From edf5c731fde69e4d509065cc6b236e973ef29c38 Mon Sep 17 00:00:00 2001
From: Orvid King <blah38621@gmail.com>
Date: Tue, 13 Oct 2015 15:26:52 -0700
Subject: [PATCH] Handle less_than_impl and greater_than_impl under MSVC

Summary: MSVC chokes on the template constraints of these functions, so use a single implementation that will be const-folded by the optimizer instead.
Closes https://github.com/facebook/folly/pull/281

Reviewed By: @yfeldblum

Differential Revision: D2419069

fb-gh-sync-id: c9ad3d135430f8265bbc90391b45d9295d6de362
---
 folly/Traits.h | 66 ++++++++------------------------------------------
 1 file changed, 10 insertions(+), 56 deletions(-)

diff --git a/folly/Traits.h b/folly/Traits.h
index 0a291024..9701aa15 100644
--- a/folly/Traits.h
+++ b/folly/Traits.h
@@ -320,67 +320,21 @@ struct is_negative_impl<T, false> {
 #pragma GCC diagnostic ignored "-Wsign-compare"
 
 template <typename RHS, RHS rhs, typename LHS>
-bool less_than_impl(
-  typename std::enable_if<
-    (rhs <= std::numeric_limits<LHS>::max()
-      && rhs > std::numeric_limits<LHS>::min()),
-    LHS
-  >::type const lhs
-) {
-  return lhs < rhs;
-}
-
-template <typename RHS, RHS rhs, typename LHS>
-bool less_than_impl(
-  typename std::enable_if<
-    (rhs > std::numeric_limits<LHS>::max()),
-    LHS
-  >::type const
-) {
-  return true;
-}
-
-template <typename RHS, RHS rhs, typename LHS>
-bool less_than_impl(
-  typename std::enable_if<
-    (rhs <= std::numeric_limits<LHS>::min()),
-    LHS
-  >::type const
-) {
-  return false;
+bool less_than_impl(LHS const lhs) {
+  return
+    rhs > std::numeric_limits<LHS>::max() ? true :
+    rhs <= std::numeric_limits<LHS>::min() ? false :
+    lhs < rhs;
 }
 
 #pragma GCC diagnostic pop
 
 template <typename RHS, RHS rhs, typename LHS>
-bool greater_than_impl(
-  typename std::enable_if<
-    (rhs <= std::numeric_limits<LHS>::max()
-      && rhs >= std::numeric_limits<LHS>::min()),
-    LHS
-  >::type const lhs
-) {
-  return lhs > rhs;
-}
-
-template <typename RHS, RHS rhs, typename LHS>
-bool greater_than_impl(
-  typename std::enable_if<
-    (rhs > std::numeric_limits<LHS>::max()),
-    LHS
-  >::type const
-) {
-  return false;
-}
-
-template <typename RHS, RHS rhs, typename LHS>
-bool greater_than_impl(
-  typename std::enable_if<
-    (rhs < std::numeric_limits<LHS>::min()),
-    LHS
-  >::type const
-) {
-  return true;
+bool greater_than_impl(LHS const lhs) {
+  return
+    rhs > std::numeric_limits<LHS>::max() ? false :
+    rhs < std::numeric_limits<LHS>::min() ? true :
+    lhs > rhs;
 }
 
 } // namespace detail {
-- 
2.34.1