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

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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)
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 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.
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.

If T is not a complete type, (possibly cv-qualified) void, or an array of unknown bound, 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.

If the program adds specializations for any of the templates described on this page, the behavior is undefined.

Contents

Helper variable templates

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

Inherited from std::integral_constant

Member constants

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

Member functions

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

Possible implementation

is_destructible (1) 
// C++20 required
template<typename t>
struct is_destructible
    : std::integral_constant<bool, requires(t object) { object.~t(); }>
{};
is_trivially_destructible (2) 
// Not real C++. Shall P2996 be approved, the following implementation will be available:
template<typename t>
struct is_trivially_destructible
     : std::integral_constant<bool, std::meta::type_is_trivially_destructible(^t)>
{};
is_nothrow_destructible (3) 
// C++20 required
template<typename t>
struct is_nothrow_destructible
    : std::integral_constant<bool, requires(t object) { {object.~t()} noexcept; }>
{};

Example

Run this code
#include <iostream>
#include <string>
#include <type_traits>
 
struct Foo
{
    std::string str;
    ~Foo() noexcept {};
};
 
struct Bar
{
    ~Bar() = default;
};
 
static_assert(std::is_destructible<std::string>::value == true);
static_assert(std::is_trivially_destructible_v<Foo> == false);
static_assert(std::is_nothrow_destructible<Foo>() == true);
static_assert(std::is_trivially_destructible<Bar>{} == true);
 
int main() {}

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 the imaginary wrapping struct made complete

See also

(C++11)(C++11)(C++11)
 checks if a type has a constructor for specific arguments
(class template) [edit]
(C++11)
 checks if a type has a virtual destructor
(class template) [edit]
(C++20)
 specifies that an object of the type can be destroyed
(concept) [edit]
destructor releases claimed resources[edit]
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