C structs are record types, but, while the standard does guarantees an in-memory ordering, in the general case you can't really iterate through members and always have to access by tag, so it might as well be unordered.

Also in C++:

   struct A { int x; int y; } a;
   struct B { int y; int x; } b;
   template<class C> concept has_x_y = requires(C c) {
     { c.x } -> std::convertible_to<int>; 
     { c.y } -> std::convertible_to<int>; 
    };

   int sum(has_x_y auto z) { return z.x + z.y; }
   ...
   sum(a);
   sum(b);