C++ C++;:多态容器/迭代器与编译时概念/特征
背景 这纯粹是为了教育目的。如果你不想阅读整个背景,你可以跳到底部的问题 我已经编写了一个队列接口(抽象类),以及两个基于调整数组和链表大小的派生实现C++ C++;:多态容器/迭代器与编译时概念/特征,c++,polymorphism,sfinae,typetraits,c++-concepts,C++,Polymorphism,Sfinae,Typetraits,C++ Concepts,背景 这纯粹是为了教育目的。如果你不想阅读整个背景,你可以跳到底部的问题 我已经编写了一个队列接口(抽象类),以及两个基于调整数组和链表大小的派生实现 template <typename T> class IQueue { public: virtual void enqueue(T item) = 0; virtual T dequeue() = 0; virtual bool isEmpty() = 0; virtual int size() = 0; } t
template <typename T>
class IQueue {
public:
virtual void enqueue(T item) = 0;
virtual T dequeue() = 0;
virtual bool isEmpty() = 0;
virtual int size() = 0;
}
template <typename T>
class LinkedListQueue : public IQueue<T> {...}
template <typename T>
class ResizingArrayQueue : public IQueue<T> {...}
其中一个派生类实现了begin()
/end()
方法和派生迭代器实现:
template <typename T>
class LinkedListQueue : public IQueue<T> {
// ... queue implementation details.
public:
class LinkedListForwardIterator : public IQueue<T>::IteratorImpl {
// ... implementation that goes through linked list.
};
typename IQueue<T>::ClientIterator begin() {
std::unique_ptr<LinkedListForwardIterator> impl(new LinkedListForwardIterator(head));
return typename IQueue<T>::iterator(std::move(impl));
}
typename IQueue<T>::ClientIterator end() {
std::unique_ptr<LinkedListForwardIterator> impl(new LinkedListForwardIterator(nullptr));
return typename IQueue<T>::iterator(std::move(impl));
}
};
下面是一个最低限度的可编译示例,说明您可能希望如何执行此操作
请注意,目前,此示例仅支持const begin()和const end()
添加更多的方法和可变迭代器对于读者来说是一个练习
EDIT:提供了共享相同策略类的编译时和运行时多态队列的工作示例
#include <iostream>
#include <list>
#include <vector>
#include <memory>
#include <typeinfo>
#include <typeindex>
/// COMPILE TIME Polymorphic queue of objects of type Element
template<typename Element, class Policy>
struct queue_concept
{
// Define interface
struct const_iterator;
void push_back(Element e);
const_iterator begin() const;
const_iterator end() const;
// Implementation
private:
Policy _policy;
};
// implement class methods an inner classes
template<typename Element, class Policy>
struct queue_concept<Element, Policy>::const_iterator
{
using iterator_type = typename Policy::container_type::const_iterator;
const_iterator(iterator_type iter = iterator_type {})
: _iter { std::move(iter) }
{}
const Element& operator*() const {
return *_iter;
}
const_iterator& operator++() {
std::advance(_iter, 1);
}
bool operator!=(const const_iterator& other) const {
return _iter != other._iter;
}
iterator_type _iter;
};
template<typename Element, class Policy>
void queue_concept<Element, Policy>::push_back(Element e)
{
_policy._data.push_back(std::move(e));
}
template<typename Element, class Policy>
typename queue_concept<Element, Policy>::const_iterator queue_concept<Element, Policy>::begin() const
{
return const_iterator { _policy._data.begin() };
}
template<typename Element, class Policy>
typename queue_concept<Element, Policy>::const_iterator queue_concept<Element, Policy>::end() const
{
return const_iterator { _policy._data.end() };
}
/// RUNTIME Polymorphic queue of objects of type Element
template<typename Element>
struct IQueue
{
struct const_iterator
{
struct Concept {
// virtual base class so make destructor virtual...
