From: Christopher Dykes <cdykes@fb.com>
Date: Tue, 16 Aug 2016 23:27:28 +0000 (-0700)
Subject: Use std::is_nothrow_swappable under MSVC
X-Git-Tag: v2016.08.22.00~26
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=30c4c2864581aa35359eb1aba09300698a383848;p=folly.git

Use std::is_nothrow_swappable under MSVC

Summary:
The current implementation didn't work for MSVC, as it tries to evaluate `noexcept` expressions in base class lists before the template is instantiated.
`std::is_nothrow_swappable` is coming in C++17, and MSVC already has it, so use it instead.

Reviewed By: yfeldblum

Differential Revision: D3724399

fbshipit-source-id: 7927584618a7870824b2e7242fcae562647f4ef4
---

diff --git a/folly/Traits.h b/folly/Traits.h
index 3421d665..fc3cba9c 100644
--- a/folly/Traits.h
+++ b/folly/Traits.h
@@ -159,6 +159,12 @@ struct IsLessThanComparable
     IsLessThanComparable;
 
 namespace traits_detail_IsNothrowSwappable {
+#if defined(_MSC_VER) || defined(__cpp_lib_is_swappable)
+// MSVC already implements the C++17 P0185R1 proposal which
+// adds std::is_nothrow_swappable, so use it instead.
+template <typename T>
+using IsNothrowSwappable = std::is_nothrow_swappable<T>;
+#else
 /* using override */ using std::swap;
 
 template <class T>
@@ -167,6 +173,7 @@ struct IsNothrowSwappable
         std::is_nothrow_move_constructible<T>::value &&
         noexcept(swap(std::declval<T&>(), std::declval<T&>()))
       > {};
+#endif
 }
 
 /* using override */ using traits_detail_IsNothrowSwappable::IsNothrowSwappable;