NAME
   Const::Dual - numeric constants that know their names

SYNOPSIS
       # create constants
       use Const::Dual (
           TYPE_FOO => 1,
           TYPE_BAR => 2,
           # ... more constants ...
           TYPE_BAZ => 99,
       );

       $type = TYPE_BAR;
       print $type + 0;                               # 2
       print $type == 2 ? "bar" : "not bar";          # bar
       print $type == TYPE_BAR ? "bar" : "not bar";   # bar
       print "type = $type";                          # type = TYPE_BAR

       # create constants and store them in %TYPES
       use Const::Dual \%TYPES => (
           TYPE_FOO => 1,
           TYPE_BAR => 2,
           # ... more constants ...
           TYPE_BAZ => 99,
       );
       @EXPORT_OK = keys %TYPES;
       @EXPORT_TAGS = (types => [ keys %TYPES ]);

       # get dual value from non-dual value
       my $type = $ARGV[0] // 99;
       my %TYPES_REVERSE; @TYPES_REVERSE{ map { int $_ } values %TYPES } = values %TYPES;
       die "Invalid type $type" unless exists $TYPES_REVERSE{$type};
       $type = $TYPES_REVERSE{$type};
       print int $type;                               # 99
       print "type = $type";                          # type = TYPE_BAZ

       # dual constants are always true!
       use Const::Dual FALSE => 0;
       print int FALSE;                               # 0
       print "FALSE is ", FALSE ? "true" : "false";   # FALSE is true

DESCRIPTION
   This module can be helpful when you use a lot of constants and really
   tired to deal with them. Numeric constants created with this module are
   dual (see "dualvar" in Scalar::Util). They have their given numeric
   values when are used in numeric context. When used in string context,
   such constants are strings with constants' names. This can be useful for
   debug purposes: constant's value "knows" constant's name and it can be
   printed. This behavior does not apply to non-numberic constants, they
   are created as usual.

CAVEATS
   Developer should ALWAYS keep in mind that he works with dual values and
   should force numeric context when necessary. This is strict rule and
   it's violation can lead to bugs. Common ways to force numeric context is
   "int $value" or "$value+0".

   Dual constant in bool context is always TRUE, because one of constant's
   value is it's name and it can not be FALSE.

SOURCE
   The development version is on github at
   <https://github.com/bambr/Const-Dual>

AUTHOR
   Sergey Panteleev, <[email protected]>

COPYRIGHT AND LICENSE
   Copyright (C) 2018 by Sergey Panteleev

   This library is free software; you can redistribute it and/or modify it
   under the same terms as Perl itself, either Perl version 5.8.8 or, at
   your option, any later version of Perl 5 you may have available.

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