fstack.hpp

#pragma once
#include <memory>
#include <cassert>

template <class T>
class FStack {
    public: // idk how to get rid of this but still have empty_node initialized
    using SELF = FStack<T>;
    std::shared_ptr<FStack> prev;
    T val;

    FStack(std::shared_ptr<FStack> prev, T val) : prev(prev), val(val) {

    }
    inline static std::shared_ptr<FStack> empty_node = std::make_shared<FStack>(nullptr, T{});

    public:

    static std::shared_ptr<FStack> empty() {
        return empty_node;
    }

    static std::shared_ptr<FStack> push(const std::shared_ptr<SELF> &stack, T new_val) {
        return std::make_shared<FStack>(stack, new_val);
    }

    static std::shared_ptr<FStack> pop(const std::shared_ptr<SELF> &stack) {
        assert(stack != empty());
        return stack->prev;
    }

    static T top(const std::shared_ptr<SELF> &stack) {
        return stack->val;
    }
};