+/**
+ * Given a map and a key, return the value corresponding to the key in the map,
+ * or throw an exception of the specified type.
+ */
+template <class E = std::out_of_range, class Map>
+typename Map::mapped_type get_or_throw(
+ const Map& map, const typename Map::key_type& key,
+ const std::string& exceptionStrPrefix = std::string()) {
+ auto pos = map.find(key);
+ if (pos != map.end()) {
+ return pos->second;
+ }
+ throw E(folly::to<std::string>(exceptionStrPrefix, key));
+}
+
+/**
+ * Given a map and a key, return a Optional<V> if the key exists and None if the
+ * key does not exist in the map.
+ */
+template <class Map>
+folly::Optional<typename Map::mapped_type> get_optional(
+ const Map& map, const typename Map::key_type& key) {
+ auto pos = map.find(key);
+ if (pos != map.end()) {
+ return folly::Optional<typename Map::mapped_type>(pos->second);
+ } else {
+ return folly::none;
+ }
+}
+