gistfile1.txt

package Role::RO;

use Moose::Role;

has 'read_only' => (
    is => 'ro',
    isa => 'Bool',
);

package Role::RO::Auto;

use Moose::Role;
with 'Role::RO';

has '+read_only' => (
    default => sub {
        ... # set read_only based on current euid
    },
);