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authorGravatar Abseil Team <absl-team@google.com>2018-04-25 10:38:08 -0700
committerGravatar Derek Mauro <dmauro@google.com>2018-04-25 13:44:41 -0400
commitea0e750e52ee223db34a242f9a7229ac04a0f473 (patch)
tree993e0c54fcab171bccc28bc5c646653f6e8c5638 /absl/utility
parent19b3c95727316cef3b0b40eaf37f6645a876f8d2 (diff)
- 2f6a3c92ce0f64e0923ad326ec5d07eae03061fd Add C++14's std::exchange to absl/utility/utility.h. by Abseil Team <absl-team@google.com>
- 9f2c9adbf998dd9062c8cc3da1076bde87081d71 Fix comment typo. by Greg Falcon <gfalcon@google.com> GitOrigin-RevId: 2f6a3c92ce0f64e0923ad326ec5d07eae03061fd Change-Id: I7b9db94ad315092baefe56b02f250acadafbe312
Diffstat (limited to 'absl/utility')
-rw-r--r--absl/utility/utility.h22
-rw-r--r--absl/utility/utility_test.cc8
2 files changed, 30 insertions, 0 deletions
diff --git a/absl/utility/utility.h b/absl/utility/utility.h
index 5b9b84e0..d73602c4 100644
--- a/absl/utility/utility.h
+++ b/absl/utility/utility.h
@@ -24,6 +24,7 @@
// * make_index_sequence<N> == std::make_index_sequence<N>
// * index_sequence_for<Ts...> == std::index_sequence_for<Ts...>
// * apply<Functor, Tuple> == std::apply<Functor, Tuple>
+// * exchange<T> == std::exchange<T>
//
// This header file also provides the tag types `in_place_t`, `in_place_type_t`,
// and `in_place_index_t`, as well as the constant `in_place`, and
@@ -264,6 +265,27 @@ auto apply(Functor&& functor, Tuple&& t)
absl::make_index_sequence<std::tuple_size<
typename std::remove_reference<Tuple>::type>::value>{});
}
+
+// exchange
+//
+// Replaces the value of `obj` with `new_value` and returns the old value of
+// `obj`. `absl::exchange` is designed to be a drop-in replacement for C++14's
+// `std::exchange`.
+//
+// Example:
+//
+// Foo& operator=(Foo&& other) {
+// ptr1_ = absl::exchange(other.ptr1_, nullptr);
+// int1_ = absl::exchange(other.int1_, -1);
+// return *this;
+// }
+template <typename T, typename U = T>
+T exchange(T& obj, U&& new_value) {
+ T old_value = absl::move(obj);
+ obj = absl::forward<U>(new_value);
+ return old_value;
+}
+
} // namespace absl
#endif // ABSL_UTILITY_UTILITY_H_
diff --git a/absl/utility/utility_test.cc b/absl/utility/utility_test.cc
index 342165ed..3c447b20 100644
--- a/absl/utility/utility_test.cc
+++ b/absl/utility/utility_test.cc
@@ -333,5 +333,13 @@ TEST(ApplyTest, FlipFlop) {
EXPECT_EQ(42, absl::apply(&FlipFlop::member, std::make_tuple(obj)));
}
+TEST(ExchangeTest, MoveOnly) {
+ auto a = Factory(1);
+ EXPECT_EQ(1, *a);
+ auto b = absl::exchange(a, Factory(2));
+ EXPECT_EQ(2, *a);
+ EXPECT_EQ(1, *b);
+}
+
} // namespace