简单工厂模式

1. 案例：营业员根据客户所购买商品的单价和数量，根据不同活动向客户收费

- 正常原价收费
- 八折收费
- 满300返100

2. 简单工厂模式结构

- 抽象产品(Abstract Product)：具体产品类的基类，包含创建产品的公共方法

enum CashType
{
    NORMAL = 0,
    REBATE,
    RETURN
};

class CashSuper
{
public:
    virtual double AcceptCash(double dMoney) = 0;
};

- 具体产品(Concrete Product)：抽象产品的派生类，包含具体产品特有的实现方法，是简单工厂模式的创建目标

class CashNormal :
    public CashSuper
{
public:
    // 通过 CashSuper 继承
    double AcceptCash(double dMoney) override;
};

double CashNormal::AcceptCash(double dMoney)
{
    return dMoney;
}

class CashRebate :
    public CashSuper
{
public:
    CashRebate(double dMoneyRebate);
    // 通过 CashSuper 继承
    double AcceptCash(double dMoney) override;
private:
    double m_dMoneyRebate;
};

CashRebate::CashRebate(double dMoneyRebate):
    m_dMoneyRebate(dMoneyRebate)
{
}

double CashRebate::AcceptCash(double dMoney)
{
    return dMoney * m_dMoneyRebate;
}

class CashReturn :
    public CashSuper
{
public:
    CashReturn(double dMoneyCondition, double dMoneyReturn);
    // 通过 CashSuper 继承
    double AcceptCash(double dMoney) override;
private:
    double m_dMoneyCondition;
    double m_dMoneyReturn;
};

CashReturn::CashReturn(double dMoneyCondition, double dMoneyReturn):
    m_dMoneyCondition(dMoneyCondition), m_dMoneyReturn(dMoneyReturn)
{
}

double CashReturn::AcceptCash(double dMoney)
{
    if (fabs(m_dMoneyCondition) < 1e-6)
        return dMoney;
    return dMoney - floor(dMoney / m_dMoneyCondition) * m_dMoneyReturn;
}

- 工厂(Factory)：根据客户提供的具体产品类的参数，创建具体产品实例

class CashFactory
{
public:
    static std::shared_ptr<CashSuper> CreatCashOperation(CashType eCashType);
};

std::shared_ptr<CashSuper> CashFactory::CreatCashOperation(CashType eCashType)
{
    switch (eCashType)
    {
    case NORMAL:
        return std::make_shared<CashNormal>();
        break;
    case REBATE:
        return std::make_shared<CashRebate>(0.8);
        break;
    case RETURN:
        return std::make_shared<CashReturn>(300.0, 100.0);
        break;
    default:
        return std::make_shared<CashNormal>();
        break;
    }
}