std::is_pointer_interconvertible_base_of

 

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integer_sequence (C++14)

 

Defined in header <type_traits>
template< class Base, class Derived > struct is_pointer_interconvertible_base_of;		(since C++20)

If Derived is unambiguously derived from Base and every Derived object is pointer-interconvertible with its Base subobject, or if both are the same non-union class (in both cases ignoring cv-qualification), provides the member constant value equal to true. Otherwise value is false.

If both Base and Derived are non-union class types, and they are not the same type (ignoring cv-qualification), Derived shall be a complete type; otherwise the behavior is undefined.

If the program adds specializations for std::is_pointer_interconvertible_base_of or std::is_pointer_interconvertible_base_of_v, the behavior is undefined.

Helper variable template

template< class Base, class Derived > inline constexpr bool is_pointer_interconvertible_base_of_v =     is_pointer_interconvertible_base_of<Base, Derived>::value;		(since C++20)

Inherited from std::integral_constant

Member constants

value [static]

true if Derived is unambiguously derived from Base and every Derived object is pointer-interconvertible with its Base subobject, or if both are the same non-union class (in both cases ignoring cv-qualification), 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>

Notes

std::is_pointer_interconvertible_base_of_v<T, U> may be true even if T is a private or protected base class of U.

Let

• U be a complete object type,
• T be a complete object type with cv-qualification not less than U,
• u be any valid lvalue of U,

reinterpret_cast<T&>(u) always has well-defined result if std::is_pointer_interconvertible_base_of_v<T, U> is true.

If T and U are not the same type (ignoring cv-qualification) and T is a pointer-interconvertible base class of U, then both std::is_standard_layout_v<T> and std::is_standard_layout_v<U> are true.

If T is standard layout class type, then all base classes of T (if any) are pointer-interconvertible base class of T.

Feature-test macro	Value	Std	Feature
__cpp_lib_is_pointer_interconvertible	201907L	(C++20)	Pointer-interconvertibility traits: std::is_pointer_interconvertible_base_of, std::is_pointer_interconvertible_with_class

Example

Run this code

#include <type_traits>
 
struct Foo {};
 
struct Bar {};
 
class Baz : Foo, public Bar { int x; };
 
class NonStdLayout : public Baz { int y; };
 
static_assert(std::is_pointer_interconvertible_base_of_v<Bar, Baz>);
static_assert(std::is_pointer_interconvertible_base_of_v<Foo, Baz>);
static_assert(not std::is_pointer_interconvertible_base_of_v<Baz, NonStdLayout>);
static_assert(std::is_pointer_interconvertible_base_of_v<NonStdLayout, NonStdLayout>);
 
int main() {}

See also

is_base_of (C++11)	checks if a type is a base of the other type (class template)
is_empty (C++11)	checks if a type is a class (but not union) type and has no non-static data members (class template)
is_standard_layout (C++11)	checks if a type is a standard-layout type (class template)