580 lines
18 KiB
Perl
580 lines
18 KiB
Perl
package NEXT;
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use Carp;
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use strict;
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use warnings;
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use overload ();
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our $VERSION = '0.67_01';
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sub NEXT::ELSEWHERE::ancestors
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{
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my @inlist = shift;
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my @outlist = ();
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while (my $next = shift @inlist) {
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push @outlist, $next;
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no strict 'refs';
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unshift @inlist, @{"$outlist[-1]::ISA"};
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}
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return @outlist;
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}
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sub NEXT::ELSEWHERE::ordered_ancestors
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{
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my @inlist = shift;
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my @outlist = ();
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while (my $next = shift @inlist) {
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push @outlist, $next;
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no strict 'refs';
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push @inlist, @{"$outlist[-1]::ISA"};
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}
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return sort { $a->isa($b) ? -1
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: $b->isa($a) ? +1
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: 0 } @outlist;
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}
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sub NEXT::ELSEWHERE::buildAUTOLOAD
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{
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my $autoload_name = caller() . '::AUTOLOAD';
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no strict 'refs';
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*{$autoload_name} = sub {
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my ($self) = @_;
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my $depth = 1;
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until (((caller($depth))[3]||q{}) !~ /^\(eval\)$/) { $depth++ }
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my $caller = (caller($depth))[3];
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my $wanted = $NEXT::AUTOLOAD || $autoload_name;
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undef $NEXT::AUTOLOAD;
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my ($caller_class, $caller_method) = do { $caller =~ m{(.*)::(.*)}g };
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my ($wanted_class, $wanted_method) = do { $wanted =~ m{(.*)::(.*)}g };
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croak "Can't call $wanted from $caller"
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unless $caller_method eq $wanted_method;
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my $key = ref $self && overload::Overloaded($self)
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? overload::StrVal($self) : $self;
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local ($NEXT::NEXT{$key,$wanted_method}, $NEXT::SEEN) =
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($NEXT::NEXT{$key,$wanted_method}, $NEXT::SEEN);
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unless ($NEXT::NEXT{$key,$wanted_method}) {
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my @forebears =
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NEXT::ELSEWHERE::ancestors ref $self || $self,
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$wanted_class;
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while (@forebears) {
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last if shift @forebears eq $caller_class
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}
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no strict 'refs';
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# Use *{"..."} when first accessing the CODE slot, to make sure
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# any typeglob stub is upgraded to a full typeglob.
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@{$NEXT::NEXT{$key,$wanted_method}} =
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map {
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my $stash = \%{"${_}::"};
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($stash->{$caller_method} && (*{"${_}::$caller_method"}{CODE}))
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? *{$stash->{$caller_method}}{CODE}
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: () } @forebears
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unless $wanted_method eq 'AUTOLOAD';
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@{$NEXT::NEXT{$key,$wanted_method}} =
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map {
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my $stash = \%{"${_}::"};
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($stash->{AUTOLOAD} && (*{"${_}::AUTOLOAD"}{CODE}))
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? "${_}::AUTOLOAD"
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: () } @forebears
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unless @{$NEXT::NEXT{$key,$wanted_method}||[]};
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$NEXT::SEEN->{$key,*{$caller}{CODE}}++;
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}
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my $call_method = shift @{$NEXT::NEXT{$key,$wanted_method}};
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while (do { $wanted_class =~ /^NEXT\b.*\b(UNSEEN|DISTINCT)\b/ }
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&& defined $call_method
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&& $NEXT::SEEN->{$key,$call_method}++) {
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$call_method = shift @{$NEXT::NEXT{$key,$wanted_method}};
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}
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unless (defined $call_method) {
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return unless do { $wanted_class =~ /^NEXT:.*:ACTUAL/ };
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(local $Carp::CarpLevel)++;
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croak qq(Can't locate object method "$wanted_method" ),
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qq(via package "$caller_class");
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};
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return $self->$call_method(@_[1..$#_]) if ref $call_method eq 'CODE';
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no strict 'refs';
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do { ($wanted_method=${$caller_class."::AUTOLOAD"}) =~ s/.*::// }
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if $wanted_method eq 'AUTOLOAD';
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$$call_method = $caller_class."::NEXT::".$wanted_method;
