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=>'%');
36 croak "Usage: use $_[0] autotie => {AttrName => TieClassName,...}";
39 my $qual_id = qr/^[_a-z]\w*(::[_a-z]\w*)*$/i;
43 return unless $class eq "Attribute::Handlers";
46 if ($cmd =~ /^autotie((?:ref)?)$/) {
47 my $tiedata = ($1 ? '$ref, ' : '') . '@$data';
49 _usage_AH_ $class unless ref($mapping) eq 'HASH';
50 while (my($attr, $tieclass) = each %$mapping) {
51 $tieclass =~ s/^([_a-z]\w*(::[_a-z]\w*)*)(.*)/$1/is;
53 _usage_AH_ $class unless $attr =~ $qual_id
54 && $tieclass =~ $qual_id
55 && eval "use base $tieclass; 1";
56 if ($tieclass->isa('Exporter')) {
57 local $Exporter::ExportLevel = 2;
58 $tieclass->import(eval $args);
60 $attr =~ s/__CALLER__/caller(1)/e;
61 $attr = caller()."::".$attr unless $attr =~ /::/;
63 sub $attr : ATTR(VAR) {
64 my (\$ref, \$data) = \@_[2,4];
65 my \$was_arrayref = ref \$data eq 'ARRAY';
66 \$data = [ \$data ] unless \$was_arrayref;
67 my \$type = ref(\$ref)||"value (".(\$ref||"<undef>").")";
68 (\$type eq 'SCALAR')? tie \$\$ref,'$tieclass',$tiedata
69 :(\$type eq 'ARRAY') ? tie \@\$ref,'$tieclass',$tiedata
70 :(\$type eq 'HASH') ? tie \%\$ref,'$tieclass',$tiedata
71 : die "Can't autotie a \$type\n"
73 } or die "Internal error: $@";
77 croak "Can't understand $_";
81 sub _resolve_lastattr {
82 return unless $lastattr{ref};
83 my $sym = findsym @lastattr{'pkg','ref'}
84 or die "Internal error: $lastattr{pkg} symbol went missing";
85 my $name = *{$sym}{NAME};
86 warn "Declaration of $name attribute in package $lastattr{pkg} may clash with future reserved word\n"
87 if $^W and $name !~ /[A-Z]/;
88 foreach ( @{$validtype{$lastattr{type}}} ) {
89 *{"$lastattr{pkg}::_ATTR_${_}_${name}"} = $lastattr{ref};
95 my ($class) = $AUTOLOAD =~ m/(.*)::/g;
96 $AUTOLOAD =~ m/_ATTR_(.*?)_(.*)/ or
97 croak "Can't locate class method '$AUTOLOAD' via package '$class'";
98 croak "Attribute handler '$3' doesn't handle $2 attributes";
103 my $builtin = qr/lvalue|method|locked/;
105 sub _gen_handler_AH_() {
108 my ($pkg, $ref, @attrs) = @_;
110 my ($attr, $data) = /^([a-z_]\w*)(?:[(](.*)[)])?$/is or next;
111 if ($attr eq 'ATTR') {
113 $raw{$ref} = $data =~ s/\s*,?\s*RAWDATA\s*,?\s*//;
114 $phase{$ref}{BEGIN} = 1
115 if $data =~ s/\s*,?\s*(BEGIN)\s*,?\s*//;
116 $phase{$ref}{INIT} = 1
117 if $data =~ s/\s*,?\s*(INIT)\s*,?\s*//;
118 $phase{$ref}{END} = 1
119 if $data =~ s/\s*,?\s*(END)\s*,?\s*//;
120 $phase{$ref}{CHECK} = 1
121 if $data =~ s/\s*,?\s*(CHECK)\s*,?\s*//
122 || ! keys %{$phase{$ref}};
123 croak "Can't have two ATTR specifiers on one subroutine"
125 croak "Bad attribute type: ATTR($data)"
126 unless $validtype{$data};
127 %lastattr=(pkg=>$pkg,ref=>$ref,type=>$data);
130 my $handler = $pkg->can($attr);
131 next unless $handler;
132 my $decl = [$pkg, $ref, $attr, $data,
133 $raw{$handler}, $phase{$handler}];
134 _apply_handler_AH_($decl,'BEGIN');
135 push @declarations, $decl;
139 return grep {defined && !/$builtin/} @attrs;
143 *{"MODIFY_${_}_ATTRIBUTES"} = _gen_handler_AH_ foreach @{$validtype{ANY}};
144 push @UNIVERSAL::ISA, 'Attribute::Handlers'
145 unless grep /^Attribute::Handlers$/, @UNIVERSAL::ISA;
