std::destroy_at() algorithm
- since C++17
// (1)
template< class T >
void destroy_at( T* p );
If T
is not an array type, calls the destructor of the object pointed to by p
, as if by p->~T()
.
If T
is an array type, the program is ill-formed (until C++20) recursively destroys elements of *p
in order, as if by calling std::destroy(std::begin(*p), std::end(*p))
(since C++20).
Parameters
p | A pointer to the object to be destroyed. |
Return value
(none)
Complexity
O(1)
Exceptions
(none)
Possible implementation
destroy_at(1)
template<class T>
constexpr void destroy_at(T* p)
{
if constexpr (std::is_array_v<T>)
for (auto &elem : *p)
(destroy_at)(std::addressof(elem));
else
p->~T();
}
// C++17 version:
// template<class T> void destroy_at(T* p) { p->~T(); }
Notes
destroy_at
deduces the type of object to be destroyed and hence avoids writing it explicitly in the destructor call.
- since C++20
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
.Examples
#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::destroy_at(ptr + i);
}
0 destructed
1 destructed
2 destructed
3 destructed
4 destructed
5 destructed
6 destructed
7 destructed
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