package Attribute::Handlers;
use 5.006;
use Carp;
use warnings;
use strict;
use vars qw($VERSION $AUTOLOAD);
$VERSION = '0.85'; # remember to update version in POD!
# $DB::single=1;
my %symcache;
sub findsym {
my ($pkg, $ref, $type) = @_;
return $symcache{$pkg,$ref} if $symcache{$pkg,$ref};
$type ||= ref($ref);
no strict 'refs';
foreach my $sym ( values %{$pkg."::"} ) {
use strict;
next unless ref ( \$sym ) eq 'GLOB';
return $symcache{$pkg,$ref} = \$sym
if *{$sym}{$type} && *{$sym}{$type} == $ref;
}
}
my %validtype = (
VAR => [qw[SCALAR ARRAY HASH]],
ANY => [qw[SCALAR ARRAY HASH CODE]],
"" => [qw[SCALAR ARRAY HASH CODE]],
SCALAR => [qw[SCALAR]],
ARRAY => [qw[ARRAY]],
HASH => [qw[HASH]],
CODE => [qw[CODE]],
);
my %lastattr;
my @declarations;
my %raw;
my %phase;
my %sigil = (SCALAR=>'$', ARRAY=>'@', HASH=>'%');
my $global_phase = 0;
my %global_phases = (
BEGIN => 0,
CHECK => 1,
INIT => 2,
END => 3,
);
my @global_phases = qw(BEGIN CHECK INIT END);
sub _usage_AH_ {
croak "Usage: use $_[0] autotie => {AttrName => TieClassName,...}";
}
my $qual_id = qr/^[_a-z]\w*(::[_a-z]\w*)*$/i;
sub import {
my $class = shift @_;
return unless $class eq "Attribute::Handlers";
while (@_) {
my $cmd = shift;
if ($cmd =~ /^autotie((?:ref)?)$/) {
my $tiedata = ($1 ? '$ref, ' : '') . '@$data';
my $mapping = shift;
_usage_AH_ $class unless ref($mapping) eq 'HASH';
while (my($attr, $tieclass) = each %$mapping) {
$tieclass =~ s/^([_a-z]\w*(::[_a-z]\w*)*)(.*)/$1/is;
my $args = $3||'()';
_usage_AH_ $class unless $attr =~ $qual_id
&& $tieclass =~ $qual_id
&& eval "use base q\0$tieclass\0; 1";
if ($tieclass->isa('Exporter')) {
local $Exporter::ExportLevel = 2;
$tieclass->import(eval $args);
}
$attr =~ s/__CALLER__/caller(1)/e;
$attr = caller()."::".$attr unless $attr =~ /::/;
eval qq{
sub $attr : ATTR(VAR) {
my (\$ref, \$data) = \@_[2,4];
my \$was_arrayref = ref \$data eq 'ARRAY';
\$data = [ \$data ] unless \$was_arrayref;
my \$type = ref(\$ref)||"value (".(\$ref||"").")";
(\$type eq 'SCALAR')? tie \$\$ref,'$tieclass',$tiedata
:(\$type eq 'ARRAY') ? tie \@\$ref,'$tieclass',$tiedata
:(\$type eq 'HASH') ? tie \%\$ref,'$tieclass',$tiedata
: die "Can't autotie a \$type\n"
} 1
} or die "Internal error: $@";
}
}
else {
croak "Can't understand $_";
}
}
}
sub _resolve_lastattr {
return unless $lastattr{ref};
my $sym = findsym @lastattr{'pkg','ref'}
or die "Internal error: $lastattr{pkg} symbol went missing";
my $name = *{$sym}{NAME};
warn "Declaration of $name attribute in package $lastattr{pkg} may clash with future reserved word\n"
if $^W and $name !~ /[A-Z]/;
foreach ( @{$validtype{$lastattr{type}}} ) {
no strict 'refs';
*{"$lastattr{pkg}::_ATTR_${_}_${name}"} = $lastattr{ref};
}
%lastattr = ();
}
sub AUTOLOAD {
return if $AUTOLOAD =~ /::DESTROY$/;
my ($class) = $AUTOLOAD =~ m/(.*)::/g;
$AUTOLOAD =~ m/_ATTR_(.*?)_(.*)/ or
croak "Can't locate class method '$AUTOLOAD' via package '$class'";
croak "Attribute handler '$2' doesn't handle $1 attributes";
}
my $builtin = qr/lvalue|method|locked|unique|shared/;
sub _gen_handler_AH_() {
return sub {
_resolve_lastattr;
my ($pkg, $ref, @attrs) = @_;
my (undef, $filename, $linenum) = caller 2;
foreach (@attrs) {
my ($attr, $data) = /^([a-z_]\w*)(?:[(](.*)[)])?$/is or next;
if ($attr eq 'ATTR') {
no strict 'refs';
$data ||= "ANY";
$raw{$ref} = $data =~ s/\s*,?\s*RAWDATA\s*,?\s*//;
$phase{$ref}{BEGIN} = 1
if $data =~ s/\s*,?\s*(BEGIN)\s*,?\s*//;
$phase{$ref}{INIT} = 1
if $data =~ s/\s*,?\s*(INIT)\s*,?\s*//;
$phase{$ref}{END} = 1
if $data =~ s/\s*,?\s*(END)\s*,?\s*//;
$phase{$ref}{CHECK} = 1
if $data =~ s/\s*,?\s*(CHECK)\s*,?\s*//
|| ! keys %{$phase{$ref}};
