std::is_copy_constructible,std::is_trivially_copy_constructible,std::is_nothrow_copy_constructible (3) Linux Manual Page

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

Synopsis

Defined in header<type_traits>

    template <class T>
    (1)(since C++ 11)

        struct is_copy_constructible;

template <class T>
(2)(since C++ 11)

    struct is_trivially_copy_constructible;

template <class T>
(3)(since C++ 11)

    struct is_nothrow_copy_constructible;

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.
If an instantiation of a template above depends, directly or indirectly, on an incomplete type, and that instantiation could yield a different result if that type were hypothetically completed, the behavior is undefined.
Helper variable templates

template< class T >                                                                                   (since C++17)

inline constexpr bool is_copy_constructible_v = is_copy_constructible<T>::value;

template< class T >                                                                                   (since C++17)

inline constexpr bool is_trivially_copy_constructible_v = is_trivially_copy_constructible<T>::value;

template< class T >                                                                                   (since C++17)

inline constexpr bool is_nothrow_copy_constructible_v = is_nothrow_copy_constructible<T>::value;

Inherited from std::integral_constant

Member constants

value true if T is copy-constructible , false otherwise
         (public static member constant)
[static]

Member functions

              converts the object to bool, returns value
operator bool (public member function)

operator() returns value
              (public member function)
(C++14)

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, 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>> {};

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.

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

See also

is_constructible
is_trivially_constructible
is_nothrow_constructible checks if a type has a constructor for specific arguments
                                   (class template)
(C++11)
(C++11)
(C++11)
is_default_constructible
is_trivially_default_constructible
is_nothrow_default_constructible checks if a type has a default constructor
                                   (class template)
(C++11)
(C++11)
(C++11)
is_move_constructible
is_trivially_move_constructible
is_nothrow_move_constructible checks if a type can be constructed from an rvalue reference
                                   (class template)
(C++11)
(C++11)
(C++11)