property.cpp

#include <type_traits>

template<class, auto, auto, auto>
class accessor;

template<class C, auto id, auto getter, auto setter>
class property : public decltype(
    id.template operator()<accessor<C, id, getter, setter>>())::type {};

template<class C, auto id, auto getter, auto setter>
class accessor {
private:
    using P = property<C, id, getter, setter>;
    C& self() { return *static_cast<C*>(reinterpret_cast<P*>(this)); }
    C const& self() const { return *static_cast<C const*>(reinterpret_cast<P const*>(this)); }
public:
    decltype(auto) get() { return getter(self()); }
    decltype(auto) get() const { return getter(self()); }
    operator decltype(auto)() { return get(); }
    operator decltype(auto)() const { return get(); }
    decltype(auto) operator=(auto value) { return setter(self(), value); }
};

#define ID(id) []<class T> { struct B { T id; }; return std::type_identity<B>(); }
#define PROPERTY(C, id, getter, setter) \
    property<C, ID(id), getter, setter>

#include <chrono>
#include <string>

class Person :
    public PROPERTY(Person, name,
        [](auto const& self) { return self.mName; },
        [](auto& self, auto name) { self.mName = name; }),
    public PROPERTY(Person, age,
        [](auto const& self) { return self.mAge; },
        [](auto& self, auto age) { self.mAge = age; })
{
private:
    std::string mName;
    std::chrono::years mAge;
};

#include <iostream>
int main() {
    Person p;
    p.name = "Fred";
    p.age = std::chrono::years(22);
    std::cout << "Happy " << p.age.get() << " birthday, " << p.name.get() << "!" << std::endl;
}