From 8242c688e7965c66edba806b000bcf3ec7642312 Mon Sep 17 00:00:00 2001
From: Kohei Takahashi <flast@flast.jp>
Date: Mon, 3 Aug 2015 00:03:40 +0900
Subject: [PATCH] Older GCC doesn't accept use of `this` in constexpr.

Fix #11517
---
 include/boost/fusion/container/generation/ignore.hpp | 4 +++-
 include/boost/fusion/support/config.hpp              | 8 ++++++++
 include/boost/fusion/support/unused.hpp              | 4 ++--
 3 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/include/boost/fusion/container/generation/ignore.hpp b/include/boost/fusion/container/generation/ignore.hpp
index 889f17d2..78196632 100644
--- a/include/boost/fusion/container/generation/ignore.hpp
+++ b/include/boost/fusion/container/generation/ignore.hpp
@@ -9,6 +9,8 @@
 #if !defined(FUSION_IGNORE_07192005_0329)
 #define FUSION_IGNORE_07192005_0329
 
+#include <boost/fusion/support/config.hpp>
+
 namespace boost { namespace fusion
 {
     //  Swallows any assignment (by Doug Gregor)
@@ -17,7 +19,7 @@ namespace boost { namespace fusion
         struct swallow_assign
         {
             template<typename T>
-            BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
+            BOOST_FUSION_CONSTEXPR_THIS BOOST_FUSION_GPU_ENABLED
             swallow_assign const&
             operator=(const T&) const
             {
diff --git a/include/boost/fusion/support/config.hpp b/include/boost/fusion/support/config.hpp
index 1ce042a8..23554531 100644
--- a/include/boost/fusion/support/config.hpp
+++ b/include/boost/fusion/support/config.hpp
@@ -88,4 +88,12 @@ namespace std
 }
 #endif
 
+
+// Workaround for older GCC that doesn't accept `this` in constexpr.
+#if BOOST_WORKAROUND(BOOST_GCC, < 40700)
+#define BOOST_FUSION_CONSTEXPR_THIS
+#else
+#define BOOST_FUSION_CONSTEXPR_THIS BOOST_CONSTEXPR
+#endif
+
 #endif
diff --git a/include/boost/fusion/support/unused.hpp b/include/boost/fusion/support/unused.hpp
index 7e2a6eee..964839ab 100644
--- a/include/boost/fusion/support/unused.hpp
+++ b/include/boost/fusion/support/unused.hpp
@@ -34,7 +34,7 @@ namespace boost { namespace fusion
         }
 
         template <typename T>
-        BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
+        BOOST_FUSION_CONSTEXPR_THIS BOOST_FUSION_GPU_ENABLED
         unused_type const&
         operator=(T const&) const BOOST_NOEXCEPT
         {
@@ -49,7 +49,7 @@ namespace boost { namespace fusion
             return *this;
         }
 
-        BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
+        BOOST_FUSION_CONSTEXPR_THIS BOOST_FUSION_GPU_ENABLED
         unused_type const&
         operator=(unused_type const&) const BOOST_NOEXCEPT
         {