std::is_pointer_interconvertible_base_of

template< class Base, class Derived >
struct is_pointer_interconvertible_base_of;

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.

The behavior of a program that adds specializations for std::is_pointer_interconvertible_base_of or std::is_pointer_interconvertible_base_of_v 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;

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.

Example

#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