gcc/testsuite/g++.dg/cpp2a/construct_at.h

   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; }