1 //===----------------------------------------------------------------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is dual licensed under the MIT and the University of Illinois Open 6 // Source Licenses. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 10 // <optional> 11 12 // A program that necessitates the instantiation of template optional for a 13 // reference type is ill-formed. 14 15 #include <experimental/optional> 16 17 int main() 18 { 19 #if _LIBCPP_STD_VER > 11 20 using std::experimental::optional; 21 22 optional<const int&> opt; 23 #else 24 #error 25 #endif // _LIBCPP_STD_VER > 11 26 } 27