1 package Attribute::Handlers;
6 use vars qw($VERSION $AUTOLOAD);
7 $VERSION = '0.87'; # remember to update version in POD!
12 my ($pkg, $ref, $type) = @_;
13 return $symcache{$pkg,$ref} if $symcache{$pkg,$ref};
16 foreach my $sym ( values %{$pkg."::"} ) {
18 next unless ref ( \$sym ) eq 'GLOB';
19 return $symcache{$pkg,$ref} = \$sym
20 if *{$sym}{$type} && *{$sym}{$type} == $ref;
25 VAR => [qw[SCALAR ARRAY HASH]],
26 ANY => [qw[SCALAR ARRAY HASH CODE]],
27 "" => [qw[SCALAR ARRAY HASH CODE]],
28 SCALAR => [qw[SCALAR]],
37 my %sigil = (SCALAR=>'$', ARRAY=>'@', HASH=>'%');
45 my @global_phases = qw(BEGIN CHECK INIT END);
48 croak "Usage: use $_[0] autotie => {AttrName => TieClassName,...}";
51 my $qual_id = qr/^[_a-z]\w*(::[_a-z]\w*)*$/i;
55 return unless $class eq "Attribute::Handlers";
58 if ($cmd =~ /^autotie((?:ref)?)$/) {
59 my $tiedata = ($1 ? '$ref, ' : '') . '@$data';
61 _usage_AH_ $class unless ref($mapping) eq 'HASH';
62 while (my($attr, $tieclass) = each %$mapping) {
63 $tieclass =~ s/^([_a-z]\w*(::[_a-z]\w*)*)(.*)/$1/is;
65 _usage_AH_ $class unless $attr =~ $qual_id
66 && $tieclass =~ $qual_id
67 && eval "use base q\0$tieclass\0; 1";
68 if ($tieclass->isa('Exporter')) {
69 local $Exporter::ExportLevel = 2;
70 $tieclass->import(eval $args);
72 $attr =~ s/__CALLER__/caller(1)/e;
73 $attr = caller()."::".$attr unless $attr =~ /::/;
75 sub $attr : ATTR(VAR) {
76 my (\$ref, \$data) = \@_[2,4];
77 my \$was_arrayref = ref \$data eq 'ARRAY';
78 \$data = [ \$data ] unless \$was_arrayref;
79 my \$type = ref(\$ref)||"value (".(\$ref||"<undef>").")";
80 (\$type eq 'SCALAR')? tie \$\$ref,'$tieclass',$tiedata
81 :(\$type eq 'ARRAY') ? tie \@\$ref,'$tieclass',$tiedata
82 :(\$type eq 'HASH') ? tie \%\$ref,'$tieclass',$tiedata
83 : die "Can't autotie a \$type\n"
85 } or die "Internal error: $@";
89 croak "Can't understand $_";
94 # On older perls, code attribute handlers run before the sub gets placed
95 # in its package. Since the :ATTR handlers need to know the name of the
96 # sub they're applied to, the name lookup (via findsym) needs to be
97 # delayed: we do it immediately before we might need to find attribute
98 # handlers from their name. However, on newer perls (which fix some
99 # problems relating to attribute application), a sub gets placed in its
100 # package before its attributes are processed. In this case, the
101 # delayed name lookup might be too late, because the sub we're looking
102 # for might have already been replaced. So we need to detect which way
103 # round this perl does things, and time the name lookup accordingly.
