Defined in header <type_traits> | ||
|---|---|---|
template< class T > struct is_destructible; | (1) | (since C++11) |
template< class T > struct is_trivially_destructible; | (2) | (since C++11) |
template< class T > struct is_nothrow_destructible; | (3) | (since C++11) |
T is a reference type, provides the member constant value equal to true.T is (possibly cv-qualified) void, a function type, or an array of unknown bound, value equals false.T is an object type, then, for the type U that is std::remove_all_extents<T>::type, if the expression std::declval<U&>().~U() is well-formed in unevaluated context, value equals true. Otherwise, value equals false.std::remove_all_extents<T>::type is either a non-class type or a class type with a trivial destructor.T shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. Otherwise, the behavior is undefined.
If an instantiation of a template above depends, directly or indirectly, on an incomplete type, and that instantiation could yield a different result if that type were hypothetically completed, the behavior is undefined.
The behavior of a program that adds specializations for any of the templates described on this page is undefined.
template< class T > inline constexpr bool is_destructible_v = is_destructible<T>::value; | (since C++17) | |
template< class T > inline constexpr bool is_trivially_destructible_v = is_trivially_destructible<T>::value; | (since C++17) | |
template< class T > inline constexpr bool is_nothrow_destructible_v = is_nothrow_destructible<T>::value; | (since C++17) |
| value
[static] | true if T is destructible, false otherwise (public static member constant) |
| operator bool | converts the object to bool, returns value (public member function) |
| operator()
(C++14) | returns value (public member function) |
| Type | Definition |
|---|---|
value_type | bool |
type | std::integral_constant<bool, value> |
Because the C++ program terminates if a destructor throws an exception during stack unwinding (which usually cannot be predicted), all practical destructors are non-throwing even if they are not declared noexcept. All destructors found in the C++ standard library are non-throwing.
Storage occupied by trivially destructible objects may be reused without calling the destructor.
#include <iostream>
#include <string>
#include <type_traits>
struct Foo
{
std::string str;
~Foo() noexcept {};
};
struct Bar
{
~Bar() = default;
};
int main()
{
std::cout << std::boolalpha
<< "std::string is destructible? "
<< std::is_destructible<std::string>::value << '\n'
<< "Foo is trivially destructible? "
<< std::is_trivially_destructible_v<Foo> << '\n'
<< "Foo is nothrow destructible? "
<< std::is_nothrow_destructible<Foo>() << '\n'
<< "Bar is trivially destructible? "
<< std::is_trivially_destructible<Bar>{} << '\n';
}Output:
std::string is destructible? true Foo is trivially destructible? false Foo is nothrow destructible? true Bar is trivially destructible? true
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 2049 | C++11 | the specification was incompletable because of the imaginary wrapping struct | made complete |
|
(C++11)(C++11)(C++11) | checks if a type has a constructor for specific arguments (class template) |
|
(C++11) | checks if a type has a virtual destructor (class template) |
|
(C++20) | specifies that an object of the type can be destroyed (concept) |
| destructor | releases claimed resources |
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