virtual ~Concept() = default;
virtual const Element& get_element() const = 0;
virtual void increment(std::size_t distance) = 0;
bool equal_to(const Concept& rhs)
{
if (this->get_type() == rhs.get_type()) {
return unsafe_is_equal(rhs);
}
return false;
}
virtual bool unsafe_is_equal(const Concept& rhs) const = 0;
virtual std::type_index get_type() const = 0;
// provide copy support
virtual std::unique_ptr<Concept> clone() const = 0;
};
template<class Iter>
struct Model : public Concept {
Model(Iter iter) : _iter { std::move(iter) }
{}
const Element& get_element() const override {
return *_iter;
}
void increment(std::size_t distance) override {
std::advance(_iter, distance);
}
bool unsafe_is_equal(const Concept& rhs) const override {
auto _rhs = static_cast<const Model&>(rhs);
return _iter == _rhs._iter;
}
std::type_index get_type() const override {
return std::type_index(typeid(*this));
}
std::unique_ptr<Concept> clone() const override {
return std::unique_ptr<Concept> { new Model(*this) };
}
private:
Iter _iter;
};
// constructor
template<class Iter>
const_iterator(Iter iter)
: _impl { new Model<Iter> { std::move(iter) } }
{}
// default constructor - constructs an invalid iterator
const_iterator()
{}
// provide copy support since impl is a unique_ptr
const_iterator(const const_iterator& other)
: _impl { other._impl ? other._impl->clone() : std::unique_ptr<Concept>{} }
{}
const_iterator& operator=(const_iterator& other)
{
auto p = other._impl ? other._impl->clone() : std::unique_ptr<Concept>{};
std::swap(_impl, p);
}
// since we provided copy support we must provide move support
const_iterator(const_iterator&& rhs) = default;
const_iterator& operator=(const_iterator&& rhs) = default;
const Element& operator*() const {
return _impl->get_element();
}
const_iterator& operator++() {
_impl->increment(1);
return *this;
}
bool operator!=(const const_iterator& rhs) const
{
return !(_impl->equal_to(*(rhs._impl)));
}
private:
std::unique_ptr<Concept> _impl;
};
virtual void push_back(Element e) = 0;
virtual const_iterator begin() const = 0;
virtual const_iterator end() const = 0;
};
template<class Element, class Policy>
struct QueueImpl : public IQueue<Element>
{
void push_back(Element e) override {
_policy._data.push_back(std::move(e));
}
typename IQueue<Element>::const_iterator begin() const override {
return typename IQueue<Element>::const_iterator { std::begin(_policy._data) };
}
typename IQueue<Element>::const_iterator end() const override {
return typename IQueue<Element>::const_iterator { std::end(_policy._data) };
}
Policy _policy;
};
template<class Element>
struct ResizingArrayPolicy
{
using container_type = std::vector<Element>;
container_type _data;
};
template<class Element>
struct LinkedListPolicy
{
using container_type = std::list<Element>;
container_type _data;
};
template<class Element>
std::unique_ptr<IQueue<Element>> make_poly_resizing_array_queue()
{
return std::unique_ptr<IQueue<Element>> { new QueueImpl<Element, ResizingArrayPolicy<Element>> };
}
template<class Element>
std::unique_ptr<IQueue<Element>> make_poly_linked_list_queue()
{
return std::unique_ptr<IQueue<Element>> { new QueueImpl<Element, LinkedListPolicy<Element>>{} };
}
template<class Element>
queue_concept<Element, ResizingArrayPolicy<Element>> make_static_resizing_array_queue()
{
return queue_concept<Element, ResizingArrayPolicy<Element>>{};
