NAME

       Parse::Binary::FixedFormat::Variants - Convert between variant records and hashes

DESCRIPTION

       Parse::Binary::FixedFormat supports variant record formats.  To describe a variant
       structure, pass a hash reference containing the following elements to new.  The object
       returned to handle variant records will be a Parse::Binary::FixedFormat::Variants.

       Chooser
           When converting a buffer to a hash, this subroutine is invoked after applying the
           first format to the buffer.  The generated hash reference is passed to this routine.
           Any field names specified in the first format are available to be used in making a
           decision on which format to use to decipher the buffer.  This routine should return
           the index of the proper format specification.

           When converting a hash to a buffer, this subroutine is invoked first to choose a
           packing format.  Since the same function is used for both conversions, this function
           should restrict itself to field names that exist in format 0 and those fields should
           exist in the same place in all formats.

       Formats
           This is a reference to a list of formats.  Each format contains a list of field
           specifications.

       For example:

           my $cvt = new Parse::Binary::FixedFormat {
               Chooser => sub { my $rec=shift;
                                $rec->{RecordType} eq '0' ? 1 : 2
                              },
               Formats => [ [ 'RecordType:A1' ],
                            [ 'RecordType:A1', 'FieldA:A6', 'FieldB:A4:4' ],
                            [ 'RecordType:A1', 'FieldC:A4', 'FieldD:A18' ] ]
               };
           my $rec0 = $cvt->unformat("0FieldAB[0]B[1]B[2]B[3]");
           my $rec1 = $cvt->unformat("1FldC<-----FieldD----->");

       In the above example, the "Chooser" function looks at the contents of the "RecordType"
       field.  If it contains a '0', format 1 is used.  Otherwise, format 2 is used.

       Parse::Binary::FixedFormat::Variants can be used is if it were a
       Parse::Binary::FixedFormat.  The "format" and "unformat" methods will determine which
       variant to use automatically.  The "blank" method requires an argument that specifies the
       variant number.

ATTRIBUTES

       Each Parse::Binary::FixedFormat::Variants instance contains the following attributes.

       Layouts
           Contains an array of Parse::Binary::FixedFormat objects.  Each of these objects is
           responsible for converting a single record format variant.

       Chooser
           This attribute contains the function that chooses which variant to apply to the
           record.

AUTHORS

       Audrey Tang <cpan@audreyt.org>

       Based on Data::FixedFormat::Variants, written by Thomas Pfau <pfau@nbpfaus.net>
       http://nbpfaus.net/~pfau/.

COPYRIGHT

       Copyright 2004-2009 by Audrey Tang <cpan@audreyt.org>.

       Copyright (C) 2000,2002 Thomas Pfau.  All rights reserved.

       This module is free software; you can redistribute it and/or modify it under the terms of
       the GNU General Public License as published by the Free Software Foundation; either
       version 2 of the License, or (at your option) any later version.

       This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
       without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
       See the GNU Library General Public License for more details.

       You should have received a copy of the GNU General Public License along with this program;
       if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
       MA 02111-1307, USA.