#ifndef stack_h
#define stack_h

#include <memory>   // std::unique_ptr
#include <optional> // std::optional

template<typename T> class stack
{
public:
    ~stack() { while (pop()); }

    void push(T t) { head = std::make_unique<node>(std::move(head), t); }

    std::optional<T> pop()
    {
        if (head)
        {
            T data = head->data;
            head = std::move(head->next);
            return std::optional<T>(data);
        }
        else
        {
            return std::nullopt;
        }
    }

private:
    struct node
    {
        std::unique_ptr<node> next;
        T data;
    };

    std::unique_ptr<node> head = nullptr;
};

#endif // stack_h