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NAME ^

Tree - An N-ary tree

SYNOPSIS ^

  my $tree = Tree->new( 'root' );
  my $child = Tree->new( 'child' );
  $tree->add_child( $child );

  $tree->add_child( { at => 0 }, Tree->new( 'first child' ) );
  $tree->add_child( { at => -1 }, Tree->new( 'last child' ) );

  $tree->set_value( 'toor' );
  my $value = $tree->value;

  my @children = $tree->children;
  my @some_children = $tree->children( 0, 2 );

  my $height = $tree->height;
  my $width  = $tree->width;
  my $depth  = $tree->depth;
  my $size   = $tree->size;

  if ( $tree->has_child( $child ) ) {
      $tree->remove_child( $child );
  }

  $tree->remove_child( 0 );

  my @nodes = $tree->traverse( $tree->POST_ORDER );
  my $clone = $tree->clone;
  my $mirror = $tree->clone->mirror;

  $tree->add_event_handler({
      add_child    => sub { ... },
      remove_child => sub { ... },
      value        => sub { ... },
  });

  my $old_default_error_handler = $tree->error_handler(Tree->DIE);
  my $old_object_error_handler  = $tree->error_handler($tree->DIE);

DESCRIPTION ^

This is meant to be a full-featured N-ary tree representation with configurable error-handling and a simple events system that allows for transparent persistence to a variety of datastores. It is derived from Tree::Simple, but has a simpler interface and much, much more.

METHODS ^

Constructors

new([$value])

Here, [] indicate an optional parameter.

This will return a Tree object. It will accept one parameter which, if passed, will become the value (accessible by value()). All other parameters will be ignored.

If you call $tree->new([$value]), it will instead call clone(), then set the value of the clone to $value.

clone()

This will return a clone of $tree. The clone will be a root tree, but all children will be cloned.

If you call Tree->clone([$value]), it will instead call new($value).

NOTE: the value is merely a shallow copy. This means that all references will be kept.

Behaviors

add_child([$options], @nodes)

This will add all the @nodes as children of $tree. $options is a optional unblessed hashref that specifies options for add_child(). The optional parameters are:

add_child() resets last_error() upon entry.

remove_child([$options], @nodes)

Here, [] indicate an optional parameter.

This will remove all the @nodes from the children of $tree. You can either pass in the actual child object you wish to remove, the index of the child you wish to remove, or a combination of both.

$options is a optional unblessed hashref that specifies parameters for remove_child(). Currently, no parameters are used.

remove_child() resets last_error() upon entry.

mirror()

This will modify the tree such that it is a mirror of what it was before. This means that the order of all children is reversed.

NOTE: This is a destructive action. It will modify the tree's internal structure. If you wish to get a mirror, yet keep the original tree intact, use my $mirror = $tree->clone->mirror.

mirror() does not reset last_error() because it (mirror() ) is implemented in Tree::Fast, which has no error handling.

traverse([$order])

Here, [] indicate an optional parameter.

This will return a list of the nodes in the given traversal order. The default traversal order is pre-order.

The various traversal orders do the following steps:

traverse() does not reset last_error() because it (traverse() ) is implemented in Tree::Fast, which has no error handling.

State Queries

is_root()

This will return true if $tree has no parent and false otherwise.

is_leaf()

This will return true if $tree has no children and false otherwise.

has_child(@nodes)

This will return true if $tree has each of the @nodes as a child. Otherwise, it will return false.

The test to see if a node is in the tree uses refaddr() from Scalar::Util, not the value of the node. This means @nodes must be an array of Tree objects.

get_index_for(@nodes)

This will return the index into the children list of $tree for each of the @nodes passed in.

Accessors

parent()

This will return the parent of $tree.

children( [ $idx, [$idx, ..] ] )

Here, [] indicate optional parameters.

This will return the children of $tree. If called in list context, it will return all the children. If called in scalar context, it will return the number of children.

You may optionally pass in a list of indices to retrieve. This will return the children in the order you asked for them. This is very much like an arrayslice.

root()

This will return the root node of the tree that $tree is in. The root of the root node is itself.

height()

This will return the height of $tree. A leaf has a height of 1. A parent has a height of its tallest child, plus 1.

width()

This will return the width of $tree. A leaf has a width of 1. A parent has a width equal to the sum of all the widths of its children.

depth()

This will return the depth of $tree. A root has a depth of 0. A child has the depth of its parent, plus 1.

This is the distance from the root. It's useful for things like pretty-printing the tree.

size()

This will return the number of nodes within $tree. A leaf has a size of 1. A parent has a size equal to the 1 plus the sum of all the sizes of its children.

value()

This will return the value stored in the node.

set_value([$value])

Here, [] indicate an optional parameter.

This will set the value stored in the node to $value, then return $self.

If $value is not provided, undef is used.

meta()

This will return a hashref that can be used to store whatever metadata the client wishes to store. For example, Tree::Persist::DB uses this to store database row ids.

