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std:: is_corresponding_member

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Compile-time rational arithmetic
Compile-time integer sequences
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Defined in header <type_traits>
template < class S1, class S2, class M1, class M2 >
constexpr bool is_corresponding_member ( M1 S1 :: * mp, M2 S2 :: * mq ) noexcept ;
(since C++20)

Determines whether mp and mq refer corresponding members in the common initial sequence of S1 and S2 . The program is ill-formed if either S1 or S2 is an incomplete type .

If either S1 or S2 is not a StandardLayoutType , or either M1 or M2 is not an object type, or either mp or mq is equal to nullptr , the result is always false .

Contents

Parameters

mp, mq - pointers-to-member to detect

Return value

true if mp and mq refer corresponding members in the common initial sequence of S1 and S2 , otherwise false .

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.

Example

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

See also

(C++11)
checks if a type is a standard-layout type
(class template)
(C++20)
checks if two types are layout-compatible
(class template)
(C++11)
checks if a type is a non-static member object pointer
(class template)