Add implementation for std::hash<MacAddress>

Summary:
Add implementation for std::hash<MacAddress> so that it can be used in
maps.

Reviewed By: yfeldblum

Differential Revision: D10004544

fbshipit-source-id: 46cb177577123b1248cd8ff679f0fbe286596819

folly/MacAddress.h

@@ -231,3 +231,15 @@ typename std::enable_if<IsSomeString<Tgt>::value>::type toAppend(
 std::ostream& operator<<(std::ostream& os, MacAddress address);
 
 } // namespace folly
+
+namespace std {
+
+// Provide an implementation for std::hash<MacAddress>
+template <>
+struct hash<folly::MacAddress> {
+  size_t operator()(const folly::MacAddress& address) const {
+    return std::hash<uint64_t>()(address.u64HBO());
+  }
+};
+
+} // namespace std

folly/test/MacAddressTest.cpp

@@ -167,3 +167,12 @@ TEST(MacAddress, ordering) {
   testCmp("01:00:00:00:00:00", "02:00:00:00:00:00");
   testCmp("00:00:00:00:00:01", "00:00:00:00:01:00");
 }
+
+TEST(MacAddress, hash) {
+  EXPECT_EQ(
+      std::hash<MacAddress>()(MacAddress("00:11:22:33:44:55")),
+      std::hash<MacAddress>()(MacAddress("00-11-22-33-44-55")));
+  EXPECT_NE(
+      std::hash<MacAddress>()(MacAddress("00:11:22:33:44:55")),
+      std::hash<MacAddress>()(MacAddress("00:11:22:33:44:56")));
+}