c++property.cpp

#include <cstddef>
#include <cstdlib>
#include <utility>

template <typename R, auto getter, auto setter, auto offset>
struct property {
    inline R *self() {
        return reinterpret_cast<R *>(reinterpret_cast<size_t>(this) -
                                     offset((R *)0));
    }
    inline operator auto() { return (self()->*getter)(); }
    inline void operator=(auto t) { (self()->*setter)(t); }
};

struct X {
   private:
    int get_a();
    void set_a(int);

   public:
    int padding[25];
    [[no_unique_address]] property<
        X, &X::get_a, &X::set_a, []<typename T>(T *) { return offsetof(T, a); }>
        a;
};

int test(X &x, int val) {
    x.a = val;
    return x.a;
}