#include <iostream>

template <class T>
class ListNode {
private:
    T* hd;
    ListNode<T>* tl;
public:
    ListNode<T>(T * head, ListNode<T> * tail)
        : hd(head), tl(tail) {}
    T* head() { return hd; }
    ListNode<T>* tail() { return tl; }
};

class Whale {
public: int len;
        Whale(int length) : len(length) {}
        int add(Whale * other) { return len + other->len; }
};

template <class T>
T sum_good(ListNode<T> * list)
{
    return *(list->head()) + sum_good<T>(list->tail());
}

template <class Elem, class List>
Elem sum(List* list)
{
    if (list == NULL)
        return Elem(0);
    else
        return *(list->head()) + sum<Elem, List>(list->tail());
}

template <class List>
int length(List* list)
{
    if (list == NULL) {
        return 0;
    } else {
        return 1 + length(list->tail());
    }
}

int length(double x) {
    return int(x - 10);
}

class A {
public:
    double tail() { return 10.0; }
};

int main()
{
//    Whale * orca = new Whale(10);
//    ListNode<Whale> * node = new ListNode<Whale>(orca, NULL);

    ListNode<int> * nums
        = new ListNode<int>(new int(10), 
                            new ListNode<int>(new int(30), NULL));

    int val = sum< int, ListNode<int> >(nums);
    cout << val << endl;

    A my_a;
    int result = length<A>(&my_a);
    cout << result << endl;

    return 0;
}