147 sub _apply_handler_AH_ {
148 my ($declaration, $phase) = @_;
149 my ($pkg, $ref, $attr, $data, $raw, $handlerphase) = @$declaration;
150 return unless $handlerphase->{$phase};
151 # print STDERR "Handling $attr on $ref in $phase with [$data]\n";
153 my $handler = "_ATTR_${type}_${attr}";
154 my $sym = findsym($pkg, $ref);
155 $sym ||= $type eq 'CODE' ? 'ANON' : 'LEXICAL';
157 my $evaled = !$raw && eval("package $pkg; no warnings;
158 local \$SIG{__WARN__}=sub{die}; [$data]");
159 $data = ($evaled && $data =~ /^\s*\[/) ? [$evaled]
160 : ($evaled) ? $evaled
163 (ref $sym eq 'GLOB' ? *{$sym}{ref $ref}||$ref : $ref),
165 (@$data>1? $data : $data->[0]),
173 _apply_handler_AH_($_,'CHECK') foreach @declarations;
176 INIT { _apply_handler_AH_($_,'INIT') foreach @declarations }
178 END { _apply_handler_AH_($_,'END') foreach @declarations }
185 Attribute::Handlers - Simpler definition of attribute handlers
189 This document describes version 0.76 of Attribute::Handlers,
190 released November 15, 2001.
196 use Attribute::Handlers;
197 no warnings 'redefine';
200 sub Good : ATTR(SCALAR) {
201 my ($package, $symbol, $referent, $attr, $data) = @_;
203 # Invoked for any scalar variable with a :Good attribute,
204 # provided the variable was declared in MyClass (or
205 # a derived class) or typed to MyClass.
207 # Do whatever to $referent here (executed in CHECK phase).
211 sub Bad : ATTR(SCALAR) {
212 # Invoked for any scalar variable with a :Bad attribute,
213 # provided the variable was declared in MyClass (or
214 # a derived class) or typed to MyClass.
218 sub Good : ATTR(ARRAY) {
219 # Invoked for any array variable with a :Good attribute,
220 # provided the variable was declared in MyClass (or
221 # a derived class) or typed to MyClass.
225 sub Good : ATTR(HASH) {
226 # Invoked for any hash variable with a :Good attribute,
227 # provided the variable was declared in MyClass (or
228 # a derived class) or typed to MyClass.
232 sub Ugly : ATTR(CODE) {
233 # Invoked for any subroutine declared in MyClass (or a
234 # derived class) with an :Ugly attribute.
239 # Invoked for any scalar, array, hash, or subroutine
240 # with an :Omni attribute, provided the variable or
241 # subroutine was declared in MyClass (or a derived class)
242 # or the variable was typed to MyClass.
243 # Use ref($_[2]) to determine what kind of referent it was.
248 use Attribute::Handlers autotie => { Cycle => Tie::Cycle };
250 my $next : Cycle(['A'..'Z']);
255 This module, when inherited by a package, allows that package's class to
256 define attribute handler subroutines for specific attributes. Variables
257 and subroutines subsequently defined in that package, or in packages
258 derived from that package may be given attributes with the same names as
259 the attribute handler subroutines, which will then be called in one of
260 the compilation phases (i.e. in a C<BEGIN>, C<CHECK>, C<INIT>, or C<END>
263 To create a handler, define it as a subroutine with the same name as
264 the desired attribute, and declare the subroutine itself with the
265 attribute C<:ATTR>. For example:
268 use Attribute::Handlers;