# Added for cleanup to not pollute next call.
(%lastattr = ()),
croak "Can't have two ATTR specifiers on one subroutine"
if keys %lastattr;
croak "Bad attribute type: ATTR($data)"
unless $validtype{$data};
%lastattr=(pkg=>$pkg,ref=>$ref,type=>$data);
}
else {
my $type = ref $ref;
my $handler = $pkg->can("_ATTR_${type}_${attr}");
next unless $handler;
my $decl = [$pkg, $ref, $attr, $data,
$raw{$handler}, $phase{$handler}, $filename, $linenum];
foreach my $gphase (@global_phases) {
_apply_handler_AH_($decl,$gphase)
if $global_phases{$gphase} <= $global_phase;
}
if ($global_phase != 0) {
# if _gen_handler_AH_ is being called after
# CHECK it's for a lexical, so make sure
# it didn't want to run anything later
local $Carp::CarpLevel = 2;
carp "Won't be able to apply END handler"
if $phase{$handler}{END};
}
else {
push @declarations, $decl
}
}
$_ = undef;
}
return grep {defined && !/$builtin/} @attrs;
}
}
{
no strict 'refs';
*{"Attribute::Handlers::UNIVERSAL::MODIFY_${_}_ATTRIBUTES"} =
_gen_handler_AH_ foreach @{$validtype{ANY}};
}
push @UNIVERSAL::ISA, 'Attribute::Handlers::UNIVERSAL'
unless grep /^Attribute::Handlers::UNIVERSAL$/, @UNIVERSAL::ISA;
sub _apply_handler_AH_ {
my ($declaration, $phase) = @_;
my ($pkg, $ref, $attr, $data, $raw, $handlerphase, $filename, $linenum) = @$declaration;
return unless $handlerphase->{$phase};
# print STDERR "Handling $attr on $ref in $phase with [$data]\n";
my $type = ref $ref;
my $handler = "_ATTR_${type}_${attr}";
my $sym = findsym($pkg, $ref);
$sym ||= $type eq 'CODE' ? 'ANON' : 'LEXICAL';
no warnings;
if (!$raw && defined($data)) {
if ($data ne '') {
my $evaled = eval("package $pkg; no warnings; no strict;
local \$SIG{__WARN__}=sub{die}; [$data]");
$data = $evaled unless $@;
}
else { $data = undef }
}
$pkg->$handler($sym,
(ref $sym eq 'GLOB' ? *{$sym}{ref $ref}||$ref : $ref),
$attr,
$data,
$phase,
$filename,
$linenum,
);
return 1;
}
{
no warnings 'void';
CHECK {
$global_phase++;
_resolve_lastattr;
_apply_handler_AH_($_,'CHECK') foreach @declarations;
}
INIT {
$global_phase++;
_apply_handler_AH_($_,'INIT') foreach @declarations
}
}
END { $global_phase++; _apply_handler_AH_($_,'END') foreach @declarations }
1;
__END__
=head1 NAME
Attribute::Handlers - Simpler definition of attribute handlers
=head1 VERSION
This document describes version 0.85 of Attribute::Handlers,
released June 11, 2009.
=head1 SYNOPSIS
package MyClass;
require 5.006;
use Attribute::Handlers;
no warnings 'redefine';
sub Good : ATTR(SCALAR) {
my ($package, $symbol, $referent, $attr, $data) = @_;
# Invoked for any scalar variable with a :Good attribute,
# provided the variable was declared in MyClass (or
# a derived class) or typed to MyClass.
# Do whatever to $referent here (executed in CHECK phase).
...
}
sub Bad : ATTR(SCALAR) {
# Invoked for any scalar variable with a :Bad attribute,
# provided the variable was declared in MyClass (or
# a derived class) or typed to MyClass.
...
}
sub Good : ATTR(ARRAY) {
# Invoked for any array variable with a :Good attribute,
# provided the variable was declared in MyClass (or
# a derived class) or typed to MyClass.
...
