std::is_copy_assignable, std::is_trivially_copy_assignable, std::is_nothrow_copy_assignable

 

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is_copy_constructible is_trivially_copy_constructible is_nothrow_copy_constructible (C++11) (C++11) (C++11)
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is_copy_assignable is_trivially_copy_assignable is_nothrow_copy_assignable (C++11) (C++11) (C++11)
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Defined in header <type_traits>
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)

1) Checks whether a type is CopyAssignable, i.e. has an accessible explicit or implicit copy assignment operator. If the requirement is met, a member constant value equal true is provided, otherwise value is false.

2) Same as 1), but evaluation of the copy-assignment expression will not call any operation that is not trivial.

3) Same as 1), but the evaluation of the copy-assignment expression will not call any operation that is not noexcept.

Inherited from std::integral_constant

Member constants

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

Member functions

operator bool	converts the object to bool, returns value (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, const typename std::add_lvalue_reference<T>::type> {};   template< class T> struct is_trivially_copy_assignable : std::is_trivially_assignable< typename std::add_lvalue_reference<T>::type, const typename std::add_lvalue_reference<T>::type> {};   template< class T> struct is_nothrow_copy_assignable : std::is_nothrow_assignable< typename std::add_lvalue_reference<T>::type, const typename std::add_lvalue_reference<T>::type> {};

Example

#include <iostream>
#include <utility>
#include <type_traits>
struct Foo { int n; };
int main() {
    std::cout << std::boolalpha
              << "Foo is trivally 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 trivally copy-assignable? true
int[2] is copy-assignable? false
int is nothrow copy-assignable? true

See also

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