NAME

       Tree::Simple::Visitor - Visitor object for Tree::Simple objects

SYNOPSIS

         use Tree::Simple;
         use Tree::Simple::Visitor;

         # create a visitor instance
         my $visitor = Tree::Simple::Visitor->new();

         # create a tree to visit
         my $tree = Tree::Simple->new(Tree::Simple->ROOT)
                                ->addChildren(
                                    Tree::Simple->new("1.0"),
                                    Tree::Simple->new("2.0")
                                                ->addChild(
                                                    Tree::Simple->new("2.1.0")
                                                    ),
                                    Tree::Simple->new("3.0")
                                    );

         # by default this will collect all the
         # node values in depth-first order into
         # our results
         $tree->accept($visitor);

         # get our results and print them
         print join ", ", $visitor->getResults();  # prints "1.0, 2.0, 2.1.0, 3.0"

         # for more complex node objects, you can specify
         # a node filter which will be used to extract the
         # information desired from each node
         $visitor->setNodeFilter(sub {
                       my ($t) = @_;
                       return $t->getNodeValue()->description();
                       });

         # NOTE: this object has changed, but it still remains
         # backwards compatible to the older version, see the
         # DESCRIPTION section below for more details

DESCRIPTION

       This object has been revised into what I think is more intelligent approach to Visitor
       objects. This is now a more suitable base class for building your own Visitors. It is also
       the base class for the visitors found in the Tree::Simple::VisitorFactory distribution,
       which includes a number of useful pre-built Visitors.

       While I have changed a number of things about this module, I have kept it backwards
       compatible to the old way of using it. So the original example code still works:

         my @accumulator;
         my $visitor = Tree::Simple::Visitor->new(sub {
                               my ($tree) = @_;
                               push @accumulator, $tree->getNodeValue();
                               },
                               Tree::Simple::Visitor->RECURSIVE);

         $tree->accept($visitor);

         print join ", ", @accumulator;  # prints "1.0, 2.0, 2.1.0, 3.0"

       But is better expressed as this:

         my $visitor = Tree::Simple::Visitor->new();
         $tree->accept($visitor);
         print join ", ", $visitor->getResults();  # prints "1.0, 2.0, 2.1.0, 3.0"

       This object is still pretty much a wrapper around the Tree::Simple "traverse" method, and
       can be thought of as a depth-first traversal Visitor object.

METHODS

       new ($func, $depth)
           The new style interface means that all arguments to the constructor are now optional.
           As a means of defining the usage of the old and new, when no arguments are sent to the
           constructor, it is assumed that the new style interface is being used. In the new
           style, the $depth is always assumed to be equivalent to "RECURSIVE" and the $func
           argument can be set with "setNodeFilter" instead. This is the recommended way of doing
           things now. If you have been using the old way, it is still there, and I will maintain
           backwards compatibility for a few more version before removing it entirely. If you are
           using this module (and I don't even know if anyone actually is) you have been warned.
           Please contact me if this will be a problem.

           The old style constructor documentation is retained her for reference:

           The first argument to the constructor is a code reference to a function which expects
           a Tree::Simple object as its only argument. The second argument is optional, it can be
           used to set the depth to which the function is applied. If no depth is set, the
           function is applied to the current Tree::Simple instance. If $depth is set to
           "CHILDREN_ONLY", then the function will be applied to the current Tree::Simple
           instance and all its immediate children. If $depth is set to "RECURSIVE", then the
           function will be applied to the current Tree::Simple instance and all its immediate
           children, and all of their children recursively on down the tree. If no $depth is
           passed to the constructor, then the function will only be applied to the current
           Tree::Simple object and none of its children.

       includeTrunk ($boolean)
           Based upon the value of $boolean, this will tell the visitor to collect the trunk of
           the tree as well. It is defaulted to false (0) in the new style interface, but is
           defaulted to true (1) in the old style interface.

       getNodeFilter
           This method returns the CODE reference set with "setNodeFilter" argument.

       clearNodeFilter
           This method clears node filter field.

       setNodeFilter ($filter_function)
           This method accepts a CODE reference as its $filter_function argument. This code
           reference is used to filter the tree nodes as they are collected. This can be used to
           customize output, or to gather specific information from a more complex tree node. The
           filter function should accept a single argument, which is the current Tree::Simple
           object.

       getResults
           This method returns the accumulated results of the application of the node filter to
           the tree.

       setResults
           This method should not really be used outside of this class, as it just would not make
           any sense to. It is included in this class and in this documentation to facilitate
           subclassing of this class for your own needs. If you desire to clear the results, then
           you can simply call "setResults" with no argument.

       visit ($tree)
           The "visit" method accepts a Tree::Simple and applies the function set in "new" or
           "setNodeFilter" appropriately. The results of this application can be retrieved with
           "getResults"

CONSTANTS

       These constants are part of the old-style interface, and therefore will eventually be
       deprecated.

       RECURSIVE
           If passed this constant in the constructor, the function will be applied recursively
           down the hierarchy of Tree::Simple objects.

       CHILDREN_ONLY
           If passed this constant in the constructor, the function will be applied to the
           immediate children of the Tree::Simple object.

BUGS

       None that I am aware of. The code is pretty thoroughly tested (see CODE COVERAGE section
       in Tree::Simple) and is based on an (non-publicly released) module which I had used in
       production systems for about 2 years without incident. Of course, if you find a bug, let
       me know, and I will be sure to fix it.

SEE ALSO

       I have written a set of pre-built Visitor objects, available on CPAN as
       Tree::Simple::VisitorFactory.

AUTHOR

       stevan little, <stevan@iinteractive.com>

COPYRIGHT AND LICENSE

       Copyright 2004-2006 by Infinity Interactive, Inc.

       <http://www.iinteractive.com>

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