Provided by: libtree-simple-perl_1.23-1_all 
NAME
Tree::Simple - A simple tree object
SYNOPSIS
use Tree::Simple;
# make a tree root
my $tree = Tree::Simple->new("0", Tree::Simple->ROOT);
# explicity add a child to it
$tree->addChild(Tree::Simple->new("1"));
# specify the parent when creating
# an instance and it adds the child implicity
my $sub_tree = Tree::Simple->new("2", $tree);
# chain method calls
$tree->getChild(0)->addChild(Tree::Simple->new("1.1"));
# add more than one child at a time
$sub_tree->addChildren(
Tree::Simple->new("2.1"),
Tree::Simple->new("2.2")
);
# add siblings
$sub_tree->addSibling(Tree::Simple->new("3"));
# insert children a specified index
$sub_tree->insertChild(1, Tree::Simple->new("2.1a"));
# clean up circular references
$tree->DESTROY();
DESCRIPTION
This module in an fully object-oriented implementation of a simple n-ary tree. It is built
upon the concept of parent-child relationships, so therefore every Tree::Simple object has
both a parent and a set of children (who themselves may have children, and so on). Every
Tree::Simple object also has siblings, as they are just the children of their immediate
parent.
It is can be used to model hierarchal information such as a file-system, the
organizational structure of a company, an object inheritance hierarchy, versioned files
from a version control system or even an abstract syntax tree for use in a parser. It
makes no assumptions as to your intended usage, but instead simply provides the structure
and means of accessing and traversing said structure.
This module uses exceptions and a minimal Design By Contract style. All method arguments
are required unless specified in the documentation, if a required argument is not defined
an exception will usually be thrown. Many arguments are also required to be of a specific
type, for instance the $parent argument to the constructor must be a Tree::Simple object
or an object derived from Tree::Simple, otherwise an exception is thrown. This may seems
harsh to some, but this allows me to have the confidence that my code works as I intend,
and for you to enjoy the same level of confidence when using this module. Note however
that this module does not use any Exception or Error module, the exceptions are just
strings thrown with "die".
I consider this module to be production stable, it is based on a module which has been in
use on a few production systems for approx. 2 years now with no issue. The only
difference is that the code has been cleaned up a bit, comments added and the thorough
tests written for its public release. I am confident it behaves as I would expect it to,
and is (as far as I know) bug-free. I have not stress-tested it under extreme duress, but
I don't so much intend for it to be used in that type of situation. If this module cannot
keep up with your Tree needs, i suggest switching to one of the modules listed in the
"OTHER TREE MODULES" section below.
CONSTANTS
ROOT
This class constant serves as a placeholder for the root of our tree. If a tree does
not have a parent, then it is considered a root.
METHODS
Constructor
new ($node, $parent)
The constructor accepts two arguments a $node value and an optional $parent. The
$node value can be any scalar value (which includes references and objects). The
optional $parent value must be a Tree::Simple object, or an object derived from
Tree::Simple. Setting this value implies that your new tree is a child of the parent
tree, and therefore adds it to the parent's children. If the $parent is not specified
then its value defaults to ROOT.
Mutator Methods
setNodeValue ($node_value)
This sets the node value to the scalar $node_value, an exception is thrown if
$node_value is not defined.
setUID ($uid)
This allows you to set your own unique ID for this specific Tree::Simple object. A
default value derived from the object's hex address is provided for you, so use of
this method is entirely optional. It is the responsibility of the user to ensure the
value's uniqueness, all that is tested by this method is that $uid is a true value
(evaluates to true in a boolean context). For even more information about the
Tree::Simple UID see the "getUID" method.
addChild ($tree)
This method accepts only Tree::Simple objects or objects derived from Tree::Simple, an
exception is thrown otherwise. This method will append the given $tree to the end of
it's children list, and set up the correct parent-child relationships. This method is
set up to return its invocant so that method call chaining can be possible. Such as:
my $tree = Tree::Simple->new("root")->addChild(Tree::Simple->new("child one"));
Or the more complex:
my $tree = Tree::Simple->new("root")->addChild(
Tree::Simple->new("1.0")->addChild(
Tree::Simple->new("1.0.1")
)
);
addChildren (@trees)
This method accepts an array of Tree::Simple objects, and adds them to it's children
list. Like "addChild" this method will return its invocant to allow for method call
chaining.
