From e19260fd7dbef881492fd73891e0be5bd4a09b95 Mon Sep 17 00:00:00 2001
From: Abseil Team <absl-team@google.com>
Date: Fri, 20 Nov 2020 09:52:55 -0800
Subject: Export of internal Abseil changes

--
1f91ba7fcb79244fce1fe448c1d31fb5b0580584 by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 343511158

--
8dcd61fed44f4e56044aa4a899cc3124117fa21f by Abseil Team <absl-team@google.com>:

refactors result_of so it doesn't unnecessarily break in C++20 mode

std::result_of was deprecated in C++17 and removed in C++20. This CL
adds an implementation detail so it transparently continues to work
when external users turn up to C++20 or later.

The implementation is derived from C++17's specification of result_of
[depr.meta.types][1].

[1]: https://timsong-cpp.github.io/cppwp/n4659/depr.meta.types

Fixes #649

PiperOrigin-RevId: 343395432
GitOrigin-RevId: 1f91ba7fcb79244fce1fe448c1d31fb5b0580584
Change-Id: Id5d9c55dc7547737bade48a15f2f5740f414d811
---
 absl/meta/type_traits.h | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

(limited to 'absl')

diff --git a/absl/meta/type_traits.h b/absl/meta/type_traits.h
index 75689bb6..d5cb5f3b 100644
--- a/absl/meta/type_traits.h
+++ b/absl/meta/type_traits.h
@@ -610,8 +610,22 @@ using common_type_t = typename std::common_type<T...>::type;
 template <typename T>
 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 {
+
+#if __cplusplus >= 201703L
+// std::result_of is deprecated (C++17) or removed (C++20)
+template<typename> struct result_of;
+template<typename F, typename... Args>
+struct result_of<F(Args...)> : std::invoke_result<F, Args...> {};
+#else
+template<typename F> using result_of = std::result_of<F>;
+#endif
+
+}  // namespace type_traits_internal
+
+template<typename F>
+using result_of_t = typename type_traits_internal::result_of<F>::type;
 
 namespace type_traits_internal {
 // In MSVC we can't probe std::hash or stdext::hash because it triggers a
-- 
cgit v1.2.3