}
sub Good : ATTR(HASH) {
# Invoked for any hash variable with a :Good attribute,
# provided the variable was declared in MyClass (or
# a derived class) or typed to MyClass.
...
}
sub Ugly : ATTR(CODE) {
# Invoked for any subroutine declared in MyClass (or a
# derived class) with an :Ugly attribute.
...
}
sub Omni : ATTR {
# Invoked for any scalar, array, hash, or subroutine
# with an :Omni attribute, provided the variable or
# subroutine was declared in MyClass (or a derived class)
# or the variable was typed to MyClass.
# Use ref($_[2]) to determine what kind of referent it was.
...
}
use Attribute::Handlers autotie => { Cycle => Tie::Cycle };
my $next : Cycle(['A'..'Z']);
=head1 DESCRIPTION
This module, when inherited by a package, allows that package's class to
define attribute handler subroutines for specific attributes. Variables
and subroutines subsequently defined in that package, or in packages
derived from that package may be given attributes with the same names as
the attribute handler subroutines, which will then be called in one of
the compilation phases (i.e. in a C, C, C, or C
block). (C blocks don't correspond to a global compilation
phase, so they can't be specified here.)
To create a handler, define it as a subroutine with the same name as
the desired attribute, and declare the subroutine itself with the
attribute C<:ATTR>. For example:
package LoudDecl;
use Attribute::Handlers;
sub Loud :ATTR {
my ($package, $symbol, $referent, $attr, $data, $phase, $filename, $linenum) = @_;
print STDERR
ref($referent), " ",
*{$symbol}{NAME}, " ",
"($referent) ", "was just declared ",
"and ascribed the ${attr} attribute ",
"with data ($data)\n",
"in phase $phase\n",
"in file $filename at line $linenum\n";
}
This creates a handler for the attribute C<:Loud> in the class LoudDecl.
Thereafter, any subroutine declared with a C<:Loud> attribute in the class
LoudDecl:
package LoudDecl;
sub foo: Loud {...}
causes the above handler to be invoked, and passed:
=over
=item [0]
the name of the package into which it was declared;
=item [1]
a reference to the symbol table entry (typeglob) containing the subroutine;
=item [2]
a reference to the subroutine;
=item [3]
the name of the attribute;
=item [4]
any data associated with that attribute;
=item [5]
the name of the phase in which the handler is being invoked;
=item [6]
the filename in which the handler is being invoked;
=item [7]
the line number in this file.
=back
Likewise, declaring any variables with the C<:Loud> attribute within the
package:
package LoudDecl;
my $foo :Loud;
my @foo :Loud;
my %foo :Loud;
will cause the handler to be called with a similar argument list (except,
of course, that C<$_[2]> will be a reference to the variable).
The package name argument will typically be the name of the class into
which the subroutine was declared, but it may also be the name of a derived
class (since handlers are inherited).
If a lexical variable is given an attribute, there is no symbol table to
which it belongs, so the symbol table argument (C<$_[1]>) is set to the
string C<'LEXICAL'> in that case. Likewise, ascribing an attribute to
an anonymous subroutine results in a symbol table argument of C<'ANON'>.
The data argument passes in the value (if any) associated with the
attribute. For example, if C<&foo> had been declared:
sub foo :Loud("turn it up to 11, man!") {...}
then a reference to an array containing the string
C<"turn it up to 11, man!"> would be passed as the last argument.
Attribute::Handlers makes strenuous efforts to convert
the data argument (C<$_[4]>) to a useable form before passing it to
the handler (but see L<"Non-interpretive attribute handlers">).
If those efforts succeed, the interpreted data is passed in an array
reference; if they fail, the raw data is passed as a string.
For example, all of these:
sub foo :Loud(till=>ears=>are=>bleeding) {...}
sub foo :Loud(qw/till ears are bleeding/) {...}
sub foo :Loud(qw/my, ears, are, bleeding/) {...}
sub foo :Loud(till,ears,are,bleeding) {...}
causes it to pass C<['till','ears','are','bleeding']> as the handler's
data argument. While:
sub foo :Loud(['till','ears','are','bleeding']) {...}
causes it to pass C<[ ['till','ears','are','bleeding'] ]>; the array
reference specified in the data being passed inside the standard
array reference indicating successful interpretation.
However, if the data can't be parsed as valid Perl, then
it is passed as an uninterpreted string. For example:
sub foo :Loud(my,ears,are,bleeding) {...}
sub foo :Loud(qw/my ears are bleeding) {...}
cause the strings C<'my,ears,are,bleeding'> and
C<'qw/my ears are bleeding'> respectively to be passed as the
data argument.
If no value is associated with the attribute, C is passed.