insertChild ($index, $tree)
This method accepts a numeric $index and a Tree::Simple object ($tree), and inserts
the $tree into the children list at the specified $index. This results in the
shifting down of all children after the $index. The $index is checked to be sure it is
the bounds of the child list, if it out of bounds an exception is thrown. The $tree
argument's type is verified to be a Tree::Simple or Tree::Simple derived object, if
this condition fails, an exception is thrown.
insertChildren ($index, @trees)
This method functions much as insertChild does, but instead of inserting a single
Tree::Simple, it inserts an array of Tree::Simple objects. It too bounds checks the
value of $index and type checks the objects in @trees just as "insertChild" does.
removeChild ($child | $index)>
Accepts two different arguments. If given a Tree::Simple object ($child), this method
finds that specific $child by comparing it with all the other children until it finds
a match. At which point the $child is removed. If no match is found, and exception is
thrown. If a non-Tree::Simple object is given as the $child argument, an exception is
thrown.
This method also accepts a numeric $index and removes the child found at that index
from it's list of children. The $index is bounds checked, if this condition fail, an
exception is thrown.
When a child is removed, it results in the shifting up of all children after it, and
the removed child is returned. The removed child is properly disconnected from the
tree and all its references to its old parent are removed. However, in order to
properly clean up and circular references the removed child might have, it is advised
to call it's "DESTROY" method. See the "CIRCULAR REFERENCES" section for more
information.
addSibling ($tree)
addSiblings (@trees)
insertSibling ($index, $tree)
insertSiblings ($index, @trees)
The "addSibling", "addSiblings", "insertSibling" and "insertSiblings" methods pass
along their arguments to the "addChild", "addChildren", "insertChild" and
"insertChildren" methods of their parent object respectively. This eliminates the need
to overload these methods in subclasses which may have specialized versions of the
*Child(ren) methods. The one exceptions is that if an attempt it made to add or insert
siblings to the ROOT of the tree then an exception is thrown.
NOTE: There is no "removeSibling" method as I felt it was probably a bad idea. The same
effect can be achieved by manual upwards traversal.
Accessor Methods
getNodeValue
This returns the value stored in the object's node field.
getUID
This returns the unique ID associated with this particular tree. This can be custom
set using the "setUID" method, or you can just use the default. The default is the
hex-address extracted from the stringified Tree::Simple object. This may not be a
universally unique identifier, but it should be adequate for at least the current
instance of your perl interpreter. If you need a UUID, one can be generated with an
outside module (there are
many to choose from on CPAN) and the "setUID" method (see above).
getChild ($index)
This returns the child (a Tree::Simple object) found at the specified $index. Note
that we do use standard zero-based array indexing.
getAllChildren
This returns an array of all the children (all Tree::Simple objects). It will return
an array reference in scalar context.
getSibling ($index)
getAllSiblings
Much like "addSibling" and "addSiblings", these two methods simply call "getChild" and
"getAllChildren" on the invocant's parent.
getDepth
Returns a number representing the invocant's depth within the hierarchy of
Tree::Simple objects.
NOTE: A "ROOT" tree has the depth of -1. This be because Tree::Simple assumes that a
tree's root will usually not contain data, but just be an anchor for the data-
containing branches. This may not be intuitive in all cases, so I mention it here.
getParent
Returns the invocant's parent, which could be either ROOT or a Tree::Simple object.
getHeight
Returns a number representing the length of the longest path from the current tree to
the furthest leaf node.
getWidth
Returns the a number representing the breadth of the current tree, basically it is a
count of all the leaf nodes.
getChildCount
Returns the number of children the invocant contains.
getIndex
Returns the index of this tree within its parent's child list. Returns -1 if the tree
is the root.
Predicate Methods
isLeaf
Returns true (1) if the invocant does not have any children, false (0) otherwise.
isRoot
Returns true (1) if the invocant's "parent" field is ROOT, returns false (0)
otherwise.
Recursive Methods
traverse ($func, ?$postfunc)
This method accepts two arguments a mandatory $func and an optional $postfunc. If the
argument $func is not defined then an exception is thrown. If $func or $postfunc are
not in fact CODE references then an exception is thrown. The function $func is then
applied recursively to all the children of the invocant. If given, the function
$postfunc will be applied to each child after the child's children have been
traversed.
Here is an example of a traversal function that will print out the hierarchy as a
tabbed in list.