106 sub Attribute::Handlers::_TEST_::MODIFY_CODE_ATTRIBUTES {
107 $delayed = \&Attribute::Handlers::_TEST_::t != $_[1];
110 sub Attribute::Handlers::_TEST_::t :T { }
111 *_delayed_name_resolution = sub() { $delayed };
112 undef &Attribute::Handlers::_TEST_::MODIFY_CODE_ATTRIBUTES;
113 undef &Attribute::Handlers::_TEST_::t;
116 sub _resolve_lastattr {
117 return unless $lastattr{ref};
118 my $sym = findsym @lastattr{'pkg','ref'}
119 or die "Internal error: $lastattr{pkg} symbol went missing";
120 my $name = *{$sym}{NAME};
121 warn "Declaration of $name attribute in package $lastattr{pkg} may clash with future reserved word\n"
122 if $^W and $name !~ /[A-Z]/;
123 foreach ( @{$validtype{$lastattr{type}}} ) {
125 *{"$lastattr{pkg}::_ATTR_${_}_${name}"} = $lastattr{ref};
131 return if $AUTOLOAD =~ /::DESTROY$/;
132 my ($class) = $AUTOLOAD =~ m/(.*)::/g;
133 $AUTOLOAD =~ m/_ATTR_(.*?)_(.*)/ or
134 croak "Can't locate class method '$AUTOLOAD' via package '$class'";
135 croak "Attribute handler '$2' doesn't handle $1 attributes";
138 my $builtin = qr/lvalue|method|locked|unique|shared/;
140 sub _gen_handler_AH_() {
142 _resolve_lastattr if _delayed_name_resolution;
143 my ($pkg, $ref, @attrs) = @_;
144 my (undef, $filename, $linenum) = caller 2;
146 my ($attr, $data) = /^([a-z_]\w*)(?:[(](.*)[)])?$/is or next;
147 if ($attr eq 'ATTR') {
150 $raw{$ref} = $data =~ s/\s*,?\s*RAWDATA\s*,?\s*//;
151 $phase{$ref}{BEGIN} = 1
152 if $data =~ s/\s*,?\s*(BEGIN)\s*,?\s*//;
153 $phase{$ref}{INIT} = 1
154 if $data =~ s/\s*,?\s*(INIT)\s*,?\s*//;
155 $phase{$ref}{END} = 1
156 if $data =~ s/\s*,?\s*(END)\s*,?\s*//;
157 $phase{$ref}{CHECK} = 1
158 if $data =~ s/\s*,?\s*(CHECK)\s*,?\s*//
159 || ! keys %{$phase{$ref}};
160 # Added for cleanup to not pollute next call.
162 croak "Can't have two ATTR specifiers on one subroutine"
164 croak "Bad attribute type: ATTR($data)"
165 unless $validtype{$data};
166 %lastattr=(pkg=>$pkg,ref=>$ref,type=>$data);
167 _resolve_lastattr unless _delayed_name_resolution;
171 my $handler = $pkg->can("_ATTR_${type}_${attr}");
172 next unless $handler;
173 my $decl = [$pkg, $ref, $attr, $data,
174 $raw{$handler}, $phase{$handler}, $filename, $linenum];
175 foreach my $gphase (@global_phases) {
176 _apply_handler_AH_($decl,$gphase)
177 if $global_phases{$gphase} <= $global_phase;
179 if ($global_phase != 0) {
180 # if _gen_handler_AH_ is being called after
181 # CHECK it's for a lexical, so make sure
182 # it didn't want to run anything later
184 local $Carp::CarpLevel = 2;
185 carp "Won't be able to apply END handler"
186 if $phase{$handler}{END};
189 push @declarations, $decl
194 return grep {defined && !/$builtin/} @attrs;
200 *{"Attribute::Handlers::UNIVERSAL::MODIFY_${_}_ATTRIBUTES"} =
201 _gen_handler_AH_ foreach @{$validtype{ANY}};
203 push @UNIVERSAL::ISA, 'Attribute::Handlers::UNIVERSAL'
204 unless grep /^Attribute::Handlers::UNIVERSAL$/, @UNIVERSAL::ISA;
206 sub _apply_handler_AH_ {
207 my ($declaration, $phase) = @_;
208 my ($pkg, $ref, $attr, $data, $raw, $handlerphase, $filename, $linenum) = @$declaration;
209 return unless $handlerphase->{$phase};
210 # print STDERR "Handling $attr on $ref in $phase with [$data]\n";
212 my $handler = "_ATTR_${type}_${attr}";
213 my $sym = findsym($pkg, $ref);
214 $sym ||= $type eq 'CODE' ? 'ANON' : 'LEXICAL';
216 if (!$raw && defined($data)) {
218 my $evaled = eval("package $pkg; no warnings; no strict;
219 local \$SIG{__WARN__}=sub{die}; [$data]");
220 $data = $evaled unless $@;
222 else { $data = undef }
225 (ref $sym eq 'GLOB' ? *{$sym}{ref $ref}||$ref : $ref),
239 _resolve_lastattr if _delayed_name_resolution;
240 _apply_handler_AH_($_,'CHECK') foreach @declarations;
245 _apply_handler_AH_($_,'INIT') foreach @declarations
249 END { $global_phase++; _apply_handler_AH_($_,'END') foreach @declarations }
256 Attribute::Handlers - Simpler definition of attribute handlers
260 This document describes version 0.87 of Attribute::Handlers,
261 released September 21, 2009.
