实在忍不住，模仿STL写了个阉割版的List，还没加迭代器，等搞完STL源码再说吧。

```c++

pragma once

include

namespace vlyf
{
template
struct Node
{
using pointer = Node ;
Key key;
Node prev{nullptr};
Node* next{nullptr};
Node() = default;
Node(Key const& k) : key(k) {}
};

template <typename T>
class List
{
   private:
    using linkType = Node<T>::pointer;
    linkType head{new Node<T>};

   public:
    List()
    {
        head->prev = head;
        head->next = head;
    }
    ~List();
    linkType Begin() const { return head->next; }
    linkType End() const { return head; }
    linkType Search(T const&) const;
    linkType Erase(linkType position);
    void     Insert(linkType position, T const& x);
    void     PushBack(T const& x) { Insert(End(), x); }
    void     PushFront(T const& x) { Insert(Begin(), x); }
    void     PopFront() { Erase(Begin()); }
    void     PopBack()
    {
        linkType tmp = End()->prev;
        Erase(tmp);
    }
    void Clear();
    void Remove(T const& x);
    void Unique();
    void Delete(T const& x);

   protected:
    void Transfer(linkType position, linkType first, linkType last);
};

template <typename T>
inline List<T>::linkType List<T>::Search(T const& k) const
{
    if (!head)
        throw std::out_of_range("List is empty");
    linkType p = head;
    while (p->key != k)
    {
        p = p->next;
    }
    return p;
}

template <typename T>
inline void List<T>::Insert(List<T>::linkType position, T const& x)
{
    linkType node        = new Node<T>(x);
    node->next           = position;
    node->prev           = position->prev;
    position->prev->next = node;
    position->prev       = node;
}

template <typename T>
inline void List<T>::Delete(T const& x)
{
    if (!x->prev)
        x->prev->next = x->next;
    else
        head->next = x->next;
    if (!x->next)
        x->next->prev = x->prev;
    delete x;
}

template <typename T>
inline List<T>::linkType List<T>::Erase(List<T>::linkType position)
{
    linkType nextNode = position->next;
    linkType prevNode = position->prev;
    prevNode->next    = nextNode;
    nextNode->prev    = prevNode;
    delete position;
    return nextNode;
}

template <typename T>
inline void List<T>::Clear()
{
    linkType cur = head->next;
    while (cur != head)
    {
        linkType tmp = cur;
        cur          = cur->next;
        delete tmp;
    }
    head->next = head;
    head->prev = head;
}

template <typename T>
inline void List<T>::Remove(T const& x)
{
    linkType first = Begin();
    linkType last  = End();
    while (first != last)
    {
        linkType tmp = first;
        tmp          = tmp->next;
        if (x == first->key)
        {
            Erase(first);
        }
        first = tmp;
    }
}

template <typename T>
inline void List<T>::Unique()
{
    linkType first = Begin();
    linkType last  = End();
    if (first == last)
        return;
    linkType next = first->next;
    while (next != last)
    {
        if (next->key == first->key)
            Erase(next);
        else
            first = next;
        next = first->next;
    }
}

template <typename T>
inline void List<T>::Transfer(linkType position,
                              linkType first,
                              linkType last)
{
    last->prev->next     = position;
    first->prev->next    = last;
    position->prev->next = first;
    linkType tmp         = postion->prev;
    postion->prev        = last->prev;
    last->prev           = first->prev;
    first->prev          = tmp;
}

} // namespace vlyf
```c++