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 # if _gen_handler_AH_ is being called after CHECK it's
149 # for a lexical, so we don't want to keep a reference
151 push @declarations, $decl
152 if $global_phase == 0;
156 return grep {defined && !/$builtin/} @attrs;
160 *{"MODIFY_${_}_ATTRIBUTES"} = _gen_handler_AH_ foreach @{$validtype{ANY}};
161 push @UNIVERSAL::ISA, 'Attribute::Handlers'
162 unless grep /^Attribute::Handlers$/, @UNIVERSAL::ISA;
164 sub _apply_handler_AH_ {
165 my ($declaration, $phase) = @_;
166 my ($pkg, $ref, $attr, $data, $raw, $handlerphase) = @$declaration;
167 return unless $handlerphase->{$phase};
168 # print STDERR "Handling $attr on $ref in $phase with [$data]\n";
170 my $handler = "_ATTR_${type}_${attr}";
171 my $sym = findsym($pkg, $ref);
172 $sym ||= $type eq 'CODE' ? 'ANON' : 'LEXICAL';
174 my $evaled = !$raw && eval("package $pkg; no warnings;
175 local \$SIG{__WARN__}=sub{die}; [$data]");
176 $data = ($evaled && $data =~ /^\s*\[/) ? [$evaled]
177 : ($evaled) ? $evaled
180 (ref $sym eq 'GLOB' ? *{$sym}{ref $ref}||$ref : $ref),
182 (@$data>1? $data : $data->[0]),
191 _apply_handler_AH_($_,'CHECK') foreach @declarations;
194 INIT { $global_phase++; _apply_handler_AH_($_,'INIT') foreach @declarations }
196 END { $global_phase++; _apply_handler_AH_($_,'END') foreach @declarations }
203 Attribute::Handlers - Simpler definition of attribute handlers
207 This document describes version 0.76 of Attribute::Handlers,
208 released November 15, 2001.
214 use Attribute::Handlers;
215 no warnings 'redefine';
218 sub Good : ATTR(SCALAR) {
219 my ($package, $symbol, $referent, $attr, $data) = @_;
221 # Invoked for any scalar variable with a :Good attribute,
222 # provided the variable was declared in MyClass (or
223 # a derived class) or typed to MyClass.
225 # Do whatever to $referent here (executed in CHECK phase).
229 sub Bad : ATTR(SCALAR) {
230 # Invoked for any scalar variable with a :Bad attribute,
231 # provided the variable was declared in MyClass (or
232 # a derived class) or typed to MyClass.
236 sub Good : ATTR(ARRAY) {
237 # Invoked for any array variable with a :Good attribute,
238 # provided the variable was declared in MyClass (or
239 # a derived class) or typed to MyClass.
243 sub Good : ATTR(HASH) {
244 # Invoked for any hash variable with a :Good attribute,
245 # provided the variable was declared in MyClass (or
246 # a derived class) or typed to MyClass.
250 sub Ugly : ATTR(CODE) {
251 # Invoked for any subroutine declared in MyClass (or a
252 # derived class) with an :Ugly attribute.
257 # Invoked for any scalar, array, hash, or subroutine
258 # with an :Omni attribute, provided the variable or
259 # subroutine was declared in MyClass (or a derived class)
260 # or the variable was typed to MyClass.
261 # Use ref($_[2]) to determine what kind of referent it was.
266 use Attribute::Handlers autotie => { Cycle => Tie::Cycle };
268 my $next : Cycle(['A'..'Z']);
273 This module, when inherited by a package, allows that package's class to
274 define attribute handler subroutines for specific attributes. Variables
275 and subroutines subsequently defined in that package, or in packages
276 derived from that package may be given attributes with the same names as
277 the attribute handler subroutines, which will then be called in one of
278 the compilation phases (i.e. in a C<BEGIN>, C<CHECK>, C<INIT>, or C<END>
281 To create a handler, define it as a subroutine with the same name as
282 the desired attribute, and declare the subroutine itself with the
283 attribute C<:ATTR>. For example:
286 use Attribute::Handlers;
