From 1e551f4e557c498e4d33ddda92ecd1a825c5e244 Mon Sep 17 00:00:00 2001
From: Jinhao <cnjinhao@hotmail.com>
Date: Mon, 18 Dec 2017 22:10:01 +0800
Subject: [PATCH] add check for C++17 constexpr if

---
 include/nana/c++defines.hpp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/nana/c++defines.hpp b/include/nana/c++defines.hpp
index 04b5113f..70db8f8f 100644
--- a/include/nana/c++defines.hpp
+++ b/include/nana/c++defines.hpp
@@ -199,6 +199,11 @@
 #	define _enable_std_clamp
 #endif
 
+#undef _nana_cxx_constexpr_if
+#if (defined(_MSC_VER) && (_MSC_VER >= 1912) && defined(_MSVC_LANG) && _MSVC_LANG>= 201703)
+#	define _nana_cxx_constexpr_if
+#endif
+
 
 #if defined(NANA_WINDOWS)
 	#ifndef _UNICODE