std::is_copy_constructible, std::is_trivially_copy_constructible, std::is_nothrow_copy_constructible - cppreference.com (original) (raw)

If T is not a complete type, (possibly cv-qualified) void, or an array of unknown bound, 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.

If the program adds specializations for any of the templates described on this page, the behavior is undefined.

Contents

• 1 Helper variable templates
• 2 Inherited from std::integral_constant
  • 2.1 Member constants
  • 2.2 Member functions
  • 2.3 Member types
  • 2.4 Possible implementation
  • 2.5 Notes
  • 2.6 Example
  • 2.7 Defect reports
  • 2.8 See also

[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

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

Member functions

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

Member types

[edit] Possible implementation

[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 #include   struct S1 { std::string str; // member has a non-trivial copy constructor }; static_assert(std::is_copy_constructible_v); static_assert(!std::is_trivially_copy_constructible_v);   struct S2 { int n; S2(const S2&) = default; // trivial and non-throwing }; static_assert(std::is_trivially_copy_constructible_v); static_assert(std::is_nothrow_copy_constructible_v);   struct S3 { S3(const S3&) = delete; // explicitly deleted }; static_assert(!std::is_copy_constructible_v);   struct S4 { S4(S4&) {}; // cannot bind const, hence not a copy-constructible }; static_assert(!std::is_copy_constructible_v);   int main() {}

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also