289 my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
292 *{$symbol}{NAME}, " ",
293 "($referent) ", "was just declared ",
294 "and ascribed the ${attr} attribute ",
295 "with data ($data)\n",
299 This creates a handler for the attribute C<:Loud> in the class LoudDecl.
300 Thereafter, any subroutine declared with a C<:Loud> attribute in the class
307 causes the above handler to be invoked, and passed:
313 the name of the package into which it was declared;
317 a reference to the symbol table entry (typeglob) containing the subroutine;
321 a reference to the subroutine;
325 the name of the attribute;
329 any data associated with that attribute;
333 the name of the phase in which the handler is being invoked.
337 Likewise, declaring any variables with the C<:Loud> attribute within the
346 will cause the handler to be called with a similar argument list (except,
347 of course, that C<$_[2]> will be a reference to the variable).
349 The package name argument will typically be the name of the class into
350 which the subroutine was declared, but it may also be the name of a derived
351 class (since handlers are inherited).
353 If a lexical variable is given an attribute, there is no symbol table to
354 which it belongs, so the symbol table argument (C<$_[1]>) is set to the
355 string C<'LEXICAL'> in that case. Likewise, ascribing an attribute to
356 an anonymous subroutine results in a symbol table argument of C<'ANON'>.
358 The data argument passes in the value (if any) associated with the
359 attribute. For example, if C<&foo> had been declared:
361 sub foo :Loud("turn it up to 11, man!") {...}
363 then the string C<"turn it up to 11, man!"> would be passed as the
366 Attribute::Handlers makes strenuous efforts to convert
367 the data argument (C<$_[4]>) to a useable form before passing it to
368 the handler (but see L<"Non-interpretive attribute handlers">).
369 For example, all of these:
371 sub foo :Loud(till=>ears=>are=>bleeding) {...}
372 sub foo :Loud(['till','ears','are','bleeding']) {...}
373 sub foo :Loud(qw/till ears are bleeding/) {...}
374 sub foo :Loud(qw/my, ears, are, bleeding/) {...}
375 sub foo :Loud(till,ears,are,bleeding) {...}
377 causes it to pass C<['till','ears','are','bleeding']> as the handler's
378 data argument. However, if the data can't be parsed as valid Perl, then
379 it is passed as an uninterpreted string. For example:
381 sub foo :Loud(my,ears,are,bleeding) {...}
382 sub foo :Loud(qw/my ears are bleeding) {...}
384 cause the strings C<'my,ears,are,bleeding'> and C<'qw/my ears are bleeding'>
385 respectively to be passed as the data argument.
387 If the attribute has only a single associated scalar data value, that value is
388 passed as a scalar. If multiple values are associated, they are passed as an
389 array reference. If no value is associated with the attribute, C<undef> is
393 =head2 Typed lexicals
395 Regardless of the package in which it is declared, if a lexical variable is
396 ascribed an attribute, the handler that is invoked is the one belonging to
397 the package to which it is typed. For example, the following declarations:
401 my LoudDecl $loudobj : Loud;
402 my LoudDecl @loudobjs : Loud;
403 my LoudDecl %loudobjex : Loud;
405 causes the LoudDecl::Loud handler to be invoked (even if OtherClass also
406 defines a handler for C<:Loud> attributes).
