use strict;
use warnings;
-our $VERSION = '0.01';
-
use Scalar::Util 'blessed';
-my %MRO;
+our $VERSION = '0.08';
+
+# this is our global stash of both
+# MRO's and method dispatch tables
+# the structure basically looks like
+# this:
+#
+# $MRO{$class} = {
+# MRO => [ <class precendence list> ],
+# methods => {
+# orig => <original location of method>,
+# code => \&<ref to original method>
+# },
+# has_overload_fallback => (1 | 0)
+# }
+#
+our %MRO;
+
+# use these for debugging ...
+sub _dump_MRO_table { %MRO }
+our $TURN_OFF_C3 = 0;
sub import {
my $class = caller();
+ # skip if the caller is main::
+ # since that is clearly not relevant
return if $class eq 'main';
- $MRO{$class} = undef;
+ return if $TURN_OFF_C3;
+ # make a note to calculate $class
+ # during INIT phase
+ $MRO{$class} = undef unless exists $MRO{$class};
+}
+
+## initializers
+
+# NOTE:
+# this will not run under the following
+# conditions:
+# - mod_perl
+# - require Class::C3;
+# - eval "use Class::C3"
+# in all those cases, you need to call
+# the initialize() function manually
+INIT { initialize() }
+
+sub initialize {
+ # why bother if we don't have anything ...
+ return unless keys %MRO;
+ _calculate_method_dispatch_tables();
+ _apply_method_dispatch_tables();
+ %next::METHOD_CACHE = ();
+}
+
+sub uninitialize {
+ # why bother if we don't have anything ...
+ return unless keys %MRO;
+ _remove_method_dispatch_tables();
+ %next::METHOD_CACHE = ();
+}
+
+sub reinitialize {
+ uninitialize();
+ # clean up the %MRO before we re-initialize
+ $MRO{$_} = undef foreach keys %MRO;
+ initialize();
}
-INIT {
- no strict 'refs';
+## functions for applying C3 to classes
+
+sub _calculate_method_dispatch_tables {
foreach my $class (keys %MRO) {
- my @MRO = calculateMRO($class);
- $MRO{$class} = { MRO => \@MRO };
- my %methods;
- foreach my $local (@MRO[1 .. $#MRO]) {
- foreach my $method (grep { defined &{"${local}::$_"} } keys %{"${local}::"}) {
- next unless !defined *{"${class}::$method"}{CODE};
- if (!exists $methods{$method}) {
- $methods{$method} = {
- orig => "${local}::$method",
- code => \&{"${local}::$method"}
- };
- }
- }
- }
- $MRO{$class}->{methods} = \%methods;
+ _calculate_method_dispatch_table($class);
}
- #use Data::Dumper; warn Dumper \%MRO;
- foreach my $class (keys %MRO) {
- #warn "installing methods (" . (join ", " => keys %{$MRO{$class}->{methods}}) . ") for $class";
- foreach my $method (keys %{$MRO{$class}->{methods}}) {
- #warn "Installing ${class}::$method using " . $MRO{$class}->{methods}->{$method}->{orig};
- *{"${class}::$method"} = $MRO{$class}->{methods}->{$method}->{code};
+}
+
+sub _calculate_method_dispatch_table {
+ my $class = shift;
+ no strict 'refs';
+ my @MRO = calculateMRO($class);
+ $MRO{$class} = { MRO => \@MRO };
+ my $has_overload_fallback = 0;
+ my %methods;
+ # NOTE:
+ # we do @MRO[1 .. $#MRO] here because it
+ # makes no sense to interogate the class
+ # which you are calculating for.
+ foreach my $local (@MRO[1 .. $#MRO]) {
+ # if overload has tagged this module to
+ # have use "fallback", then we want to
+ # grab that value
+ $has_overload_fallback = ${"${local}::()"}
+ if defined ${"${local}::()"};
+ foreach my $method (grep { defined &{"${local}::$_"} } keys %{"${local}::"}) {
+ # skip if already overriden in local class
+ next unless !defined *{"${class}::$method"}{CODE};
+ $methods{$method} = {
+ orig => "${local}::$method",
+ code => \&{"${local}::$method"}
+ } unless exists $methods{$method};
}
+ }
+ # now stash them in our %MRO table
+ $MRO{$class}->{methods} = \%methods;
+ $MRO{$class}->{has_overload_fallback} = $has_overload_fallback;
+}
+
+sub _apply_method_dispatch_tables {
+ foreach my $class (keys %MRO) {
+ _apply_method_dispatch_table($class);
+ }
+}
+
+sub _apply_method_dispatch_table {
+ my $class = shift;
+ no strict 'refs';
+ ${"${class}::()"} = $MRO{$class}->{has_overload_fallback}
+ if $MRO{$class}->{has_overload_fallback};
+ foreach my $method (keys %{$MRO{$class}->{methods}}) {
+ *{"${class}::$method"} = $MRO{$class}->{methods}->{$method}->{code};
+ }
+}
+
+sub _remove_method_dispatch_tables {
+ foreach my $class (keys %MRO) {
+ _remove_method_dispatch_table($class);
+ }
+}
+
+sub _remove_method_dispatch_table {
+ my $class = shift;
+ no strict 'refs';
+ delete ${"${class}::"}{"()"} if $MRO{$class}->{has_overload_fallback};
+ foreach my $method (keys %{$MRO{$class}->{methods}}) {
+ delete ${"${class}::"}{$method}
+ if defined *{"${class}::${method}"}{CODE} &&
+ (*{"${class}::${method}"}{CODE} eq $MRO{$class}->{methods}->{$method}->{code});
}
}
+## functions for calculating C3 MRO
+
+# this function is a perl-port of the
+# python code on this page:
+# http://www.python.org/2.3/mro.html
sub _merge {
my (@seqs) = @_;
+ my $class_being_merged = $seqs[0]->[0];
my @res;
while (1) {
# remove all empty seqences
my @nonemptyseqs = (map { (@{$_} ? $_ : ()) } @seqs);
# return the list if we have no more no-empty sequences
return @res if not @nonemptyseqs;
+ my $reject;
my $cand; # a canidate ..