It is recommended that you store your metadata in a subhashref and not in the top-level metadata hashref, keyed by your package name. Tree::Persist does this, using a unique key for each persistence layer associated with that tree. This will help prevent clobbering of metadata.

ERROR HANDLING ^

Describe what the default error handlers do and what a custom error handler is expected to do.

Error-related methods

error_handler( [ $handler ] )

This will return the current error handler for the tree. If a value is passed in, then it will be used to set the error handler for the tree.

If called as a class method, this will instead work with the default error handler.

error( $error, [ arg1 [, arg2 ...] ] )

Call this when you wish to report an error using the currently defined error_handler for the tree. The only guaranteed parameter is an error string describing the issue. There may be other arguments, and you may certainly provide other arguments in your subclass to be passed to your custom handler.

last_error()

If an error occurred during the last behavior, this will return the error string. It is reset only by add_child() and remove_child().

Default error handlers

QUIET

Use this error handler if you want to have quiet error-handling. The "last_error()" method will retrieve the error from the last operation, if there was one. If an error occurs, the operation will return undefined.

WARN
DIE

EVENT HANDLING ^

Tree provides for basic event handling. You may choose to register one or more callbacks to be called when the appropriate event occurs. The events are:

Event handling methods

add_event_handler( {$type => $callback [, $type => $callback, ... ]} )

You may choose to add event handlers for any known type. Callbacks must be references to subroutines. They will be called in the order they are defined.

event( $type, $actor, @args )

This will trigger an event of type $type. All event handlers registered on $tree will be called with parameters of ($actor, @args). Then, the parent will be notified of the event and its handlers will be called, on up to the root.

This allows you specify an event handler on the root and be guaranteed that it will fire every time the appropriate event occurs anywhere in the tree.

NULL TREE ^

If you call $self->parent on a root node, it will return a Tree::Null object. This is an implementation of the Null Object pattern optimized for usage with Tree. It will evaluate as false in every case (using overload) and all methods called on it will return a Tree::Null object.

Notes

CIRCULAR REFERENCES ^

Please q.v. Forest for more info on this topic.

FAQ ^

Which is the best tree processing module?

Tree::DAG_Node. More details: "SEE ALSO".

How do I implement the visitor pattern?

I have deliberately chosen to not implement the Visitor pattern as described by Gamma et al. Given a sufficiently powerful traverse() and Perl's capabilities, an explicit visitor object is almost always unneeded. If you want one, it's easy to write one yourself. Here's a simple one I wrote in 5 minutes:

  package My::Visitor;

  sub new {
      my $class = shift;
      my $opts  = @_;

      return bless {
          tree => $opts->{tree},
          action => $opts->{action},
      }, $class;
  }

  sub visit {
      my $self = shift;
      my ($mode) = @_;

      foreach my $node ( $self->{tree}->traverse( $mode ) ) {
          $self->{action}->( $node );
      }
  }

Should I implement the visitor pattern?

No. You're better off using the "walk_down($options)" in Tree::DAG_Node method.

SEE ALSO ^

o Tree::Binary

Lightweight.

o Tree::DAG_Node

Lightweight, and with a long list of methods.

o Tree::DAG_Node::Persist

Lightweight.

o Tree::Persist

Lightweight.

o Forest

Uses Moose.

Tree itself is also lightweight.

CODE COVERAGE ^

These statistics are as of V 1.01.

We use Devel::Cover to test the code coverage of our tests. Below is the Devel::Cover report on this module's test suite.

  ---------------------------- ------ ------ ------ ------ ------ ------ ------
  File                           stmt   bran   cond    sub    pod   time  total
  ---------------------------- ------ ------ ------ ------ ------ ------ ------
  blib/lib/Tree.pm              100.0  100.0   94.4  100.0  100.0   67.3   99.7
  blib/lib/Tree/Binary.pm        96.4   95.0  100.0  100.0  100.0   10.7   96.7
  blib/lib/Tree/Fast.pm          99.4   95.5   91.7  100.0  100.0   22.0   98.6
  Total                          98.9   96.8   94.9  100.0  100.0  100.0   98.5
  ---------------------------- ------ ------ ------ ------ ------ ------ ------

ACKNOWLEDGEMENTS ^

SUPPORT ^

The mailing list is at TreeCPAN@googlegroups.com. I also read http://www.perlmonks.com on a daily basis.

AUTHORS ^

Rob Kinyon <rob.kinyon@iinteractive.com>

Stevan Little <stevan.little@iinteractive.com>

Thanks to Infinity Interactive for generously donating our time.

Co-maintenance since V 1.02 is by Ron Savage <rsavage@cpan.org>. Uses of 'I' in previous versions is not me, but will be hereafter.

COPYRIGHT AND LICENSE ^

Copyright 2004, 2005 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.

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