use strict;
use warnings;
-use Scalar::Util 'blessed';
+our $VERSION = '0.23';
-our $VERSION = '0.02';
+our $C3_IN_CORE;
+our $C3_XS;
-# this is our global stash of both
+BEGIN {
+ if($] > 5.009_004) {
+ $C3_IN_CORE = 1;
+ require mro;
+ }
+ elsif($C3_XS or not defined $C3_XS) {
+ my $error = do {
+ local $@;
+ eval { require Class::C3::XS };
+ $@;
+ };
+
+ if ($error) {
+ die $error if $error !~ /\blocate\b/;
+
+ if ($C3_XS) {
+ require Carp;
+ Carp::croak( "XS explicitly requested but Class::C3::XS is not available" );
+ }
+
+ require Algorithm::C3;
+ require Class::C3::next;
+ }
+ else {
+ $C3_XS = 1;
+ }
+ }
+}
+
+# this is our global stash of both
# MRO's and method dispatch tables
# the structure basically looks like
# this:
# methods => {
# orig => <original location of method>,
# code => \&<ref to original method>
-# }
+# },
+# has_overload_fallback => (1 | 0)
# }
#
-my %MRO;
+our %MRO;
-# use this for debugging ...
+# use these for debugging ...
sub _dump_MRO_table { %MRO }
-
our $TURN_OFF_C3 = 0;
+# state tracking for initialize()/uninitialize()
+our $_initialized = 0;
+
sub import {
my $class = caller();
# skip if the caller is main::
# since that is clearly not relevant
return if $class eq 'main';
+
return if $TURN_OFF_C3;
- # make a note to calculate $class
+ mro::set_mro($class, 'c3') if $C3_IN_CORE;
+
+ # make a note to calculate $class
# during INIT phase
- $MRO{$class} = undef;
+ $MRO{$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() }
+# This prevents silly warnings when Class::C3 is
+# used explicitly along with MRO::Compat under 5.9.5+
+
+{ no warnings 'redefine';
sub initialize {
+ %next::METHOD_CACHE = ();
# why bother if we don't have anything ...
return unless keys %MRO;
- _calculate_method_dispatch_tables();
- _apply_method_dispatch_tables();
+ if($C3_IN_CORE) {
+ mro::set_mro($_, 'c3') for keys %MRO;
+ }
+ else {
+ if($_initialized) {
+ uninitialize();
+ $MRO{$_} = undef foreach keys %MRO;
+ }
+ _calculate_method_dispatch_tables();
+ _apply_method_dispatch_tables();
+ $_initialized = 1;
+ }
}
+sub uninitialize {
+ # why bother if we don't have anything ...
+ %next::METHOD_CACHE = ();
+ return unless keys %MRO;
+ if($C3_IN_CORE) {
+ mro::set_mro($_, 'dfs') for keys %MRO;
+ }
+ else {
+ _remove_method_dispatch_tables();
+ $_initialized = 0;
+ }
+}
+
+sub reinitialize { goto &initialize }
+
+} # end of "no warnings 'redefine'"
+
## functions for applying C3 to classes
sub _calculate_method_dispatch_tables {
+ return if $C3_IN_CORE;
+ my %merge_cache;
foreach my $class (keys %MRO) {
- _calculate_method_dispatch_table($class);
+ _calculate_method_dispatch_table($class, \%merge_cache);
}
}
sub _calculate_method_dispatch_table {
- my $class = shift;
+ return if $C3_IN_CORE;
+ my ($class, $merge_cache) = @_;
no strict 'refs';
- my @MRO = calculateMRO($class);
+ my @MRO = calculateMRO($class, $merge_cache);
$MRO{$class} = { MRO => \@MRO };
+ my $has_overload_fallback;
my %methods;
- # NOTE:
+ # NOTE:
# we do @MRO[1 .. $#MRO] here because it
# makes no sense to interogate the class
- # which you are calculating for.
