std::is_object
From cppreference.com
| Defined in header <type_traits>
|
||
| template< class T > struct is_object; |
(since C++11) | |
std::is_object is a UnaryTypeTrait.
If T is an object type (that is any possibly cv-qualified type other than function, reference, or void types), provides the member constant value equal true. For any other type, value is false.
If the program adds specializations for std::is_object or std::is_object_v, the behavior is undefined.
Contents |
[edit] Template parameters
| T | - | a type to check |
[edit] Helper variable template
| template< class T > constexpr bool is_object_v = is_object<T>::value; |
(since C++17) | |
Inherited from std::integral_constant
Member constants
| value [static] |
true if T is an object type, 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_object : std::integral_constant<bool, std::is_scalar<T>::value || std::is_array<T>::value || std::is_union<T>::value || std::is_class<T>::value> {}; |
[edit] Example
Run this code
#include <iomanip> #include <iostream> #include <type_traits> #define IS_OBJECT(...) \ std::cout << std::boolalpha << std::left << std::setw(9) << #__VA_ARGS__ \ << (std::is_object_v<__VA_ARGS__> ? " is object\n" \ : " is not an object\n") int main() { class cls {}; IS_OBJECT(void); IS_OBJECT(int); IS_OBJECT(int&); IS_OBJECT(int*); IS_OBJECT(int*&); IS_OBJECT(cls); IS_OBJECT(cls&); IS_OBJECT(cls*); IS_OBJECT(int()); IS_OBJECT(int(*)()); IS_OBJECT(int(&)()); }
Output:
void is not an object int is object int& is not an object int* is object int*& is not an object cls is object cls& is not an object cls* is object int() is not an object int(*)() is object int(&)() is not an object
[edit] See also
| (C++11) |
checks if a type is a scalar type (class template) |
| (C++11) |
checks if a type is an array type (class template) |
| (C++11) |
checks if a type is a union type (class template) |
| (C++11) |
checks if a type is a non-union class type (class template) |
