klotski/src/core_test/utility/exposer.h

#pragma once

/// The exposer can forcibly access private members of a class without changing
/// any code. It uses macros to construct a function that returns a reference
/// to the target member variable.

namespace exposer {

template <typename T>
struct Exposer {
    static T ptr;
};

template <typename T>
T Exposer<T>::ptr;

template <typename T, T Ptr>
struct ExposerImpl {
    static struct Factory {
        Factory() { Exposer<T>::ptr = Ptr; }
    } factory;
};

template <typename T, T Ptr>
typename ExposerImpl<T, Ptr>::Factory ExposerImpl<T, Ptr>::factory;

} // namespace exposer

#define FORCIBLY_ACCESS(Class, Member, Type)                                   \
    namespace exposer {                                                        \
        template struct ExposerImpl<decltype(&Class::Member), &Class::Member>; \
        inline auto& Class##_##Member(Class &T) {                              \
            return T.*exposer::Exposer<Type Class::*>::ptr;                    \
        }                                                                      \
    }