+ # 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 $has_overload_fallback && defined ${"${local}::()"};
foreach my $method (grep { defined &{"${local}::$_"} } keys %{"${local}::"}) {
# skip if already overriden in local class
next unless !defined *{"${class}::$method"}{CODE};
code => \&{"${local}::$method"}
} unless exists $methods{$method};
}
- }
+ }
# now stash them in our %MRO table
- $MRO{$class}->{methods} = \%methods;
+ $MRO{$class}->{methods} = \%methods;
+ $MRO{$class}->{has_overload_fallback} = $has_overload_fallback;
}
sub _apply_method_dispatch_tables {
+ return if $C3_IN_CORE;
foreach my $class (keys %MRO) {
_apply_method_dispatch_table($class);
- }
+ }
}
sub _apply_method_dispatch_table {
+ return if $C3_IN_CORE;
my $class = shift;
no strict 'refs';
+ ${"${class}::()"} = $MRO{$class}->{has_overload_fallback}
+ if !defined &{"${class}::()"}
+ && defined $MRO{$class}->{has_overload_fallback};
foreach my $method (keys %{$MRO{$class}->{methods}}) {
+ if ( $method =~ /^\(/ ) {
+ my $orig = $MRO{$class}->{methods}->{$method}->{orig};
+ ${"${class}::$method"} = $$orig if defined $$orig;
+ }
*{"${class}::$method"} = $MRO{$class}->{methods}->{$method}->{code};
- }
+ }
}
-## functions for calculating C3 MRO
-
-# this function is a perl-port of the
-# python code on this page:
-# http://www.python.org/2.3/mro.html
-sub _merge {
- my (@seqs) = @_;
- my @res;
- while (1) {
- # remove all empty seqences
- my @nonemptyseqs = (map { (@{$_} ? $_ : ()) } @seqs);
- # return the list if we have no more no-empty sequences
- return @res if not @nonemptyseqs;
- my $cand; # a canidate ..
- foreach my $seq (@nonemptyseqs) {
- $cand = $seq->[0]; # get the head of the list
- my $nothead;
- foreach my $sub_seq (@nonemptyseqs) {
- # XXX - this is instead of the python "in"
- my %in_tail = (map { $_ => 1 } @{$sub_seq}[ 1 .. $#{$sub_seq} ]);
- # NOTE:
- # 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};
- }
- last unless $nothead; # leave the loop with our canidate ...
- $cand = undef; # otherwise, reject it ...
- }
- die "Inconsistent hierarchy" if not $cand;
- push @res => $cand;
- # now loop through our non-empties and pop
- # off the head if it matches our canidate
- foreach my $seq (@nonemptyseqs) {
- shift @{$seq} if $seq->[0] eq $cand;
- }
+sub _remove_method_dispatch_tables {
+ return if $C3_IN_CORE;
+ foreach my $class (keys %MRO) {
+ _remove_method_dispatch_table($class);
}
}
-sub calculateMRO {
- my ($class) = @_;
+sub _remove_method_dispatch_table {
+ return if $C3_IN_CORE;
+ my $class = shift;
no strict 'refs';
- return _merge(
- [ $class ], # the class we are linearizing
- (map { [ calculateMRO($_) ] } @{"${class}::ISA"}), # the MRO of all the superclasses
- [ @{"${class}::ISA"} ] # a list of all the superclasses
- );
+ 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}->{$method}->{code});
+ }
+}
+
+sub calculateMRO {
+ my ($class, $merge_cache) = @_;
+
+ return Algorithm::C3::merge($class, sub {
+ no strict 'refs';
+ @{$_[0] . '::ISA'};
+ }, $merge_cache);
+}
+
+# Method overrides to support 5.9.5+ or Class::C3::XS
+
+sub _core_calculateMRO { @{mro::get_linear_isa($_[0], 'c3')} }
+
+if($C3_IN_CORE) {
+ no warnings 'redefine';
+ *Class::C3::calculateMRO = \&_core_calculateMRO;
+}
+elsif($C3_XS) {
+ no warnings 'redefine';
+ *Class::C3::calculateMRO = \&Class::C3::XS::calculateMRO;
+ *Class::C3::_calculate_method_dispatch_table
+ = \&Class::C3::XS::_calculate_method_dispatch_table;
}
1;
=head1 SYNOPSIS
+ # NOTE - DO NOT USE Class::C3 directly as a user, use MRO::Compat instead!
package A;
- use Class::C3;
+ use Class::C3;
sub hello { 'A::hello' }
package B;
use base 'A';
- use Class::C3;
+ use Class::C3;
package C;
use base 'A';
- use Class::C3;
+ use Class::C3;
sub hello { 'C::hello' }
package D;
use base ('B', 'C');
- use Class::C3;
+ use Class::C3;
# Classic Diamond MI pattern
# <A>
package main;
+ # initializez the C3 module
+ # (formerly called in INIT)
+ Class::C3::initialize();
+
print join ', ' => Class::C3::calculateMRO('Diamond_D') # prints D, B, C, A
print D->hello() # prints 'C::hello' instead of the standard p5 'A::hello'
-
+
D->can('hello')->(); # can() also works correctly
UNIVERSAL::can('D', 'hello'); # as does UNIVERSAL::can()
=head1 DESCRIPTION
-This is currently an experimental pragma to change Perl 5's standard method resolution order
-from depth-first left-to-right (a.k.a - pre-order) to the more sophisticated C3 method resolution
-order.