}
template<class Element>
queue_concept<Element, LinkedListPolicy<Element>> make_static_linked_list_queue()
{
return queue_concept<Element, LinkedListPolicy<Element>>{};
}
using namespace std;
int main()
{
// create the queues
auto pq1 = make_poly_resizing_array_queue<int>();
auto pq2 = make_poly_linked_list_queue<int>();
// put data in them
pq1->push_back(10);
pq1->push_back(20);
pq2->push_back(30);
pq2->push_back(40);
// prove that iterators are assignable and moveable
IQueue<int>::const_iterator it;
it = pq1->begin();
cout << *it << endl; // should print 10
auto i2 = pq2->begin();
it = move(i2);
cout << *it << endl; // should print 30
// prove that queues are polymorphic
auto queues = vector<unique_ptr<IQueue<int>>>{};
queues.push_back(move(pq1));
queues.push_back(move(pq2));
// print the vector of queues
for(const auto& queue_ptr : queues) {
for(const auto& item : *queue_ptr) {
cout << item << endl;
}
cout << endl;
}
// now the static versions
auto q1 = make_static_resizing_array_queue<int>();
auto q2 = make_static_linked_list_queue<int>();
q1.push_back(10);
q1.push_back(20);
q2.push_back(30);
q2.push_back(40);
cout << "static queues\n";
for(const auto& item : q1) {
cout << item << endl;
}
cout << endl;
for(const auto& item : q2) {
cout << item << endl;
}
return 0;
}
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///元素类型的对象的编译时多态队列
模板
结构队列概念
{
//定义接口
结构常量迭代器;
无效推回(元素e);
常量迭代器begin()常量;
常量迭代器end()常量;
//实施
私人:
政策(政策),;
};
//在内部类中实现类方法
模板
结构队列概念::常量迭代器
{
使用迭代器\类型=类型名策略::容器\类型::常量\迭代器;
常量迭代器(迭代器类型iter=迭代器类型{})
:_iter{std::move(iter)}
{}
常量元素和运算符*()常量{
返回*\u iter;
}
常量迭代器和运算符++(){
标准:国际热核实验堆1号;
}
布尔运算符!=(常量迭代器和其他)常量{
返回_iter!=其他。_iter;
}
迭代器类型;
};
模板
无效队列概念::推回(元素e)
{
_策略._data.push_back(std::move(e));
}
模板
typename队列概念::常量迭代器队列概念::begin()常量
{
返回常量迭代器{u policy.\u data.begin()};
}
模板
typename队列概念::常量迭代器队列概念::end()常量
{
返回常量迭代器{u policy.\u data.end()};
}
///元素类型的对象的运行时多态队列
模板
伊奎厄结构
{
结构常量迭代器
{
结构概念{
//虚拟基类使析构函数虚拟。。。
virtual~Concept()=默认值;
虚拟常量元素&get_元素()常量=0;
虚拟空隙增量(标准::尺寸距离)=0;
布尔等于(常数概念和rhs)
{
if(this->get_type()==rhs.get_type()){
返回值等于(rhs);
}
返回false;
}
虚拟布尔不安全等于(常数概念和rhs)常数=0;
虚拟std::type_index get_type()const=0;
//提供拷贝支持
虚拟std::unique_ptr clone()const=0;
};
模板
结构模型:公共概念{
模型(国际热核实验堆):国际热核实验堆{std::move(国际热核实验堆)}
{}
常量元素&get_Element()常量覆盖{
返回*\u iter;
}
无效增量(标准::大小\u t距离)覆盖{
标准:前进(_iter,距离);
}
布尔不安全等于(常数概念和rhs)常数覆盖{
自动旋转=静态旋转(rhs);
return(返回)iter==(返回);
}
std::type_index get_type()常量重写{
返回std::type_索引(typeid(*this));
}
std::unique_ptr clone()常量覆盖{
返回std::unique_ptr{newmodel(*this)};
}
私人:
国际热核实验堆;
};
//建造师
模板
常量迭代器(Iter)
:_impl{new Model{std::move(iter)}
{}
//默认构造函数-构造无效的迭代器
常量迭代器()
{}
//提供拷贝支持,因为impl是唯一的\u ptr
常量迭代器(常量迭代器和其他)
:_impl{other._impl?other._impl->clone():std::unique_ptr{}
{}
常量迭代器和运算符=(常量迭代器和其他)
{
auto p=other.\u impl?other.\u impl->clone():std::unique\u ptr{};
标准::交换(_impl,p);
}
//既然我们提供了复制支持,我们就必须提供移动支持
常量迭代器(常量迭代器&&rhs)=默认值;
常量迭代器和运算符=(常量迭代器和rhs)=默认值;
常量元素和运算符*()常量{
返回_impl->get_元素();
}
常量迭代器和运算符++(){
_impl->increment(1);
归还*这个;
}
布尔运算符!=(常量迭代器和rhs)常量
{
返回!(_impl->等于(*(rhs._impl));
}
私人:
std::唯一的\u ptr\u impl;
};
虚空推回(元素e)=0;
虚拟常量迭代器begin()常量=0;
虚拟常量迭代器end()常量=0;
};
模板
结构QueueImpl:公共IQueue
{
无效推回(元素e)覆盖{
_策略._data.push_back(std::move(e));
}
typename IQueue::常量迭代器begin()常量重写{
返回typename IQueue::const_迭代器{std::begin(_policy._data)};
}
typename IQueue::常量迭代器end()常量重写{
