1  
       2  template <typename _Tp>
       3  struct Base
       4  {
       5    // template constructor
       6    template<typename _Del> Base(_Tp *__p, _Del __d);
       7  };
       8  
       9  template <typename _Tp, typename _Dp>
      10  struct Derived : Base<_Tp>
      11  {
      12    // Inheriting the template constructor
      13    using Base<_Tp>::Base;
      14  };
      15  
      16  template <typename _Tp>
      17  class unique_ptr
      18  {
      19    Derived<_Tp, int> _M_t;
      20  
      21  public:
      22    // Instantiates Derived<ResultDerived,int>::Derived
      23    template<typename _Up> unique_ptr(unique_ptr<_Up>&& __u) noexcept
      24      : _M_t ((_Tp *)0, 1) { }
      25  };
      26  
      27  struct ResultBase { };
      28  struct ResultDerived : ResultBase { };
      29  
      30  void Frob (unique_ptr<ResultBase> &&__res) ;
      31  
      32  inline void X (unique_ptr<ResultDerived> &parm)
      33  {
      34    Frob (static_cast <unique_ptr<ResultDerived> &&> (parm));
      35  }