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) Checks whether a type is CopyConstructible, i.e. can be constructed from a const T& argument. 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)
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, 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> {};

[edit] Example

Run this code

#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

is_constructibleis_trivially_constructibleis_nothrow_constructible (C++11)(C++11)(C++11)	checks if a type has a constructor for specific arguments (class template)
is_default_constructibleis_trivially_default_constructibleis_nothrow_default_constructible (C++11)(C++11)(C++11)	checks if a type has a default constructor (class template)
is_move_constructibleis_trivially_move_constructibleis_nothrow_move_constructible (C++11)(C++11)(C++11)	checks if a type has a move constructor (class template)

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