【设计模式】2.策略模式

UML

code

#pragma once

#define DISCOUNT 0.5
class CashBase
{
public:
	virtual double getCash(double price, int num) = 0;
};

class CashNormal : public CashBase
{
public:
	double getCash(double price, int num) override
	{	
		return price * num;
	}
private:
};

class CashDiscount : public CashBase
{
public:
	CashDiscount(double discount)
	{
		this->discount = discount;
	}
	double getCash(double price, int num) override
	{
		return price * num * this->discount;
	}
private:
	double discount;
};

class CashReturn : public CashBase
{
public:
	CashReturn(double moneyCondition, double moneyReturn)
	{
		this->moneyCondition = moneyCondition;
		this->moneyReturn = moneyReturn;
	}
	double getCash(double price, int num) override
	{
		double res = price * num;
		if (moneyCondition > 0 && res >= moneyCondition)
		{
			res -= moneyReturn * (res / moneyCondition);
		}
		return res;
	}
private:
	double moneyCondition;
	double moneyReturn;
};

enum class CashType
{
	Normal,
	Discount,
	Return
};

// 策略类：包含一个基类的指针，构造函数中做策略的选择，选择合适的对象赋值给基类指针，然后提供一个上层调用接口，去调用子类的重写函数
// 工厂类：提供一个全局的接口，根据传入的参数，返回最终的对象实例
class CashContext
{
public:
	~CashContext() = default;
	// 通过构造函数，传入具体的收费策略
	CashContext(CashType type) : cashbase(nullptr)
	{
		switch (type)
		{
		case CashType::Normal:
			this->cashbase = new CashNormal();
			break;
		case CashType::Discount:
			this->cashbase = new CashDiscount(DISCOUNT);
			break;
		case CashType::Return:
			this->cashbase = new CashReturn(500, 100);
			break;
		default:
			break;
		}
	}
	double getCash(double price, int num)
	{
		return this->cashbase->getCash(price, num);
	}
private:
	CashBase* cashbase;
};```