271 my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
274 *{$symbol}{NAME}, " ",
275 "($referent) ", "was just declared ",
276 "and ascribed the ${attr} attribute ",
277 "with data ($data)\n",
281 This creates a handler for the attribute C<:Loud> in the class LoudDecl.
282 Thereafter, any subroutine declared with a C<:Loud> attribute in the class
289 causes the above handler to be invoked, and passed:
295 the name of the package into which it was declared;
299 a reference to the symbol table entry (typeglob) containing the subroutine;
303 a reference to the subroutine;
307 the name of the attribute;
311 any data associated with that attribute;
315 the name of the phase in which the handler is being invoked.
319 Likewise, declaring any variables with the C<:Loud> attribute within the
328 will cause the handler to be called with a similar argument list (except,
329 of course, that C<$_[2]> will be a reference to the variable).
331 The package name argument will typically be the name of the class into
332 which the subroutine was declared, but it may also be the name of a derived
333 class (since handlers are inherited).
335 If a lexical variable is given an attribute, there is no symbol table to
336 which it belongs, so the symbol table argument (C<$_[1]>) is set to the
337 string C<'LEXICAL'> in that case. Likewise, ascribing an attribute to
338 an anonymous subroutine results in a symbol table argument of C<'ANON'>.
340 The data argument passes in the value (if any) associated with the
341 attribute. For example, if C<&foo> had been declared:
343 sub foo :Loud("turn it up to 11, man!") {...}
345 then the string C<"turn it up to 11, man!"> would be passed as the
348 Attribute::Handlers makes strenuous efforts to convert
349 the data argument (C<$_[4]>) to a useable form before passing it to
350 the handler (but see L<"Non-interpretive attribute handlers">).
351 For example, all of these:
353 sub foo :Loud(till=>ears=>are=>bleeding) {...}
354 sub foo :Loud(['till','ears','are','bleeding']) {...}
355 sub foo :Loud(qw/till ears are bleeding/) {...}
356 sub foo :Loud(qw/my, ears, are, bleeding/) {...}
357 sub foo :Loud(till,ears,are,bleeding) {...}
359 causes it to pass C<['till','ears','are','bleeding']> as the handler's
360 data argument. However, if the data can't be parsed as valid Perl, then
361 it is passed as an uninterpreted string. For example:
363 sub foo :Loud(my,ears,are,bleeding) {...}
364 sub foo :Loud(qw/my ears are bleeding) {...}
366 cause the strings C<'my,ears,are,bleeding'> and C<'qw/my ears are bleeding'>
367 respectively to be passed as the data argument.
369 If the attribute has only a single associated scalar data value, that value is
370 passed as a scalar. If multiple values are associated, they are passed as an
371 array reference. If no value is associated with the attribute, C<undef> is
375 =head2 Typed lexicals
377 Regardless of the package in which it is declared, if a lexical variable is
378 ascribed an attribute, the handler that is invoked is the one belonging to
379 the package to which it is typed. For example, the following declarations:
383 my LoudDecl $loudobj : Loud;
384 my LoudDecl @loudobjs : Loud;
385 my LoudDecl %loudobjex : Loud;
387 causes the LoudDecl::Loud handler to be invoked (even if OtherClass also
388 defines a handler for C<:Loud> attributes).
