Не шмогла.

// We use __COUNTER__ to generate a unique integral at each instantiation
template<typename T>
struct first_call {
    static constexpr int value = __COUNTER__;
};

template<typename T, int N = __COUNTER__>
struct tick_count {
    static constexpr int value = N - first_call<T>::value - 1;
};

template<typename T>
constexpr int ct_tick = tick_count<T>::value;

template<typename T>
constexpr int ct_peek = ct_tick<T> + 1;

На gcc не работает.

Не шмогла. Думала минут 10, кстати.

// We use __COUNTER__ to generate a unique integral at each instantiation
template<typename T>
struct first_call {
    static constexpr int value = __COUNTER__;
};

template<typename T, int N = __COUNTER__>
struct tick_count {
    static constexpr int value = N - first_call<T>::value - 1;
};

template<typename T>
constexpr int ct_tick = tick_count<T>::value;

template<typename T>
constexpr int ct_peek = ct_tick<T> + 1;

На gcc не работает.