未设置Perl Moose的默认值

package Cat;
use 5.010;
use strict;
use Moose;

has \'name\',       is => \'ro\', isa => \'Str\', default => \'Beauty\';
#has \'age\',       is => \'ro\';
has \'diet\',       is => \'rw\', default => \'fish\';
has \'birth_year\', is => \'ro\', isa=> \'Int\',
                  default => 1997;
sub age
{
    my $self = shift;
    my $year = (localtime)[5] + 1900;

    return $year - $self->birth_year();
}

use 5.010;
use strict;
use Cat;

my $kitty = Cat->new();
say \'I have a kitten named \', $kitty->name(), \' eats \', $kitty->diet(),
    \'in age \', $kitty->age();