267 use Attribute::Handlers;
268 no warnings 'redefine';
271 sub Good : ATTR(SCALAR) {
272 my ($package, $symbol, $referent, $attr, $data) = @_;
274 # Invoked for any scalar variable with a :Good attribute,
275 # provided the variable was declared in MyClass (or
276 # a derived class) or typed to MyClass.
278 # Do whatever to $referent here (executed in CHECK phase).
282 sub Bad : ATTR(SCALAR) {
283 # Invoked for any scalar variable with a :Bad attribute,
284 # provided the variable was declared in MyClass (or
285 # a derived class) or typed to MyClass.
289 sub Good : ATTR(ARRAY) {
290 # Invoked for any array variable with a :Good attribute,
291 # provided the variable was declared in MyClass (or
292 # a derived class) or typed to MyClass.
296 sub Good : ATTR(HASH) {
297 # Invoked for any hash variable with a :Good attribute,
298 # provided the variable was declared in MyClass (or
299 # a derived class) or typed to MyClass.
303 sub Ugly : ATTR(CODE) {
304 # Invoked for any subroutine declared in MyClass (or a
305 # derived class) with an :Ugly attribute.
310 # Invoked for any scalar, array, hash, or subroutine
311 # with an :Omni attribute, provided the variable or
312 # subroutine was declared in MyClass (or a derived class)
313 # or the variable was typed to MyClass.
314 # Use ref($_[2]) to determine what kind of referent it was.
319 use Attribute::Handlers autotie => { Cycle => Tie::Cycle };
321 my $next : Cycle(['A'..'Z']);
326 This module, when inherited by a package, allows that package's class to
327 define attribute handler subroutines for specific attributes. Variables
328 and subroutines subsequently defined in that package, or in packages
329 derived from that package may be given attributes with the same names as
330 the attribute handler subroutines, which will then be called in one of
331 the compilation phases (i.e. in a C<BEGIN>, C<CHECK>, C<INIT>, or C<END>
332 block). (C<UNITCHECK> blocks don't correspond to a global compilation
333 phase, so they can't be specified here.)
335 To create a handler, define it as a subroutine with the same name as
336 the desired attribute, and declare the subroutine itself with the
337 attribute C<:ATTR>. For example:
340 use Attribute::Handlers;
343 my ($package, $symbol, $referent, $attr, $data, $phase, $filename, $linenum) = @_;
346 *{$symbol}{NAME}, " ",
347 "($referent) ", "was just declared ",
348 "and ascribed the ${attr} attribute ",
349 "with data ($data)\n",
351 "in file $filename at line $linenum\n";
354 This creates a handler for the attribute C<:Loud> in the class LoudDecl.
355 Thereafter, any subroutine declared with a C<:Loud> attribute in the class
362 causes the above handler to be invoked, and passed:
368 the name of the package into which it was declared;
372 a reference to the symbol table entry (typeglob) containing the subroutine;
376 a reference to the subroutine;
380 the name of the attribute;
384 any data associated with that attribute;
388 the name of the phase in which the handler is being invoked;
392 the filename in which the handler is being invoked;
396 the line number in this file.
400 Likewise, declaring any variables with the C<:Loud> attribute within the
409 will cause the handler to be called with a similar argument list (except,
410 of course, that C<$_[2]> will be a reference to the variable).
412 The package name argument will typically be the name of the class into
413 which the subroutine was declared, but it may also be the name of a derived
414 class (since handlers are inherited).
