oracular (3) Graph::Writer.3pm.gz

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.

REPOSITORY

       <https://github.com/neilb/Graph-ReadWrite>

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.