From 0e0d7fae4ec7a0da71f691376419b5b0b5706da8 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@pdimov.com>
Date: Wed, 24 May 2017 06:16:17 +0300
Subject: [PATCH] Enable fold expressions on g++

---
 include/boost/mp11/algorithm.hpp     | 4 ++--
 include/boost/mp11/detail/config.hpp | 6 +++++-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/include/boost/mp11/algorithm.hpp b/include/boost/mp11/algorithm.hpp
index 9f0a6f7..e31e3b7 100644
--- a/include/boost/mp11/algorithm.hpp
+++ b/include/boost/mp11/algorithm.hpp
@@ -499,7 +499,7 @@ namespace detail
 
 template<class L, class V> struct mp_find_impl;
 
-#if defined( BOOST_MP11_HAS_FOLD_EXPRESSIONS )
+#if defined( BOOST_CLANG ) && defined( BOOST_MP11_HAS_FOLD_EXPRESSIONS )
 
 struct mp_index_holder
 {
@@ -589,7 +589,7 @@ namespace detail
 
 template<class L, template<class...> class P> struct mp_find_if_impl;
 
-#if defined( BOOST_MP11_HAS_FOLD_EXPRESSIONS )
+#if defined( BOOST_CLANG ) && defined( BOOST_MP11_HAS_FOLD_EXPRESSIONS )
 
 template<template<class...> class L, class... T, template<class...> class P> struct mp_find_if_impl<L<T...>, P>
 {
diff --git a/include/boost/mp11/detail/config.hpp b/include/boost/mp11/detail/config.hpp
index 75c5caa..a152f46 100644
--- a/include/boost/mp11/detail/config.hpp
+++ b/include/boost/mp11/detail/config.hpp
@@ -21,7 +21,11 @@
 
 #endif
 
-#if defined(BOOST_CLANG) && defined(__has_cpp_attribute)
+#if defined(__cpp_fold_expressions) && __cpp_fold_expressions >= 201603
+
+#  define BOOST_MP11_HAS_FOLD_EXPRESSIONS
+
+#elif defined(BOOST_CLANG) && defined(__has_cpp_attribute)
 # if __has_cpp_attribute(fallthrough) && __cplusplus >= 201406L // Clang 3.9+ in c++1z mode
 
 #  define BOOST_MP11_HAS_FOLD_EXPRESSIONS