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return $call_method->(@_);
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};
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}
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no strict 'vars';
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package NEXT; NEXT::ELSEWHERE::buildAUTOLOAD();
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package NEXT::UNSEEN; @ISA = 'NEXT'; NEXT::ELSEWHERE::buildAUTOLOAD();
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package NEXT::DISTINCT; @ISA = 'NEXT'; NEXT::ELSEWHERE::buildAUTOLOAD();
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package NEXT::ACTUAL; @ISA = 'NEXT'; NEXT::ELSEWHERE::buildAUTOLOAD();
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package NEXT::ACTUAL::UNSEEN; @ISA = 'NEXT'; NEXT::ELSEWHERE::buildAUTOLOAD();
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package NEXT::ACTUAL::DISTINCT; @ISA = 'NEXT'; NEXT::ELSEWHERE::buildAUTOLOAD();
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package NEXT::UNSEEN::ACTUAL; @ISA = 'NEXT'; NEXT::ELSEWHERE::buildAUTOLOAD();
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package NEXT::DISTINCT::ACTUAL; @ISA = 'NEXT'; NEXT::ELSEWHERE::buildAUTOLOAD();
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package
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EVERY;
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sub EVERY::ELSEWHERE::buildAUTOLOAD {
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my $autoload_name = caller() . '::AUTOLOAD';
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no strict 'refs';
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*{$autoload_name} = sub {
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my ($self) = @_;
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my $depth = 1;
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until (((caller($depth))[3]||q{}) !~ /^\(eval\)$/) { $depth++ }
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my $caller = (caller($depth))[3];
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my $wanted = $EVERY::AUTOLOAD || $autoload_name;
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undef $EVERY::AUTOLOAD;
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my ($wanted_class, $wanted_method) = do { $wanted =~ m{(.*)::(.*)}g };
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my $key = ref($self) && overload::Overloaded($self)
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? overload::StrVal($self) : $self;
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local $NEXT::ALREADY_IN_EVERY{$key,$wanted_method} =
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$NEXT::ALREADY_IN_EVERY{$key,$wanted_method};
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return if $NEXT::ALREADY_IN_EVERY{$key,$wanted_method}++;
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my @forebears = NEXT::ELSEWHERE::ordered_ancestors ref $self || $self,
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$wanted_class;
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@forebears = reverse @forebears if do { $wanted_class =~ /\bLAST\b/ };
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no strict 'refs';
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my %seen;
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my @every = map { my $sub = "${_}::$wanted_method";
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!*{$sub}{CODE} || $seen{$sub}++ ? () : $sub
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} @forebears
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unless $wanted_method eq 'AUTOLOAD';
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my $want = wantarray;
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if (@every) {
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if ($want) {
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return map {($_, [$self->$_(@_[1..$#_])])} @every;
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}
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elsif (defined $want) {
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return { map {($_, scalar($self->$_(@_[1..$#_])))}
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@every
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};
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}
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else {
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$self->$_(@_[1..$#_]) for @every;
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return;
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}
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}
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@every = map { my $sub = "${_}::AUTOLOAD";
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!*{$sub}{CODE} || $seen{$sub}++ ? () : "${_}::AUTOLOAD"
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} @forebears;
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if ($want) {
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return map { $$_ = ref($self)."::EVERY::".$wanted_method;
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($_, [$self->$_(@_[1..$#_])]);
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} @every;
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}
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elsif (defined $want) {
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return { map { $$_ = ref($self)."::EVERY::".$wanted_method;
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($_, scalar($self->$_(@_[1..$#_])))
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} @every
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};
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}
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else {
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for (@every) {
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$$_ = ref($self)."::EVERY::".$wanted_method;
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$self->$_(@_[1..$#_]);
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}
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return;
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}
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};
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}
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package EVERY::LAST; @ISA = 'EVERY'; EVERY::ELSEWHERE::buildAUTOLOAD();
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package
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EVERY; @ISA = 'NEXT'; EVERY::ELSEWHERE::buildAUTOLOAD();
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1;
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__END__
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=head1 NAME
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NEXT - Provide a pseudo-class NEXT (et al) that allows method redispatch
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=head1 SYNOPSIS
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use NEXT;
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package P;
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sub P::method { print "$_[0]: P method\n"; $_[0]->NEXT::method() }
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sub P::DESTROY { print "$_[0]: P dtor\n"; $_[0]->NEXT::DESTROY() }
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package Q;
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use base qw( P );
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sub Q::AUTOLOAD { print "$_[0]: Q AUTOLOAD\n"; $_[0]->NEXT::AUTOLOAD() }
