net.IP as map key type in golang?

Question

I have map with key as net.IP and value as a channel. But I'm getting a weird compile time error (invalid map key type)

17 type UdpServer struct {
18     ListenPort int
19
20     ConnRef *net.UDPConn
21     Log_ref *Logger
22     MapOfValues map[net.IP]chan string
23 }


$ go build c-manager.go
cmanager/c-udp_server.go:22:14: invalid map key type net.IP

$ go version
  go version go1.10.2 linux/amd64

What am I doing wrong? Can't we have net.IP as map key type?

Answer 1

A net.IP is a slice type. Because slices are mutable, they cannot be used as map keys. Use a string as the key type:

MapOfValues map[string]chan string

Use a type conversion to convert from net.IP to string and back. Use IP.To16 to normalize addresses to the 16 byte representation.

x.MapOfValues[string(ip.To16())] = v

for k, v := range x.MapOfValues {
   ip := net.IP(k) // convert string to net.IP
   ...
}

If you want the keys to be printable, then use the IP.String and net.ParseIP functions to do the conversions:

x.MapOfValues[ip.String()] = v

for k, v := range x.MapOfValues {
   ip := net.ParseIP(k) 
   ...
}