定义一个用于创建对象的接口，让子类决定实例化哪一个类。Factory Method 使得一个类的实例化延迟到子类
Facroty Method模式用于隔离类对象的使用者和具体类型之间的耦合关系。面对一个经常变化的具体类型，紧耦合关系会导致软件的脆弱。
Factory Method模式通过面向对象的手法，将所要创建的具体对象工作延迟到子类，从而实现一种扩展（而非更改）的策略，较好地解决了这种紧耦合关系。
Factory Method模式解决“单个对象”的需求变化。缺点在于要求创建方法/参数相同
#include <iostream>
using namespace std;
class Product{
public:
virtual void show() = 0;
};
class Product_A : public Product{
public:
void show(){
cout << "product A" << endl;
}
};
class Product_B : public Product{
public:
void show(){
cout << "product B" << endl;
}
};
class Factory{
public:
virtual Product * create_product() = 0;
};
class Factory_A : public Factory{
public:
Product * create_product(){
return new Product_A();
}
};
class Factory_B : public Factory{
public:
Product * create_product(){
return new Product_B();
}
};
class ShowProduct{
private:
Factory * m_factory;
public:
ShowProduct(Factory * factory = nullptr) : m_factory(factory){}
~ShowProduct(){
delete m_factory;
}
void set_factory(Factory * factory){ delete m_factory; m_factory = factory; }
void show(){
if(m_factory == nullptr){
return;
}
Product * product = m_factory->create_product();
product->show();
delete product;
}
};
int main(){
ShowProduct * show_product = new ShowProduct(new Factory_A);
show_product->show();
show_product->set_factory(new Factory_B);
show_product->show();
delete show_product;
return 0;
}
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