416 If a lexical variable is given an attribute, there is no symbol table to
417 which it belongs, so the symbol table argument (C<$_[1]>) is set to the
418 string C<'LEXICAL'> in that case. Likewise, ascribing an attribute to
419 an anonymous subroutine results in a symbol table argument of C<'ANON'>.
421 The data argument passes in the value (if any) associated with the
422 attribute. For example, if C<&foo> had been declared:
424 sub foo :Loud("turn it up to 11, man!") {...}
426 then a reference to an array containing the string
427 C<"turn it up to 11, man!"> would be passed as the last argument.
429 Attribute::Handlers makes strenuous efforts to convert
430 the data argument (C<$_[4]>) to a useable form before passing it to
431 the handler (but see L<"Non-interpretive attribute handlers">).
432 If those efforts succeed, the interpreted data is passed in an array
433 reference; if they fail, the raw data is passed as a string.
434 For example, all of these:
436 sub foo :Loud(till=>ears=>are=>bleeding) {...}
437 sub foo :Loud(qw/till ears are bleeding/) {...}
438 sub foo :Loud(qw/my, ears, are, bleeding/) {...}
439 sub foo :Loud(till,ears,are,bleeding) {...}
441 causes it to pass C<['till','ears','are','bleeding']> as the handler's
442 data argument. While:
444 sub foo :Loud(['till','ears','are','bleeding']) {...}
446 causes it to pass C<[ ['till','ears','are','bleeding'] ]>; the array
447 reference specified in the data being passed inside the standard
448 array reference indicating successful interpretation.
450 However, if the data can't be parsed as valid Perl, then
451 it is passed as an uninterpreted string. For example:
453 sub foo :Loud(my,ears,are,bleeding) {...}
454 sub foo :Loud(qw/my ears are bleeding) {...}
456 cause the strings C<'my,ears,are,bleeding'> and
457 C<'qw/my ears are bleeding'> respectively to be passed as the
460 If no value is associated with the attribute, C<undef> is passed.
462 =head2 Typed lexicals
464 Regardless of the package in which it is declared, if a lexical variable is
465 ascribed an attribute, the handler that is invoked is the one belonging to
466 the package to which it is typed. For example, the following declarations:
470 my LoudDecl $loudobj : Loud;
471 my LoudDecl @loudobjs : Loud;
472 my LoudDecl %loudobjex : Loud;
474 causes the LoudDecl::Loud handler to be invoked (even if OtherClass also
475 defines a handler for C<:Loud> attributes).
478 =head2 Type-specific attribute handlers
480 If an attribute handler is declared and the C<:ATTR> specifier is
481 given the name of a built-in type (C<SCALAR>, C<ARRAY>, C<HASH>, or C<CODE>),
482 the handler is only applied to declarations of that type. For example,
483 the following definition:
487 sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" }
489 creates an attribute handler that applies only to scalars:
495 my $metal : RealLoud; # invokes &LoudDecl::RealLoud
496 my @metal : RealLoud; # error: unknown attribute
497 my %metal : RealLoud; # error: unknown attribute
498 sub metal : RealLoud {...} # error: unknown attribute
500 You can, of course, declare separate handlers for these types as well
501 (but you'll need to specify C<no warnings 'redefine'> to do it quietly):
504 use Attribute::Handlers;
505 no warnings 'redefine';
507 sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" }
508 sub RealLoud :ATTR(ARRAY) { print "Urrrrrrrrrr!" }
509 sub RealLoud :ATTR(HASH) { print "Arrrrrgggghhhhhh!" }
510 sub RealLoud :ATTR(CODE) { croak "Real loud sub torpedoed" }
512 You can also explicitly indicate that a single handler is meant to be
513 used for all types of referents like so:
516 use Attribute::Handlers;
518 sub SeriousLoud :ATTR(ANY) { warn "Hearing loss imminent" }
520 (I.e. C<ATTR(ANY)> is a synonym for C<:ATTR>).
523 =head2 Non-interpretive attribute handlers
525 Occasionally the strenuous efforts Attribute::Handlers makes to convert
526 the data argument (C<$_[4]>) to a useable form before passing it to
527 the handler get in the way.
