3.16 以字段取代子类

【1】原代码

class Person
{
public:
    virtual bool isMale() = 0;
    virtual char getCode() = 0;
};

class Male : public Person
{
public:
    bool isMale() { return true; }
    char getCode() { return 'M';  }
};

class FeMale : public Person
{
public:
    bool isMale() { return false; }
    char getCode() { return 'F'; }
};

【2】以字段取代子类

class Person
{
public:
    static Person* createMale()
    {
        return (new Person(true, 'M'));
    }
    static Person* createFeMale()
    {
        return (new Person(false, 'F'));
    }

    bool isMale() { return m_bMale;  }
    char getCode() { return m_sChar; }

protected:
    Person(bool bMale, char sChar)
        : m_bMale(bMale)
        , m_sChar(sChar)
    {}

private:
    bool m_bMale;
    char m_sChar;
};

【3】总结

各个子类的唯一差别只在”返回常量数据“的函数身上。修改这些函数，使它们返回超类中的某个（新增）字段，然后销毁子类。

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