391 =head2 Type-specific attribute handlers
393 If an attribute handler is declared and the C<:ATTR> specifier is
394 given the name of a built-in type (C<SCALAR>, C<ARRAY>, C<HASH>, or C<CODE>),
395 the handler is only applied to declarations of that type. For example,
396 the following definition:
400 sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" }
402 creates an attribute handler that applies only to scalars:
408 my $metal : RealLoud; # invokes &LoudDecl::RealLoud
409 my @metal : RealLoud; # error: unknown attribute
410 my %metal : RealLoud; # error: unknown attribute
411 sub metal : RealLoud {...} # error: unknown attribute
413 You can, of course, declare separate handlers for these types as well
414 (but you'll need to specify C<no warnings 'redefine'> to do it quietly):
417 use Attribute::Handlers;
418 no warnings 'redefine';
420 sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" }
421 sub RealLoud :ATTR(ARRAY) { print "Urrrrrrrrrr!" }
422 sub RealLoud :ATTR(HASH) { print "Arrrrrgggghhhhhh!" }
423 sub RealLoud :ATTR(CODE) { croak "Real loud sub torpedoed" }
425 You can also explicitly indicate that a single handler is meant to be
426 used for all types of referents like so:
429 use Attribute::Handlers;
431 sub SeriousLoud :ATTR(ANY) { warn "Hearing loss imminent" }
433 (I.e. C<ATTR(ANY)> is a synonym for C<:ATTR>).
436 =head2 Non-interpretive attribute handlers
438 Occasionally the strenuous efforts Attribute::Handlers makes to convert
439 the data argument (C<$_[4]>) to a useable form before passing it to
440 the handler get in the way.
442 You can turn off that eagerness-to-help by declaring
443 an attribute handler with the keyword C<RAWDATA>. For example:
445 sub Raw : ATTR(RAWDATA) {...}
446 sub Nekkid : ATTR(SCALAR,RAWDATA) {...}
447 sub Au::Naturale : ATTR(RAWDATA,ANY) {...}
449 Then the handler makes absolutely no attempt to interpret the data it
450 receives and simply passes it as a string:
452 my $power : Raw(1..100); # handlers receives "1..100"
454 =head2 Phase-specific attribute handlers
456 By default, attribute handlers are called at the end of the compilation
457 phase (in a C<CHECK> block). This seems to be optimal in most cases because
458 most things that can be defined are defined by that point but nothing has
461 However, it is possible to set up attribute handlers that are called at
462 other points in the program's compilation or execution, by explicitly
463 stating the phase (or phases) in which you wish the attribute handler to
464 be called. For example:
466 sub Early :ATTR(SCALAR,BEGIN) {...}
467 sub Normal :ATTR(SCALAR,CHECK) {...}
468 sub Late :ATTR(SCALAR,INIT) {...}
469 sub Final :ATTR(SCALAR,END) {...}
470 sub Bookends :ATTR(SCALAR,BEGIN,END) {...}
472 As the last example indicates, a handler may be set up to be (re)called in
473 two or more phases. The phase name is passed as the handler's final argument.
475 Note that attribute handlers that are scheduled for the C<BEGIN> phase
476 are handled as soon as the attribute is detected (i.e. before any
477 subsequently defined C<BEGIN> blocks are executed).
480 =head2 Attributes as C<tie> interfaces
482 Attributes make an excellent and intuitive interface through which to tie
483 variables. For example:
485 use Attribute::Handlers;
488 sub UNIVERSAL::Cycle : ATTR(SCALAR) {
489 my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
490 $data = [ $data ] unless ref $data eq 'ARRAY';
491 tie $$referent, 'Tie::Cycle', $data;
498 my $next : Cycle('A'..'Z'); # $next is now a tied variable
504 Note that, because the C<Cycle> attribute receives its arguments in the
505 C<$data> variable, if the attribute is given a list of arguments, C<$data>
506 will consist of a single array reference; otherwise, it will consist of the
507 single argument directly. Since Tie::Cycle requires its cycling values to
508 be passed as an array reference, this means that we need to wrap
509 non-array-reference arguments in an array constructor:
511 $data = [ $data ] unless ref $data eq 'ARRAY';
513 Typically, however, things are the other way around: the tieable class expects
514 its arguments as a flattened list, so the attribute looks like:
516 sub UNIVERSAL::Cycle : ATTR(SCALAR) {
517 my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
518 my @data = ref $data eq 'ARRAY' ? @$data : $data;
519 tie $$referent, 'Tie::Whatever', @data;
523 This software pattern is so widely applicable that Attribute::Handlers
524 provides a way to automate it: specifying C<'autotie'> in the
525 C<use Attribute::Handlers> statement. So, the cycling example,
526 could also be written:
528 use Attribute::Handlers autotie => { Cycle => 'Tie::Cycle' };
534 my $next : Cycle(['A'..'Z']); # $next is now a tied variable
539 Note that we now have to pass the cycling values as an array reference,
540 since the C<autotie> mechanism passes C<tie> a list of arguments as a list
541 (as in the Tie::Whatever example), I<not> as an array reference (as in
542 the original Tie::Cycle example at the start of this section).
