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.