《重构：改善既有代码的设计》 重新组织数据 之 4

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《重构：改善既有代码的设计》中提到过很多重构方法，关于重新组织数据的方法有8种。本文介绍：
将引用对象改为值对象 change reference to value

• 名称：将引用对象改为值对象 change reference to value
• 概要：有一个引用对象，很小且不可变，而且不易管理。将它变成一个值对象
• 动机： 无论何时，只要调用同一对象的同一个查询函数，都应该得到同样的结果。

• 做法：
  • 检查重构目标是否为不可变对象，或是否可修改为不可变对象。如果该对象目前还不是不可变的，就使用remove setting method,直到它成为不可变的为止
  • 将调用Map修改为直接调用构造函数（c++中没有java的实现方法，所以修改成此）
  • 编译，测试
  • 考虑是否可以删除工厂函数，并将构造函数声明为public
• 代码演示

修改之前的代码：

///////////////////////////.h
#ifndef REFACTORDATA_H
#define REFACTORDATA_H
#include <QMap>
class Customer
{
public:
    QString getName() const;
    static Customer* GetNamedCustomer(QString name);
    static void LoadCustomers();
private:
    Customer(QString name);
private:
    QString m_name;
    static QMap<QString, Customer*> m_Instance;
};

class Order
{
public:
    Order(QString customer);
    QString getCustomerName() const;
    void setCustomer(const QString &customer);

private:
    Customer *m_pcustomer;

};
#endif // REFACTORDATA_H

///////////////////////////.cpp

Order::Order(QString customerName)
{
    m_pcustomer = Customer::GetNamedCustomer(customerName);
}

QString Order::getCustomerName() const
{
    return m_pcustomer->getName();
}

void Order::setCustomer(const QString &customerName)
{
    m_pcustomer = Customer::GetNamedCustomer(customerName);
}

QMap<QString, Customer*>  Customer::m_Instance;

Customer::Customer(QString name)
{
    m_name = name;
}

QString Customer::getName() const
{
    return m_name;
}

Customer* Customer::GetNamedCustomer(QString name)
{
    return m_Instance[name];
}

void Customer::LoadCustomers()
{
    m_Instance["Test1"] = new Customer("Test1");
    m_Instance["Test2"] = new Customer("Test2");
    m_Instance["Test3"] = new Customer("Test3");
}

修改之后的代码：

///////////////////////////.h
#ifndef REFACTORDATA_H
#define REFACTORDATA_H
class Customer
{
public:
    Customer(QString name);
    QString getName() const;

private:
    QString m_name;
};

class Order
{
public:
    Order(QString customer);
    QString getCustomerName() const;
    void setCustomer(const QString &customer);

private:
    Customer *m_pcustomer;
};
#endif // REFACTORDATA_H
///////////////////////////.cpp
Order::Order(QString customerName)
{
    m_pcustomer = new Customer(customerName);
}

QString Order::getCustomerName() const
{
    return m_pcustomer->getName();
}

void Order::setCustomer(const QString &customerName)
{
    m_pcustomer = new Customer(customerName);
}

Customer::Customer(QString name)
{
    m_name = name;
}

QString Customer::getName() const
{
    return m_name;
}


///////////////////////////main.cpp
int numberOfOrdersFor(vector<Order *> orders, QString customerName)
{
    int result = 0;
    for (auto iter = orders.begin(); iter != orders.end(); iter++)
    {
        if (!(*iter)->getCustomerName().compare(customerName))
        {
            result++;
        }
    }
    return  result;
}


    vector<Order *> orders;
    int order1number = 0;
    orders.push_back(new Order("Order1"));
    orders.push_back(new Order("Order2"));
    orders.push_back(new Order("Order3"));
    order1number = numberOfOrdersFor(orders, "Order1");
    qDebug() << "order1 number = " << order1number;