C++设计模式——迭代器模式（Iterator）

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我不是萧海哇 2022-06-13 18:05:50

文章标签 ide 迭代器 #include 文章分类 C/C++ 后端开发

迭代器模式

提供一种方法顺序访问一个聚合对象中的各个元素，而又不需要暴露该对象的内部表示。

#include<iostream>
#include<string>
#include<vector>
using namespace std;

class Iterator {
public:
  virtual string first() = 0;
  virtual string next() = 0;
  virtual bool isDone() const = 0;
  virtual string current() = 0;

  virtual ~Iterator() {}
};
class Aggregate {//聚合类
public:
  virtual void push(const string& s) = 0;
  virtual string pop(int index) = 0;
  virtual int Count() const = 0;
  virtual Iterator* createIterator() = 0;
  
  virtual ~Aggregate() {}
};

class ConcreteIterator :public Iterator {
private:
  Aggregate* aggregate;
  int index;
public:
  ConcreteIterator(Aggregate* aggregate) :aggregate(aggregate),index(0) {}

  string first() override {
    if (aggregate->Count() == 0)
      return string();
    return aggregate->pop(0);
  }
  string next() override {
    if (++index >= aggregate->Count())
      return string();
    return aggregate->pop(index);
  }
  string current() override {
    if (index >= aggregate->Count()) {
      return string();
    }
    return aggregate->pop(index);
  }
  bool isDone() const override {
    return index < 0 || index >= aggregate->Count();
  }
};

class ConcreteAggregate :public Aggregate {
private:
  vector<string> strs;
public:
  void push(const string& s) override {
    return strs.emplace_back(s);
  }
  string pop(int index) override {
    if (index >= strs.size())
      return string();
    return strs.at(index);
  }
  int Count() const override {
    return strs.size();
  }
  Iterator* createIterator() {//创建相应迭代器
    //多态迭代器(此处依赖于具体类的实现，为了代码的稳定性，可以结合工厂模式)
    return new ConcreteIterator(this);
  }
};


int main()
{
  Aggregate* aggregate = new ConcreteAggregate();
  aggregate->push("hello");
  aggregate->push("world");

  Iterator* iter = aggregate->createIterator();
  cout << iter->first() << endl;
  while (!iter->isDone())
  {
    cout << iter->next();
  }
  delete aggregate, iter;
  return 0;
}