1 package Attribute::Handlers;
10 my ($pkg, $ref, $type) = @_;
11 return $symcache{$pkg,$ref} if $symcache{$pkg,$ref};
14 foreach my $sym ( values %{$pkg."::"} ) {
15 return $symcache{$pkg,$ref} = \$sym
16 if *{$sym}{$type} && *{$sym}{$type} == $ref;
21 VAR => [qw[SCALAR ARRAY HASH]],
22 ANY => [qw[SCALAR ARRAY HASH CODE]],
23 "" => [qw[SCALAR ARRAY HASH CODE]],
24 SCALAR => [qw[SCALAR]],
33 my %sigil = (SCALAR=>'$', ARRAY=>'@', HASH=>'%');
41 my @global_phases = qw(BEGIN CHECK INIT END);
44 croak "Usage: use $_[0] autotie => {AttrName => TieClassName,...}";
47 my $qual_id = qr/^[_a-z]\w*(::[_a-z]\w*)*$/i;
51 return unless $class eq "Attribute::Handlers";
54 if ($cmd =~ /^autotie((?:ref)?)$/) {
55 my $tiedata = ($1 ? '$ref, ' : '') . '@$data';
57 _usage_AH_ $class unless ref($mapping) eq 'HASH';
58 while (my($attr, $tieclass) = each %$mapping) {
59 $tieclass =~ s/^([_a-z]\w*(::[_a-z]\w*)*)(.*)/$1/is;
61 _usage_AH_ $class unless $attr =~ $qual_id
62 && $tieclass =~ $qual_id
63 && eval "use base $tieclass; 1";
64 if ($tieclass->isa('Exporter')) {
65 local $Exporter::ExportLevel = 2;
66 $tieclass->import(eval $args);
68 $attr =~ s/__CALLER__/caller(1)/e;
69 $attr = caller()."::".$attr unless $attr =~ /::/;
71 sub $attr : ATTR(VAR) {
72 my (\$ref, \$data) = \@_[2,4];
73 my \$was_arrayref = ref \$data eq 'ARRAY';
74 \$data = [ \$data ] unless \$was_arrayref;
75 my \$type = ref(\$ref)||"value (".(\$ref||"<undef>").")";
76 (\$type eq 'SCALAR')? tie \$\$ref,'$tieclass',$tiedata
77 :(\$type eq 'ARRAY') ? tie \@\$ref,'$tieclass',$tiedata
78 :(\$type eq 'HASH') ? tie \%\$ref,'$tieclass',$tiedata
79 : die "Can't autotie a \$type\n"
81 } or die "Internal error: $@";
85 croak "Can't understand $_";
89 sub _resolve_lastattr {
90 return unless $lastattr{ref};
91 my $sym = findsym @lastattr{'pkg','ref'}
92 or die "Internal error: $lastattr{pkg} symbol went missing";
93 my $name = *{$sym}{NAME};
94 warn "Declaration of $name attribute in package $lastattr{pkg} may clash with future reserved word\n"
95 if $^W and $name !~ /[A-Z]/;
96 foreach ( @{$validtype{$lastattr{type}}} ) {
97 *{"$lastattr{pkg}::_ATTR_${_}_${name}"} = $lastattr{ref};
103 my ($class) = $AUTOLOAD =~ m/(.*)::/g;
104 $AUTOLOAD =~ m/_ATTR_(.*?)_(.*)/ or
105 croak "Can't locate class method '$AUTOLOAD' via package '$class'";
106 croak "Attribute handler '$3' doesn't handle $2 attributes";
111 my $builtin = qr/lvalue|method|locked/;
113 sub _gen_handler_AH_() {
116 my ($pkg, $ref, @attrs) = @_;
118 my ($attr, $data) = /^([a-z_]\w*)(?:[(](.*)[)])?$/is or next;
119 if ($attr eq 'ATTR') {
121 $raw{$ref} = $data =~ s/\s*,?\s*RAWDATA\s*,?\s*//;
122 $phase{$ref}{BEGIN} = 1
123 if $data =~ s/\s*,?\s*(BEGIN)\s*,?\s*//;
124 $phase{$ref}{INIT} = 1
125 if $data =~ s/\s*,?\s*(INIT)\s*,?\s*//;
126 $phase{$ref}{END} = 1
127 if $data =~ s/\s*,?\s*(END)\s*,?\s*//;
128 $phase{$ref}{CHECK} = 1
129 if $data =~ s/\s*,?\s*(CHECK)\s*,?\s*//
130 || ! keys %{$phase{$ref}};
131 # Added for cleanup to not pollute next call.