+This is pragma to change Perl 5's standard method resolution order from depth-first left-to-right
+(a.k.a - pre-order) to the more sophisticated C3 method resolution order.
+
+B<NOTE:> YOU SHOULD NOT USE THIS MODULE DIRECTLY - The feature provided
+is integrated into perl version >= 5.9.5, and you should use L<MRO::Compat>
+instead, which will use the core implementation in newer perls, but fallback
+to using this implementation on older perls.
=head2 What is C3?
C3 is the name of an algorithm which aims to provide a sane method resolution order under multiple
-inheritence. It was first introduced in the langauge Dylan (see links in the L<SEE ALSO> section),
-and then later adopted as the prefered MRO (Method Resolution Order) for the new-style classes in
-Python 2.3. Most recently it has been adopted as the 'canonical' MRO for Perl 6 classes, and the
+inheritance. It was first introduced in the langauge Dylan (see links in the L<SEE ALSO> section),
+and then later adopted as the prefered MRO (Method Resolution Order) for the new-style classes in
+Python 2.3. Most recently it has been adopted as the 'canonical' MRO for Perl 6 classes, and the
default MRO for Parrot objects as well.
=head2 How does C3 work.
-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:
+C3 works by always preserving local precendence ordering. This essentially means that no class will
+appear before any of its subclasses. Take the classic diamond inheritance pattern for instance:
<A>
/ \
\ /
<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
+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
(D, B, C, A), which does not have this same issue.
This example is fairly trival, for more complex examples and a deeper explaination, see the links in
=head2 How does this module work?
-This module uses a technique similar to Perl 5's method caching. During the INIT phase, this module
-calculates the MRO of all the classes which called C<use Class::C3>. It then gathers information from
-the symbol tables of each of those classes, and builds a set of method aliases for the correct
-dispatch ordering. Once all these C3-based method tables are created, it then adds the method aliases
-into the local classes symbol table.
+This module uses a technique similar to Perl 5's method caching. When C<Class::C3::initialize> is
+called, this module calculates the MRO of all the classes which called C<use Class::C3>. It then
+gathers information from the symbol tables of each of those classes, and builds a set of method
+aliases for the correct dispatch ordering. Once all these C3-based method tables are created, it
+then adds the method aliases into the local classes symbol table.
The end result is actually classes with pre-cached method dispatch. However, this caching does not
do well if you start changing your C<@ISA> or messing with class symbol tables, so you should consider
=head1 OPTIONAL LOWERCASE PRAGMA
-This release also includes an optional module B<c3> in the F<opt/> folder. I did not include this in
+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
=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.
+This B<must be called> to initalize the C3 method dispatch tables, this module B<will not work> if
+you do not do this. It is advised to do this as soon as possible B<after> loading any classes which
+use C3. Here is a quick code example:
-NOTE:
-This can B<not> be used to re-load the dispatch tables for all classes. This is because it does not first
-return the classes to their virginal state, which would need to happen in order for the dispatch tables
-to be properly reloaded.
+ package Foo;
+ use Class::C3;
+ # ... Foo methods here
+
+ package Bar;
+ use Class::C3;
+ use base 'Foo';
+ # ... Bar methods here
+
+ package main;
+
+ Class::C3::initialize(); # now it is safe to use Foo and Bar
+
+This function used to be called automatically for you in the INIT phase of the perl compiler, but
+that lead to warnings if this module was required at runtime. After discussion with my user base
+(the L<DBIx::Class> folks), we decided that calling this in INIT was more of an annoyance than a
+convience. I apologize to anyone this causes problems for (although i would very suprised if I had
+any other users other than the L<DBIx::Class> folks). The simplest solution of course is to define
+your own INIT method which calls this function.
+
+NOTE:
+
+If C<initialize> detects that C<initialize> has already been executed, it will L</uninitialize> and
+clear the MRO cache first.
+
+=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 is an alias for L</initialize> above.
=back
-=head1 CAVEATS
+=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 shown with an example.
+
+ # 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 C;
+ 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).
-Let me first say, this is an experimental module, and so it should not be used for anything other
-then other experimentation for the time being.
+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<@_>.
-That said, it is the authors intention to make this into a completely usable and production stable
-module if possible. Time will tell.
+If C<next::method> cannot find a next method to re-dispatch the call to, it will throw an exception.
+You can use C<next::can> to see if C<next::method> will succeed before you call it like so:
-And now, onto the caveats.
+ $self->next::method(@_) if $self->next::can;
+
+Additionally, you can use C<maybe::next::method> as a shortcut to only call the next method if it exists.
+The previous example could be simply written as:
+
+ $self->maybe::next::method(@_);
+
+There are some caveats about using C<next::method>, see below for those.