返回typename IQueue::const_迭代器{std::end(_policy._data)};
}
政策(政策),;
};
模板
结构调整大小策略
{
使用容器_type=std::vector;
容器类型数据;
};
模板
结构LinkedListPolicy
{
使用容器类型=标准::列表;
容器类型数据;
};
模板
std::unique_ptr make_poly_resizing_array_queue()
{
返回std::unique_ptr{new QueueImpl};
}
模板
std::唯一的\u ptr生成\u多边形\u链接的\u列表\u队列()
{
返回
template <typename T>
void testQueueImpl(std::shared_ptr<IQueue<T> > queue) {
queue->enqueue(1);
queue->enqueue(2);
queue->enqueue(3);
queue->enqueue(4);
queue->enqueue(5);
queue->enqueue(6);
std::cout << "Iterator behavior check 1st: ";
for (auto e: *queue) {
std::cout << e << " ";
}
std::cout << std::endl;
std::cout << "Iterator behavior check 2nd: ";
for (auto it = queue->begin(); it != queue->end(); it++) {
std::cout << *it << " ";
}
}
void testQueue() {
auto queue = std::make_shared<LinkedListQueue<int> >();
testQueueImpl<int>(queue);
auto queue2 = std::make_shared<ResizingArrayQueue<int> >();
testQueueImpl<int>(queue2);
}
template <typename Container>
void testQueueImpl(Container queue) {
queue->enqueue(1);
queue->enqueue(2);
queue->enqueue(3);
queue->enqueue(4);
queue->enqueue(5);
queue->enqueue(6);
std::cout << "Size: " << queue->size() << std::endl;
std::cout << "Iterator behavior check 1st: ";
for (auto e: *queue) {
std::cout << e << " ";
}
std::cout << std::endl;
std::cout << "Iterator behavior check 2nd: ";
for (auto it = queue->begin(); it != queue->end(); it++) {
std::cout << *it << " ";
}
std::cout << std::endl;
}
void testQueue() {
auto queue = std::make_shared<LinkedListQueue<int> >();
testQueueImpl<std::shared_ptr<LinkedListQueue<int> > >(queue);
auto queue2 = std::make_shared<ResizingArrayQueue<int> >();
testQueueImpl<std::shared_ptr<ResizingArrayQueue<int> > >(queue2);
}
#include <iostream>
#include <list>
#include <vector>
#include <memory>
#include <typeinfo>
#include <typeindex>
/// COMPILE TIME Polymorphic queue of objects of type Element
template<typename Element, class Policy>
struct queue_concept
{
// Define interface
struct const_iterator;
void push_back(Element e);
const_iterator begin() const;
const_iterator end() const;
// Implementation
private:
Policy _policy;
};
// implement class methods an inner classes
template<typename Element, class Policy>
struct queue_concept<Element, Policy>::const_iterator
{
using iterator_type = typename Policy::container_type::const_iterator;
const_iterator(iterator_type iter = iterator_type {})
: _iter { std::move(iter) }
{}
const Element& operator*() const {
return *_iter;
}
const_iterator& operator++() {
std::advance(_iter, 1);
}
bool operator!=(const const_iterator& other) const {
return _iter != other._iter;
}
iterator_type _iter;
};
template<typename Element, class Policy>
void queue_concept<Element, Policy>::push_back(Element e)
{
_policy._data.push_back(std::move(e));
}
template<typename Element, class Policy>
typename queue_concept<Element, Policy>::const_iterator queue_concept<Element, Policy>::begin() const
{
return const_iterator { _policy._data.begin() };
}
template<typename Element, class Policy>
typename queue_concept<Element, Policy>::const_iterator queue_concept<Element, Policy>::end() const
{
return const_iterator { _policy._data.end() };
}
/// RUNTIME Polymorphic queue of objects of type Element
template<typename Element>
struct IQueue
{
struct const_iterator
{
struct Concept {
// virtual base class so make destructor virtual...