133 croak "Can't have two ATTR specifiers on one subroutine"
135 croak "Bad attribute type: ATTR($data)"
136 unless $validtype{$data};
137 %lastattr=(pkg=>$pkg,ref=>$ref,type=>$data);
140 my $handler = $pkg->can($attr);
141 next unless $handler;
142 my $decl = [$pkg, $ref, $attr, $data,
143 $raw{$handler}, $phase{$handler}];
144 foreach my $gphase (@global_phases) {
145 _apply_handler_AH_($decl,$gphase)
146 if $global_phases{$gphase} <= $global_phase;
148 push @declarations, $decl;
152 return grep {defined && !/$builtin/} @attrs;
156 *{"MODIFY_${_}_ATTRIBUTES"} = _gen_handler_AH_ foreach @{$validtype{ANY}};
157 push @UNIVERSAL::ISA, 'Attribute::Handlers'
158 unless grep /^Attribute::Handlers$/, @UNIVERSAL::ISA;
160 sub _apply_handler_AH_ {
161 my ($declaration, $phase) = @_;
162 my ($pkg, $ref, $attr, $data, $raw, $handlerphase) = @$declaration;
163 return unless $handlerphase->{$phase};
164 # print STDERR "Handling $attr on $ref in $phase with [$data]\n";
166 my $handler = "_ATTR_${type}_${attr}";
167 my $sym = findsym($pkg, $ref);
168 $sym ||= $type eq 'CODE' ? 'ANON' : 'LEXICAL';
170 my $evaled = !$raw && eval("package $pkg; no warnings;
171 local \$SIG{__WARN__}=sub{die}; [$data]");
172 $data = ($evaled && $data =~ /^\s*\[/) ? [$evaled]
173 : ($evaled) ? $evaled
176 (ref $sym eq 'GLOB' ? *{$sym}{ref $ref}||$ref : $ref),
178 (@$data>1? $data : $data->[0]),
187 _apply_handler_AH_($_,'CHECK') foreach @declarations;
190 INIT { $global_phase++; _apply_handler_AH_($_,'INIT') foreach @declarations }
192 END { $global_phase++; _apply_handler_AH_($_,'END') foreach @declarations }
199 Attribute::Handlers - Simpler definition of attribute handlers
203 This document describes version 0.76 of Attribute::Handlers,
204 released November 15, 2001.
210 use Attribute::Handlers;
211 no warnings 'redefine';
214 sub Good : ATTR(SCALAR) {
215 my ($package, $symbol, $referent, $attr, $data) = @_;
217 # Invoked for any scalar variable with a :Good attribute,
218 # provided the variable was declared in MyClass (or
219 # a derived class) or typed to MyClass.
221 # Do whatever to $referent here (executed in CHECK phase).
225 sub Bad : ATTR(SCALAR) {
226 # Invoked for any scalar variable with a :Bad attribute,
227 # provided the variable was declared in MyClass (or
228 # a derived class) or typed to MyClass.
232 sub Good : ATTR(ARRAY) {
233 # Invoked for any array variable with a :Good attribute,
234 # provided the variable was declared in MyClass (or
235 # a derived class) or typed to MyClass.
239 sub Good : ATTR(HASH) {
240 # Invoked for any hash variable with a :Good attribute,
241 # provided the variable was declared in MyClass (or
242 # a derived class) or typed to MyClass.
246 sub Ugly : ATTR(CODE) {
247 # Invoked for any subroutine declared in MyClass (or a
248 # derived class) with an :Ugly attribute.
253 # Invoked for any scalar, array, hash, or subroutine
254 # with an :Omni attribute, provided the variable or
255 # subroutine was declared in MyClass (or a derived class)
256 # or the variable was typed to MyClass.
