code: func MyIp6() *net.IPAddr {
  	myIp6Once.Do(func() {
  		var err error
  		myIp6, err = net.ResolveIPAddr("ip6", MyHostname())
  		if err != nil {
  			log.Fatal(err)
  		}
  	})
  	return myIp6
  }
docs: // Resolves `MyHostname()` to an Ip6 address. Caches first successful result, making it
  // cheap to call it over and over.
  // It will also crash whole process if resolving the IP fails!