code: func (f *FlagSet) IPVar(p *net.IP, name string, value net.IP, usage string) {
  	f.VarP(newIPValue(value, p), name, "", usage)
  }
docs: // IPVar defines an net.IP flag with specified name, default value, and usage string.
  // The argument p points to an net.IP variable in which to store the value of the flag.