257 # Use ref($_[2]) to determine what kind of referent it was.
262 use Attribute::Handlers autotie => { Cycle => Tie::Cycle };
264 my $next : Cycle(['A'..'Z']);
269 This module, when inherited by a package, allows that package's class to
270 define attribute handler subroutines for specific attributes. Variables
271 and subroutines subsequently defined in that package, or in packages
272 derived from that package may be given attributes with the same names as
273 the attribute handler subroutines, which will then be called in one of
274 the compilation phases (i.e. in a C<BEGIN>, C<CHECK>, C<INIT>, or C<END>
277 To create a handler, define it as a subroutine with the same name as
278 the desired attribute, and declare the subroutine itself with the
279 attribute C<:ATTR>. For example:
282 use Attribute::Handlers;
285 my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
288 *{$symbol}{NAME}, " ",
289 "($referent) ", "was just declared ",
290 "and ascribed the ${attr} attribute ",
291 "with data ($data)\n",
295 This creates a handler for the attribute C<:Loud> in the class LoudDecl.
296 Thereafter, any subroutine declared with a C<:Loud> attribute in the class
303 causes the above handler to be invoked, and passed:
309 the name of the package into which it was declared;
313 a reference to the symbol table entry (typeglob) containing the subroutine;
317 a reference to the subroutine;
321 the name of the attribute;
325 any data associated with that attribute;
329 the name of the phase in which the handler is being invoked.
333 Likewise, declaring any variables with the C<:Loud> attribute within the
342 will cause the handler to be called with a similar argument list (except,
343 of course, that C<$_[2]> will be a reference to the variable).
345 The package name argument will typically be the name of the class into
346 which the subroutine was declared, but it may also be the name of a derived
347 class (since handlers are inherited).
349 If a lexical variable is given an attribute, there is no symbol table to
350 which it belongs, so the symbol table argument (C<$_[1]>) is set to the
351 string C<'LEXICAL'> in that case. Likewise, ascribing an attribute to
352 an anonymous subroutine results in a symbol table argument of C<'ANON'>.
354 The data argument passes in the value (if any) associated with the
355 attribute. For example, if C<&foo> had been declared:
357 sub foo :Loud("turn it up to 11, man!") {...}
359 then the string C<"turn it up to 11, man!"> would be passed as the
362 Attribute::Handlers makes strenuous efforts to convert
363 the data argument (C<$_[4]>) to a useable form before passing it to
364 the handler (but see L<"Non-interpretive attribute handlers">).
365 For example, all of these:
367 sub foo :Loud(till=>ears=>are=>bleeding) {...}
368 sub foo :Loud(['till','ears','are','bleeding']) {...}
369 sub foo :Loud(qw/till ears are bleeding/) {...}
370 sub foo :Loud(qw/my, ears, are, bleeding/) {...}
371 sub foo :Loud(till,ears,are,bleeding) {...}
373 causes it to pass C<['till','ears','are','bleeding']> as the handler's
374 data argument. However, if the data can't be parsed as valid Perl, then
375 it is passed as an uninterpreted string. For example:
377 sub foo :Loud(my,ears,are,bleeding) {...}
378 sub foo :Loud(qw/my ears are bleeding) {...}
380 cause the strings C<'my,ears,are,bleeding'> and C<'qw/my ears are bleeding'>
381 respectively to be passed as the data argument.
383 If the attribute has only a single associated scalar data value, that value is
384 passed as a scalar. If multiple values are associated, they are passed as an
385 array reference. If no value is associated with the attribute, C<undef> is
389 =head2 Typed lexicals
391 Regardless of the package in which it is declared, if a lexical variable is
392 ascribed an attribute, the handler that is invoked is the one belonging to
393 the package to which it is typed. For example, the following declarations:
397 my LoudDecl $loudobj : Loud;
398 my LoudDecl @loudobjs : Loud;
399 my LoudDecl %loudobjex : Loud;
401 causes the LoudDecl::Loud handler to be invoked (even if OtherClass also
402 defines a handler for C<:Loud> attributes).
