('(') # ()-string not balanced
288 5x5 # "5x5" not a valid identifier
289 Y2::north # "Y2::north" not a simple identifier
290 foo + bar # "+" neither a comma nor whitespace
294 Here are some samples of syntactically valid declarations, with annotation
295 as to how they resolve internally into C<use attributes> invocations by
296 perl. These examples are primarily useful to see how the "appropriate
297 package" is found for the possible method lookups for package-defined
308 my Canine $spot : Watchful ;
312 use attributes Canine => \$spot, "Watchful";
323 use attributes Felis => \$cat, "Nervous";
334 use attributes X => \&foo, "locked";
341 sub Y::x : locked { 1 }
345 use attributes Y => \&Y::x, "locked";
355 BEGIN { *bar = \&X::foo; }
358 sub Y::bar : locked ;
362 use attributes X => \&X::foo, "locked";
366 This last example is purely for purposes of completeness. You should not
367 be trying to mess with the attributes of something in a package that's
372 L<perlsub/"Private Variables via my()"> and
373 L<perlsub/"Subroutine Attributes"> for details on the basic declarations;
374 L<attrs> for the obsolescent form of subroutine attribute specification
375 which this module replaces;
376 L<perlfunc/use> for details on the normal invocation mechanism.