Deprecate `absl::exchange`, `absl::forward` and `absl::move`, which

were only useful before C++14.

Callers should use `std::exchange`, `std::forward` and `std::move`
instead.

One thing to note is that some compilers issue warnings about pessimizing
and redundant moves. Some compilers were able to apply this analysis to
std::move but not absl::move. If you get a warning about one of these issues
now that absl::move is an alias for std::move, you should remove this use of
move.
See https://developers.redhat.com/blog/2019/04/12/understanding-when-not-to-stdmove-in-c
PiperOrigin-RevId: 621861324
Change-Id: I60f98b59be5ff425bd17fbce43d9218c361720c2

2 files changed, 3 insertions, 49 deletions

diff --git a/absl/utility/utility.h b/absl/utility/utility.h
index fc0d1f65..ebbb49b7 100644
--- a/absl/utility/utility.h
+++ b/absl/utility/utility.h
@@ -51,11 +51,14 @@ ABSL_NAMESPACE_BEGIN
 // abstractions for platforms that had not yet provided them. Those
 // platforms are no longer supported. New code should simply use the
 // the ones from std directly.
+using std::exchange;
+using std::forward;
 using std::index_sequence;
 using std::index_sequence_for;
 using std::integer_sequence;
 using std::make_index_sequence;
 using std::make_integer_sequence;
+using std::move;
 
 namespace utility_internal {
 
@@ -129,27 +132,6 @@ template <size_t I>
 void in_place_index(utility_internal::InPlaceIndexTag<I>) {}
 #endif  // ABSL_USES_STD_VARIANT
 
-// Constexpr move and forward
-
-// move()
-//
-// A constexpr version of `std::move()`, designed to be a drop-in replacement
-// for C++14's `std::move()`.
-template <typename T>
-constexpr absl::remove_reference_t<T>&& move(T&& t) noexcept {
-  return static_cast<absl::remove_reference_t<T>&&>(t);
-}
-
-// forward()
-//
-// A constexpr version of `std::forward()`, designed to be a drop-in replacement
-// for C++14's `std::forward()`.
-template <typename T>
-constexpr T&& forward(
-    absl::remove_reference_t<T>& t) noexcept {  // NOLINT(runtime/references)
-  return static_cast<T&&>(t);
-}
-
 namespace utility_internal {
 // Helper method for expanding tuple into a called method.
 template <typename Functor, typename Tuple, std::size_t... Indexes>
@@ -215,26 +197,6 @@ auto apply(Functor&& functor, Tuple&& t)
           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 utility_internal {
 template <typename T, typename Tuple, size_t... I>
 T make_from_tuple_impl(Tuple&& tup, absl::index_sequence<I...>) {
diff --git a/absl/utility/utility_test.cc b/absl/utility/utility_test.cc
index 1af68136..c540b22f 100644
--- a/absl/utility/utility_test.cc
+++ b/absl/utility/utility_test.cc
@@ -205,14 +205,6 @@ 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);
-}
-
 TEST(MakeFromTupleTest, String) {
   EXPECT_EQ(
       absl::make_from_tuple<std::string>(std::make_tuple("hello world", 5)),