544 The argument after C<'autotie'> is a reference to a hash in which each key is
545 the name of an attribute to be created, and each value is the class to which
546 variables ascribed that attribute should be tied.
548 Note that there is no longer any need to import the Tie::Cycle module --
549 Attribute::Handlers takes care of that automagically. You can even pass
550 arguments to the module's C<import> subroutine, by appending them to the
551 class name. For example:
553 use Attribute::Handlers
554 autotie => { Dir => 'Tie::Dir qw(DIR_UNLINK)' };
556 If the attribute name is unqualified, the attribute is installed in the
557 current package. Otherwise it is installed in the qualifier's package:
561 use Attribute::Handlers autotie => {
562 Other::Good => Tie::SecureHash, # tie attr installed in Other::
563 Bad => Tie::Taxes, # tie attr installed in Here::
564 UNIVERSAL::Ugly => Software::Patent # tie attr installed everywhere
567 Autoties are most commonly used in the module to which they actually tie,
568 and need to export their attributes to any module that calls them. To
569 facilitiate this, Attribute::Handlers recognizes a special "pseudo-class" --
570 C<__CALLER__>, which may be specified as the qualifier of an attribute:
572 package Tie::Me::Kangaroo:Down::Sport;
574 use Attribute::Handlers autotie => { __CALLER__::Roo => __PACKAGE__ };
576 This causes Attribute::Handlers to define the C<Roo> attribute in the package
577 that imports the Tie::Me::Kangaroo:Down::Sport module.
579 =head3 Passing the tied object to C<tie>
581 Occasionally it is important to pass a reference to the object being tied
582 to the TIESCALAR, TIEHASH, etc. that ties it.
584 The C<autotie> mechanism supports this too. The following code:
586 use Attribute::Handlers autotieref => { Selfish => Tie::Selfish };
587 my $var : Selfish(@args);
589 has the same effect as:
591 tie my $var, 'Tie::Selfish', @args;
593 But when C<"autotieref"> is used instead of C<"autotie">:
595 use Attribute::Handlers autotieref => { Selfish => Tie::Selfish };
596 my $var : Selfish(@args);
598 the effect is to pass the C<tie> call an extra reference to the variable
601 tie my $var, 'Tie::Selfish', \$var, @args;
607 If the class shown in L<SYNOPSIS> were placed in the MyClass.pm
608 module, then the following code:
613 my MyClass $slr :Good :Bad(1**1-1) :Omni(-vorous);
615 package SomeOtherClass;
620 sub fn :Ugly(sister) :Omni('po',tent()) {...}
621 my @arr :Good :Omni(s/cie/nt/);
622 my %hsh :Good(q/bye) :Omni(q/bus/);
625 would cause the following handlers to be invoked:
627 # my MyClass $slr :Good :Bad(1**1-1) :Omni(-vorous);
629 MyClass::Good:ATTR(SCALAR)( 'MyClass', # class
630 'LEXICAL', # no typeglob
634 'CHECK', # compiler phase
637 MyClass::Bad:ATTR(SCALAR)( 'MyClass', # class
638 'LEXICAL', # no typeglob
642 'CHECK', # compiler phase
645 MyClass::Omni:ATTR(SCALAR)( 'MyClass', # class
646 'LEXICAL', # no typeglob
649 '-vorous' # eval'd attr data
650 'CHECK', # compiler phase
654 # sub fn :Ugly(sister) :Omni('po',tent()) {...}
656 MyClass::UGLY:ATTR(CODE)( 'SomeOtherClass', # class
657 \*SomeOtherClass::fn, # typeglob
658 \&SomeOtherClass::fn, # referent
660 'sister' # eval'd attr data
661 'CHECK', # compiler phase
664 MyClass::Omni:ATTR(CODE)( 'SomeOtherClass', # class
