X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=lib%2FNEXT.pm;h=68b3df25477cf784a01e951cec24f2486e9c6493;hb=e7ec2331900cd22a50f48dd01fa18bd3026f6253;hp=144b14572942d0e20bdc730ab757fe974477b2d8;hpb=e4783b1cfc9dd8d29eeb056a14be5c1e534ede17;p=p5sagit%2Fp5-mst-13.2.git diff --git a/lib/NEXT.pm b/lib/NEXT.pm index 144b145..68b3df2 100644 --- a/lib/NEXT.pm +++ b/lib/NEXT.pm @@ -1,13 +1,14 @@ package NEXT; +$VERSION = '0.50'; use Carp; use strict; sub ancestors { - my @inlist = @_; + my @inlist = shift; my @outlist = (); - while (@inlist) { - push @outlist, shift @inlist; + while (my $next = shift @inlist) { + push @outlist, $next; no strict 'refs'; unshift @inlist, @{"$outlist[-1]::ISA"}; } @@ -25,26 +26,49 @@ sub AUTOLOAD croak "Can't call $wanted from $caller" unless $caller_method eq $wanted_method; - local $NEXT::NEXT{$self,$wanted_method} = - $NEXT::NEXT{$self,$wanted_method}; + local ($NEXT::NEXT{$self,$wanted_method}, $NEXT::SEEN) = + ($NEXT::NEXT{$self,$wanted_method}, $NEXT::SEEN); - unless (@{$NEXT::NEXT{$self,$wanted_method}||[]}) { - my @forebears = ancestors ref $self; + + unless ($NEXT::NEXT{$self,$wanted_method}) { + my @forebears = + ancestors ref $self || $self, $wanted_class; while (@forebears) { last if shift @forebears eq $caller_class } no strict 'refs'; @{$NEXT::NEXT{$self,$wanted_method}} = - map { *{"${_}::$caller_method"}{CODE}||() } @forebears; + map { *{"${_}::$caller_method"}{CODE}||() } @forebears + unless $wanted_method eq 'AUTOLOAD'; @{$NEXT::NEXT{$self,$wanted_method}} = - map { *{"${_}::AUTOLOAD"}{CODE}||() } @forebears - unless @{$NEXT::NEXT{$self,$wanted_method}}; + map { (*{"${_}::AUTOLOAD"}{CODE}) ? "${_}::AUTOLOAD" : ()} @forebears + unless @{$NEXT::NEXT{$self,$wanted_method}||[]}; + } + my $call_method = shift @{$NEXT::NEXT{$self,$wanted_method}}; + while ($wanted_class =~ /^NEXT:.*:UNSEEN/ && defined $call_method + && $NEXT::SEEN->{$self,$call_method}++) { + $call_method = shift @{$NEXT::NEXT{$self,$wanted_method}}; } - $wanted_method = shift @{$NEXT::NEXT{$self,$wanted_method}}; - return shift()->$wanted_method(@_) if $wanted_method; - return; + unless (defined $call_method) { + return unless $wanted_class =~ /^NEXT:.*:ACTUAL/; + (local $Carp::CarpLevel)++; + croak qq(Can't locate object method "$wanted_method" ), + qq(via package "$caller_class"); + }; + return shift()->$call_method(@_) if ref $call_method eq 'CODE'; + no strict 'refs'; + ($wanted_method=${$caller_class."::AUTOLOAD"}) =~ s/.*::// + if $wanted_method eq 'AUTOLOAD'; + $$call_method = $caller_class."::NEXT::".$wanted_method; + return $call_method->(@_); } +no strict 'vars'; +package NEXT::UNSEEN; @ISA = 'NEXT'; +package NEXT::ACTUAL; @ISA = 'NEXT'; +package NEXT::ACTUAL::UNSEEN; @ISA = 'NEXT'; +package NEXT::UNSEEN::ACTUAL; @ISA = 'NEXT'; + 1; __END__ @@ -56,36 +80,36 @@ NEXT.pm - Provide a pseudo-class NEXT that allows method redispatch =head1 SYNOPSIS - use NEXT; + use NEXT; - package A; - sub A::method { print "$_[0]: A method\n"; $_[0]->NEXT::method() } - sub A::DESTROY { print "$_[0]: A dtor\n"; $_[0]->NEXT::DESTROY() } + package A; + sub A::method { print "$_[0]: A method\n"; $_[0]->NEXT::method() } + sub A::DESTROY { print "$_[0]: A dtor\n"; $_[0]->NEXT::DESTROY() } - package B; - use base qw( A ); - sub B::AUTOLOAD { print "$_[0]: B AUTOLOAD\n"; $_[0]->NEXT::AUTOLOAD() } - sub B::DESTROY { print "$_[0]: B dtor\n"; $_[0]->NEXT::DESTROY() } + package B; + use base qw( A ); + sub B::AUTOLOAD { print "$_[0]: B AUTOLOAD\n"; $_[0]->NEXT::AUTOLOAD() } + sub B::DESTROY { print "$_[0]: B dtor\n"; $_[0]->NEXT::DESTROY() } - package C; - sub C::method { print "$_[0]: C method\n"; $_[0]->NEXT::method() } - sub C::AUTOLOAD { print "$_[0]: C AUTOLOAD\n"; $_[0]->NEXT::AUTOLOAD() } - sub C::DESTROY { print "$_[0]: C dtor\n"; $_[0]->NEXT::DESTROY() } + package C; + sub C::method { print "$_[0]: C method\n"; $_[0]->NEXT::method() } + sub C::AUTOLOAD { print "$_[0]: C AUTOLOAD\n"; $_[0]->NEXT::AUTOLOAD() } + sub C::DESTROY { print "$_[0]: C dtor\n"; $_[0]->NEXT::DESTROY() } - package D; - use base qw( B C ); - sub D::method { print "$_[0]: D method\n"; $_[0]->NEXT::method() } - sub D::AUTOLOAD { print "$_[0]: D AUTOLOAD\n"; $_[0]->NEXT::AUTOLOAD() } - sub D::DESTROY { print "$_[0]: D dtor\n"; $_[0]->NEXT::DESTROY() } + package D; + use base qw( B C ); + sub D::method { print "$_[0]: D method\n"; $_[0]->NEXT::method() } + sub D::AUTOLOAD { print "$_[0]: D AUTOLOAD\n"; $_[0]->NEXT::AUTOLOAD() } + sub D::DESTROY { print "$_[0]: D dtor\n"; $_[0]->NEXT::DESTROY() } - package main; + package main; - my $obj = bless {}, "D"; + my $obj = bless {}, "D"; - $obj->method(); # Calls D::method, A::method, C::method - $obj->missing_method(); # Calls D::AUTOLOAD, B::AUTOLOAD, C::AUTOLOAD + $obj->method(); # Calls D::method, A::method, C::method + $obj->missing_method(); # Calls D::AUTOLOAD, B::AUTOLOAD, C::AUTOLOAD - # Clean-up calls D::DESTROY, B::DESTROY, A::DESTROY, C::DESTROY + # Clean-up calls D::DESTROY, B::DESTROY, A::DESTROY, C::DESTROY =head1 DESCRIPTION @@ -95,8 +119,14 @@ that uses it. If a method C calls C<$self->NEXT::m()>, the call to C is redispatched as if the calling method had not originally been found. In other words, a call to C<$self->NEXT::m()> resumes the depth-first, -left-to-right search of parent classes that resulted in the original -call to C. +left-to-right search of C<$self>'s class hierarchy that resulted in the +original call to C. + +Note that this is not the same thing as C<$self->SUPER::m()>, which +begins a new dispatch that is restricted to searching the ancestors +of the current class. C<$self->NEXT::m()> can backtrack +past the current class -- to look for a suitable method in other +ancestors of C<$self> -- whereas C<$self->SUPER::m()> cannot. A typical use would be in the destructors of a class hierarchy, as illustrated in the synopsis above. Each class in the hierarchy @@ -111,10 +141,150 @@ particular call, it might choose to redispatch that call, in the hope that some other C (above it, or to its left) might do better. +By default, if a redispatch attempt fails to find another method +elsewhere in the objects class hierarchy, it quietly gives up and does +nothing (but see L<"Enforcing redispatch">). This gracious acquiesence +is also unlike the (generally annoying) behaviour of C, which +throws an exception if it cannot redispatch. + Note that it is a fatal error for any method (including C) -to attempt to redispatch any method except itself. For example: +to attempt to redispatch any method that does not have the +same name. For example: + + sub D::oops { print "oops!