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

< cpp‎ | types
Metaprogramming library
Type traits
Type categories
Type properties
(C++11)(until C++20*)
(C++11)(deprecated in C++20)
Type trait constants
Supported operations

Relationships and property queries
Type modifications
Type transformations
(C++11)(deprecated in C++23)
(C++11)(deprecated in C++23)

(C++11)(until C++20*)(C++17)
Compile-time rational arithmetic
Compile-time integer sequences
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.


[edit] Helper variable templates

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)

Inherited from std::integral_constant

Member constants

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)
returns value
(public member function)

Member types

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

[edit] 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.

[edit] Example

#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';


std::string is destructible? true
Foo is trivially destructible? false
Foo is nothrow destructible? true
Bar is trivially destructible? true

[edit] 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

[edit] See also

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