#include <folly/Conv.h>
#include <folly/Optional.h>
+#include <folly/functional/Invoke.h>
#include <tuple>
namespace folly {
* Given a map and a key, return the value corresponding to the key in the map,
* or a given default value if the key doesn't exist in the map.
*/
-template <class Map, typename Key = typename Map::key_type>
-typename Map::mapped_type get_default(
- const Map& map,
- const Key& key,
- const typename Map::mapped_type& dflt = typename Map::mapped_type()) {
+template <typename Map, typename Key>
+typename Map::mapped_type get_default(const Map& map, const Key& key) {
auto pos = map.find(key);
- return (pos != map.end() ? pos->second : dflt);
+ return (pos != map.end()) ? (pos->second) : (typename Map::mapped_type{});
+}
+template <
+ class Map,
+ typename Key = typename Map::key_type,
+ typename Value = typename Map::mapped_type,
+ typename std::enable_if<!is_invocable<Value>::value>::type* = nullptr>
+typename Map::mapped_type
+get_default(const Map& map, const Key& key, Value&& dflt) {
+ auto pos = map.find(key);
+ if (pos != map.end()) {
+ return pos->second;
+ } else {
+ // if elision from function parameters was allowed, then we could make the
+ // third parameter a value parameter and just elide that into the return
+ // value, but sadly that is not allowed (yet)
+ return std::forward<Value>(dflt);
+ }
}
/**
#include <folly/MapUtil.h>
+#include <cstddef>
#include <map>
#include <unordered_map>
std::declval<int>(),
std::declval<int>(),
std::declval<T>()))>> : std::true_type {};
+
} // namespace
TEST(MapUtil, get_ref_default_path_temporary) {
EXPECT_FALSE(GetRefDefaultPathCompiles<const int&&>::value);
EXPECT_FALSE(GetRefDefaultPathCompiles<int&&>::value);
}
+
+namespace {
+
+class TestConstruction {
+ public:
+ static std::size_t numberDefaultConstructs;
+ TestConstruction() {
+ ++numberDefaultConstructs;
+ }
+ TestConstruction(TestConstruction&&) = default;
+ TestConstruction(const TestConstruction&) = default;
+
+ TestConstruction& operator=(const TestConstruction&) = delete;
+ TestConstruction& operator=(TestConstruction&&) = delete;
+};
+
+std::size_t TestConstruction::numberDefaultConstructs = 0;
+
+} // namespace
+
+TEST(MapUtil, test_get_default_deferred_construction) {
+ auto map = std::unordered_map<int, TestConstruction>{};
+ map.insert({1, TestConstruction{}});
+
+ EXPECT_EQ(TestConstruction::numberDefaultConstructs, 1);
+
+ {
+ auto val = get_default(map, 1);
+ EXPECT_EQ(TestConstruction::numberDefaultConstructs, 1);
+ static_cast<void>(val);
+ }
+
+ {
+ auto val = get_default(map, 1, TestConstruction{});
+ EXPECT_EQ(TestConstruction::numberDefaultConstructs, 2);
+ static_cast<void>(val);
+ }
+}