From 9982d892aa81516bb737ceb97879e7a8b35f4b05 Mon Sep 17 00:00:00 2001
From: Christopher Dykes <cdykes@fb.com>
Date: Tue, 26 Jul 2016 15:48:54 -0700
Subject: [PATCH] Make RangeEnumerator C++17 compliant (Generalizing the
 Range-Based For Loop)

Summary:
Specifically the loosening of the definition of a range where-by the end of an iterator may be represented by a different type than the beginning of the range.
Oh, and it also fixes compilation on MSVC, which didn't like the decltype being used to determine the iterator type.

Reviewed By: yfeldblum

Differential Revision: D3613993

fbshipit-source-id: 2940a15d0f93c5b6310d0b1896f5d12ca9aec639
---
 folly/Enumerate.h | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/folly/Enumerate.h b/folly/Enumerate.h
index 2a2ce220..5733bfb6 100644
--- a/folly/Enumerate.h
+++ b/folly/Enumerate.h
@@ -124,16 +124,17 @@ class Enumerator {
 template <class Range>
 class RangeEnumerator {
   Range r_;
-  using Iterator = decltype(r_.begin());
+  using BeginIteratorType = decltype(std::declval<Range>().begin());
+  using EndIteratorType = decltype(std::declval<Range>().end());
 
  public:
   explicit RangeEnumerator(Range&& r) : r_(std::forward<Range>(r)) {}
 
-  Enumerator<Iterator> begin() {
-    return Enumerator<Iterator>(r_.begin());
+  Enumerator<BeginIteratorType> begin() {
+    return Enumerator<BeginIteratorType>(r_.begin());
   }
-  Enumerator<Iterator> end() {
-    return Enumerator<Iterator>(r_.end());
+  Enumerator<EndIteratorType> end() {
+    return Enumerator<EndIteratorType>(r_.end());
   }
 };
 
-- 
2.34.1