my @colors = qw(red green blue);
enum 'colors', \@colors;
has scores => 
  ( is => 'rw', 
    isa => 'HashRef', 
    default => sub {
        use Hash::Util 'lock_keys';
        my %hash; 
        lock_keys %hash, @colors;
        return \%hash;
      } 
  );