cppListFwClass

#include <iostream>

template <typename ElemT>
class ListFw
{
    class Node
    {
        ElemT data;
        Node* next;
    public:
        Node(const ElemT& dataP, Node* nextP = nullptr) : data{ dataP }, next{ nextP }{}
        friend ListFw;
    };

    Node* head;
    Node* tail;
    size_t size;
public:
    ListFw() : head{ nullptr }, tail{ nullptr }, size{ 0 } {}
    bool empty()const { return size == 0; }
    size_t get_size()const { return size; }
    ElemT& front() { return head->data; }
    const ElemT& front()const { return head->data; }
    ElemT& back() { return tail->data; }
    const ElemT& back()const { return tail->data; }
    void push_front(const ElemT& data);
    void push_back(const ElemT& data);
    bool pop_front();
    bool pop_back();
    void clear();
    ~ListFw();
};

template <typename ElemT>
void ListFw<ElemT>::push_front(const ElemT& data)
{
    head = new Node{ data, head };

    if (!tail)
    {
        tail = head;
    }
    ++size;
}

template <typename ElemT>
void ListFw<ElemT>::push_back(const ElemT& data)
{
    if (!head)
    {
        head = new Node{ data, head };
        tail = head;
    }
    else
    {
        tail->next = new Node{ data, nullptr };
        tail = tail->next;
    }
    ++size;
}

template <typename ElemT>
bool ListFw<ElemT>::pop_front()
{
    if (head)
    {
        Node* oldHead{ head };
        head = head->next;
        delete oldHead;
        --size;
        if (!size) { tail = nullptr; }
        return true;
    }
    return false;
}

template <typename ElemT>
bool ListFw<ElemT>::pop_back()
{
    if (tail)
    {
        if (tail == head)
        {
            delete tail;
            head = nullptr;
            tail = nullptr;
            size = 0;
            return true;
        }

        Node* curr{ head };
        for (; !(curr->next == tail); curr = curr->next);

        delete tail;
        curr->next = nullptr;
        tail = curr;
        --size;
        return true;
    }
    return false;
}

template <typename ElemT>
void ListFw<ElemT>::clear()
{
    while (head)
    {
        std::cout << "Clear for: " << front() << '\n';
        pop_front();
    }
}

template <typename ElemT>
ListFw<ElemT>::~ListFw()
{
    // BAD! VERY INEFFICIENT!
    while (tail)
    {
        std::cout << "Destruct for: " << back() << '\n';
        pop_back();
    }
}

template <typename ElemT>
void printListState(const ListFw<ElemT>& l)
{
    std::cout << "Size: " << l.get_size() << '\n';
    std::cout << "Front: " << l.front() << '\n';
    std::cout << "Back: " << l.back() << '\n';
}

int main()
{
    ListFw<int> l;

    std::cout << "Size: " << l.get_size() << '\n';

    // [42,33]

    l.push_back(42);
    l.push_back(33);

    printListState(l);

    l.pop_front();
    l.pop_back();
    std::cout << "Size: " << l.get_size() << '\n';

    for (int i{ 0 }; i < 4; l.push_back(i++));

    printListState(l);
    l.clear();

    // [3,2,1,0]
    for (int i{ 0 }; i < 4; l.push_front(i++));
    printListState(l);

    return 0;
}