I'm struggling with OOP again. I tried to implement signgly linked list, here's the code:

template <typename T>
class node
{
    T value;
    node* next;

public:
    node(const T& n)
    {
        this->value = n;
        this->next = nullptr;
    }
    ~node()
    {
        //is it ok to leave destructor empty in my case?
    }
};

template <typename T>
class list
{
    node<T>* head;
    node<T>* tail;

public:
    list()
    {
        this->head = nullptr;
        this->tail = nullptr;
    }
    list(const list& arr)
    {
        *this = list(); //<================== the line I mentioned
        node* current_this = this->head;
        node* current_arr = this->arr;
        while (current_arr != nullptr)
        {
            current_this = new node(current_arr);
            current_arr = current_arr->next;
            current_this = current_this->next;
        }
    }
    list(list&& arr)
    {
        this->head = arr.head;
        this->tail = arr.tail;
        arr = list(); //<================== the line I mentioned
    }
    ~list()
    {
        node* current = this->head;
        while (current != nullptr)
        {
            node* next = current->next;
            delete current;
            current = next;
        }
    }
};

I wrote some lines without thinking, i.e. arr = list() and *this = list(). I didn't implemented operator= so there should be some troubles. I thought compiler has decided to generate copy/move assigment for me, so I decided to add these lines, just for curiosity sake:

list& operator=(const list& arr) = delete;
list& operator=(list&& arr) = delete;

But it still compiled and I don't understand why. What's the deal here? Shoudn't assignment be forbidden and therefore arr = list() and *this = list() be illegal?

CodePudding user response：

Templates aren't evaluated unless/until you instantiate them. If you don't use the copy or move constructor, then their bugs don't produce errors.