Emplace method in own deque

Question

How can I write my own emplace method in my deque?

For example, I have this emplace_front function

template <typename ... Args>
void emplace_front(Args&& ...val) {
???
}

and Node constructor

template <typename ... Args>
Node(Args&&... val) : element(std::forward<Args>(val)...), next(nullptr),prev(nullptr) { }

I can't figure out how to write it correctly

Answer 1

If you have a continuous container, it looks something like:

// first find/create free memory for your data, call it p
new (p) T(std::forward<Args>(args)...);

This is called 'placement new', and does not allocate, only construct
p should be a T*

---

If you have a node-based container, it looks something like:

struct Node {
    Node *prev, *next;
    T value;
    template<typename... Args>
    Node(Args&&... args) : value(std::forward<Args>(args)...) {}
};

template<typename... Args>
iterator emplace(Args&&... args) {
    Node* p = new Node(std::forward<Args>(args)...);
    // fill in p->next and p->prev here
    return {p};
}

you also need a constructor to your iterator that takes a Node*