$tree->traverse(sub {
my ($_tree) = @_;
print (("\t" x $_tree->getDepth()), $_tree->getNodeValue(), "\n");
});
Here is an example of a traversal function that will print out the hierarchy in an
XML-style format.
$tree->traverse(sub {
my ($_tree) = @_;
print ((' ' x $_tree->getDepth()),
'<', $_tree->getNodeValue(),'>',"\n");
},
sub {
my ($_tree) = @_;
print ((' ' x $_tree->getDepth()),
'</', $_tree->getNodeValue(),'>',"\n");
});
size
Returns the total number of nodes in the current tree and all its sub-trees.
height
This method has also been deprecated in favor of the "getHeight" method above, it
remains as an alias to "getHeight" for backwards compatibility.
NOTE: This is also no longer a recursive method which get's it's value on demand, but
a value stored in the Tree::Simple object itself, hopefully making it much more
efficient and usable.
Visitor Methods
accept ($visitor)
It accepts either a Tree::Simple::Visitor object (which includes classes derived
from Tree::Simple::Visitor), or an object who has the "visit" method available
(tested with "$visitor->can('visit')"). If these qualifications are not met,
and exception will be thrown. We then run the Visitor's "visit" method giving the
current tree as its argument.
I have also created a number of Visitor objects and packaged them into the
Tree::Simple::VisitorFactory.
Cloning Methods
Cloning a tree can be an extremely expensive operation for large trees, so we provide two
options for cloning, a deep clone and a shallow clone.
When a Tree::Simple object is cloned, the node is deep-copied in the following manner. If
we find a normal scalar value (non-reference), we simply copy it. If we find an object, we
attempt to call "clone" on it, otherwise we just copy the reference (since we assume the
object does not want to be cloned). If we find a SCALAR, REF reference we copy the value
contained within it. If we find a HASH or ARRAY reference we copy the reference and
recursively copy all the elements within it (following these exact guidelines). We also do
our best to assure that circular references are cloned only once and connections restored
correctly. This cloning will not be able to copy CODE, RegExp and GLOB references, as they
are pretty much impossible to clone. We also do not handle "tied" objects, and they will
simply be copied as plain references, and not re-"tied".
clone
The clone method does a full deep-copy clone of the object, calling "clone"
recursively on all its children. This does not call "clone" on the parent tree
however. Doing this would result in a slowly degenerating spiral of recursive death,
so it is not recommended and therefore not implemented. What happens is that the tree
instance that "clone" is actually called upon is detached from the tree, and becomes a
root node, all if the cloned children are then attached as children of that tree. I
personally think this is more intuitive then to have the cloning crawl back up the
tree is not what I think most people would expect.
cloneShallow
This method is an alternate option to the plain "clone" method. This method allows the
cloning of single Tree::Simple object while retaining connections to the rest of the
tree/hierarchy.
Misc. Methods
DESTROY
To avoid memory leaks through uncleaned-up circular references, we implement the
"DESTROY" method. This method will attempt to call "DESTROY" on each of its children
(if it has any). This will result in a cascade of calls to "DESTROY" on down the tree.
It also cleans up it's parental relations as well.
Because of perl's reference counting scheme and how that interacts with circular
references, if you want an object to be properly reaped you should manually call
"DESTROY". This is especially necessary if your object has any children. See the
section on "CIRCULAR REFERENCES" for more information.
fixDepth
Tree::Simple will manage your tree's depth field for you using this method. You should
never need to call it on your own, however if you ever did need to, here is it.
Running this method will traverse your all the invocant's sub-trees correcting the
depth as it goes.
fixHeight
Tree::Simple will manage your tree's height field for you using this method. You
should never need to call it on your own, however if you ever did need to, here is it.
Running this method will correct the heights of the current tree and all it's
ancestors.
fixWidth
Tree::Simple will manage your tree's width field for you using this method. You should
never need to call it on your own, however if you ever did need to, here is it.
Running this method will correct the widths of the current tree and all it's
ancestors.
Private Methods
I would not normally document private methods, but in case you need to subclass
Tree::Simple, here they are.
_init ($node, $parent, $children)
This method is here largely to facilitate subclassing. This method is called by new to
initialize the object, where new's primary responsibility is creating the instance.
_setParent ($parent)
This method sets up the parental relationship. It is for internal use only.
_setHeight ($child)
This method will set the height field based upon the height of the given $child.
CIRCULAR REFERENCES
I have revised the model by which Tree::Simple deals with circular references. In the
past all circular references had to be manually destroyed by calling DESTROY. The call to
DESTROY would then call DESTROY on all the children, and therefore cascade down the tree.
