创建型模式 抽象工厂

/**
 * 创建型模式 抽象工厂
 * 抽象工厂模式是所有形态的工厂模式中最为抽象和最其一般性的。抽象工厂模式可以向客户端提供一个接口，使得客户端在不必指定产品的具体类型的情况下，能够创建多个产品族的产品对象。
 *
 * 抽象工厂（Creator）角色
 * 抽象工厂模式的核心，包含对多个产品结构的声明，任何工厂类都必须实现这个接口。
 * 具体工厂（ Concrete  Creator）角色
 * 具体工厂类是抽象工厂的一个实现，负责实例化某个产品族中的产品对象。
 * 抽象（Product）角色
 * 抽象模式所创建的所有对象的父类，它负责描述所有实例所共有的公共接口。
 * 具体产品（Concrete Product）角色
 * 抽象模式所创建的具体实例对象
 *
 */

#include <iostream>

class Fruit
{
public:
    virtual void sayname()
    {
        std::cout << "I‘am fruit" << std::endl;
    }
};

class FruitFactory
{
public:
    virtual Fruit * CreateBanana()
    {
        return new Fruit();
    }
    virtual Fruit * CreatePear()
    {
        return new Fruit();
    }
};

class SouthBanana: public Fruit
{
public:
    virtual void sayname() override
    {
        std::cout << "South Banana" << std::endl;
    }
};

class NorthBanana: public Fruit
{
public:
    virtual void sayname() override
    {
        std::cout << "North Banana" << std::endl;
    }
};

class SouthPear: public Fruit
{
public:
    virtual void sayname() override
    {
        std::cout << "South Pear" << std::endl;
    }
};

class NorthPear: public Fruit
{
public:
    virtual void sayname() override
    {
        std::cout << "North Pear" << std::endl;
    }
};

// 在C++中，只要原来的返回类型是指向类的指针或引用，新的返回类型是指向派生类的指针或引用，覆盖的方法就可以改变返回类型。这样的类型称为协变返回类型（Covariant returns type).
class SouthFactory: public FruitFactory
{
public:
    virtual SouthBanana * CreateBanana() override
    {
        return new SouthBanana();
    }
    virtual SouthPear * CreatePear() override
    {
        return new SouthPear();
    }
};

// 在C++中，只要原来的返回类型是指向类的指针或引用，新的返回类型是指向派生类的指针或引用，覆盖的方法就可以改变返回类型。这样的类型称为协变返回类型（Covariant returns type).
class NorthFactory: public FruitFactory
{
public:
    virtual NorthBanana * CreateBanana() override
    {
        return new NorthBanana();
    }
    virtual NorthPear * CreatePear() override
    {
        return new NorthPear();
    }
};

void mytest()
{
    FruitFactory * factory = nullptr;
    Fruit * fruit = nullptr;

    factory = new SouthFactory();
    fruit = factory->CreateBanana();
    fruit->sayname();
    delete fruit;
    fruit = nullptr;
    fruit = factory->CreatePear();
    fruit->sayname();
    delete fruit;
    fruit = nullptr;
    delete factory;
    factory = nullptr;

    factory = new NorthFactory();
    fruit = factory->CreateBanana();
    fruit->sayname();
    delete fruit;
    fruit = nullptr;
    fruit = factory->CreatePear();
    fruit->sayname();
    delete fruit;
    fruit = nullptr;
    delete factory;
    factory = nullptr;

    return;
}

int main()
{
    mytest();

    system("pause");
    return 0;
}