529 You can turn off that eagerness-to-help by declaring
530 an attribute handler with the keyword C<RAWDATA>. For example:
532 sub Raw : ATTR(RAWDATA) {...}
533 sub Nekkid : ATTR(SCALAR,RAWDATA) {...}
534 sub Au::Naturale : ATTR(RAWDATA,ANY) {...}
536 Then the handler makes absolutely no attempt to interpret the data it
537 receives and simply passes it as a string:
539 my $power : Raw(1..100); # handlers receives "1..100"
541 =head2 Phase-specific attribute handlers
543 By default, attribute handlers are called at the end of the compilation
544 phase (in a C<CHECK> block). This seems to be optimal in most cases because
545 most things that can be defined are defined by that point but nothing has
548 However, it is possible to set up attribute handlers that are called at
549 other points in the program's compilation or execution, by explicitly
550 stating the phase (or phases) in which you wish the attribute handler to
551 be called. For example:
553 sub Early :ATTR(SCALAR,BEGIN) {...}
554 sub Normal :ATTR(SCALAR,CHECK) {...}
555 sub Late :ATTR(SCALAR,INIT) {...}
556 sub Final :ATTR(SCALAR,END) {...}
557 sub Bookends :ATTR(SCALAR,BEGIN,END) {...}
559 As the last example indicates, a handler may be set up to be (re)called in
560 two or more phases. The phase name is passed as the handler's final argument.
562 Note that attribute handlers that are scheduled for the C<BEGIN> phase
563 are handled as soon as the attribute is detected (i.e. before any
564 subsequently defined C<BEGIN> blocks are executed).
567 =head2 Attributes as C<tie> interfaces
569 Attributes make an excellent and intuitive interface through which to tie
570 variables. For example:
572 use Attribute::Handlers;
575 sub UNIVERSAL::Cycle : ATTR(SCALAR) {
576 my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
577 $data = [ $data ] unless ref $data eq 'ARRAY';
578 tie $$referent, 'Tie::Cycle', $data;
585 my $next : Cycle('A'..'Z'); # $next is now a tied variable
591 Note that, because the C<Cycle> attribute receives its arguments in the
592 C<$data> variable, if the attribute is given a list of arguments, C<$data>
593 will consist of a single array reference; otherwise, it will consist of the
594 single argument directly. Since Tie::Cycle requires its cycling values to
595 be passed as an array reference, this means that we need to wrap
596 non-array-reference arguments in an array constructor:
598 $data = [ $data ] unless ref $data eq 'ARRAY';
600 Typically, however, things are the other way around: the tieable class expects
601 its arguments as a flattened list, so the attribute looks like:
603 sub UNIVERSAL::Cycle : ATTR(SCALAR) {
604 my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
605 my @data = ref $data eq 'ARRAY' ? @$data : $data;
606 tie $$referent, 'Tie::Whatever', @data;
610 This software pattern is so widely applicable that Attribute::Handlers
611 provides a way to automate it: specifying C<'autotie'> in the
612 C<use Attribute::Handlers> statement. So, the cycling example,
613 could also be written:
615 use Attribute::Handlers autotie => { Cycle => 'Tie::Cycle' };
621 my $next : Cycle(['A'..'Z']); # $next is now a tied variable
626 Note that we now have to pass the cycling values as an array reference,
627 since the C<autotie> mechanism passes C<tie> a list of arguments as a list
628 (as in the Tie::Whatever example), I<not> as an array reference (as in
629 the original Tie::Cycle example at the start of this section).
631 The argument after C<'autotie'> is a reference to a hash in which each key is
632 the name of an attribute to be created, and each value is the class to which
633 variables ascribed that attribute should be tied.