This however was not always what was needed, nor what made sense, so I have now revised
the model to handle things in what I feel is a more consistent and sane way.
Circular references are now managed with the simple idea that the parent makes the
decisions for the child. This means that child-to-parent references are weak, while
parent-to-child references are strong. So if a parent is destroyed it will force all it's
children to detach from it, however, if a child is destroyed it will not be detached from
it's parent.
Optional Weak References
By default, you are still required to call DESTROY in order for things to happen. However
I have now added the option to use weak references, which alleviates the need for the
manual call to DESTROY and allows Tree::Simple to manage this automatically. This is
accomplished with a compile time setting like this:
use Tree::Simple 'use_weak_refs';
And from that point on Tree::Simple will use weak references to allow for perl's reference
counting to clean things up properly.
For those who are unfamiliar with weak references, and how they affect the reference
counts, here is a simple illustration. First is the normal model that Tree::Simple uses:
+---------------+
| Tree::Simple1 |<---------------------+
+---------------+ |
| parent | |
| children |-+ |
+---------------+ | |
| |
| +---------------+ |
+->| Tree::Simple2 | |
+---------------+ |
| parent |-+
| children |
+---------------+
Here, Tree::Simple1 has a reference count of 2 (one for the original variable it is
assigned to, and one for the parent reference in Tree::Simple2), and Tree::Simple2 has a
reference count of 1 (for the child reference in Tree::Simple1).
Now, with weak references:
+---------------+
| Tree::Simple1 |.......................
+---------------+ :
| parent | :
| children |-+ : <--[ weak reference ]
+---------------+ | :
| :
| +---------------+ :
+->| Tree::Simple2 | :
+---------------+ :
| parent |..
| children |
+---------------+
Now Tree::Simple1 has a reference count of 1 (for the variable it is assigned to) and 1
weakened reference (for the parent reference in Tree::Simple2). And Tree::Simple2 has a
reference count of 1, just as before.
BUGS
None that I am aware of. The code is pretty thoroughly tested (see "CODE COVERAGE" below)
and is based on an (non-publicly released) module which I had used in production systems
for about 3 years without incident. Of course, if you find a bug, let me know, and I will
be sure to fix it.
CODE COVERAGE
I use Devel::Cover to test the code coverage of my tests, below is the Devel::Cover report
on this module's test suite.
---------------------------- ------ ------ ------ ------ ------ ------ ------
File stmt branch cond sub pod time total
---------------------------- ------ ------ ------ ------ ------ ------ ------
Tree/Simple.pm 99.6 96.0 92.3 100.0 97.0 95.5 98.0
Tree/Simple/Visitor.pm 100.0 96.2 88.2 100.0 100.0 4.5 97.7
---------------------------- ------ ------ ------ ------ ------ ------ ------
Total 99.7 96.1 91.1 100.0 97.6 100.0 97.9
---------------------------- ------ ------ ------ ------ ------ ------ ------
SEE ALSO
I have written a number of other modules which use or augment this module, they are
describes below and available on CPAN.
Tree::Parser - A module for parsing formatted files into Tree::Simple hierarchies.
Tree::Simple::View - A set of classes for viewing Tree::Simple hierarchies in various
output formats.
Tree::Simple::VisitorFactory - A set of several useful Visitor objects for Tree::Simple
objects.
Tree::Binary - If you are looking for a binary tree, this you might want to check this one
out.
Also, the author of Data::TreeDumper and I have worked together to make sure that
Tree::Simple and his module work well together. If you need a quick and handy way to dump
out a Tree::Simple hierarchy, this module does an excellent job (and plenty more as well).
I have also recently stumbled upon some packaged distributions of Tree::Simple for the
various Unix flavors. Here are some links:
FreeBSD Port - <http://www.freshports.org/devel/p5-Tree-Simple/>
Debian Package - <http://packages.debian.org/unstable/perl/libtree-simple-perl>
Linux RPM - <http://rpmpan.sourceforge.net/Tree.html>
OTHER TREE MODULES
There are a few other Tree modules out there, here is a quick comparison between
Tree::Simple and them. Obviously I am biased, so take what I say with a grain of salt, and
keep in mind, I wrote Tree::Simple because I could not find a Tree module that suited my
needs. If Tree::Simple does not fit your needs, I recommend looking at these modules.
