std::is_copy_constructible, std::is_trivially_copy_constructible, std::is_nothrow_copy_constructible
| Defined in header <type_traits>
|
||
| template< class T > struct is_copy_constructible; |
(1) | (since C++11) |
| template< class T > struct is_trivially_copy_constructible; |
(2) | (since C++11) |
| template< class T > struct is_nothrow_copy_constructible; |
(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_constructible<T, const T&>::value.
2) Same as (1), but uses std::is_trivially_constructible<T, const T&>.
3) Same as (1), but uses std::is_nothrow_constructible<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 > inline constexpr bool is_copy_constructible_v = is_copy_constructible<T>::value; |
(since C++17) | |
| template< class T > inline constexpr bool is_trivially_copy_constructible_v = is_trivially_copy_constructible<T>::value; |
(since C++17) | |
| template< class T > inline constexpr bool is_nothrow_copy_constructible_v = is_nothrow_copy_constructible<T>::value; |
(since C++17) | |
Inherited from std::integral_constant
Member constants
| value [static] |
true if T is copy-constructible , 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_constructible : std::is_constructible<T, typename std::add_lvalue_reference< typename std::add_const<T>::type>::type>> {}; template<class T> struct is_trivially_copy_constructible : std::is_trivially_constructible<T, typename std::add_lvalue_reference< typename std::add_const<T>::type>::type>> {}; template<class T> struct is_nothrow_copy_constructible : std::is_nothrow_constructible<T, typename std::add_lvalue_reference< typename std::add_const<T>::type>::type>> {}; |
[edit] Notes
In many implementations, is_nothrow_copy_constructible also checks if the destructor throws because it is effectively noexcept(T(arg)). Same applies to is_trivially_copy_constructible, which, in these implementations, also requires that the destructor is trivial: GCC bug 51452 LWG issue 2116.
[edit] Example
#include <iostream> #include <type_traits> struct Ex1 { std::string str; // member has a non-trivial copy ctor }; struct Ex2 { int n; Ex2(const Ex2&) = default; // trivial and non-throwing }; int main() { std::cout << std::boolalpha << "Ex1 is copy-constructible? " << std::is_copy_constructible<Ex1>::value << '\n' << "Ex1 is trivially copy-constructible? " << std::is_trivially_copy_constructible<Ex1>::value << '\n' << "Ex2 is trivially copy-constructible? " << std::is_trivially_copy_constructible<Ex2>::value << '\n' << "Ex2 is nothrow copy-constructible? " << std::is_nothrow_copy_constructible<Ex2>::value << '\n'; }
Output:
Ex1 is copy-constructible? true Ex1 is trivially copy-constructible? false Ex2 is trivially copy-constructible? true Ex2 is nothrow copy-constructible? true
[edit] See also
| (C++11)(C++11)(C++11) |
checks if a type has a constructor for specific arguments (class template) |
| checks if a type has a default constructor (class template) | |
| (C++11)(C++11)(C++11) |
checks if a type can be constructed from an rvalue reference (class template) |