c++ - c++如何扩展组成类？

我最近遇到以下问题。我有一个具有Base_encapsulated_class的基类。

class Base_class
{
public:
    Base_class(int int_value, short short_value) :
      m_encapsulated_class(int_value, short_value)
    {};

    ~Base_class(void){};

    Base_encapsulated_class  m_encapsulated_class;
};

class Base_encapsulated_class
{
public:
    Base_encapsulated_class(int int_value, short short_value)
        : m_int(int_value),
        m_short(short_value)
    {};

    ~Base_encapsulated_class(void){};

private:
    int m_int;
    short m_short;
};

现在，我想扩展Base_class和Base_encapsulated_class来实现：

class Derived_class : public Base_class
{
public:
    Derived_class(int int_value, short short_value, bool boolean_value) :
      Base_class(int_value, short_value)
    {};

    ~Derived_class(void)
    {};

    Derived_encapsulated_class m_encapsulated_class;

};

class Derived_encapsulated_class : public Base_encapsulated_class
{
public:
    Derived_encapsulated_class(int int_value, short short_value, bool boolean_value) :
      Base_encapsulated_class(int_value, short_value),
          m_bool(boolean_value)
    {
    }

    ~Derived_encapsulated_class(void)
    {
    }

private:
    bool m_bool;
};

这种方法在派生类对象中为我提供了m_encapsulated_class的两个实例，这在c ++中显然是合法的（我感到有些惊讶）。

但这不是我想要的。我在派生类中需要一个m_encapsulated_class成员。那么可以在基类中扩展复合成员吗？

最佳答案

您可以使用虚拟getter强制成员继承：

class Base_class
{
public:
    Base_class(int int_value, short short_value) :
      m_encapsulated_class(int_value, short_value)
    {};

protected:
    virtual Base_encapsulated_class Get_encapsulated_class() /* = 0 if you want to enforce encapsulated derivation */
    {
       return m_encapsulated_class;
    }


private:
    Base_encapsulated_class  m_encapsulated_class;
};


class Derived_class : public Base_class
{
public:
    Derived_class(int int_value, short short_value, bool boolean_value) :
      Base_class(int_value, short_value)
    {};

    ~Derived_class(void)
    {};

protected:
    virtual Base_encapsulated_class Get_encapsulated_class()
    {
       return m_derived_encapsulated_class;
    }

private:

    Derived_encapsulated_class m_derived_encapsulated_class;

};