std::is_copy_assignable, std::is_trivially_copy_assignable, std::is_nothrow_copy_assignable
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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) If 
T is not a referenceable type (i.e., possibly cv-qualified void or a function type with a cv-qualifier-seq or a ref-qualifier), provides a member constant value equal to false. Otherwise, provides a member constant value equal to std::is_assignable<T&, const T&>::value.2) Same as 1), but uses std::is_trivially_assignable<T&, const T&>
2) Same as 1), but uses std::is_nothrow_assignable<T&, const T&>
T  shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound. Otherwise, the behavior is undefined.
| Contents | 
[edit] Helper variable templates
| template< class T > constexpr bool is_copy_assignable_v = is_copy_assignable<T>::value; | (since C++17) | |
| template< class T > constexpr bool is_trivially_copy_assignable_v = is_trivially_copy_assignable<T>::value; | (since C++17) | |
| template< class T > constexpr bool is_nothrow_copy_assignable_v = is_nothrow_copy_assignable<T>::value; | (since C++17) | |
Inherited from std::integral_constant
Member constants
| value [static] | true if Tis copy-assignable, false otherwise(public static member constant) | 
Member functions
| operator bool | converts the object to bool, returns value(public member function) | 
| operator() (C++14) | 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] 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
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
| (C++11)(C++11)(C++11) | checks if a type has a assignment operator for a specific argument (class template) | 
| (C++11)(C++11)(C++11) | checks if a type has a move assignment operator (class template) | 
| (library fundamentals TS) | variable template alias of std::is_copy_assignable::value(variable template) | 
| (library fundamentals TS) | variable template alias of std::is_trivially_copy_assignable::value(variable template) | 
| (library fundamentals TS) | variable template alias of std::is_nothrow_copy_assignable::value(variable template) | 


