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 ($) ;
24 #sub _guess_stash ($) ;
27 # The extra trips through newATTRSUB in the interpreter wipe out any savings
28 # from avoiding the BEGIN block. Just do the bootstrap now.
29 BEGIN { bootstrap attributes }
32 @_ > 2 && ref $_[2] or do {
34 goto &Exporter::import;
36 my (undef,$home_stash,$svref,@attrs) = @_;
38 my $svtype = uc reftype($svref);
40 $pkgmeth = UNIVERSAL::can($home_stash, "MODIFY_${svtype}_ATTRIBUTES")
41 if defined $home_stash && $home_stash ne '';
44 my @pkgattrs = _modify_attrs($svref, @attrs);
45 @badattrs = $pkgmeth->($home_stash, $svref, @pkgattrs);
46 if (!@badattrs && @pkgattrs) {
48 return unless warnings::enabled('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 = 1;
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:
125 attributes::->import(__PACKAGE__, \$x, 'Bent');
126 attributes::->import(__PACKAGE__, \@y, 'Bent');
127 attributes::->import(__PACKAGE__, \%z, 'Bent');
130 Yes, that's a lot of expansion.
132 B<WARNING>: attribute declarations for variables are still evolving.
133 The semantics and interfaces of such declarations could change in
134 future versions. They are present for purposes of experimentation
135 with what the semantics ought to be. Do not rely on the current
136 implementation of this feature.
138 There are only a few attributes currently handled by Perl itself (or
139 directly by this module, depending on how you look at it.) However,
140 package-specific attributes are allowed by an extension mechanism.
141 (See L<"Package-specific Attribute Handling"> below.)
143 The setting of subroutine attributes happens at compile time.
144 Variable attributes in C<our> declarations are also applied at compile time.
145 However, C<my> variables get their attributes applied at run-time.
146 This means that you have to I<reach> the run-time component of the C<my>
147 before those attributes will get applied. For example:
149 my $x : Bent = 42 if 0;
151 will neither assign 42 to $x I<nor> will it apply the C<Bent> attribute
154 An attempt to set an unrecognized attribute is a fatal error. (The
155 error is trappable, but it still stops the compilation within that
156 C<eval>.) Setting an attribute with a name that's all lowercase
157 letters that's not a built-in attribute (such as "foo") will result in
158 a warning with B<-w> or C<use warnings 'reserved'>.
160 =head2 What C<import> does
162 In the description it is mentioned that
168 use attributes __PACKAGE__, \&foo, 'method';
170 As you might know this calls the C<import> function of C<attributes> at compile
171 time with these parameters: 'attributes', the caller's package name, the reference
172 to the code and 'method'.
174 attributes->import( __PACKAGE__, \&foo, 'method' );
176 So you want to know what C<import> actually does?
178 First of all C<import> gets the type of the third parameter ('CODE' in this case).
179 C<attributes.pm> checks if there is a subroutine called C<< MODIFY_<reftype>_ATTRIBUTES >>
180 in the caller's namespace (here: 'main'). In this case a subroutine C<MODIFY_CODE_ATTRIBUTES> is
181 required. Then this method is called to check if you have used a "bad attribute".
182 The subroutine call in this example would look like
184 MODIFY_CODE_ATTRIBUTES( 'main', \&foo, 'method' );
186 C<< MODIFY_<reftype>_ATTRIBUTES >> has to return a list of all "bad attributes".
187 If there are any bad attributes C<import> croaks.
189 (See L<"Package-specific Attribute Handling"> below.)
191 =head2 Built-in Attributes
193 The following are the built-in attributes for subroutines:
199 B<5.005 threads only! The use of the "locked" attribute currently
200 only makes sense if you are using the deprecated "Perl 5.005 threads"
201 implementation of threads.>
203 Setting this attribute is only meaningful when the subroutine or
204 method is to be called by multiple threads. When set on a method
205 subroutine (i.e., one marked with the B<method> attribute below),
206 Perl ensures that any invocation of it implicitly locks its first
207 argument before execution. When set on a non-method subroutine,
208 Perl ensures that a lock is taken on the subroutine itself before
209 execution. The semantics of the lock are exactly those of one
210 explicitly taken with the C<lock> operator immediately after the
211 subroutine is entered.
215 Indicates that the referenced subroutine is a method.
216 This has a meaning when taken together with the B<locked> attribute,
217 as described there. It also means that a subroutine so marked
218 will not trigger the "Ambiguous call resolved as CORE::%s" warning.
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>.
228 For global variables there is C<unique> attribute: see L<perlfunc/our>.
230 =head2 Available Subroutines
232 The following subroutines are available for general use once this module
239 This routine expects a single parameter--a reference to a
240 subroutine or variable. It returns a list of attributes, which may be
241 empty. If passed invalid arguments, it uses die() (via L<Carp::croak|Carp>)
242 to raise a fatal exception. If it can find an appropriate package name
243 for a class method lookup, it will include the results from a
244 C<FETCH_I<type>_ATTRIBUTES> call in its return list, as described in
245 L<"Package-specific Attribute Handling"> below.
246 Otherwise, only L<built-in attributes|"Built-in Attributes"> will be returned.
250 This routine expects a single parameter--a reference to a subroutine or
251 variable. It returns the built-in type of the referenced variable,
252 ignoring any package into which it might have been blessed.
253 This can be useful for determining the I<type> value which forms part of
254 the method names described in L<"Package-specific Attribute Handling"> below.
