1  // A minimal conforming implementation of std::construct_at/destroy_at,
       2  // used by some C++20 constexpr tests to avoid including all of <memory>.
       3  
       4  namespace std
       5  {
       6    typedef __SIZE_TYPE__ size_t;
       7  
       8    template <typename T>
       9    struct allocator
      10    {
      11      constexpr allocator () noexcept {}
      12  
      13      constexpr T *allocate (size_t n)
      14      { return static_cast<T *> (::operator new (n * sizeof(T))); }
      15  
      16      constexpr void
      17      deallocate (T *p, size_t n)
      18      { ::operator delete (p); }
      19    };
      20  
      21    template <typename T, typename U = T &&>
      22    U __declval (int);
      23    template <typename T>
      24    T __declval (long);
      25    template <typename T>
      26    auto declval () noexcept -> decltype (__declval<T> (0));
      27  
      28    template <typename T>
      29    struct remove_reference
      30    { typedef T type; };
      31    template <typename T>
      32    struct remove_reference<T &>
      33    { typedef T type; };
      34    template <typename T>
      35    struct remove_reference<T &&>
      36    { typedef T type; };
      37  
      38    template <typename T>
      39    constexpr T &&
      40    forward (typename std::remove_reference<T>::type &t) noexcept
      41    { return static_cast<T&&> (t); }
      42  
      43    template<typename T>
      44    constexpr T &&
      45    forward (typename std::remove_reference<T>::type &&t) noexcept
      46    { return static_cast<T&&> (t); }
      47  
      48    template <typename T, typename... A>
      49    constexpr auto
      50    construct_at (T *l, A &&... a)
      51    noexcept (noexcept (::new ((void *) 0) T (std::declval<A> ()...)))
      52    -> decltype (::new ((void *) 0) T (std::declval<A> ()...))
      53    { return ::new ((void *) l) T (std::forward<A> (a)...); }
      54  
      55    template <typename T>
      56    constexpr inline void
      57    destroy_at (T *l)
      58    { l->~T (); }
      59  }
      60  
      61  inline void *operator new (std::size_t, void *p) noexcept
      62  { return p; }