virtual ~Concept() = default;
virtual const Element& get_element() const = 0;
virtual void increment(std::size_t distance) = 0;
bool equal_to(const Concept& rhs)
{
if (this->get_type() == rhs.get_type()) {
return unsafe_is_equal(rhs);
}
return false;
}
virtual bool unsafe_is_equal(const Concept& rhs) const = 0;
virtual std::type_index get_type() const = 0;
// provide copy support
virtual std::unique_ptr<Concept> clone() const = 0;
};
template<class Iter>
struct Model : public Concept {
Model(Iter iter) : _iter { std::move(iter) }
{}
const Element& get_element() const override {
return *_iter;
}
void increment(std::size_t distance) override {
std::advance(_iter, distance);
}
bool unsafe_is_equal(const Concept& rhs) const override {
auto _rhs = static_cast<const Model&>(rhs);
return _iter == _rhs._iter;
}
std::type_index get_type() const override {
return std::type_index(typeid(*this));
}
std::unique_ptr<Concept> clone() const override {
return std::unique_ptr<Concept> { new Model(*this) };
}
private:
Iter _iter;
};
// constructor
template<class Iter>
const_iterator(Iter iter)
: _impl { new Model<Iter> { std::move(iter) } }
{}
// default constructor - constructs an invalid iterator
const_iterator()
{}
// provide copy support since impl is a unique_ptr
const_iterator(const const_iterator& other)
: _impl { other._impl ? other._impl->clone() : std::unique_ptr<Concept>{} }
{}
const_iterator& operator=(const_iterator& other)
{
auto p = other._impl ? other._impl->clone() : std::unique_ptr<Concept>{};
std::swap(_impl, p);
}
// since we provided copy support we must provide move support
const_iterator(const_iterator&& rhs) = default;
const_iterator& operator=(const_iterator&& rhs) = default;
const Element& operator*() const {
return _impl->get_element();
}
const_iterator& operator++() {
_impl->increment(1);
return *this;
}
bool operator!=(const const_iterator& rhs) const
{
return !(_impl->equal_to(*(rhs._impl)));
}
private:
std::unique_ptr<Concept> _impl;
};
virtual void push_back(Element e) = 0;
virtual const_iterator begin() const = 0;
virtual const_iterator end() const = 0;
};
template<class Element, class Policy>
struct QueueImpl : public IQueue<Element>
{
void push_back(Element e) override {
_policy._data.push_back(std::move(e));
}
typename IQueue<Element>::const_iterator begin() const override {
return typename IQueue<Element>::const_iterator { std::begin(_policy._data) };
}
typename IQueue<Element>::const_iterator end() const override {
return typename IQueue<Element>::const_iterator { std::end(_policy._data) };
}
Policy _policy;
};
template<class Element>
struct ResizingArrayPolicy
{
using container_type = std::vector<Element>;
container_type _data;
};
template<class Element>
struct LinkedListPolicy
{
using container_type = std::list<Element>;
container_type _data;
};
template<class Element>
std::unique_ptr<IQueue<Element>> make_poly_resizing_array_queue()
{
return std::unique_ptr<IQueue<Element>> { new QueueImpl<Element, ResizingArrayPolicy<Element>> };
}
template<class Element>
std::unique_ptr<IQueue<Element>> make_poly_linked_list_queue()
{
return std::unique_ptr<IQueue<Element>> { new QueueImpl<Element, LinkedListPolicy<Element>>{} };
}
template<class Element>
queue_concept<Element, ResizingArrayPolicy<Element>> make_static_resizing_array_queue()
{
return queue_concept<Element, ResizingArrayPolicy<Element>>{};
}
template<class Element>
queue_concept<Element, LinkedListPolicy<Element>> make_static_linked_list_queue()
{
return queue_concept<Element, LinkedListPolicy<Element>>{};
}
using namespace std;
int main()
{
// create the queues
auto pq1 = make_poly_resizing_array_queue<int>();
auto pq2 = make_poly_linked_list_queue<int>();
// put data in them
pq1->push_back(10);
pq1->push_back(20);
pq2->push_back(30);
pq2->push_back(40);
// prove that iterators are assignable and moveable
IQueue<int>::const_iterator it;
it = pq1->begin();
cout << *it << endl; // should print 10
auto i2 = pq2->begin();
it = move(i2);
cout << *it << endl; // should print 30
// prove that queues are polymorphic
auto queues = vector<unique_ptr<IQueue<int>>>{};
queues.push_back(move(pq1));
queues.push_back(move(pq2));
// print the vector of queues
for(const auto& queue_ptr : queues) {
for(const auto& item : *queue_ptr) {
cout << item << endl;
}
cout << endl;
}
// now the static versions
auto q1 = make_static_resizing_array_queue<int>();
auto q2 = make_static_linked_list_queue<int>();
q1.push_back(10);
q1.push_back(20);
q2.push_back(30);
q2.push_back(40);
cout << "static queues\n";
for(const auto& item : q1) {
cout << item << endl;
}
cout << endl;
for(const auto& item : q2) {
cout << item << endl;
}
return 0;
}
template <typename T, class Allocator>
class Queue
{
Allocator myAllocator;
public:
void enqueue(T item)
{
myAllocator.push(item);
}
// other operations.
};
template <class T, template <typename ...> class Container, class ... Args>
class BasicAllocator
{
Container<T, Args...> M_list;
public:
void push(T element)
{
M_list.push_back(element);
}
auto begin() -> decltype( std::begin(M_list) )
{ return std::begin(M_list); }
auto end() -> decltype( std::end(M_list) )
{ return std::end(M_list); }
};
template<class T>
using LinkedListAllocator = BasicAllocator<T, std::list>;
template<class T>
using LinkedListQueue = Queue<T, LinkedListAllocator<T>>;