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

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

From cppreference.com
< cpp‎ | types

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>

### [edit] 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> {};

### [edit] Example

Run this code

    #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

### [edit] See also

is_assignableis_trivially_assignableis_nothrow_assignable (C++11)(C++11)(C++11) | checks if a type has a assignment operator for a specific argument (class template) [edit]
is_move_assignableis_trivially_move_assignableis_nothrow_move_assignable (C++11)(C++11)(C++11) | checks if a type has a move assignment operator (class template) [edit]

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