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sub Q::DESTROY { print "$_[0]: Q dtor\n"; $_[0]->NEXT::DESTROY() }
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package R;
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sub R::method { print "$_[0]: R method\n"; $_[0]->NEXT::method() }
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sub R::AUTOLOAD { print "$_[0]: R AUTOLOAD\n"; $_[0]->NEXT::AUTOLOAD() }
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sub R::DESTROY { print "$_[0]: R dtor\n"; $_[0]->NEXT::DESTROY() }
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package S;
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use base qw( Q R );
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sub S::method { print "$_[0]: S method\n"; $_[0]->NEXT::method() }
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sub S::AUTOLOAD { print "$_[0]: S AUTOLOAD\n"; $_[0]->NEXT::AUTOLOAD() }
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sub S::DESTROY { print "$_[0]: S dtor\n"; $_[0]->NEXT::DESTROY() }
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package main;
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my $obj = bless {}, "S";
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$obj->method(); # Calls S::method, P::method, R::method
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$obj->missing_method(); # Calls S::AUTOLOAD, Q::AUTOLOAD, R::AUTOLOAD
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# Clean-up calls S::DESTROY, Q::DESTROY, P::DESTROY, R::DESTROY
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=head1 DESCRIPTION
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The C<NEXT> module adds a pseudoclass named C<NEXT> to any program
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that uses it. If a method C<m> calls C<$self-E<gt>NEXT::m()>, the call to
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C<m> is redispatched as if the calling method had not originally been found.
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B<Note:> before using this module,
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you should look at L<next::method|https://metacpan.org/pod/mro#next::method>
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in the core L<mro> module.
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C<mro> has been a core module since Perl 5.9.5.
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In other words, a call to C<$self-E<gt>NEXT::m()> resumes the depth-first,
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left-to-right search of C<$self>'s class hierarchy that resulted in the
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original call to C<m>.
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Note that this is not the same thing as C<$self-E<gt>SUPER::m()>, which
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begins a new dispatch that is restricted to searching the ancestors
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of the current class. C<$self-E<gt>NEXT::m()> can backtrack
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past the current class -- to look for a suitable method in other
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ancestors of C<$self> -- whereas C<$self-E<gt>SUPER::m()> cannot.
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A typical use would be in the destructors of a class hierarchy,
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as illustrated in the SYNOPSIS above. Each class in the hierarchy
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has a DESTROY method that performs some class-specific action
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and then redispatches the call up the hierarchy. As a result,
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when an object of class S is destroyed, the destructors of I<all>
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its parent classes are called (in depth-first, left-to-right order).
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Another typical use of redispatch would be in C<AUTOLOAD>'ed methods.
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If such a method determined that it was not able to handle a
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particular call, it might choose to redispatch that call, in the
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hope that some other C<AUTOLOAD> (above it, or to its left) might
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do better.
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By default, if a redispatch attempt fails to find another method
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elsewhere in the objects class hierarchy, it quietly gives up and does
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nothing (but see L<"Enforcing redispatch">). This gracious acquiescence
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is also unlike the (generally annoying) behaviour of C<SUPER>, which
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throws an exception if it cannot redispatch.
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Note that it is a fatal error for any method (including C<AUTOLOAD>)
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to attempt to redispatch any method that does not have the
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same name. For example:
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sub S::oops { print "oops!\n"; $_[0]->NEXT::other_method() }
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=head2 Enforcing redispatch
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It is possible to make C<NEXT> redispatch more demandingly (i.e. like
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C<SUPER> does), so that the redispatch throws an exception if it cannot
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find a "next" method to call.
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To do this, simple invoke the redispatch as:
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$self->NEXT::ACTUAL::method();
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rather than:
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$self->NEXT::method();
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The C<ACTUAL> tells C<NEXT> that there must actually be a next method to call,
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or it should throw an exception.
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C<NEXT::ACTUAL> is most commonly used in C<AUTOLOAD> methods, as a means to
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decline an C<AUTOLOAD> request, but preserve the normal exception-on-failure
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semantics:
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sub AUTOLOAD {
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if ($AUTOLOAD =~ /foo|bar/) {
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# handle here
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}
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else { # try elsewhere
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shift()->NEXT::ACTUAL::AUTOLOAD(@_);
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}
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}
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By using C<NEXT::ACTUAL>, if there is no other C<AUTOLOAD> to handle the
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method call, an exception will be thrown (as usually happens in the absence of
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a suitable C<AUTOLOAD>).