405 =head2 Type-specific attribute handlers
407 If an attribute handler is declared and the C<:ATTR> specifier is
408 given the name of a built-in type (C<SCALAR>, C<ARRAY>, C<HASH>, or C<CODE>),
409 the handler is only applied to declarations of that type. For example,
410 the following definition:
414 sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" }
416 creates an attribute handler that applies only to scalars:
422 my $metal : RealLoud; # invokes &LoudDecl::RealLoud
423 my @metal : RealLoud; # error: unknown attribute
424 my %metal : RealLoud; # error: unknown attribute
425 sub metal : RealLoud {...} # error: unknown attribute
427 You can, of course, declare separate handlers for these types as well
428 (but you'll need to specify C<no warnings 'redefine'> to do it quietly):
431 use Attribute::Handlers;
432 no warnings 'redefine';
434 sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" }
435 sub RealLoud :ATTR(ARRAY) { print "Urrrrrrrrrr!" }
436 sub RealLoud :ATTR(HASH) { print "Arrrrrgggghhhhhh!" }
437 sub RealLoud :ATTR(CODE) { croak "Real loud sub torpedoed" }
439 You can also explicitly indicate that a single handler is meant to be
440 used for all types of referents like so:
443 use Attribute::Handlers;
445 sub SeriousLoud :ATTR(ANY) { warn "Hearing loss imminent" }
447 (I.e. C<ATTR(ANY)> is a synonym for C<:ATTR>).
450 =head2 Non-interpretive attribute handlers
452 Occasionally the strenuous efforts Attribute::Handlers makes to convert
453 the data argument (C<$_[4]>) to a useable form before passing it to
454 the handler get in the way.
456 You can turn off that eagerness-to-help by declaring
457 an attribute handler with the keyword C<RAWDATA>. For example:
459 sub Raw : ATTR(RAWDATA) {...}
460 sub Nekkid : ATTR(SCALAR,RAWDATA) {...}
461 sub Au::Naturale : ATTR(RAWDATA,ANY) {...}
463 Then the handler makes absolutely no attempt to interpret the data it
464 receives and simply passes it as a string:
466 my $power : Raw(1..100); # handlers receives "1..100"
468 =head2 Phase-specific attribute handlers
470 By default, attribute handlers are called at the end of the compilation
471 phase (in a C<CHECK> block). This seems to be optimal in most cases because
472 most things that can be defined are defined by that point but nothing has
475 However, it is possible to set up attribute handlers that are called at
476 other points in the program's compilation or execution, by explicitly
477 stating the phase (or phases) in which you wish the attribute handler to
478 be called. For example:
480 sub Early :ATTR(SCALAR,BEGIN) {...}
481 sub Normal :ATTR(SCALAR,CHECK) {...}
482 sub Late :ATTR(SCALAR,INIT) {...}
483 sub Final :ATTR(SCALAR,END) {...}
484 sub Bookends :ATTR(SCALAR,BEGIN,END) {...}
486 As the last example indicates, a handler may be set up to be (re)called in
487 two or more phases. The phase name is passed as the handler's final argument.
489 Note that attribute handlers that are scheduled for the C<BEGIN> phase
490 are handled as soon as the attribute is detected (i.e. before any
491 subsequently defined C<BEGIN> blocks are executed).
494 =head2 Attributes as C<tie> interfaces
496 Attributes make an excellent and intuitive interface through which to tie
497 variables. For example:
499 use Attribute::Handlers;
502 sub UNIVERSAL::Cycle : ATTR(SCALAR) {
503 my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
504 $data = [ $data ] unless ref $data eq 'ARRAY';
505 tie $$referent, 'Tie::Cycle', $data;
512 my $next : Cycle('A'..'Z'); # $next is now a tied variable
518 Note that, because the C<Cycle> attribute receives its arguments in the
519 C<$data> variable, if the attribute is given a list of arguments, C<$data>
520 will consist of a single array reference; otherwise, it will consist of the
521 single argument directly. Since Tie::Cycle requires its cycling values to
522 be passed as an array reference, this means that we need to wrap
523 non-array-reference arguments in an array constructor:
525 $data = [ $data ] unless ref $data eq 'ARRAY';
527 Typically, however, things are the other way around: the tieable class expects
528 its arguments as a flattened list, so the attribute looks like:
530 sub UNIVERSAL::Cycle : ATTR(SCALAR) {
531 my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
532 my @data = ref $data eq 'ARRAY' ? @$data : $data;
533 tie $$referent, 'Tie::Whatever', @data;
537 This software pattern is so widely applicable that Attribute::Handlers
538 provides a way to automate it: specifying C<'autotie'> in the
539 C<use Attribute::Handlers> statement. So, the cycling example,
540 could also be written:
542 use Attribute::Handlers autotie => { Cycle => 'Tie::Cycle' };
548 my $next : Cycle(['A'..'Z']); # $next is now a tied variable
553 Note that we now have to pass the cycling values as an array reference,
554 since the C<autotie> mechanism passes C<tie> a list of arguments as a list
555 (as in the Tie::Whatever example), I<not> as an array reference (as in
556 the original Tie::Cycle example at the start of this section).