foreach my $seq (@nonemptyseqs) {
$cand = $seq->[0]; # get the head of the list
# jump out as soon as we find one matching
# there is no reason not too. However, if
# we find one, then just remove the '&& last'
- $nothead++ && last if exists $in_tail{$cand};
+ ++$nothead && last if exists $in_tail{$cand};
}
last unless $nothead; # leave the loop with our canidate ...
+ $reject = $cand;
$cand = undef; # otherwise, reject it ...
}
- die "Inconsistent hierarchy" if not $cand;
+ die "Inconsistent hierarchy found while merging '$class_being_merged':\n\t" .
+ "current merge results [\n\t\t" . (join ",\n\t\t" => @res) . "\n\t]\n\t" .
+ "mergeing failed on '$reject'\n" if not $cand;
push @res => $cand;
# now loop through our non-empties and pop
# off the head if it matches our canidate
);
}
+package # hide me from PAUSE
+ next;
+
+use strict;
+use warnings;
+
+use Scalar::Util 'blessed';
+
+our $VERSION = '0.05';
+
+our %METHOD_CACHE;
+
+sub method {
+ my $level = 1;
+ my $method_caller;
+ while ($method_caller = (caller($level++))[3]) {
+ last unless $method_caller eq '(eval)';
+ }
+ my @label = (split '::', $method_caller);
+ my $label = pop @label;
+ my $caller = join '::' => @label;
+ my $self = $_[0];
+ my $class = blessed($self) || $self;
+
+ goto &{ $METHOD_CACHE{"$class|$caller|$label"} ||= do {
+
+ my @MRO = Class::C3::calculateMRO($class);
+
+ my $current;
+ while ($current = shift @MRO) {
+ last if $caller eq $current;
+ }
+
+ no strict 'refs';
+ my $found;
+ foreach my $class (@MRO) {
+ next if (defined $Class::C3::MRO{$class} &&
+ defined $Class::C3::MRO{$class}{methods}{$label});
+ last if (defined ($found = *{$class . '::' . $label}{CODE}));
+ }
+
+ die "No next::method '$label' found for $self" unless $found;
+
+ $found;
+ } };
+}
+
1;
__END__
use Class::C3;
# Classic Diamond MI pattern
- # [ A ]
- # / \
- # [ B ] [ C ]
- # \ /
- # [ D ]
+ # <A>
+ # / \
+ # <B> <C>
+ # \ /
+ # <D>
package main;
C3 works by always preserving local precendence ordering. This essentially means that no class will
appear before any of it's subclasses. Take the classic diamond inheritence pattern for instance:
- [ A ]
- / \
- [ B ] [ C ]
- \ /
- [ D ]
+ <A>
+ / \
+ <B> <C>
+ \ /
+ <D>
The standard Perl 5 MRO would be (D, B, A, C). The result being that B<A> appears before B<C>, even
though B<C> is the subclass of B<A>. The C3 MRO algorithm however, produces the following MRO
do well if you start changing your C<@ISA> or messing with class symbol tables, so you should consider
your classes to be effectively closed. See the L<CAVEATS> section for more details.
+=head1 OPTIONAL LOWERCASE PRAGMA
+
+This release also includes an optional module B<c3> in the F<opt/> folder. I did not include this in
+the regular install since lowercase module names are considered I<"bad"> by some people. However I
+think that code looks much nicer like this:
+
+ package MyClass;
+ use c3;
+
+The the more clunky:
+
+ package MyClass;
+ use Class::C3;
+
+But hey, it's your choice, thats why it is optional.
+
=head1 FUNCTIONS
=over 4
Given a C<$class> this will return an array of class names in the proper C3 method resolution order.
