Tree::Simple::Visitor::FromNestedHash - A Visitor for creating Tree::Simple objects from nested hash trees.


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

  my $visitor = Tree::Simple::Visitor::FromNestedHash->new();

  # given this nested hash tree
  my $hash_tree = {
                Root => {
                        Child1 => {
                                GrandChild1 => {},
                                GrandChild2 => {}
                        Child2 => {}

  # set the array tree we
  # are going to convert


  # this then creates the equivalent Tree::Simple object:
  # Tree::Simple->new("Root")
  #     ->addChildren(
  #         Tree::Simple->new("Child1")
  #             ->addChildren(
  #                 Tree::Simple->new("GrandChild1"),
  #                 Tree::Simple->new("GrandChild2")
  #             ),
  #         Tree::Simple->new("Child2"),
  #     );


Given a tree constructed from nested hashes, this Visitor will create the equivalent Tree::Simple hierarchy.



There are no arguments to the constructor the object will be in its default state. You can use the setNodeFilter methods to customize its behavior.

setNodeFilter ($filter_function)

This method accepts a CODE reference as its $filter_function argument and throws an exception if it is not a code reference. This code reference is used to filter the tree nodes as they are created, the $filter_function is passed the node value extracted from the hash prior to it being inserted into the tree being built. The $filter_function is expected to return the value desired for inclusion into the tree.

setHashTree ($hash_tree)

This method is used to set the $hash_tree that our Tree::Simple hierarchy will be constructed from. It must be in the following form:

    Root => {
          Child1 => {
                  GrandChild1 => {},
                  GrandChild2 => {}
          Child2 => {}

Basically each key in the hash is considered a node, values are ignored unless it is a hash reference with at least one key in it, in which case it is interpreted as containing the children of the node created from the key.

The tree is validated prior being accepted, if it fails validation an exception will be thrown. The rules are as follows;

The hash tree must not be empty.

It makes not sense to create a tree out of nothing, so it is assumed that this is a sign of something wrong.

The hash tree must be a single rooted tree.

The hash tree should have only one key in the first level. If it has more than one, then it is not a single rooted tree.

NOTE: Hash keys are sorted ascii-betically before being added to the tree, this results in a somewhat more predictable hierarchy.

visit ($tree)

This is the method that is used by the Tree::Simple accept method. It can also be used on its own, it requires the $tree argument to be a Tree::Simple object (or derived from a Tree::Simple object), and will throw and exception otherwise.



Bugs should be reported via the CPAN bug tracker at


See the CODE COVERAGE section in Tree::Simple::VisitorFactory for more information.


These Visitor classes are all subclasses of Tree::Simple::Visitor, which can be found in the Tree::Simple module, you should refer to that module for more information.


stevan little, <>


Copyright 2004, 2005 by Infinity Interactive, Inc.

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