text: //===----------------------------------------------------------------------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is dual licensed under the MIT and the University of Illinois Open
  // Source Licenses. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  
  // UNSUPPORTED: c++98, c++03, c++11
  // <optional>
  
  // template <class T> constexpr bool operator==(const optional<T>& x, const T& v);
  // template <class T> constexpr bool operator==(const T& v, const optional<T>& x);
  
  #include <experimental/optional>
  
  using std::experimental::optional;
  
  struct X
  {
      int i_;
  
      constexpr X(int i) : i_(i) {}
  };
  
  constexpr bool operator == ( const X &lhs, const X &rhs )
      { return lhs.i_ == rhs.i_ ; }
  
  int main()
  {
      {
      typedef X T;
      typedef optional<T> O;
  
      constexpr T val(2);
      constexpr O o1;       // disengaged
      constexpr O o2{1};    // engaged
      constexpr O o3{val};  // engaged
  
      static_assert ( !(o1 == T(1)), "" );
      static_assert (  (o2 == T(1)), "" );
      static_assert ( !(o3 == T(1)), "" );
      static_assert (  (o3 == T(2)), "" );
      static_assert (  (o3 == val),  "" );
  
      static_assert ( !(T(1) == o1), "" );
      static_assert (  (T(1) == o2), "" );
      static_assert ( !(T(1) == o3), "" );
      static_assert (  (T(2) == o3), "" );
      static_assert (  (val  == o3), "" );
      }
  }
  