#!/usr/bin/perl 
package Foo;

use Moose;
use Moose::Util::TypeConstraints;

enum 'Status' => qw(success error pending);

has 'status' => (is => 'rw', isa => 'Status|Undef');

package main;
use strict;
use warnings;

my $o = Foo->new;
foreach (undef, 'success', 'bar', 'error') {
    $o->status($_);
    printf "status: %s\n", $o->status;
}