阉割的List

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。

#pragma once

#include <stdexcept>
namespace vlyf
{
    template <typename Key>
    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
    {
    public:
        typedef typename Node<T>::pointer linkType;

    private:
        linkType head{ new Node<T> };

    public:
        List()
        {
            head->prev = head;
            head->next = head;
        }
        ~List() = default;
        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 typename 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 typename List<T>::linkType List<T>::Erase(typename 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 = position->prev;
        position->prev = last->prev;
        last->prev = first->prev;
        first->prev = tmp;
    }
}  // namespace vlyf