oracular (3) Tree::Simple.3pm.gz
NAME
Tree::Simple - A simple tree object
SYNOPSIS
use Tree::Simple;
# make a tree root
my $tree = Tree::Simple->new("0", Tree::Simple->ROOT);
# explicitly add a child to it
$tree->addChild(Tree::Simple->new("1"));
# specify the parent when creating
# an instance and it adds the child implicitly
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
$tree->DESTROY();
Alternately, to avoid calling Tree::Simple->new(...) just to add a node:
use Tree::Simple;
use Data::TreeDumper; # Provides DumpTree().
# ---------------
my($root) = Tree::Simple->new('Root', Tree::Simple->ROOT);
$root->generateChild('Child 1.0');
$root->generateChild('Child 2.0');
$root->getChild(0)->generateChild('Grandchild 1.1');
print DumpTree($root);
$root->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 $parent argument to
the constructor must be a Tree::Simple object or an object derived from Tree::Simple, otherwise an
exception is thrown. This may seems harsh to some, but this allows me to have the confidence that my code
works as I intend, and for you to enjoy the same level of confidence when using this module. Note however
that this module does not use any Exception or Error module, the exceptions are just strings thrown with
"die".
I consider this module to be production stable, it is based on a module which has been in use on a few
production systems for approx. 2 years now with no issue. The only difference is that the code has been
cleaned up a bit, comments added and the thorough tests written for its public release. I am confident it
behaves as I would expect it to, and is (as far as I know) bug-free. I have not stress-tested it under
extreme duress, but I do not so much intend for it to be used in that type of situation. If this module
cannot keep up with your Tree needs, i suggest switching to one of the modules listed in the "OTHER TREE
MODULES" section below.
CONSTANTS
ROOT
This class constant serves as a placeholder for the root of our tree. If a tree does not have a
parent, then it is considered a root.
METHODS
Constructor
new ($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 children of that parent. 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 hex address of the object is provided for you, so use of this method is entirely
optional. It is the responsibility of the user to ensure the value has 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 the 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 $tree = Tree::Simple->new("root")->addChild(
Tree::Simple->new("1.0")->addChild(
Tree::Simple->new("1.0.1")
)
);
generateChild ($scalar)
This method accepts a scalar and calls addChild(Tree::Simple->new($scalar) ) purely to save you the
effort of needing to use "Tree::Simple->new(...)" as the parameter.
addChildren (@trees)
This method accepts an array of Tree::Simple objects, and adds them to the children list. Like
"addChild" this method will return its invocant to allow for method call chaining.
insertChild ($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 $tree argument is verified to be a Tree::Simple or Tree::Simple derived
object, if this condition fails, an exception is thrown.
insertChildren ($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 within the list
of children. The $index is bounds checked, if this condition fail, an exception is thrown.
When a child is removed, it results in the shifting up of all children after it, and the removed
child is returned. The removed child is properly disconnected from the tree and all its references to
its old parent are removed. However, in order to properly clean up and circular references the
removed child might have, it is advised to call the "DESTROY" method. See the "CIRCULAR REFERENCES"
section for more information.
addSibling ($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 node field of the object.
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 parent of the invocant.
See also </getSiblingCount>.
Warning: This method includes the invocant, so it is not really all siblings but rather all children
of the parent!
getSiblingCount
Returns 0 if the invocant is the root node. Otherwise returns the count of siblings, which excludes
the invocant.
See also </getAllSiblings>.
Warning: This differs from scalar(parent->getAllSiblings() ) just above, which for some reason
includes the invocant. I cannot change getAllSiblings() now for a module first released in 2004.
getDepth
Returns a number representing the depth of the invocant within the hierarchy of Tree::Simple objects.
NOTE: A "ROOT" tree has the depth of -1. This be because Tree::Simple assumes that a root node 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 parent of the invocant, 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 sibling 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 has a "parent" of ROOT, returns false (0) otherwise.
isFistChild
Returns 0 if the invocant is the root node.
Returns 1 if the invocant is the first child in the parental list of children. Otherwise returns 0.
isLastChild
Returns 0 if the invocant is the root node.
Returns 1 if the invocant is the last child in the parental list of children. Otherwise returns 0.
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, or until $func returns 'ABORT'. If given, the function $postfunc will be applied to
each child after the children of the child 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) = @_;
my $tag = $_tree->getNodeValue();
print (("\t" x $_tree->getDepth()), $tag, "\n");
return 'ABORT' if 'foo' eq $tag;
});
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");
});
Note that aborting traverse is not recommended when using $postfunc because post-function will not be
called for any nodes after aborting which might lead to less than predictable results.
size
Returns the total number of nodes in the current tree and all its sub-trees.
height
This method has also been deprecated in favor of the "getHeight" method above, it remains as an alias
to "getHeight" for backwards compatibility.
NOTE: This is also no longer a recursive method which get's it's value on demand, but a value stored
in the Tree::Simple object itself, hopefully making it much more efficient and usable.
Visitor Methods
accept ($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 "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 the 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 sub-trees of the invocant, correcting the depth as it goes.
fixHeight
Tree::Simple will manage the 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 ancestors heights too.
fixWidth
Tree::Simple will manage the 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 ancestors widths too.
Private Methods
I would not normally document private methods, but in case you need to subclass Tree::Simple, here they
are.
_init ($node, $parent, $children)
This method is here largely to facilitate subclassing. This method is called by new to initialize the
object, where new has the primary responsibility of creating the instance.
_setParent ($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 the children to detach from it, however, if a child is
destroyed it will not be detached from the 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
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 the 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 - For viewing Tree::Simple hierarchies in various output formats
Tree::Simple::VisitorFactory - Useful Visitor objects for Tree::Simple objects
Tree::Binary - If you are looking for a binary tree, 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. But it only comes with
1 sophisticated test, t/cut.and.paste.subtrees.t. 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 does not 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 cannot 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.
REPOSITORY
<https://github.com/ronsavage/Tree-Simple>.
SUPPORT
Bugs should be reported via the CPAN bug tracker at
<https://github.com/ronsavage/Tree-Simple/issues>
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.
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.