设计模式2：策略模式工厂

减少算法类与使用算法类之间的耦合；简化了单元测试，因为每个算法都有自己的类，可以单独测试

Operation.h:

#pragma once

#include<iostream>
#include<string>

using namespace std;

class Operation
{
 public:
    virtual double GetResult(){return 0};
public:
    double numA_;
    double numB_;
};

class OperationAdd :public Operation
{
public:
    virtual double GetResult()
    {
        return numA_+numB_;
    }
}

class OperationSub: public Operation
{
public:
    virtual double GetResult()
    {
        return numA_ - numB_;
    }
};

class OperationFactory    //简单模式工厂
{
public:
    Operation* CreateOperation(tstring oper)
    {
        Operation*op = NULL;
        if(wcscmp(oper.c_str(),L"+") == 0)
            op = new OperationAdd();
        else
            op = new OperationSub();
        return op;
    }
};

class OperationFactoryS //策略模式工厂
{
public:
    OperationFactionS(wstring oper)
    {
        if(wcscmp(oper.c_str(),L"+") == 0)
            op = new OperationAdd();
        else
            op = new OperationSub();
    }
    
    void SetNumA(double num){ op->numA_ = num; }    
    void SetNumB(double num){ op->numB_ = num; }  
    double GetResult() { return op->GetResult(); } 

private:
    Operation *op;
}

main.cpp

#define _CRTDBG_MAP_ALLOC
#include<stdlib.h>
#include<crtdbg.h>
#include"Operation.h"

int main()
{
    //需要知道所有方法类
    OperationAdd opAdd;
    opAdd.numA_ = 20;
    opAdd.NumB_ = 30;
     cout << op->GetResult() << "
";

    //需要知道工厂类和所有方法类的基类，不需要知道具体的方法类
    OperationFactory fac;
    Operation* op = fac.CreateOperation(L"+");
    op->numA_ = 20;
    op->numB_ = 30;
    cout << "简单工厂：" << op->GetResult() << "
";

    //只需要知道工厂类
    OperationFactoryS *opFacs = new OperationFactoryS(L"+");
    opFacs->SetNumA(20);
    opFacs->SetNumB(30);
    cout << "策略模式工厂：" << opFacs->GetResult() << "
";
    delete op;
    
    _CrtDumpMemoryLeaks();
    system("pause");
    return 0;
}