- 551e205ef49682a1cb7e6e0cda46957fbcf88edd Release absl::variant. by Xiaoyi Zhang <zhangxy@google.com>

- 01c52f640594d073c6e54c47e7853b25522cf085 Update comments in absl::variant (and minor changes to ab... by Tom Manshreck <shreck@google.com>
  - 064465e1e6b158abd8c38fd1942b4fc464b57d6a Documentation change. by Abseil Team <absl-team@google.com>
  - 58df2c8a27e80c9ea21d87c1acee8019246377c9 Relocates SetCountdown and UnsetCountdown to the exceptio... by Abseil Team <absl-team@google.com>
  - fd9d248d0948d472f2543f7fd9c0ae4a1cd60d01 Clarify thread_annotation.h documentation around local va... by Abseil Team <absl-team@google.com>
  - 0d0abaf7f0945ac5f2c5f49e78afe1b326d5aca0 Typo fix in comments. by Abseil Team <absl-team@google.com>
  - 67286d587cbd07508a81e5b8147c245a5b5538b4 Internal change. by Xiaoyi Zhang <zhangxy@google.com>

GitOrigin-RevId: 551e205ef49682a1cb7e6e0cda46957fbcf88edd
Change-Id: I1a343b080187293cb5f892a309618b5712e7aa14

absl/meta/type_traits.h

@@ -36,6 +36,7 @@
 #define ABSL_META_TYPE_TRAITS_H_
 
 #include <stddef.h>
+#include <functional>
 #include <type_traits>
 
 #include "absl/base/config.h"
@@ -349,5 +350,23 @@ using underlying_type_t = typename std::underlying_type<T>::type;
 template <typename T>
 using result_of_t = typename std::result_of<T>::type;
 
+namespace type_traits_internal {
+template <typename Key, typename = size_t>
+struct IsHashable : std::false_type {};
+
+template <typename Key>
+struct IsHashable<Key,
+                  decltype(std::declval<std::hash<Key>>()(std::declval<Key>()))>
+    : std::true_type {};
+
+template <typename Key>
+struct IsHashEnabled
+    : absl::conjunction<std::is_default_constructible<std::hash<Key>>,
+                        std::is_copy_constructible<std::hash<Key>>,
+                        std::is_destructible<std::hash<Key>>,
+                        std::is_copy_assignable<std::hash<Key>>,
+                        IsHashable<Key>> {};
+}  // namespace type_traits_internal
+
 }  // namespace absl
 #endif  // ABSL_META_TYPE_TRAITS_H_