409 =head2 Type-specific attribute handlers
411 If an attribute handler is declared and the C<:ATTR> specifier is
412 given the name of a built-in type (C<SCALAR>, C<ARRAY>, C<HASH>, or C<CODE>),
413 the handler is only applied to declarations of that type. For example,
414 the following definition:
418 sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" }
420 creates an attribute handler that applies only to scalars:
426 my $metal : RealLoud; # invokes &LoudDecl::RealLoud
427 my @metal : RealLoud; # error: unknown attribute
428 my %metal : RealLoud; # error: unknown attribute
429 sub metal : RealLoud {...} # error: unknown attribute
431 You can, of course, declare separate handlers for these types as well
432 (but you'll need to specify C<no warnings 'redefine'> to do it quietly):
435 use Attribute::Handlers;
436 no warnings 'redefine';
438 sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" }
439 sub RealLoud :ATTR(ARRAY) { print "Urrrrrrrrrr!" }
440 sub RealLoud :ATTR(HASH) { print "Arrrrrgggghhhhhh!" }
441 sub RealLoud :ATTR(CODE) { croak "Real loud sub torpedoed" }
443 You can also explicitly indicate that a single handler is meant to be
444 used for all types of referents like so:
447 use Attribute::Handlers;
449 sub SeriousLoud :ATTR(ANY) { warn "Hearing loss imminent" }
451 (I.e. C<ATTR(ANY)> is a synonym for C<:ATTR>).
454 =head2 Non-interpretive attribute handlers
456 Occasionally the strenuous efforts Attribute::Handlers makes to convert
457 the data argument (C<$_[4]>) to a useable form before passing it to
458 the handler get in the way.
460 You can turn off that eagerness-to-help by declaring
461 an attribute handler with the keyword C<RAWDATA>. For example:
463 sub Raw : ATTR(RAWDATA) {...}
464 sub Nekkid : ATTR(SCALAR,RAWDATA) {...}
465 sub Au::Naturale : ATTR(RAWDATA,ANY) {...}
467 Then the handler makes absolutely no attempt to interpret the data it
468 receives and simply passes it as a string:
470 my $power : Raw(1..100); # handlers receives "1..100"
472 =head2 Phase-specific attribute handlers
474 By default, attribute handlers are called at the end of the compilation
475 phase (in a C<CHECK> block). This seems to be optimal in most cases because
476 most things that can be defined are defined by that point but nothing has
479 However, it is possible to set up attribute handlers that are called at
480 other points in the program's compilation or execution, by explicitly
481 stating the phase (or phases) in which you wish the attribute handler to
482 be called. For example:
484 sub Early :ATTR(SCALAR,BEGIN) {...}
485 sub Normal :ATTR(SCALAR,CHECK) {...}
486 sub Late :ATTR(SCALAR,INIT) {...}
487 sub Final :ATTR(SCALAR,END) {...}
488 sub Bookends :ATTR(SCALAR,BEGIN,END) {...}
490 As the last example indicates, a handler may be set up to be (re)called in
491 two or more phases. The phase name is passed as the handler's final argument.
493 Note that attribute handlers that are scheduled for the C<BEGIN> phase
494 are handled as soon as the attribute is detected (i.e. before any
495 subsequently defined C<BEGIN> blocks are executed).
498 =head2 Attributes as C<tie> interfaces
500 Attributes make an excellent and intuitive interface through which to tie
501 variables. For example:
503 use Attribute::Handlers;
506 sub UNIVERSAL::Cycle : ATTR(SCALAR) {
507 my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
508 $data = [ $data ] unless ref $data eq 'ARRAY';
509 tie $$referent, 'Tie::Cycle', $data;
516 my $next : Cycle('A'..'Z'); # $next is now a tied variable
522 Note that, because the C<Cycle> attribute receives its arguments in the
523 C<$data> variable, if the attribute is given a list of arguments, C<$data>
524 will consist of a single array reference; otherwise, it will consist of the
525 single argument directly. Since Tie::Cycle requires its cycling values to
526 be passed as an array reference, this means that we need to wrap
527 non-array-reference arguments in an array constructor:
529 $data = [ $data ] unless ref $data eq 'ARRAY';
531 Typically, however, things are the other way around: the tieable class expects
532 its arguments as a flattened list, so the attribute looks like:
534 sub UNIVERSAL::Cycle : ATTR(SCALAR) {
535 my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
536 my @data = ref $data eq 'ARRAY' ? @$data : $data;
537 tie $$referent, 'Tie::Whatever', @data;
541 This software pattern is so widely applicable that Attribute::Handlers
542 provides a way to automate it: specifying C<'autotie'> in the
543 C<use Attribute::Handlers> statement. So, the cycling example,
544 could also be written:
546 use Attribute::Handlers autotie => { Cycle => 'Tie::Cycle' };
552 my $next : Cycle(['A'..'Z']); # $next is now a tied variable
557 Note that we now have to pass the cycling values as an array reference,
558 since the C<autotie> mechanism passes C<tie> a list of arguments as a list
559 (as in the Tie::Whatever example), I<not> as an array reference (as in
560 the original Tie::Cycle example at the start of this section).
