🐸 组合模式(Composite模式)

/*
组合模式(Composite)，将对象组合成树形结构以表示‘部分-整体’的层次结构，
组合模式使得用户对单个对象和组合对象的使用具有一致性
*/
#include<iostream>
#include<list>
using namespace std;

//基本对象
class Component {
public:
    Component() {};
    virtual ~Component() {}
    virtual void operation() = 0;//整体与部分具有相同的操作
    virtual void add(Component*pChild);
    virtual void remove(Component* pChild);
    virtual Component* getChild(int index);
};

void Component::add(Component* pChild) {}

void Component::remove(Component* pChild) {}
Component* Component::getChild(int index) {
    return nullptr;
}

//部分个体
class Leaf :public Component {
public:
    Leaf() {}
    virtual ~Leaf() {}
    virtual void operation();
};

void Leaf::operation() {
    cout << "Leaf::operation" << endl;
}

//组合体
class Composite :public Component {
public:
    Composite();
    virtual ~Composite();
    virtual void operation();
    virtual void add(Component* pChild);
    virtual void remove(Component* pChild);
    virtual Component* getChild(int index);
private:
    list<Component*> m_listOfComponent;//双向链表
};

Composite::Composite(){}
Composite::~Composite() {
    auto end = m_listOfComponent.end();
    auto now = m_listOfComponent.begin();
    while (end != now) {
        delete (*now);
        m_listOfComponent.erase(now);
        now = m_listOfComponent.begin();
        end = m_listOfComponent.end();
    }
}

void Composite::add(Component* pChild) {
    m_listOfComponent.push_back(pChild);
}

void Composite::remove(Component* pChild) {
    auto res = find(m_listOfComponent.begin(),m_listOfComponent.end(),pChild);
    if (res != m_listOfComponent.end()) {
        m_listOfComponent.erase(res);
    }
}

Component* Composite::getChild(int index) {
    if (index < 0 || index >= m_listOfComponent.size()) {
        return nullptr;
    }
    auto begin = m_listOfComponent.begin();
    while (index--) {
        begin++;
    }
    return *begin;
}

void Composite::operation() {
    for (auto item : m_listOfComponent) {
        (item)->operation();
    }
}

int main() {
    Composite* composite = new Composite;
    composite->add(new Leaf);
    composite->add(new Leaf);
    //整体与部分具有使用一致性operation
    composite->operation();//整体
    //Leaf::operation
    //Leaf::operation
    composite->getChild(1)->operation();//个体
    //Leaf::operation
    //例如composite下面还有一个小整体
    Composite* compositeChild = new Composite;
    compositeChild->add(new Leaf);
    composite->add(new Leaf);
    composite->add(compositeChild);
    composite->operation();
    //Leaf::operation
    //Leaf::operation
    //Leaf::operation
    //Leaf::operation
    delete composite;
    return 0;
}