558 The argument after C<'autotie'> is a reference to a hash in which each key is
559 the name of an attribute to be created, and each value is the class to which
560 variables ascribed that attribute should be tied.
562 Note that there is no longer any need to import the Tie::Cycle module --
563 Attribute::Handlers takes care of that automagically. You can even pass
564 arguments to the module's C<import> subroutine, by appending them to the
565 class name. For example:
567 use Attribute::Handlers
568 autotie => { Dir => 'Tie::Dir qw(DIR_UNLINK)' };
570 If the attribute name is unqualified, the attribute is installed in the
571 current package. Otherwise it is installed in the qualifier's package:
575 use Attribute::Handlers autotie => {
576 Other::Good => Tie::SecureHash, # tie attr installed in Other::
577 Bad => Tie::Taxes, # tie attr installed in Here::
578 UNIVERSAL::Ugly => Software::Patent # tie attr installed everywhere
581 Autoties are most commonly used in the module to which they actually tie,
582 and need to export their attributes to any module that calls them. To
583 facilitiate this, Attribute::Handlers recognizes a special "pseudo-class" --
584 C<__CALLER__>, which may be specified as the qualifier of an attribute:
586 package Tie::Me::Kangaroo:Down::Sport;
588 use Attribute::Handlers autotie => { __CALLER__::Roo => __PACKAGE__ };
590 This causes Attribute::Handlers to define the C<Roo> attribute in the package
591 that imports the Tie::Me::Kangaroo:Down::Sport module.
593 =head3 Passing the tied object to C<tie>
595 Occasionally it is important to pass a reference to the object being tied
596 to the TIESCALAR, TIEHASH, etc. that ties it.
598 The C<autotie> mechanism supports this too. The following code:
600 use Attribute::Handlers autotieref => { Selfish => Tie::Selfish };
601 my $var : Selfish(@args);
603 has the same effect as:
605 tie my $var, 'Tie::Selfish', @args;
607 But when C<"autotieref"> is used instead of C<"autotie">:
609 use Attribute::Handlers autotieref => { Selfish => Tie::Selfish };
610 my $var : Selfish(@args);
612 the effect is to pass the C<tie> call an extra reference to the variable
615 tie my $var, 'Tie::Selfish', \$var, @args;
621 If the class shown in L<SYNOPSIS> were placed in the MyClass.pm
622 module, then the following code:
627 my MyClass $slr :Good :Bad(1**1-1) :Omni(-vorous);
629 package SomeOtherClass;
634 sub fn :Ugly(sister) :Omni('po',tent()) {...}
635 my @arr :Good :Omni(s/cie/nt/);
636 my %hsh :Good(q/bye) :Omni(q/bus/);
639 would cause the following handlers to be invoked:
641 # my MyClass $slr :Good :Bad(1**1-1) :Omni(-vorous);
643 MyClass::Good:ATTR(SCALAR)( 'MyClass', # class
644 'LEXICAL', # no typeglob
648 'CHECK', # compiler phase
651 MyClass::Bad:ATTR(SCALAR)( 'MyClass', # class
652 'LEXICAL', # no typeglob
656 'CHECK', # compiler phase
659 MyClass::Omni:ATTR(SCALAR)( 'MyClass', # class
660 'LEXICAL', # no typeglob
663 '-vorous' # eval'd attr data
664 'CHECK', # compiler phase
668 # sub fn :Ugly(sister) :Omni('po',tent()) {...}
670 MyClass::UGLY:ATTR(CODE)( 'SomeOtherClass', # class
671 \*SomeOtherClass::fn, # typeglob
672 \&SomeOtherClass::fn, # referent
674 'sister' # eval'd attr data
675 'CHECK', # compiler phase
678 MyClass::Omni:ATTR(CODE)( 'SomeOtherClass', # class