562 The argument after C<'autotie'> is a reference to a hash in which each key is
563 the name of an attribute to be created, and each value is the class to which
564 variables ascribed that attribute should be tied.
566 Note that there is no longer any need to import the Tie::Cycle module --
567 Attribute::Handlers takes care of that automagically. You can even pass
568 arguments to the module's C<import> subroutine, by appending them to the
569 class name. For example:
571 use Attribute::Handlers
572 autotie => { Dir => 'Tie::Dir qw(DIR_UNLINK)' };
574 If the attribute name is unqualified, the attribute is installed in the
575 current package. Otherwise it is installed in the qualifier's package:
579 use Attribute::Handlers autotie => {
580 Other::Good => Tie::SecureHash, # tie attr installed in Other::
581 Bad => Tie::Taxes, # tie attr installed in Here::
582 UNIVERSAL::Ugly => Software::Patent # tie attr installed everywhere
585 Autoties are most commonly used in the module to which they actually tie,
586 and need to export their attributes to any module that calls them. To
587 facilitiate this, Attribute::Handlers recognizes a special "pseudo-class" --
588 C<__CALLER__>, which may be specified as the qualifier of an attribute:
590 package Tie::Me::Kangaroo:Down::Sport;
592 use Attribute::Handlers autotie => { __CALLER__::Roo => __PACKAGE__ };
594 This causes Attribute::Handlers to define the C<Roo> attribute in the package
595 that imports the Tie::Me::Kangaroo:Down::Sport module.
597 =head3 Passing the tied object to C<tie>
599 Occasionally it is important to pass a reference to the object being tied
600 to the TIESCALAR, TIEHASH, etc. that ties it.
602 The C<autotie> mechanism supports this too. The following code:
604 use Attribute::Handlers autotieref => { Selfish => Tie::Selfish };
605 my $var : Selfish(@args);
607 has the same effect as:
609 tie my $var, 'Tie::Selfish', @args;
611 But when C<"autotieref"> is used instead of C<"autotie">:
613 use Attribute::Handlers autotieref => { Selfish => Tie::Selfish };
614 my $var : Selfish(@args);
616 the effect is to pass the C<tie> call an extra reference to the variable
619 tie my $var, 'Tie::Selfish', \$var, @args;
625 If the class shown in L<SYNOPSIS> were placed in the MyClass.pm
626 module, then the following code:
631 my MyClass $slr :Good :Bad(1**1-1) :Omni(-vorous);
633 package SomeOtherClass;
638 sub fn :Ugly(sister) :Omni('po',tent()) {...}
639 my @arr :Good :Omni(s/cie/nt/);
640 my %hsh :Good(q/bye) :Omni(q/bus/);
643 would cause the following handlers to be invoked:
645 # my MyClass $slr :Good :Bad(1**1-1) :Omni(-vorous);
647 MyClass::Good:ATTR(SCALAR)( 'MyClass', # class
648 'LEXICAL', # no typeglob
652 'CHECK', # compiler phase
655 MyClass::Bad:ATTR(SCALAR)( 'MyClass', # class
656 'LEXICAL', # no typeglob
660 'CHECK', # compiler phase
663 MyClass::Omni:ATTR(SCALAR)( 'MyClass', # class
664 'LEXICAL', # no typeglob
667 '-vorous' # eval'd attr data
668 'CHECK', # compiler phase
672 # sub fn :Ugly(sister) :Omni('po',tent()) {...}
674 MyClass::UGLY:ATTR(CODE)( 'SomeOtherClass', # class
675 \*SomeOtherClass::fn, # typeglob
676 \&SomeOtherClass::fn, # referent
678 'sister' # eval'd attr data
679 'CHECK', # compiler phase
682 MyClass::Omni:ATTR(CODE)( 'SomeOtherClass', # class
