21 Metaprogramming library [meta]

21.3 Metaprogramming and type traits [type.traits]

21.3.10 Member relationships [meta.member]

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template<class S, class M> constexpr bool is_pointer_interconvertible_with_class(M S::*m) noexcept;
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Mandates: S is a complete type.
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Returns: true if and only if S is a standard-layout type, M is an object type, m is not null, and each object s of type S is pointer-interconvertible ([basic.compound]) with its subobject s.*m.
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template<class S1, class S2, class M1, class M2> constexpr bool is_corresponding_member(M1 S1::*m1, M2 S2::*m2) noexcept;
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Mandates: S1 and S2 are complete types.
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Returns: true if and only if S1 and S2 are standard-layout struct ([class.prop]) types, M1 and M2 are object types, m1 and m2 are not null, and m1 and m2 point to corresponding members of the common initial sequence ([class.mem]) of S1 and S2.
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[Note 1: 
The type of a pointer-to-member expression &C​::​b is not always a pointer to member of C, leading to potentially surprising results when using these functions in conjunction with inheritance.
[Example 1: struct A { int a; }; // a standard-layout class struct B { int b; }; // a standard-layout class struct C: public A, public B { }; // not a standard-layout class static_assert( is_pointer_interconvertible_with_class( &C::b ) ); // Succeeds because, despite its appearance, &C​::​b has type // “pointer to member of B of type int''. static_assert( is_pointer_interconvertible_with_class<C>( &C::b ) ); // Forces the use of class C, and fails. static_assert( is_corresponding_member( &C::a, &C::b ) ); // Succeeds because, despite its appearance, &C​::​a and &C​::​b have types // “pointer to member of A of type int'' and // “pointer to member of B of type int'', respectively. static_assert( is_corresponding_member<C, C>( &C::a, &C::b ) ); // Forces the use of class C, and fails. — end example]
— end note]