Please note that I am only listing Tree::* modules I am familiar with here, if you think I
have missed a module, please let me know. I have also seen a few tree-ish modules outside
of the Tree::* namespace, but most of them are part of another distribution (HTML::Tree,
Pod::Tree, etc) and are likely specialized in purpose.
Tree::DAG_Node
This module seems pretty stable and very robust with a lot of functionality. However,
Tree::DAG_Node does not come with any automated tests. It's test.pl file simply checks
the module loads and nothing else. While I am sure the author tested his code, I would
feel better if I was able to see that. The module is approx. 3000 lines with POD, and
1,500 without the POD. The shear depth and detail of the documentation and the ratio
of code to documentation is impressive, and not to be taken lightly. But given that it
is a well known fact that the likeliness of bugs increases along side the size of the
code, I do not feel comfortable with large modules like this which have no tests.
All this said, I am not a huge fan of the API either, I prefer the gender neutral
approach in Tree::Simple to the mother/daughter style of Tree::DAG_Node. I also feel
very strongly that Tree::DAG_Node is trying to do much more than makes sense in a
single module, and is offering too many ways to do the same or similar things.
However, of all the Tree::* modules out there, Tree::DAG_Node seems to be one of the
favorites, so it may be worth investigating.
Tree::MultiNode
I am not very familiar with this module, however, I have heard some good reviews of
it, so I thought it deserved mention here. I believe it is based upon C++ code found
in the book Algorithms in C++ by Robert Sedgwick. It uses a number of interesting
ideas, such as a ::Handle object to traverse the tree with (similar to Visitors, but
also seem to be to be kind of like a cursor). However, like Tree::DAG_Node, it is
somewhat lacking in tests and has only 6 tests in its suite. It also has one glaring
bug, which is that there is currently no way to remove a child node.
Tree::Nary
It is a (somewhat) direct translation of the N-ary tree from the GLIB library, and the
API is based on that. GLIB is a C library, which means this is a very C-ish API. That
doesn't appeal to me, it might to you, to each their own.
This module is similar in intent to Tree::Simple. It implements a tree with n branches
and has polymorphic node containers. It implements much of the same methods as
Tree::Simple and a few others on top of that, but being based on a C library, is not
very OO. In most of the method calls the $self argument is not used and the second
argument $node is. Tree::Simple is a much more OO module than Tree::Nary, so while
they are similar in functionality they greatly differ in implementation style.
Tree
This module is pretty old, it has not been updated since Oct. 31, 1999 and is still on
version 0.01. It also seems to be (from the limited documentation) a binary and a
balanced binary tree, Tree::Simple is an n-ary tree, and makes no attempt to balance
anything.
Tree::Ternary
This module is older than Tree, last update was Sept. 24th, 1999. It seems to be a
special purpose tree, for storing and accessing strings, not general purpose like
Tree::Simple.
Tree::Ternary_XS
This module is an XS implementation of the above tree type.
Tree::Trie
This too is a specialized tree type, it sounds similar to the Tree::Ternary, but it
much newer (latest release in 2003). It seems specialized for the lookup and retrieval
of information like a hash.
Tree::M
Is a wrapper for a C++ library, whereas Tree::Simple is pure-perl. It also seems to be
a more specialized implementation of a tree, therefore not really the same as
Tree::Simple.
Tree::Fat
Is a wrapper around a C library, again Tree::Simple is pure-perl. The author describes
FAT-trees as a combination of a Tree and an array. It looks like a pretty mean and
lean module, and good if you need speed and are implementing a custom data-store of
some kind. The author points out too that the module is designed for embedding and
there is not default embedding, so you can't really use it "out of the box".
ACKNOWLEDGEMENTS
Thanks to Nadim Ibn Hamouda El Khemir for making Data::TreeDumper work with Tree::Simple.
Thanks to Brett Nuske for his idea for the "getUID" and "setUID" methods.
Thanks to whomever submitted the memory leak bug to RT (#7512).
Thanks to Mark Thomas for his insight into how to best handle the height and width
properties without unnecessary recursion.
Thanks for Mark Lawrence for the &traverse post-func patch, tests and docs.
AUTHOR
Stevan Little, <stevan@iinteractive.com>
Rob Kinyon, <rob@iinteractive.com>
Ron Savage <ron@savage.net.au> has taken over maintenance as of V 1.19.
REPOSITORY
<https://github.com/stevan/tree-simple>.
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.