679 \*SomeOtherClass::fn, # typeglob
680 \&SomeOtherClass::fn, # referent
682 ['po','acle'] # eval'd attr data
683 'CHECK', # compiler phase
687 # my @arr :Good :Omni(s/cie/nt/);
689 MyClass::Good:ATTR(ARRAY)( 'SomeOtherClass', # class
690 'LEXICAL', # no typeglob
694 'CHECK', # compiler phase
697 MyClass::Omni:ATTR(ARRAY)( 'SomeOtherClass', # class
698 'LEXICAL', # no typeglob
701 "" # eval'd attr data
702 'CHECK', # compiler phase
706 # my %hsh :Good(q/bye) :Omni(q/bus/);
708 MyClass::Good:ATTR(HASH)( 'SomeOtherClass', # class
709 'LEXICAL', # no typeglob
712 'q/bye' # raw attr data
713 'CHECK', # compiler phase
716 MyClass::Omni:ATTR(HASH)( 'SomeOtherClass', # class
717 'LEXICAL', # no typeglob
720 'bus' # eval'd attr data
721 'CHECK', # compiler phase
725 Installing handlers into UNIVERSAL, makes them...err..universal.
728 package Descriptions;
729 use Attribute::Handlers;
732 sub name { return $name{$_[2]}||*{$_[1]}{NAME} }
734 sub UNIVERSAL::Name :ATTR {
735 $name{$_[2]} = $_[4];
738 sub UNIVERSAL::Purpose :ATTR {
739 print STDERR "Purpose of ", &name, " is $_[4]\n";
742 sub UNIVERSAL::Unit :ATTR {
743 print STDERR &name, " measured in $_[4]\n";
750 my $capacity : Name(capacity)
751 : Purpose(to store max storage capacity for files)
757 sub foo : Purpose(to foo all data before barring it) { }
766 =item C<Bad attribute type: ATTR(%s)>
768 An attribute handler was specified with an C<:ATTR(I<ref_type>)>, but the
769 type of referent it was defined to handle wasn't one of the five permitted:
770 C<SCALAR>, C<ARRAY>, C<HASH>, C<CODE>, or C<ANY>.
772 =item C<Attribute handler %s doesn't handle %s attributes>
774 A handler for attributes of the specified name I<was> defined, but not
775 for the specified type of declaration. Typically encountered whe trying
776 to apply a C<VAR> attribute handler to a subroutine, or a C<SCALAR>
777 attribute handler to some other type of variable.
779 =item C<Declaration of %s attribute in package %s may clash with future reserved word>
781 A handler for an attributes with an all-lowercase name was declared. An
782 attribute with an all-lowercase name might have a meaning to Perl
783 itself some day, even though most don't yet. Use a mixed-case attribute
786 =item C<Can't have two ATTR specifiers on one subroutine>
788 You just can't, okay?
789 Instead, put all the specifications together with commas between them
790 in a single C<ATTR(I<specification>)>.
792 =item C<Can't autotie a %s>
794 You can only declare autoties for types C<"SCALAR">, C<"ARRAY">, and
795 C<"HASH">. They're the only things (apart from typeglobs -- which are
796 not declarable) that Perl can tie.
798 =item C<Internal error: %s symbol went missing>
800 Something is rotten in the state of the program. An attributed
801 subroutine ceased to exist between the point it was declared and the point
802 at which its attribute handler(s) would have been called.
808 Damian Conway (damian@conway.org)
812 There are undoubtedly serious bugs lurking somewhere in code this funky :-)
813 Bug reports and other feedback are most welcome.
817 Copyright (c) 2001, Damian Conway. All Rights Reserved.
818 This module is free software. It may be used, redistributed
819 and/or modified under the same terms as Perl itself.