=head2 Typed lexicals
Regardless of the package in which it is declared, if a lexical variable is
ascribed an attribute, the handler that is invoked is the one belonging to
the package to which it is typed. For example, the following declarations:
package OtherClass;
my LoudDecl $loudobj : Loud;
my LoudDecl @loudobjs : Loud;
my LoudDecl %loudobjex : Loud;
causes the LoudDecl::Loud handler to be invoked (even if OtherClass also
defines a handler for C<:Loud> attributes).
=head2 Type-specific attribute handlers
If an attribute handler is declared and the C<:ATTR> specifier is
given the name of a built-in type (C, C, C, or C),
the handler is only applied to declarations of that type. For example,
the following definition:
package LoudDecl;
sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" }
creates an attribute handler that applies only to scalars:
package Painful;
use base LoudDecl;
my $metal : RealLoud; # invokes &LoudDecl::RealLoud
my @metal : RealLoud; # error: unknown attribute
my %metal : RealLoud; # error: unknown attribute
sub metal : RealLoud {...} # error: unknown attribute
You can, of course, declare separate handlers for these types as well
(but you'll need to specify C to do it quietly):
package LoudDecl;
use Attribute::Handlers;
no warnings 'redefine';
sub RealLoud :ATTR(SCALAR) { print "Yeeeeow!" }
sub RealLoud :ATTR(ARRAY) { print "Urrrrrrrrrr!" }
sub RealLoud :ATTR(HASH) { print "Arrrrrgggghhhhhh!" }
sub RealLoud :ATTR(CODE) { croak "Real loud sub torpedoed" }
You can also explicitly indicate that a single handler is meant to be
used for all types of referents like so:
package LoudDecl;
use Attribute::Handlers;
sub SeriousLoud :ATTR(ANY) { warn "Hearing loss imminent" }
(I.e. C is a synonym for C<:ATTR>).
=head2 Non-interpretive attribute handlers
Occasionally the strenuous efforts Attribute::Handlers makes to convert
the data argument (C<$_[4]>) to a useable form before passing it to
the handler get in the way.
You can turn off that eagerness-to-help by declaring
an attribute handler with the keyword C. For example:
sub Raw : ATTR(RAWDATA) {...}
sub Nekkid : ATTR(SCALAR,RAWDATA) {...}
sub Au::Naturale : ATTR(RAWDATA,ANY) {...}
Then the handler makes absolutely no attempt to interpret the data it
receives and simply passes it as a string:
my $power : Raw(1..100); # handlers receives "1..100"
=head2 Phase-specific attribute handlers
By default, attribute handlers are called at the end of the compilation
phase (in a C block). This seems to be optimal in most cases because
most things that can be defined are defined by that point but nothing has
been executed.
However, it is possible to set up attribute handlers that are called at
other points in the program's compilation or execution, by explicitly
stating the phase (or phases) in which you wish the attribute handler to
be called. For example:
sub Early :ATTR(SCALAR,BEGIN) {...}
sub Normal :ATTR(SCALAR,CHECK) {...}
sub Late :ATTR(SCALAR,INIT) {...}
sub Final :ATTR(SCALAR,END) {...}
sub Bookends :ATTR(SCALAR,BEGIN,END) {...}
As the last example indicates, a handler may be set up to be (re)called in
two or more phases. The phase name is passed as the handler's final argument.
Note that attribute handlers that are scheduled for the C phase
are handled as soon as the attribute is detected (i.e. before any
subsequently defined C blocks are executed).
=head2 Attributes as C interfaces
Attributes make an excellent and intuitive interface through which to tie
variables. For example:
use Attribute::Handlers;
use Tie::Cycle;
sub UNIVERSAL::Cycle : ATTR(SCALAR) {
my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
$data = [ $data ] unless ref $data eq 'ARRAY';
tie $$referent, 'Tie::Cycle', $data;
}
# and thereafter...
package main;
my $next : Cycle('A'..'Z'); # $next is now a tied variable
while (<>) {
print $next;
}
Note that, because the C attribute receives its arguments in the
C<$data> variable, if the attribute is given a list of arguments, C<$data>
will consist of a single array reference; otherwise, it will consist of the
single argument directly. Since Tie::Cycle requires its cycling values to
be passed as an array reference, this means that we need to wrap
non-array-reference arguments in an array constructor:
$data = [ $data ] unless ref $data eq 'ARRAY';
Typically, however, things are the other way around: the tieable class expects
its arguments as a flattened list, so the attribute looks like:
sub UNIVERSAL::Cycle : ATTR(SCALAR) {
my ($package, $symbol, $referent, $attr, $data, $phase) = @_;
my @data = ref $data eq 'ARRAY' ? @$data : $data;
tie $$referent, 'Tie::Whatever', @data;
}
This software pattern is so widely applicable that Attribute::Handlers
provides a way to automate it: specifying C<'autotie'> in the
C