std:: is_pointer_interconvertible_with_class

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Defined in header <type_traits>
template < class S, class M >
constexpr bool is_pointer_interconvertible_with_class ( M S :: * mp ) noexcept ;
(since C++20)

Given an object s of type S , determines whether s. * mp refers to a subobject of s and s is pointer-interconvertible with its subobject s. * mp . The program is ill-formed if S is not a complete type .

If S is not a StandardLayoutType , or M is not an object type, or mp is equal to nullptr , the result is always false .

Parameters

mp - a pointer-to-member to detect

Return value

true if s. * mp refers a subobject of s and s is pointer-interconvertible with its subobject s. * mp , otherwise false , where s is an object of type S .

Notes

The type of a pointer-to-member expression & S :: m is not always M S :: * , where m is of type M , because m may be a member inherited from a base class of S . The template arguments can be specified in order to avoid potentially surprising results.

If there is a value mp of type M S :: * such that std :: is_pointer_interconvertible_with_class ( mp ) == true , then reinterpret_cast < M & > ( s ) has well-defined result and it refers the same subobject as s. * mp , where s is a valid lvalue of type S .

On common platforms, the bit pattern of mp is all zero if std :: is_pointer_interconvertible_with_class ( mp ) == true .

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

Example

Run this code 
#include <type_traits>
 
struct Foo { int x; };
struct Bar { int y; };
 
struct Baz : Foo, Bar {}; // not standard-layout
 
static_assert( not std::is_same_v<decltype(&Baz::x), int Baz::*> );
static_assert( std::is_pointer_interconvertible_with_class(&Baz::x) );
static_assert( not std::is_pointer_interconvertible_with_class<Baz, int>(&Baz::x) );
 
int main() { }

See also

(C++11)
checks if a type is a standard-layout type
(class template)
(C++11)
checks if a type is a non-static member object pointer
(class template)
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