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Showing content from https://en.cppreference.com/w/cpp/language/../error/error_code/../../types/is_copy_assignable.html below:

std::is_copy_assignable, std::is_trivially_copy_assignable, std::is_nothrow_copy_assignable - cppreference.com

template< class T > struct is_copy_assignable;

(1) (since C++11)

template< class T > struct is_trivially_copy_assignable;

(2) (since C++11)

template< class T > struct is_nothrow_copy_assignable;

(3) (since C++11)

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_copy_assignable_v = is_copy_assignable<T>::value; (since C++17) template< class T > inline constexpr bool is_trivially_copy_assignable_v = is_trivially_copy_assignable<T>::value; (since C++17) template< class T > inline constexpr bool is_nothrow_copy_assignable_v = is_nothrow_copy_assignable<T>::value; (since C++17) Inherited from std::integral_constant Member constants true if T is copy-assignable, false otherwise
(public static member constant) Member functions converts the object to bool, returns value
(public member function) returns value
(public member function) Member types [edit] Possible implementation [edit] Notes

The trait std::is_copy_assignable is less strict than CopyAssignable because it does not check the type of the result of the assignment (which, for a CopyAssignable type, must be an lvalue of type T) and does not check the semantic requirement that the argument expression remains unchanged. It also does not check that T satisfies MoveAssignable, which is required of all CopyAssignable types.

[edit] Example

#include <iostream>
#include <type_traits>
#include <utility>
 
struct Foo { int n; };
 
int main()
{
    std::cout << std::boolalpha
              << "Foo is trivially copy-assignable? "
              << std::is_trivially_copy_assignable<Foo>::value << '\n'
              << "int[2] is copy-assignable? "
              << std::is_copy_assignable<int[2]>::value << '\n'
              << "int is nothrow copy-assignable? "
              << std::is_nothrow_copy_assignable<int>::value << '\n';
}

Output:

Foo is trivially copy-assignable? true
int[2] is copy-assignable? false
int is nothrow copy-assignable? 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 2196 C++11 the behavior was unclear if const T& cannot be formed the value produced is false in this case [edit] See also

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