Update to gobook@c6d7a22edd03e7738c38d5baa2174ff325d8d863

ch3/netflag/netflag.go

@@ -0,0 +1,30 @@
+// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+
+// See page 77.
+
+// Netflag demonstrates an integer type used as a bit field.
+package main
+
+import (
+	"fmt"
+	. "net"
+)
+
+//!+
+func IsUp(v Flags) bool     { return v&FlagUp == FlagUp }
+func TurnDown(v *Flags)     { *v &^= FlagUp }
+func SetBroadcast(v *Flags) { *v |= FlagBroadcast }
+func IsCast(v Flags) bool   { return v&(FlagBroadcast|FlagMulticast) != 0 }
+
+func main() {
+	var v Flags = FlagMulticast | FlagUp
+	fmt.Printf("%b %t\n", v, IsUp(v)) // "10001 true"
+	TurnDown(&v)
+	fmt.Printf("%b %t\n", v, IsUp(v)) // "10000 false"
+	SetBroadcast(&v)
+	fmt.Printf("%b %t\n", v, IsUp(v))   // "10010 false"
+	fmt.Printf("%b %t\n", v, IsCast(v)) // "10010 true"
+}
+
+//!-