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std::ranges::destroy_at

From cppreference.com
< cpp‎ | memory
 
 
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Defined in header <memory>
Call signature
template< std::destructible T >
constexpr void destroy_at( T* p ) noexcept;
(since C++20)

If T is not an array type, calls the destructor of the object pointed to by p, as if by p->~T(). Otherwise, recursively destroys elements of *p in order, as if by calling std::destroy(std::begin(*p), std::end(*p)).

When destroy_at is called in the evaluation of some constant expression e, the argument p must point to either storage obtained by std::allocator<T>::allocate or an object whose lifetime began within the evaluation of e.

The function-like entities described on this page are niebloids, that is:

In practice, they may be implemented as function objects, or with special compiler extensions.

Contents

[edit] Parameters

p - a pointer to the object to be destroyed

[edit] Return value

(none)

[edit] Possible implementation

struct destroy_at_fn {
  template<std::destructible T>
  constexpr void operator()(T *p) const noexcept
  {
    if constexpr (std::is_array_v<T>)
      for (auto &elem : *p)
        operator()(std::addressof(elem));
    else
      p->~T();
  }
};
 
inline constexpr destroy_at_fn destroy_at{};

[edit] Notes

destroy_at deduces the type of object to be destroyed and hence avoids writing it explicitly in the destructor call.

[edit] Example

The following example demonstrates how to use ranges::destroy_at to destroy a contiguous sequence of elements.

#include <memory>
#include <new>
#include <iostream>
 
struct Tracer {
    int value;
    ~Tracer() { std::cout << value << " destructed\n"; }
};
 
int main()
{
    alignas(Tracer) unsigned char buffer[sizeof(Tracer) * 8];
 
    for (int i = 0; i < 8; ++i)
        new(buffer + sizeof(Tracer) * i) Tracer{i}; //manually construct objects
 
    auto ptr = std::launder(reinterpret_cast<Tracer*>(buffer));
 
    for (int i = 0; i < 8; ++i)
        std::ranges::destroy_at(ptr + i);
}

Output:

0 destructed
1 destructed
2 destructed
3 destructed
4 destructed
5 destructed
6 destructed
7 destructed

[edit] See also

destroys a range of objects
(niebloid) [edit]
destroys a number of objects in a range
(niebloid) [edit]
creates an object at a given address
(niebloid) [edit]
destroys an object at a given address
(function template) [edit]