635 Note that there is no longer any need to import the Tie::Cycle module --
636 Attribute::Handlers takes care of that automagically. You can even pass
637 arguments to the module's C<import> subroutine, by appending them to the
638 class name. For example:
640 use Attribute::Handlers
641 autotie => { Dir => 'Tie::Dir qw(DIR_UNLINK)' };
643 If the attribute name is unqualified, the attribute is installed in the
644 current package. Otherwise it is installed in the qualifier's package:
648 use Attribute::Handlers autotie => {
649 Other::Good => Tie::SecureHash, # tie attr installed in Other::
650 Bad => Tie::Taxes, # tie attr installed in Here::
651 UNIVERSAL::Ugly => Software::Patent # tie attr installed everywhere
654 Autoties are most commonly used in the module to which they actually tie,
655 and need to export their attributes to any module that calls them. To
656 facilitate this, Attribute::Handlers recognizes a special "pseudo-class" --
657 C<__CALLER__>, which may be specified as the qualifier of an attribute:
659 package Tie::Me::Kangaroo:Down::Sport;
661 use Attribute::Handlers autotie => { '__CALLER__::Roo' => __PACKAGE__ };
663 This causes Attribute::Handlers to define the C<Roo> attribute in the package
664 that imports the Tie::Me::Kangaroo:Down::Sport module.
666 Note that it is important to quote the __CALLER__::Roo identifier because
667 a bug in perl 5.8 will refuse to parse it and cause an unknown error.
669 =head3 Passing the tied object to C<tie>
671 Occasionally it is important to pass a reference to the object being tied
672 to the TIESCALAR, TIEHASH, etc. that ties it.
674 The C<autotie> mechanism supports this too. The following code:
676 use Attribute::Handlers autotieref => { Selfish => Tie::Selfish };
677 my $var : Selfish(@args);
679 has the same effect as:
681 tie my $var, 'Tie::Selfish', @args;
683 But when C<"autotieref"> is used instead of C<"autotie">:
685 use Attribute::Handlers autotieref => { Selfish => Tie::Selfish };
686 my $var : Selfish(@args);
688 the effect is to pass the C<tie> call an extra reference to the variable
691 tie my $var, 'Tie::Selfish', \$var, @args;
697 If the class shown in L<SYNOPSIS> were placed in the MyClass.pm
698 module, then the following code:
703 my MyClass $slr :Good :Bad(1**1-1) :Omni(-vorous);
705 package SomeOtherClass;
710 sub fn :Ugly(sister) :Omni('po',tent()) {...}
711 my @arr :Good :Omni(s/cie/nt/);
712 my %hsh :Good(q/bye/) :Omni(q/bus/);
715 would cause the following handlers to be invoked:
717 # my MyClass $slr :Good :Bad(1**1-1) :Omni(-vorous);
719 MyClass::Good:ATTR(SCALAR)( 'MyClass', # class
720 'LEXICAL', # no typeglob
724 'CHECK', # compiler phase
727 MyClass::Bad:ATTR(SCALAR)( 'MyClass', # class
728 'LEXICAL', # no typeglob
732 'CHECK', # compiler phase
735 MyClass::Omni:ATTR(SCALAR)( 'MyClass', # class
736 'LEXICAL', # no typeglob
739 '-vorous' # eval'd attr data
740 'CHECK', # compiler phase
744 # sub fn :Ugly(sister) :Omni('po',tent()) {...}
746 MyClass::UGLY:ATTR(CODE)( 'SomeOtherClass', # class
747 \*SomeOtherClass::fn, # typeglob
748 \&SomeOtherClass::fn, # referent
750 'sister' # eval'd attr data
751 'CHECK', # compiler phase
754 MyClass::Omni:ATTR(CODE)( 'SomeOtherClass', # class
755 \*SomeOtherClass::fn, # typeglob
756 \&SomeOtherClass::fn, # referent
758 ['po','acle'] # eval'd attr data
759 'CHECK', # compiler phase
763 # my @arr :Good :Omni(s/cie/nt/);
765 MyClass::Good:ATTR(ARRAY)( 'SomeOtherClass', # class
766 'LEXICAL', # no typeglob
770 'CHECK', # compiler phase
773 MyClass::Omni:ATTR(ARRAY)( 'SomeOtherClass', # class
774 'LEXICAL', # no typeglob
777 "" # eval'd attr data
778 'CHECK', # compiler phase
782 # my %hsh :Good(q/bye) :Omni(q/bus/);
