std::ranges::destroy_at
From cppreference.com
| Defined in header <memory>
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| Call signature |
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template< std::destructible T >
constexpr void destroy_at( T* p ) noexcept;
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(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)).
The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:
- Explicit template argument lists cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.
Parameters
| p | - | a pointer to the object to be destroyed |
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{};
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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 <iostream>
#include <memory>
#include <new>
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
See also
(C++20) |
destroys a range of objects (algorithm function object) |
(C++20) |
destroys a number of objects in a range (algorithm function object) |
(C++20) |
creates an object at a given address (algorithm function object) |
(C++17) |
destroys an object at a given address (function template) |