NAME

std::ranges::destroy_at - std::ranges::destroy_at

Synopsis

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

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)).

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

* Explicit template argument lists may not be specified when calling any of them.
* None of them is visible to argument-dependent lookup.
* When one of them is found by normal unqualified lookup for the name to the left
of the function-call operator, it inhibits argument-dependent lookup.

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

Parameters

p - a pointer to the object to be destroyed

Return value

(none)

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{};

Notes

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

When destroy_at is called in the evaluation of some constant expression e, the
argument p must point to an object whose lifetime began within the evaluation of e.

Example

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

// Run this code

#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