In the assignment to the hash, Perl does not know that 'TESTVALUE' is a constant, without an additional hint.

adding a '&' or () to the constants name, will be enough of a hint to give you the desired results.

#!/usr/local/bin/perl -w
use strict;
use Data::Dumper;

use constant TESTVALUE1 => 1;
use constant TESTVALUE2 => 2;
use constant TESTVALUE3 => 3;

my %hash;

$hash{ TESTVALUE1 }     = 'OK';
$hash{ &TESTVALUE2 }    = 'OK';
$hash{ TESTVALUE3() }   = 'OK';

print Dumper( \%hash );
[download]

Outputs:

:!./test.pl
$VAR1 = {
          '2' => 'OK',
          'TESTVALUE1' => 'OK',
          '3' => 'OK'
        };
[download]

Data::Dumper, is great when there is a doubt about what is happening inside of a data structure assignment.

Wonko