683 \*SomeOtherClass::fn, # typeglob
684 \&SomeOtherClass::fn, # referent
686 ['po','acle'] # eval'd attr data
687 'CHECK', # compiler phase
691 # my @arr :Good :Omni(s/cie/nt/);
693 MyClass::Good:ATTR(ARRAY)( 'SomeOtherClass', # class
694 'LEXICAL', # no typeglob
698 'CHECK', # compiler phase
701 MyClass::Omni:ATTR(ARRAY)( 'SomeOtherClass', # class
702 'LEXICAL', # no typeglob
705 "" # eval'd attr data
706 'CHECK', # compiler phase
710 # my %hsh :Good(q/bye) :Omni(q/bus/);
712 MyClass::Good:ATTR(HASH)( 'SomeOtherClass', # class
713 'LEXICAL', # no typeglob
716 'q/bye' # raw attr data
717 'CHECK', # compiler phase
720 MyClass::Omni:ATTR(HASH)( 'SomeOtherClass', # class
721 'LEXICAL', # no typeglob
724 'bus' # eval'd attr data
725 'CHECK', # compiler phase
729 Installing handlers into UNIVERSAL, makes them...err..universal.
732 package Descriptions;
733 use Attribute::Handlers;
736 sub name { return $name{$_[2]}||*{$_[1]}{NAME} }
738 sub UNIVERSAL::Name :ATTR {
739 $name{$_[2]} = $_[4];
742 sub UNIVERSAL::Purpose :ATTR {
743 print STDERR "Purpose of ", &name, " is $_[4]\n";
746 sub UNIVERSAL::Unit :ATTR {
747 print STDERR &name, " measured in $_[4]\n";
754 my $capacity : Name(capacity)
755 : Purpose(to store max storage capacity for files)
761 sub foo : Purpose(to foo all data before barring it) { }
770 =item C<Bad attribute type: ATTR(%s)>
772 An attribute handler was specified with an C<:ATTR(I<ref_type>)>, but the
773 type of referent it was defined to handle wasn't one of the five permitted:
774 C<SCALAR>, C<ARRAY>, C<HASH>, C<CODE>, or C<ANY>.
776 =item C<Attribute handler %s doesn't handle %s attributes>
778 A handler for attributes of the specified name I<was> defined, but not
779 for the specified type of declaration. Typically encountered whe trying
780 to apply a C<VAR> attribute handler to a subroutine, or a C<SCALAR>
781 attribute handler to some other type of variable.
783 =item C<Declaration of %s attribute in package %s may clash with future reserved word>
785 A handler for an attributes with an all-lowercase name was declared. An
786 attribute with an all-lowercase name might have a meaning to Perl
787 itself some day, even though most don't yet. Use a mixed-case attribute
790 =item C<Can't have two ATTR specifiers on one subroutine>
792 You just can't, okay?
793 Instead, put all the specifications together with commas between them
794 in a single C<ATTR(I<specification>)>.
796 =item C<Can't autotie a %s>
798 You can only declare autoties for types C<"SCALAR">, C<"ARRAY">, and
799 C<"HASH">. They're the only things (apart from typeglobs -- which are
800 not declarable) that Perl can tie.
802 =item C<Internal error: %s symbol went missing>
804 Something is rotten in the state of the program. An attributed
805 subroutine ceased to exist between the point it was declared and the point
806 at which its attribute handler(s) would have been called.
812 Damian Conway (damian@conway.org)
816 There are undoubtedly serious bugs lurking somewhere in code this funky :-)
817 Bug reports and other feedback are most welcome.
821 Copyright (c) 2001, Damian Conway. All Rights Reserved.
822 This module is free software. It may be used, redistributed
823 and/or modified under the same terms as Perl itself.