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145
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1 // P0784R7
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2 // { dg-do compile { target c++2a } }
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3
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4 namespace std
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5 {
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6 inline namespace _8 { }
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7 namespace _8 {
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8
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9 typedef __SIZE_TYPE__ size_t;
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10
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11 template <typename T>
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12 struct allocator
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13 {
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14 constexpr allocator () noexcept {}
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15
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16 constexpr T *allocate (size_t n)
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17 { return static_cast<T *> (::operator new (n * sizeof(T))); }
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18
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19 constexpr void
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20 deallocate (T *p, size_t n)
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21 { ::operator delete (p); }
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22 };
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23
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24 template <typename T, typename U = T &&>
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25 U __declval (int);
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26 template <typename T>
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27 T __declval (long);
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28 template <typename T>
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29 auto declval () noexcept -> decltype (__declval<T> (0));
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30
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31 template <typename T>
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32 struct remove_reference
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33 { typedef T type; };
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34 template <typename T>
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35 struct remove_reference<T &>
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36 { typedef T type; };
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37 template <typename T>
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38 struct remove_reference<T &&>
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39 { typedef T type; };
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40
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41 template <typename T>
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42 constexpr T &&
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43 forward (typename std::remove_reference<T>::type &t) noexcept
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44 { return static_cast<T&&> (t); }
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45
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46 template<typename T>
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47 constexpr T &&
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48 forward (typename std::remove_reference<T>::type &&t) noexcept
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49 { return static_cast<T&&> (t); }
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50
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51 template <typename T, typename... A>
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52 constexpr auto
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53 construct_at (T *l, A &&... a)
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54 noexcept (noexcept (::new ((void *) 0) T (std::declval<A> ()...)))
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55 -> decltype (::new ((void *) 0) T (std::declval<A> ()...))
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56 { return ::new ((void *) l) T (std::forward<A> (a)...); }
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57
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58 template <typename T>
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59 constexpr inline void
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60 destroy_at (T *l)
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61 { l->~T (); }
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62 }
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63 }
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64
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65 inline void *operator new (std::size_t, void *p) noexcept
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66 { return p; }
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67
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68 constexpr bool
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69 foo ()
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70 {
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71 std::allocator<int> a;
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72 auto p = a.allocate (2);
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73 std::construct_at (p, 1);
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74 std::construct_at (p + 1, 2);
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75 if (p[0] != 1 || p[1] != 2)
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76 throw 1;
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77 std::destroy_at (p);
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78 std::destroy_at (p + 1);
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79 a.deallocate (p, 2);
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80 return true;
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81 }
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82
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83 static_assert (foo ());
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