665 \*SomeOtherClass::fn, # typeglob
666 \&SomeOtherClass::fn, # referent
668 ['po','acle'] # eval'd attr data
669 'CHECK', # compiler phase
673 # my @arr :Good :Omni(s/cie/nt/);
675 MyClass::Good:ATTR(ARRAY)( 'SomeOtherClass', # class
676 'LEXICAL', # no typeglob
680 'CHECK', # compiler phase
683 MyClass::Omni:ATTR(ARRAY)( 'SomeOtherClass', # class
684 'LEXICAL', # no typeglob
687 "" # eval'd attr data
688 'CHECK', # compiler phase
692 # my %hsh :Good(q/bye) :Omni(q/bus/);
694 MyClass::Good:ATTR(HASH)( 'SomeOtherClass', # class
695 'LEXICAL', # no typeglob
698 'q/bye' # raw attr data
699 'CHECK', # compiler phase
702 MyClass::Omni:ATTR(HASH)( 'SomeOtherClass', # class
703 'LEXICAL', # no typeglob
706 'bus' # eval'd attr data
707 'CHECK', # compiler phase
711 Installing handlers into UNIVERSAL, makes them...err..universal.
714 package Descriptions;
715 use Attribute::Handlers;
718 sub name { return $name{$_[2]}||*{$_[1]}{NAME} }
720 sub UNIVERSAL::Name :ATTR {
721 $name{$_[2]} = $_[4];
724 sub UNIVERSAL::Purpose :ATTR {
725 print STDERR "Purpose of ", &name, " is $_[4]\n";
728 sub UNIVERSAL::Unit :ATTR {
729 print STDERR &name, " measured in $_[4]\n";
736 my $capacity : Name(capacity)
737 : Purpose(to store max storage capacity for files)
743 sub foo : Purpose(to foo all data before barring it) { }
752 =item C<Bad attribute type: ATTR(%s)>
754 An attribute handler was specified with an C<:ATTR(I<ref_type>)>, but the
755 type of referent it was defined to handle wasn't one of the five permitted:
756 C<SCALAR>, C<ARRAY>, C<HASH>, C<CODE>, or C<ANY>.
758 =item C<Attribute handler %s doesn't handle %s attributes>
760 A handler for attributes of the specified name I<was> defined, but not
761 for the specified type of declaration. Typically encountered whe trying
762 to apply a C<VAR> attribute handler to a subroutine, or a C<SCALAR>
763 attribute handler to some other type of variable.
765 =item C<Declaration of %s attribute in package %s may clash with future reserved word>
767 A handler for an attributes with an all-lowercase name was declared. An
768 attribute with an all-lowercase name might have a meaning to Perl
769 itself some day, even though most don't yet. Use a mixed-case attribute
772 =item C<Can't have two ATTR specifiers on one subroutine>
774 You just can't, okay?
775 Instead, put all the specifications together with commas between them
776 in a single C<ATTR(I<specification>)>.
778 =item C<Can't autotie a %s>
780 You can only declare autoties for types C<"SCALAR">, C<"ARRAY">, and
781 C<"HASH">. They're the only things (apart from typeglobs -- which are
782 not declarable) that Perl can tie.
784 =item C<Internal error: %s symbol went missing>
786 Something is rotten in the state of the program. An attributed
787 subroutine ceased to exist between the point it was declared and the point
788 at which its attribute handler(s) would have been called.
794 Damian Conway (damian@conway.org)
798 There are undoubtedly serious bugs lurking somewhere in code this funky :-)
799 Bug reports and other feedback are most welcome.
803 Copyright (c) 2001, Damian Conway. All Rights Reserved.
804 This module is free software. It may be used, redistributed
805 and/or modified under the same terms as Perl itself.