\n"; $_[0]->NEXT::other_method() } + + +=head2 Enforcing redispatch + +It is possible to make C redispatch more demandingly (i.e. like +C does), so that the redispatch throws an exception if it cannot +find a "next" method to call. + +To do this, simple invoke the redispatch as: + + $self->NEXT::ACTUAL::method(); + +rather than: + + $self->NEXT::method(); + +The C tells C that there must actually be a next method to call, +or it should throw an exception. + +C is most commonly used in C methods, as a means to +decline an C request, but preserve the normal exception-on-failure +semantics: + + sub AUTOLOAD { + if ($AUTOLOAD =~ /foo|bar/) { + # handle here + } + else { # try elsewhere + shift()->NEXT::ACTUAL::AUTOLOAD(@_); + } + } + +By using C, if there is no other C to handle the +method call, an exception will be thrown (as usually happens in the absence of +a suitable C). + + +=head2 Avoiding repetitions + +If C redispatching is used in the methods of a "diamond" class hierarchy: + + # A B + # / \ / + # C D + # \ / + # E + + use NEXT; + + package A; + sub foo { print "called A::foo\n"; shift->NEXT::foo() } + + package B; + sub foo { print "called B::foo\n"; shift->NEXT::foo() } + + package C; @ISA = qw( A ); + sub foo { print "called C::foo\n"; shift->NEXT::foo() } + + package D; @ISA = qw(A B); + sub foo { print "called D::foo\n"; shift->NEXT::foo() } + + package E; @ISA = qw(C D); + sub foo { print "called E::foo\n"; shift->NEXT::foo() } + + E->foo(); + +then derived classes may (re-)inherit base-class methods through two or +more distinct paths (e.g. in the way C inherits C twice -- +through C and C). In such cases, a sequence of C redispatches +will invoke the multiply inherited method as many times as it is +inherited. For example, the above code prints: + + called E::foo + called C::foo + called A::foo + called D::foo + called A::foo + called B::foo + +(i.e. C is called twice). + +In some cases this I be the desired effect within a diamond hierarchy, +but in others (e.g. for destructors) it may be more appropriate to +call each method only once during a sequence of redispatches. + +To cover such cases, you can redispatch methods via: + + $self->NEXT::UNSEEN::method(); + +rather than: + + $self->NEXT::method(); + +This causes the redispatcher to skip any classes in the hierarchy that it has +already visited in an earlier redispatch. So, for example, if the +previous example were rewritten: + + package A; + sub foo { print "called A::foo\n"; shift->NEXT::UNSEEN::foo() } + + package B; + sub foo { print "called B::foo\n"; shift->NEXT::UNSEEN::foo() } + + package C; @ISA = qw( A ); + sub foo { print "called C::foo\n"; shift->NEXT::UNSEEN::foo() } + + package D; @ISA = qw(A B); + sub foo { print "called D::foo\n"; shift->NEXT::UNSEEN::foo() } + + package E; @ISA = qw(C D); + sub foo { print "called E::foo\n"; shift->NEXT::UNSEEN::foo() } + + E->foo(); + +then it would print: + + called E::foo + called C::foo + called A::foo + called D::foo + called B::foo + +and omit the second call to C. + +Note that you can also use: + + $self->NEXT::UNSEEN::ACTUAL::method(); + +or: + + $self->NEXT::ACTUAL::UNSEEN::method(); - sub D::oops { print "oops!\n"; $_[0]->NEXT::other_method() } +to get both unique invocation I exception-on-failure. =head1 AUTHOR @@ -134,7 +304,6 @@ Comment, suggestions, and patches welcome. =head1 COPYRIGHT - Copyright (c) 2000, Damian Conway. All Rights Reserved. + Copyright (c) 2000-2001, Damian Conway. All Rights Reserved. This module is free software. It may be used, redistributed -and/or modified under the terms of the Perl Artistic License - (see http://www.perl.com/perl/misc/Artistic.html) + and/or modified under the same terms as Perl itself.