From bd3c351f1f3cadb68ef4028d386739ac93a25fa6 Mon Sep 17 00:00:00 2001
From: Florent Rougon <f.rougon@free.fr>
Date: Sat, 18 Nov 2017 22:27:47 +0100
Subject: [PATCH] Add function template simgear::enumValue() to
 simgear/sg_inlines.h

This function template is useful to get the value of a member of a
scoped enumeration, without having to hardcode its type while casting
it.
---
 simgear/sg_inlines.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/simgear/sg_inlines.h b/simgear/sg_inlines.h
index b21304d8..4c4b4ad5 100644
--- a/simgear/sg_inlines.h
+++ b/simgear/sg_inlines.h
@@ -23,6 +23,7 @@
 //
 // $Id$
 
+#include <type_traits>
 #include <utility>
 
 #ifndef _SG_INLINES_H
@@ -123,6 +124,17 @@ void noexceptSwap(T& a, T& b) noexcept
     swap(a, b);
 }
 
+// Cast an enum value to its underlying type (useful with scoped enumerations).
+//
+// Example: enum class MyEnum { first = 1, second };
+//          auto e = MyEnum::second;
+//          std::string msg = "MyEnum::second is " +
+//                            std::to_string(simgear::enumValue(e));
+template <typename T>
+constexpr typename std::underlying_type<T>::type enumValue(T e) {
+    return static_cast<typename std::underlying_type<T>::type>(e);
+}
+
 } // of namespace simgear
 
 #endif // _SG_INLINES_H