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=head2 Avoiding repetitions
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If C<NEXT> redispatching is used in the methods of a "diamond" class hierarchy:
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# A B
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# / \ /
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# C D
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# \ /
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# E
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use NEXT;
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package A;
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sub foo { print "called A::foo\n"; shift->NEXT::foo() }
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package B;
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sub foo { print "called B::foo\n"; shift->NEXT::foo() }
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package C; @ISA = qw( A );
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sub foo { print "called C::foo\n"; shift->NEXT::foo() }
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package D; @ISA = qw(A B);
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sub foo { print "called D::foo\n"; shift->NEXT::foo() }
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package E; @ISA = qw(C D);
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sub foo { print "called E::foo\n"; shift->NEXT::foo() }
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E->foo();
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then derived classes may (re-)inherit base-class methods through two or
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more distinct paths (e.g. in the way C<E> inherits C<A::foo> twice --
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through C<C> and C<D>). In such cases, a sequence of C<NEXT> redispatches
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will invoke the multiply inherited method as many times as it is
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inherited. For example, the above code prints:
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called E::foo
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called C::foo
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called A::foo
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called D::foo
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called A::foo
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called B::foo
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(i.e. C<A::foo> is called twice).
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In some cases this I<may> be the desired effect within a diamond hierarchy,
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but in others (e.g. for destructors) it may be more appropriate to
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call each method only once during a sequence of redispatches.
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To cover such cases, you can redispatch methods via:
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$self->NEXT::DISTINCT::method();
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rather than:
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$self->NEXT::method();
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This causes the redispatcher to only visit each distinct C<method> method
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once. That is, to skip any classes in the hierarchy that it has
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already visited during redispatch. So, for example, if the
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previous example were rewritten:
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package A;
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sub foo { print "called A::foo\n"; shift->NEXT::DISTINCT::foo() }
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package B;
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sub foo { print "called B::foo\n"; shift->NEXT::DISTINCT::foo() }
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package C; @ISA = qw( A );
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sub foo { print "called C::foo\n"; shift->NEXT::DISTINCT::foo() }
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package D; @ISA = qw(A B);
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sub foo { print "called D::foo\n"; shift->NEXT::DISTINCT::foo() }
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package E; @ISA = qw(C D);
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sub foo { print "called E::foo\n"; shift->NEXT::DISTINCT::foo() }
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E->foo();
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then it would print:
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called E::foo
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called C::foo
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called A::foo
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called D::foo
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called B::foo
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and omit the second call to C<A::foo> (since it would not be distinct
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from the first call to C<A::foo>).
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Note that you can also use:
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$self->NEXT::DISTINCT::ACTUAL::method();
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or:
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$self->NEXT::ACTUAL::DISTINCT::method();
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to get both unique invocation I<and> exception-on-failure.
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Note that, for historical compatibility, you can also use
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C<NEXT::UNSEEN> instead of C<NEXT::DISTINCT>.
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=head2 Invoking all versions of a method with a single call
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Yet another pseudo-class that C<NEXT> provides is C<EVERY>.
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Its behaviour is considerably simpler than that of the C<NEXT> family.
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A call to:
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$obj->EVERY::foo();
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calls I<every> method named C<foo> that the object in C<$obj> has inherited.
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That is:
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use NEXT;
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package A; @ISA = qw(B D X);
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sub foo { print "A::foo " }
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package B; @ISA = qw(D X);
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sub foo { print "B::foo " }
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package X; @ISA = qw(D);
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sub foo { print "X::foo " }
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package D;
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sub foo { print "D::foo " }
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package main;
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my $obj = bless {}, 'A';
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$obj->EVERY::foo(); # prints" A::foo B::foo X::foo D::foo
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Prefixing a method call with C<EVERY::> causes every method in the
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object's hierarchy with that name to be invoked. As the above example
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illustrates, they are not called in Perl's usual "left-most-depth-first"
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order. Instead, they are called "breadth-first-dependency-wise".
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That means that the inheritance tree of the object is traversed breadth-first
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and the resulting order of classes is used as the sequence in which methods
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are called. However, that sequence is modified by imposing a rule that the
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appropriate method of a derived class must be called before the same method of
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any ancestral class. That's why, in the above example, C<X::foo> is called
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before C<D::foo>, even though C<D> comes before C<X> in C<@B::ISA>.
