code: func (p *Pinger) AddIPAddr(ip *net.IPAddr) {
  	p.mu.Lock()
  	p.addrs[ip.String()] = ip
  	if isIPv4(ip.IP) {
  		p.hasIPv4 = true
  	} else if isIPv6(ip.IP) {
  		p.hasIPv6 = true
  	}
  	p.mu.Unlock()
  }
docs: // AddIPAddr adds an IP address to Pinger. ip arg should be a net.IPAddr
  // pointer.