package opts import ( "fmt" "net" ) type IpOpt struct { *net.IP } func NewIpOpt(ref *net.IP, defaultVal string) *IpOpt { o := &IpOpt{ IP: ref, } o.Set(defaultVal) return o } func (o *IpOpt) Set(val string) error { ip := net.ParseIP(val) if ip == nil { return fmt.Errorf("%s is not an ip address", val) } (*o.IP) = net.ParseIP(val) return nil } func (o *IpOpt) String() string { return (*o.IP).String() }