#include <folly/Conv.h>
#include <folly/Optional.h>
+#include <tuple>
namespace folly {
return (pos != map.end() ? &pos->second : nullptr);
}
+// TODO: Remove the return type computations when clang 3.5 and gcc 5.1 are
+// the minimum supported versions.
namespace detail {
template <
class T,
struct NestedMapType<T, 1> {
using type = typename T::mapped_type;
};
+
+template <typename... KeysDefault>
+struct DefaultType;
+
+template <typename Default>
+struct DefaultType<Default> {
+ using type = Default;
+};
+
+template <typename Key, typename... KeysDefault>
+struct DefaultType<Key, KeysDefault...> {
+ using type = typename DefaultType<KeysDefault...>::type;
+};
+
+template <class... KeysDefault>
+auto extract_default(const KeysDefault&... keysDefault) ->
+ typename DefaultType<KeysDefault...>::type const& {
+ return std::get<sizeof...(KeysDefault)-1>(std::tie(keysDefault...));
+}
}
/**
return pos != map.end() ? get_ptr(pos->second, key2, keys...) : nullptr;
}
+/**
+ * Given a map and a path of keys, return the value corresponding to the nested
+ * value, or a given default value if the path doesn't exist in the map.
+ * The default value is the last parameter, and is copied when returned.
+ */
+template <
+ class Map,
+ class Key1,
+ class Key2,
+ class... KeysDefault,
+ typename = typename std::enable_if<sizeof...(KeysDefault) != 0>::type>
+auto get_default(
+ const Map& map,
+ const Key1& key1,
+ const Key2& key2,
+ const KeysDefault&... keysDefault) ->
+ typename detail::NestedMapType<Map, 1 + sizeof...(KeysDefault)>::type {
+ if (const auto* ptr = get_ptr(map, key1)) {
+ return get_default(*ptr, key2, keysDefault...);
+ }
+ return detail::extract_default(keysDefault...);
+}
+
+/**
+ * Given a map and a path of keys, return a reference to the value corresponding
+ * to the nested value, or the given default reference if the path doesn't exist
+ * in the map.
+ * The default value is the last parameter, and must be a lvalue reference.
+ */
+template <
+ class Map,
+ class Key1,
+ class Key2,
+ class... KeysDefault,
+ typename = typename std::enable_if<sizeof...(KeysDefault) != 0>::type,
+ typename = typename std::enable_if<std::is_lvalue_reference<
+ typename detail::DefaultType<KeysDefault...>::type>::value>::type>
+auto get_ref_default(
+ const Map& map,
+ const Key1& key1,
+ const Key2& key2,
+ KeysDefault&&... keysDefault) ->
+ typename detail::NestedMapType<Map, 1 + sizeof...(KeysDefault)>::type
+ const& {
+ if (const auto* ptr = get_ptr(map, key1)) {
+ return get_ref_default(*ptr, key2, keysDefault...);
+ }
+ return detail::extract_default(keysDefault...);
+}
} // namespace folly