+=item B<initialize>
+
+This can be used to initalize the C3 method dispatch tables. You need to call this if you are running
+under mod_perl, or in any other environment which does not run the INIT phase of the perl compiler.
+
+NOTE:
+This can B<not> be used to re-load the dispatch tables for all classes. Use C<reinitialize> for that.
+
+=item B<uninitialize>
+
+Calling this function results in the removal of all cached methods, and the restoration of the old Perl 5
+style dispatch order (depth-first, left-to-right).
+
+=item B<reinitialize>
+
+This effectively calls C<uninitialize> followed by C<initialize> the result of which is a reloading of
+B<all> the calculated C3 dispatch tables.
+
+It should be noted that if you have a large class library, this could potentially be a rather costly
+operation.
+
=back
+=head1 METHOD REDISPATCHING
+
+It is always useful to be able to re-dispatch your method call to the "next most applicable method". This
+module provides a pseudo package along the lines of C<SUPER::> or C<NEXT::> which will re-dispatch the
+method along the C3 linearization. This is best show with an examples.
+
+ # a classic diamond MI pattern ...
+ <A>
+ / \
+ <B> <C>
+ \ /
+ <D>
+
+ package A;
+ use c3;
+ sub foo { 'A::foo' }
+
+ package B;
+ use base 'A';
+ use c3;
+ sub foo { 'B::foo => ' . (shift)->next::method() }
+
+ package B;
+ use base 'A';
+ use c3;
+ sub foo { 'C::foo => ' . (shift)->next::method() }
+
+ package D;
+ use base ('B', 'C');
+ use c3;
+ sub foo { 'D::foo => ' . (shift)->next::method() }
+
+ print D->foo; # prints out "D::foo => B::foo => C::foo => A::foo"
+
+A few things to note. First, we do not require you to add on the method name to the C<next::method>
+call (this is unlike C<NEXT::> and C<SUPER::> which do require that). This helps to enforce the rule
+that you cannot dispatch to a method of a different name (this is how C<NEXT::> behaves as well).
+
+The next thing to keep in mind is that you will need to pass all arguments to C<next::method> it can
+not automatically use the current C<@_>.
+
=head1 CAVEATS
Let me first say, this is an experimental module, and so it should not be used for anything other
The idea of C<SUPER::> under multiple inheritence is ambigious, and generally not recomended anyway.
However, it's use in conjuntion with this module is very much not recommended, and in fact very
-discouraged. In the future I plan to support a C<NEXT::> style interface to be used to move to the
-next most appropriate method in the MRO.
+discouraged. The recommended approach is to instead use the supplied C<next::method> feature, see
+more details on it's usage above.
=item Changing C<@ISA>.
It is the author's opinion that changing C<@ISA> at runtime is pure insanity anyway. However, people
do it, so I must caveat. Any changes to the C<@ISA> will not be reflected in the MRO calculated by this
-module, and therefor probably won't even show up. I am considering some kind of C<recalculateMRO> function
-which can be used to recalculate the MRO on demand at runtime, but that is still off in the future.
+module, and therefor probably won't even show up. If you do this, you will need to call C<reinitialize>
+in order to recalulate B<all> method dispatch tables. See the C<reinitialize> documentation and an example
+in F<t/20_reinitialize.t> for more information.
=item Adding/deleting methods from class symbol tables.
This module calculates the MRO for each requested class during the INIT phase by interogatting the symbol
tables of said classes. So any symbol table manipulation which takes place after our INIT phase is run will
-not be reflected in the calculated MRO.
+not be reflected in the calculated MRO. Just as with changing the C<@ISA>, you will need to call
+C<reinitialize> for any changes you make to take effect.
-=item Not for use with mod_perl
+=back
+
+=head1 TODO
+
+=over 4
-Since this module utilizes the INIT phase, it cannot be easily used with mod_perl. If this module works out
-and proves useful in the I<real world>, I will most likely be supporting mod_perl in some way.
+=item More tests
+
+You can never have enough tests :)
=back
+=head1 CODE COVERAGE
+
+I use B<Devel::Cover> to test the code coverage of my tests, below is the B<Devel::Cover> report on this
+module's test suite.
+
+ ---------------------------- ------ ------ ------ ------ ------ ------ ------
+ File stmt bran cond sub pod time total
+ ---------------------------- ------ ------ ------ ------ ------ ------ ------
+ Class/C3.pm 98.6 90.9 73.3 96.0 100.0 96.8 95.3
+ ---------------------------- ------ ------ ------ ------ ------ ------ ------
+ Total 98.6 90.9 73.3 96.0 100.0 96.8 95.3
+ ---------------------------- ------ ------ ------ ------ ------ ------ ------
+
=head1 SEE ALSO
=head2 The original Dylan paper
=head1 AUTHOR
-stevan little, E<lt>stevan@iinteractive.comE<gt>
+Stevan Little, E<lt>stevan@iinteractive.comE<gt>
=head1 COPYRIGHT AND LICENSE
projects / gitmo/Class-C3.git / blobdiff