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.\" ========================================================================
.\"
.IX Title "Graph::Writer 3pm"
.TH Graph::Writer 3pm "2021-09-19" "perl v5.32.1" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Graph::Writer \- base class for Graph file format writers
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 4
\&  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
\&  }
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fBGraph::Writer\fR 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.
.PP
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.
.SH "METHODS"
.IX Header "METHODS"
.SS "\fBnew()\fP"
.IX Subsection "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:
.PP
.Vb 1
\&  $writer = Graph::Writer\->new();
.Ve
.PP
It will throw an exception.
.SS "\fBwrite_graph()\fP"
.IX Subsection "write_graph()"
Read a graph from the specified file:
.PP
.Vb 1
\&  $graph = $writer\->write_graph($file);
.Ve
.PP
The \f(CW$file\fR argument can either be a filename,
or a filehandle for a previously opened file.
.SH "SUBCLASSING"
.IX Header "SUBCLASSING"
To create your own graph format writer, create a module
which subclasses \fBGraph::Writer\fR. For example, suppose
\&\s-1DGF\s0 is a directed graph format \- create a \fBGraph::Writer::DGF\fR module,
with the following structure:
.PP
.Vb 1
\&  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;
.Ve
.PP
Note the leading underscore on the \fB\fB_write_graph()\fB\fR method.
The base class provides the public method, and invokes the
private method which you're expected to provide, as above.
.PP
If you want to perform additional initialisation at
construction time, you can provide an \fB\fB_init()\fB\fR method,
which will be invoked by the base class's constructor.
You should invoke the superclass's initialiser as well,
as follows:
.PP
.Vb 3
\&  sub _init
\&  {
\&    my $self = shift;
\&
\&    $self\->SUPER::_init();
\&
\&    # your initialisation here
\&  }
.Ve
.PP
Someone can then use your class as follows:
.PP
.Vb 1
\&  use Graph::Writer::DGF;
\&
\&  $writer = Graph::Writer::DGF\->new();
\&  $writer\->write_graph($graph, \*(Aqfoo.dgf\*(Aq);
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
.IP "Graph" 4
.IX Item "Graph"
Jarkko Hietaniemi's modules for representing directed graphs,
available from \s-1CPAN\s0 under modules/by\-module/Graph/
.IP "Algorithms in Perl" 4
.IX Item "Algorithms in Perl"
The O'Reilly book has a chapter on directed graphs,
which is based around Jarkko's modules.
.IP "Graph::Writer::Dot" 4
.IX Item "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 \s-1AT&T.\s0
.IP "Graph::Writer::VCG" 4
.IX Item "Graph::Writer::VCG"
A simple subclass of this class for writing graphs
in the file format used by \s-1VCG,\s0 a tool for visualising
directed graphs, initially developed for visualising
compiler graphs.
.IP "Graph::Writer::XML" 4
.IX Item "Graph::Writer::XML"
A simple subclass of this class for writing graphs
as \s-1XML,\s0 using a simple graph markup.
.IP "Graph::Reader" 4
.IX Item "Graph::Reader"
A baseclass for Graph file format readers.
.SH "REPOSITORY"
.IX Header "REPOSITORY"
<https://github.com/neilb/Graph\-ReadWrite>
.SH "AUTHOR"
.IX Header "AUTHOR"
Neil Bowers <neil@bowers.com>
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright (c) 2001\-2012, Neil Bowers. All rights reserved.
Copyright (c) 2001, Canon Research Centre Europe. All rights reserved.
.PP
This script is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.