NAME

std::is_destructible,std::is_trivially_destructible,std::is_nothrow_destructible - std::is_destructible,std::is_trivially_destructible,std::is_nothrow_destructible

Synopsis

Defined in header <type_traits>
template< class T > (1) (since C++11)
struct is_destructible;
template< class T > (2) (since C++11)
struct is_trivially_destructible;
template< class T > (3) (since C++11)
struct is_nothrow_destructible;

1) If T is a reference type, provides the member constant value equal to true.

If T is (possibly cv-qualified) void, a function type, or an array of unknown bound,
value equals false.

If T is an object type, then, for the type U equal to
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.

2) same as (1) and additionally std::remove_all_extents<T>::type is either a
non-class type or a class type with a trivial destructor.

3) same as (1), but the destructor is noexcept.

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.

Helper variable templates

template< class T > (since C++17)
inline constexpr bool is_destructible_v = is_destructible<T>::value;
template< class T >
inline constexpr bool is_trivially_destructible_v = (since C++17)
is_trivially_destructible<T>::value;
template< class T >
inline constexpr bool is_nothrow_destructible_v = (since C++17)
is_nothrow_destructible<T>::value;

Inherited from std::integral_constant

Member constants

value true if T is destructible, false otherwise
[static] (public static member constant)

Member functions

operator bool converts the object to bool, returns value
(public member function)
operator() returns value
(C++14) (public member function)

Member types

Type Definition
value_type bool
type std::integral_constant<bool, value>

Notes

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.

Example

// Run this code

#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

Defect reports

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 made complete
the imaginary wrapping struct