784 MyClass::Good:ATTR(HASH)( 'SomeOtherClass', # class
785 'LEXICAL', # no typeglob
788 'q/bye' # raw attr data
789 'CHECK', # compiler phase
792 MyClass::Omni:ATTR(HASH)( 'SomeOtherClass', # class
793 'LEXICAL', # no typeglob
796 'bus' # eval'd attr data
797 'CHECK', # compiler phase
801 Installing handlers into UNIVERSAL, makes them...err..universal.
804 package Descriptions;
805 use Attribute::Handlers;
808 sub name { return $name{$_[2]}||*{$_[1]}{NAME} }
810 sub UNIVERSAL::Name :ATTR {
811 $name{$_[2]} = $_[4];
814 sub UNIVERSAL::Purpose :ATTR {
815 print STDERR "Purpose of ", &name, " is $_[4]\n";
818 sub UNIVERSAL::Unit :ATTR {
819 print STDERR &name, " measured in $_[4]\n";
826 my $capacity : Name(capacity)
827 : Purpose(to store max storage capacity for files)
833 sub foo : Purpose(to foo all data before barring it) { }
837 =head1 UTILITY FUNCTIONS
839 This module offers a single utility function, C<findsym()>.
845 my $symbol = Attribute::Handlers::findsym($package, $referent);
847 The function looks in the symbol table of C<$package> for the typeglob for
848 C<$referent>, which is a reference to a variable or subroutine (SCALAR, ARRAY,
849 HASH, or CODE). If it finds the typeglob, it returns it. Otherwise, it returns
850 undef. Note that C<findsym> memoizes the typeglobs it has previously
851 successfully found, so subsequent calls with the same arguments should be
860 =item C<Bad attribute type: ATTR(%s)>
862 An attribute handler was specified with an C<:ATTR(I<ref_type>)>, but the
863 type of referent it was defined to handle wasn't one of the five permitted:
864 C<SCALAR>, C<ARRAY>, C<HASH>, C<CODE>, or C<ANY>.
866 =item C<Attribute handler %s doesn't handle %s attributes>
868 A handler for attributes of the specified name I<was> defined, but not
869 for the specified type of declaration. Typically encountered whe trying
870 to apply a C<VAR> attribute handler to a subroutine, or a C<SCALAR>
871 attribute handler to some other type of variable.
873 =item C<Declaration of %s attribute in package %s may clash with future reserved word>
875 A handler for an attributes with an all-lowercase name was declared. An
876 attribute with an all-lowercase name might have a meaning to Perl
877 itself some day, even though most don't yet. Use a mixed-case attribute
880 =item C<Can't have two ATTR specifiers on one subroutine>
882 You just can't, okay?
883 Instead, put all the specifications together with commas between them
884 in a single C<ATTR(I<specification>)>.
886 =item C<Can't autotie a %s>
888 You can only declare autoties for types C<"SCALAR">, C<"ARRAY">, and
889 C<"HASH">. They're the only things (apart from typeglobs -- which are
890 not declarable) that Perl can tie.
892 =item C<Internal error: %s symbol went missing>
894 Something is rotten in the state of the program. An attributed
895 subroutine ceased to exist between the point it was declared and the point
896 at which its attribute handler(s) would have been called.
898 =item C<Won't be able to apply END handler>
900 You have defined an END handler for an attribute that is being applied
901 to a lexical variable. Since the variable may not be available during END
908 Damian Conway (damian@conway.org). The maintainer of this module is now Rafael
909 Garcia-Suarez (rgarciasuarez@gmail.com).
911 Maintainer of the CPAN release is Steffen Mueller (smueller@cpan.org).
912 Contact him with technical difficulties with respect to the packaging of the
917 There are undoubtedly serious bugs lurking somewhere in code this funky :-)
918 Bug reports and other feedback are most welcome.
920 =head1 COPYRIGHT AND LICENSE
922 Copyright (c) 2001-2009, Damian Conway. All Rights Reserved.
923 This module is free software. It may be used, redistributed
924 and/or modified under the same terms as Perl itself.