+
+=head1 CAVEATS
+
+This module used to be labeled as I<experimental>, however it has now been pretty heavily tested by
+the good folks over at L<DBIx::Class> and I am confident this module is perfectly usable for
+whatever your needs might be.
+
+But there are still caveats, so here goes ...
=over 4
=item Use of C<SUPER::>.
-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.
+The idea of C<SUPER::> under multiple inheritance is ambigious, and generally not recomended anyway.
+However, its use in conjuntion with this module is very much not recommended, and in fact very
+discouraged. The recommended approach is to instead use the supplied C<next::method> feature, see
+more details on its 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 therefore 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.
+This module calculates the MRO for each requested class by interogating 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. Just as with changing the C<@ISA>, you will need to call C<reinitialize> for any
+changes you make to take effect.
-=back
+=item Calling C<next::method> from methods defined outside the class
-=head1 TODO
+There is an edge case when using C<next::method> from within a subroutine which was created in a different
+module than the one it is called from. It sounds complicated, but it really isn't. Here is an example which
+will not work correctly:
-=over 4
+ *Foo::foo = sub { (shift)->next::method(@_) };
+
+The problem exists because the anonymous subroutine being assigned to the glob C<*Foo::foo> will show up
+in the call stack as being called C<__ANON__> and not C<foo> as you might expect. Since C<next::method>
+uses C<caller> to find the name of the method it was called in, it will fail in this case.
-=item More tests
+But fear not, there is a simple solution. The module C<Sub::Name> will reach into the perl internals and
+assign a name to an anonymous subroutine for you. Simply do this:
-You can never have enough tests :)
+ use Sub::Name 'subname';
+ *Foo::foo = subname 'Foo::foo' => sub { (shift)->next::method(@_) };
-I need to convert the other MRO and class-precendence-list related tests from the Perl6-MetaModel (see link
-in L<SEE ALSO>). In addition, I need to add some method checks to these tests as well.
+and things will Just Work. Of course this is not always possible to do, but to be honest, I just can't
+manage to find a workaround for it, so until someone gives me a working patch this will be a known
+limitation of this module.
-=item call-next-method / NEXT:: / next METHOD
+=back
-I am contemplating some kind of psudeo-package which can dispatch to the next most relevant method in the
-MRO. This should not be too hard to implement when the time comes.
+=head1 COMPATIBILITY
-=item recalculateMRO
+If your software requires Perl 5.9.5 or higher, you do not need L<Class::C3>, you can simply C<use mro 'c3'>, and not worry about C<initialize()>, avoid some of the above caveats, and get the best possible performance. See L<mro> for more details.
-This being Perl, it would be remiss of me to force people to close thier classes at runtime. So I need to
-develop a means for recalculating the MRO for a given class.
+If your software is meant to work on earlier Perls, use L<Class::C3> as documented here. L<Class::C3> will detect Perl 5.9.5+ and take advantage of the core support when available.
-=back
+=head1 Class::C3::XS
+
+This module will load L<Class::C3::XS> if it's installed and you are running on a Perl version older than 5.9.5. The optional module will be automatically installed for you if a C compiler is available, as it results in significant performance improvements (but unlike the 5.9.5+ core support, it still has all of the same caveats as L<Class::C3>).
+
+=head1 CODE COVERAGE
+
+L<Devel::Cover> was reporting 94.4% overall test coverage earlier in this module's life. Currently, the test suite does things that break under coverage testing, but it is fair to assume the coverage is still close to that value.
=head1 SEE ALSO
=item L<http://www.call-with-current-continuation.org/eggs/c3.html>
-=back
+=back
+
+=head1 ACKNOWLEGEMENTS
+
+=over 4
+
+=item Thanks to Matt S. Trout for using this module in his module L<DBIx::Class>
+and finding many bugs and providing fixes.
+
+=item Thanks to Justin Guenther for making C<next::method> more robust by handling
+calls inside C<eval> and anon-subs.
+
+=item Thanks to Robert Norris for adding support for C<next::can> and
+C<maybe::next::method>.
+
+=back
=head1 AUTHOR
Stevan Little, E<lt>stevan@iinteractive.comE<gt>
+Brandon L. Black, E<lt>blblack@gmail.comE<gt>
+
=head1 COPYRIGHT AND LICENSE
-Copyright 2005 by Infinity Interactive, Inc.
+Copyright 2005, 2006 by Infinity Interactive, Inc.
L<http://www.iinteractive.com>
This library is free software; you can redistribute it and/or modify
-it under the same terms as Perl itself.
+it under the same terms as Perl itself.
-=cut
\ No newline at end of file
+=cut
projects / gitmo/Class-C3.git / blobdiff