throw a fatal error.  The functions in Class::ISA effectively ignore
this cyclicity; the Class::ISA algorithm is "never go down the same
path twice", and cyclicities are just a special case of that.

* The Class::ISA functions just look at @ISAs.  But theoretically, I
suppose, AUTOLOADs could bypass Perl's ISA-based search mechanism and
do whatever they please.  That would be bad behavior, tho; and I try
not to think about that.

* If Perl can't find a method anywhere in the ISA tree, it then looks
in the magical class UNIVERSAL.  This is rarely relevant to the tasks
that I expect Class::ISA functions to be put to, but if it matters to
you, then instead of this:

  @supers = Class::Tree::super_path($class);

do this:

  @supers = (Class::Tree::super_path($class), 'UNIVERSAL');

And don't say no-one ever told ya!

* When you call them, the Class::ISA functions look at @ISAs anew --
that is, there is no memoization, and so if ISAs change during
runtime, you get the current ISA tree's path, not anything memoized.
However, changing ISAs at runtime is probably a sign that you're out
of your mind!

=head1 COPYRIGHT

Copyright (c) 1999, 2000 Sean M. Burke. All rights reserved.

This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.

=head1 AUTHOR

Sean M. Burke C<sburke@cpan.org>

=cut

###########################################################################

sub self_and_super_versions {
  no strict 'refs';
  map {
        $_ => (defined(${"$_\::VERSION"}) ? ${"$_\::VERSION"} : undef)
      } self_and_super_path($_[0])
}

# Also consider magic like:
#   no strict 'refs';
#   my %class2SomeHashr =
#     map { defined(%{"$_\::SomeHash"}) ? ($_ => \%{"$_\::SomeHash"}) : () }
#         Class::ISA::self_and_super_path($class);
# to get a hash of refs to all the defined (and non-empty) hashes in
# $class and its superclasses.
#
# Or even consider this incantation for doing something like hash-data
# inheritance:
#   no strict 'refs';
#   %union_hash = 
#     map { defined(%{"$_\::SomeHash"}) ? %{"$_\::SomeHash"}) : () }
#         reverse(Class::ISA::self_and_super_path($class));
# Consider that reverse() is necessary because with
#   %foo = ('a', 'wun', 'b', 'tiw', 'a', 'foist');
# $foo{'a'} is 'foist', not 'wun'.

###########################################################################
sub super_path {
  my @ret = &self_and_super_path(@_);
  shift @ret if @ret;
  return @ret;
}

#--------------------------------------------------------------------------
sub self_and_super_path {
  # Assumption: searching is depth-first.
  # Assumption: '' (empty string) can't be a class package name.
  # Note: 'UNIVERSAL' is not given any special treatment.
  return () unless @_;

  my @out = ();

  my @in_stack = ($_[0]);
  my %seen = ($_[0] => 1);

  my $current;
  while(@in_stack) {
    next unless defined($current = shift @in_stack) && length($current);
    print "At $current\n" if $Debug;
    push @out, $current;
    no strict 'refs';
    unshift @in_stack,
      map
        { my $c = $_; # copy, to avoid being destructive
          substr($c,0,2) = "main::" if substr($c,0,2) eq '::';
           # Canonize the :: -> main::, ::foo -> main::foo thing.
           # Should I ever canonize the Foo'Bar = Foo::Bar thing? 
          $seen{$c}++ ? () : $c;