use threads;
use threads::shared;
my $var : shared;

##</code><code>##

use Me;
my $user : Me;
$user = "Random"; # this is OK
$user = "Deterministic"; # croaks

##</code><code>##

#!/usr/bin/perl
use strict;
use warnings;

package Me;
use Carp;
use overload '""' => \&str;

sub new {
    my ($class, $value) = @_;
    validate ($value) if defined $value;
    bless \$value, $class;
}

sub validate {
    my $value = shift;
    my @names = qw (Random_Walk Random Walk);
    croak "$value is not a good name\n" unless grep {$value eq $_} @names;
}

sub str {"Not telling you"};
1;

##</code><code>##

> perl -Mlib=. -MMe -le'my $m = new Me (Random);print $m'
Not telling you
> perl -Mlib=. -MMe -le'my $m = new Me (Determined);print $m'
Determined is not a good name
 at -e line 1
# But I can not suss out how to get his to work
> perl -Mlib=. -MMe -le'my $m : Me; $m = "Random"; print $m'
Invalid SCALAR attribute: Me at -e line 1