net: add examples for ParseIP, IP.DefaultMask & IP.Mask

Further examples to support the net package.

Updates #5757

Change-Id: I9b65521d211f6c404b9103c1eaf22b0772eb242e
Reviewed-on: https://go-review.googlesource.com/43711Reviewed-by: Mikio Hara <mikioh.mikioh@gmail.com>

src/net/example_test.go

@@ -65,6 +65,41 @@ func ExampleParseCIDR() {
 	// 2001:db8::/32
 }
 
+func ExampleParseIP() {
+	fmt.Println(net.ParseIP("192.0.2.1"))
+	fmt.Println(net.ParseIP("2001:db8::68"))
+	fmt.Println(net.ParseIP("192.0.2"))
+
+	// Output:
+	// 192.0.2.1
+	// 2001:db8::68
+	// <nil>
+}
+
+func ExampleIP_DefaultMask() {
+	ip := net.ParseIP("192.0.2.1")
+	fmt.Println(ip.DefaultMask())
+
+	// Output:
+	// ffffff00
+}
+
+func ExampleIP_Mask() {
+	ipv4Addr := net.ParseIP("192.0.2.1")
+	// This mask corresponds to a /24 subnet for IPv4.
+	ipv4Mask := net.CIDRMask(24, 32)
+	fmt.Println(ipv4Addr.Mask(ipv4Mask))
+
+	ipv6Addr := net.ParseIP("2001:db8:a0b:12f0::1")
+	// This mask corresponds to a /32 subnet for IPv6.
+	ipv6Mask := net.CIDRMask(32, 128)
+	fmt.Println(ipv6Addr.Mask(ipv6Mask))
+
+	// Output:
+	// 192.0.2.0
+	// 2001:db8::
+}
+
 func ExampleCIDRMask() {
 	// This mask corresponds to a /31 subnet for IPv4.
 	fmt.Println(net.CIDRMask(31, 32))