258 Note that these routines are I<not> exported by default.
260 =head2 Package-specific Attribute Handling
262 B<WARNING>: the mechanisms described here are still experimental. Do not
263 rely on the current implementation. In particular, there is no provision
264 for applying package attributes to 'cloned' copies of subroutines used as
265 closures. (See L<perlref/"Making References"> for information on closures.)
266 Package-specific attribute handling may change incompatibly in a future
269 When an attribute list is present in a declaration, a check is made to see
270 whether an attribute 'modify' handler is present in the appropriate package
271 (or its @ISA inheritance tree). Similarly, when C<attributes::get> is
272 called on a valid reference, a check is made for an appropriate attribute
273 'fetch' handler. See L<"EXAMPLES"> to see how the "appropriate package"
276 The handler names are based on the underlying type of the variable being
277 declared or of the reference passed. Because these attributes are
278 associated with subroutine or variable declarations, this deliberately
279 ignores any possibility of being blessed into some package. Thus, a
280 subroutine declaration uses "CODE" as its I<type>, and even a blessed
281 hash reference uses "HASH" as its I<type>.
283 The class methods invoked for modifying and fetching are these:
287 =item FETCH_I<type>_ATTRIBUTES
289 This method is called with two arguments: the relevant package name,
290 and a reference to a variable or subroutine for which package-defined
291 attributes are desired. The expected return value is a list of
292 associated attributes. This list may be empty.
294 =item MODIFY_I<type>_ATTRIBUTES
296 This method is called with two fixed arguments, followed by the list of
297 attributes from the relevant declaration. The two fixed arguments are
298 the relevant package name and a reference to the declared subroutine or
299 variable. The expected return value is a list of attributes which were
300 not recognized by this handler. Note that this allows for a derived class
301 to delegate a call to its base class, and then only examine the attributes
302 which the base class didn't already handle for it.
304 The call to this method is currently made I<during> the processing of the
305 declaration. In particular, this means that a subroutine reference will
306 probably be for an undefined subroutine, even if this declaration is
307 actually part of the definition.
311 Calling C<attributes::get()> from within the scope of a null package
312 declaration C<package ;> for an unblessed variable reference will
313 not provide any starting package name for the 'fetch' method lookup.
314 Thus, this circumstance will not result in a method call for package-defined
315 attributes. A named subroutine knows to which symbol table entry it belongs
316 (or originally belonged), and it will use the corresponding package.
317 An anonymous subroutine knows the package name into which it was compiled
318 (unless it was also compiled with a null package declaration), and so it
319 will use that package name.
321 =head2 Syntax of Attribute Lists
323 An attribute list is a sequence of attribute specifications, separated by
324 whitespace or a colon (with optional whitespace).
325 Each attribute specification is a simple
326 name, optionally followed by a parenthesised parameter list.
327 If such a parameter list is present, it is scanned past as for the rules
328 for the C<q()> operator. (See L<perlop/"Quote and Quote-like Operators">.)
329 The parameter list is passed as it was found, however, and not as per C<q()>.
331 Some examples of syntactically valid attribute lists:
333 switch(10,foo(7,3)) : expensive
338 Some examples of syntactically invalid attribute lists (with annotation):
340 switch(10,foo() # ()-string not balanced
341 Ugly('(') # ()-string not balanced
342 5x5 # "5x5" not a valid identifier
343 Y2::north # "Y2::north" not a simple identifier
344 foo + bar # "+" neither a colon nor whitespace
348 =head2 Default exports
352 =head2 Available exports
354 The routines C<get> and C<reftype> are exportable.
356 =head2 Export tags defined
358 The C<:ALL> tag will get all of the above exports.
362 Here are some samples of syntactically valid declarations, with annotation
363 as to how they resolve internally into C<use attributes> invocations by
364 perl. These examples are primarily useful to see how the "appropriate
365 package" is found for the possible method lookups for package-defined
376 my Canine $spot : Watchful ;
381 attributes::->import(Canine => \$spot, "Watchful");
393 attributes::->import(Felis => \$cat, "Nervous");
404 use attributes X => \&foo, "locked";
411 sub Y::x : locked { 1 }
415 use attributes Y => \&Y::x, "locked";
425 BEGIN { *bar = \&X::foo; }
428 sub Y::bar : locked ;
432 use attributes X => \&X::foo, "locked";
436 This last example is purely for purposes of completeness. You should not
437 be trying to mess with the attributes of something in a package that's
446 sub MODIFY_CODE_ATTRIBUTES {
447 my ($class,$code,@attrs) = @_;
449 my $allowed = 'MyAttribute';
450 my @bad = grep { $_ ne $allowed } @attrs;
455 sub foo : MyAttribute {
459 This example runs. At compile time C<MODIFY_CODE_ATTRIBUTES> is called. In that
460 subroutine, we check if any attribute is disallowed and we return a list of
461 these "bad attributes".
463 As we return an empty list, everything is fine.
467 sub MODIFY_CODE_ATTRIBUTES {
468 my ($class,$code,@attrs) = @_;
470 my $allowed = 'MyAttribute';
471 my @bad = grep{ $_ ne $allowed }@attrs;
476 sub foo : MyAttribute Test {
480 This example is aborted at compile time as we use the attribute "Test" which
481 isn't allowed. C<MODIFY_CODE_ATTRIBUTES> returns a list that contains a single
488 L<perlsub/"Private Variables via my()"> and
489 L<perlsub/"Subroutine Attributes"> for details on the basic declarations;
490 L<attrs> for the obsolescent form of subroutine attribute specification
491 which this module replaces;
492 L<perlfunc/use> for details on the normal invocation mechanism.