NAME¶
Graph::Writer - base class for Graph file format writers
SYNOPSIS¶
package Graph::Writer::MyFormat;
use Graph::Writer;
use vars qw(@ISA);
@ISA = qw(Graph::Writer);
sub _write_graph
{
my ($self, $graph, $FILE) = @_;
# write $graph to $FILE
}
DESCRIPTION¶
Graph::Writer is a base class for Graph file format writers. A particular
subclass of Graph::Writer will handle a specific file format, and generate a
Graph, represented using Jarkko Hietaniemi's Graph class.
You should never create an instance of this class yourself, it is only meant for
subclassing. If you try to create an instance of Graph::Writer, the
constructor will throw an exception.
METHODS¶
new()¶
Constructor - generate a new writer instance. This is a virtual method, or
whatever the correct lingo is. You're not meant to call this on the base
class, it is inherited by the subclasses. Ie if you do something like:
$writer = Graph::Writer->new();
It will throw an exception.
write_graph()¶
Read a graph from the specified file:
$graph = $writer->write_graph($file);
The $file argument can either be a filename, or a filehandle for a previously
opened file.
SUBCLASSING¶
To create your own graph format writer, create a module which subclasses
Graph::Writer. For example, suppose DGF is a directed graph format -
create a
Graph::Writer::DGF module, with the following structure:
package Graph::Writer::DGF;
use Graph::Writer;
use vars qw(@ISA);
@ISA = qw(Graph::Writer);
sub _write_graph
{
my $self = shift;
my $graph = shift;
my $FILE = shift;
while (<$FILE>)
{
}
return 1;
}
1;
Note the leading underscore on the
_write_graph()
method. The base class provides the public method, and invokes the private
method which you're expected to provide, as above.
If you want to perform additional initialisation at construction time, you can
provide an
_init() method, which will be invoked
by the base class's constructor. You should invoke the superclass's
initialiser as well, as follows:
sub _init
{
my $self = shift;
$self->SUPER::_init();
# your initialisation here
}
Someone can then use your class as follows:
use Graph::Writer::DGF;
$writer = Graph::Writer::DGF->new();
$writer->write_graph($graph, 'foo.dgf');
SEE ALSO¶
- Graph
- Jarkko Hietaniemi's modules for representing directed graphs, available
from CPAN under modules/by-module/Graph/
- Algorithms in Perl
- The O'Reilly book has a chapter on directed graphs, which is based around
Jarkko's modules.
- Graph::Writer::Dot
- A simple subclass of this class for writing graphs in the file format used
by dot, which is part of the graphviz package from AT&T.
- Graph::Writer::VCG
- A simple subclass of this class for writing graphs in the file format used
by VCG, a tool for visualising directed graphs, initially developed for
visualising compiler graphs.
- Graph::Writer::XML
- A simple subclass of this class for writing graphs as XML, using a simple
graph markup.
- Graph::Reader
- A baseclass for Graph file format readers.
AUTHOR¶
Neil Bowers <neil@bowers.com>
COPYRIGHT¶
Copyright (c) 2001-2012, Neil Bowers. All rights reserved. Copyright (c) 2001,
Canon Research Centre Europe. All rights reserved.
This script is free software; you can redistribute it and/or modify it under the
same terms as Perl itself.