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In general, there's no need to worry about the order of calls. They will be
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left-to-right, breadth-first, most-derived-first. This works perfectly for
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most inherited methods (including destructors), but is inappropriate for
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some kinds of methods (such as constructors, cloners, debuggers, and
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initializers) where it's more appropriate that the least-derived methods be
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called first (as more-derived methods may rely on the behaviour of their
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"ancestors"). In that case, instead of using the C<EVERY> pseudo-class:
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$obj->EVERY::foo(); # prints" A::foo B::foo X::foo D::foo
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you can use the C<EVERY::LAST> pseudo-class:
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$obj->EVERY::LAST::foo(); # prints" D::foo X::foo B::foo A::foo
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which reverses the order of method call.
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Whichever version is used, the actual methods are called in the same
|
|
context (list, scalar, or void) as the original call via C<EVERY>, and return:
|
|
|
|
=over
|
|
|
|
=item *
|
|
|
|
A hash of array references in list context. Each entry of the hash has the
|
|
fully qualified method name as its key and a reference to an array containing
|
|
the method's list-context return values as its value.
|
|
|
|
=item *
|
|
|
|
A reference to a hash of scalar values in scalar context. Each entry of the hash has the
|
|
fully qualified method name as its key and the method's scalar-context return values as its value.
|
|
|
|
=item *
|
|
|
|
Nothing in void context (obviously).
|
|
|
|
=back
|
|
|
|
=head2 Using C<EVERY> methods
|
|
|
|
The typical way to use an C<EVERY> call is to wrap it in another base
|
|
method, that all classes inherit. For example, to ensure that every
|
|
destructor an object inherits is actually called (as opposed to just the
|
|
left-most-depth-first-est one):
|
|
|
|
package Base;
|
|
sub DESTROY { $_[0]->EVERY::Destroy }
|
|
|
|
package Derived1;
|
|
use base 'Base';
|
|
sub Destroy {...}
|
|
|
|
package Derived2;
|
|
use base 'Base', 'Derived1';
|
|
sub Destroy {...}
|
|
|
|
et cetera. Every derived class than needs its own clean-up
|
|
behaviour simply adds its own C<Destroy> method (I<not> a C<DESTROY> method),
|
|
which the call to C<EVERY::LAST::Destroy> in the inherited destructor
|
|
then correctly picks up.
|
|
|
|
Likewise, to create a class hierarchy in which every initializer inherited by
|
|
a new object is invoked:
|
|
|
|
package Base;
|
|
sub new {
|
|
my ($class, %args) = @_;
|
|
my $obj = bless {}, $class;
|
|
$obj->EVERY::LAST::Init(\%args);
|
|
}
|
|
|
|
package Derived1;
|
|
use base 'Base';
|
|
sub Init {
|
|
my ($argsref) = @_;
|
|
...
|
|
}
|
|
|
|
package Derived2;
|
|
use base 'Base', 'Derived1';
|
|
sub Init {
|
|
my ($argsref) = @_;
|
|
...
|
|
}
|
|
|
|
et cetera. Every derived class than needs some additional initialization
|
|
behaviour simply adds its own C<Init> method (I<not> a C<new> method),
|
|
which the call to C<EVERY::LAST::Init> in the inherited constructor
|
|
then correctly picks up.
|
|
|
|
=head1 SEE ALSO
|
|
|
|
L<mro>
|
|
(in particular L<next::method|https://metacpan.org/pod/mro#next::method>),
|
|
which has been a core module since Perl 5.9.5.
|
|
|
|
=head1 AUTHOR
|
|
|
|
Damian Conway (damian@conway.org)
|
|
|
|
=head1 BUGS AND IRRITATIONS
|
|
|
|
Because it's a module, not an integral part of the interpreter, C<NEXT>
|
|
has to guess where the surrounding call was found in the method
|
|
look-up sequence. In the presence of diamond inheritance patterns
|
|
it occasionally guesses wrong.
|
|
|
|
It's also too slow (despite caching).
|
|
|
|
Comment, suggestions, and patches welcome.
|
|
|
|
=head1 COPYRIGHT
|
|
|
|
Copyright (c) 2000-2001, Damian Conway. All Rights Reserved.
|
|
This module is free software. It may be used, redistributed
|
|
and/or modified under the same terms as Perl itself.
|