std::is_copy_constructible, std::is_trivially_copy_constructible, std::is_nothrow_copy_constructible

 

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is_constructible is_trivially_constructible is_nothrow_constructible (C++11) (C++11) (C++11)
is_default_constructible is_trivially_default_constructible is_nothrow_default_constructible (C++11) (C++11) (C++11)
is_copy_constructible is_trivially_copy_constructible is_nothrow_copy_constructible (C++11) (C++11) (C++11)
is_move_constructible is_trivially_move_constructible is_nothrow_move_constructible (C++11) (C++11) (C++11)
is_assignable is_trivially_assignable is_nothrow_assignable (C++11) (C++11) (C++11)
is_copy_assignable is_trivially_copy_assignable is_nothrow_copy_assignable (C++11) (C++11) (C++11)
is_move_assignable is_trivially_move_assignable is_nothrow_move_assignable (C++11) (C++11) (C++11)
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Type trait constants
integral_constant (C++11)

 

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

2) Same as (1), but the copy constructor expression does not call any operation that is not trivial.

3) Same as (1), but the copy constructor expression is noexcept.

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)

Member types

Type	Definition
value_type	bool
type	std::integral_constant<bool, value>

Possible implementation

template<class T> struct is_copy_constructible : std::is_constructible<T, const typename std::add_lvalue_reference<T>::type> {};   template<class T> struct is_trivially_copy_constructible : std::is_trivially_constructible<T, const typename std::add_lvalue_reference<T>::type> {};   template<class T> struct is_nothrow_copy_constructible : std::is_nothrow_constructible<T, const typename std::add_lvalue_reference<T>::type> {};

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

See also

is_constructible is_trivially_constructible is_nothrow_constructible (C++11) (C++11) (C++11)	checks if a type has a constructor for specific arguments (class template)
is_default_constructible is_trivially_default_constructible is_nothrow_default_constructible (C++11) (C++11) (C++11)	checks if a type has a default constructor (class template)
is_move_constructible is_trivially_move_constructible is_nothrow_move_constructible (C++11) (C++11) (C++11)	checks if a type has a move constructor (class template)