Update luatype_boost_optional.h

src/lib/luatype_boost_optional.h

@@ -2,22 +2,36 @@
 #define LUATYPE_BOOST_OPTIONAL_H
 
 #include "lua_templates.h"
+#if __cplusplus >= 201703L || _MSVC_LANG >= 201703L
+#include <optional>
+#else
 #include <boost/optional.hpp>
+#endif // C++17
+
+namespace ns {
+#if __cplusplus >= 201703L || _MSVC_LANG >= 201703L
+using std::optional;
+
+#else
+using boost::optional;
+
+#endif // C++17
+
 
 template<typename T>
-struct LuaType<boost::optional<T>> {
-  static void pushdata(lua_State *L, boost::optional<T> o) {
+struct LuaType<ns::optional<T>> {
+  static void pushdata(lua_State *L, ns::optional<T> o) {
     if (o)
       LuaType<T>::pushdata(L, *o);
     else
       lua_pushnil(L);
   }
 
-  static boost::optional<T> &todata(lua_State *L, int i, C_State *C) {
+  static ns::optional<T> &todata(lua_State *L, int i, C_State *C) {
     if (lua_type(L, i) == LUA_TNIL)
-      return C->alloc<boost::optional<T>>();
+      return C->alloc<ns::optional<T>>();
     else
-      return C->alloc<boost::optional<T>>(LuaType<T>::todata(L, i, C));
+      return C->alloc<ns::optional<T>>(LuaType<T>::todata(L, i, C));
   }
 };