From 74d1af87831f9df2b5cb9d104db1d0e2edab591e Mon Sep 17 00:00:00 2001
From: Christopher Dykes <cdykes@fb.com>
Date: Mon, 15 Aug 2016 15:56:35 -0700
Subject: [PATCH] Fix applyTuple to work under MSVC again

Summary:
Because MSVC didn't like the new version used to add support for multiple tuples.
This also switches to std::index_sequence rather than our own home-grown version.

Reviewed By: yfeldblum

Differential Revision: D3706506

fbshipit-source-id: 724c995fe2671d21f78cd7ffa4b19ea1b278c308
---
 folly/ApplyTuple.h | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/folly/ApplyTuple.h b/folly/ApplyTuple.h
index 0288f567..b2298776 100644
--- a/folly/ApplyTuple.h
+++ b/folly/ApplyTuple.h
@@ -55,9 +55,14 @@ inline constexpr std::size_t sum(std::size_t v1, Args... vs) {
   return v1 + sum(vs...);
 }
 
-template <class... Tuple>
-using MakeIndexSequenceFromTuple = MakeIndexSequence<sum(
-    std::tuple_size<typename std::decay<Tuple>::type>::value...)>;
+template <typename... Tuples>
+struct TupleSizeSum {
+  static constexpr auto value = sum(std::tuple_size<Tuples>::value...);
+};
+
+template <typename... Tuples>
+using MakeIndexSequenceFromTuple = MakeIndexSequence<
+    TupleSizeSum<typename std::decay<Tuples>::type...>::value>;
 
 // This is to allow using this with pointers to member functions,
 // where the first argument in the tuple will be the this pointer.
-- 
2.34.1