perl – Tree :: Simple :: traverse()不访问树的根 – 错误或功

#!/usr/bin/env perl

use Tree::Simple;

# Tree:
#                   a
#         _________ | ________
#        /          |          
#       b           c          d 
#                 /    
#                e      f  
#                        
#                         g
#

my $tree = Tree::Simple->new('a',Tree::Simple->ROOT);

$tree->addChildren( Tree::Simple->new('b'),Tree::Simple->new('c'),Tree::Simple->new('d'),);

$tree->getChild(1)->addChildren (
                    Tree::Simple->new('e'),Tree::Simple->new('f'),);

$tree->getChild(1)->getChild(1)->addChildren (
                    Tree::Simple->new('g'),);

$trav_func= sub {
    my $node = shift;
    printf "node : %s  leaf : %3s   root : %sn",$node->getNodeValue,$node->isLeaf ? 'yes' : 'no',$node->isRoot ? 'yes' : 'no';
};


# traversal does not report the root - error ?
print "------ preorder : traverse( $trav_func ) n";
$tree->traverse( $trav_func );
print "n";

print "------ postorder : traverse( sub{},$trav_func ) n";
$tree->traverse( sub{},$trav_func );
print "n";

输出是

------ preorder : traverse( $trav_func ) 
node : b  leaf : yes   root : no
node : c  leaf :  no   root : no
node : e  leaf : yes   root : no
node : f  leaf :  no   root : no
node : g  leaf : yes   root : no
node : d  leaf : yes   root : no

------ postorder : traverse( sub{},$trav_func ) 
node : b  leaf : yes   root : no
node : e  leaf : yes   root : no
node : g  leaf : yes   root : no
node : f  leaf :  no   root : no
node : c  leaf :  no   root : no
node : d  leaf : yes   root : no

显示未访问root“a”.我对树遍历的理解是应该访问所有节点.我错了还是在某些情况下有理由不访问root？

附录：

Tree :: Simple :: traverse()实现为：

sub traverse {
    my ($self,$func,$post) = @_;
    # ... some checks here not shown

    foreach my $child ($self->getAllChildren()) { 
        $func->($child);
        $child->traverse($func,$post);
        defined($post) && $post->($child);
    }
  }

对于第一个节点(root),没有调用$func / $post,因此没有访问它.

如果使用覆盖traverse()

package My::Tree::Simple;

use parent 'Tree::Simple';

# the original code of Tree::Simple::traverse() 
# but $func() and $post() outside of foreach-loop
# allowing the root to be visited 

sub my_traverse {
    my ($self,$post) = @_;
    (defined($func)) || die "Insufficient Arguments : Cannot traverse without traversal function";
    (ref($func) eq "CODE") || die "Incorrect Object Type : traversal function is not a function";
    (ref($post) eq "CODE") || die "Incorrect Object Type : post traversal function is not a function"
        if defined($post);

    $func->($self); # put outside of foreach

    foreach my $child ($self->getAllChildren()) {
        $child->my_traverse($func,$post);
    }

    defined($post) && $post->($self); # put outside of foreach
}

它像我预期的那样工作.