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std::is_copy_assignable,std::is_trivially_copy_assignable,(3) C++ Standard Libary std::is_copy_assignable,std::is_trivially_copy_assignable,(3)

NAME

std::is_copy_assignable,std::is_trivially_copy_assignable, - std::is_copy_assignable,std::is_trivially_copy_assignable,

Synopsis


Defined in header <type_traits>
template< class T > (1) (since C++11)
struct is_copy_assignable;
template< class T > (2) (since C++11)
struct is_trivially_copy_assignable;
template< class T > (3) (since C++11)
struct is_nothrow_copy_assignable;


The value of the member constant value
Type trait T is a referenceable type T is not a
referenceable type
(1) std::is_assignable<T, const T&>::value
(2) std::is_trivially_assignable<T, const false
T&>::value
(3) std::is_nothrow_assignable<T, const T&>::value


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.

Member constants


value true if T is copy-assignable, 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>

Possible implementation


template<class T>
struct is_copy_assignable
: std::is_assignable<typename std::add_lvalue_reference<T>::type,
typename std::add_lvalue_reference<const T>::type> {};


template<class T>
struct is_trivially_copy_assignable
: std::is_trivially_assignable<typename std::add_lvalue_reference<T>::type,
typename std::add_lvalue_reference<const T>::type> {};


template<class T>
struct is_nothrow_copy_assignable
: std::is_nothrow_assignable<typename std::add_lvalue_reference<T>::type,
typename std::add_lvalue_reference<const T>::type> {};

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.

Example

// Run this code


#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

See also


is_assignable
is_trivially_assignable checks if a type has an assignment operator for a
is_nothrow_assignable specific argument
(C++11) (class template)
(C++11)
(C++11)
is_move_assignable
is_trivially_move_assignable
is_nothrow_move_assignable checks if a type has a move assignment operator
(C++11) (class template)
(C++11)
(C++11)

2024.06.10 http://cppreference.com