C++抽象类继承虚函数

Question

我有一个抽象基类，其中包含一些属性或成员元素以及一些公共(public)函数和一个公共(public)纯虚函数。在抽象类的派生类中，我想 (a) 将抽象基类的成员作为私有(private)成员访问，以及 (b) 公共(public)函数和定义的纯虚函数保持公共(public)状态。有办法吗？也就是说，AbstractBase 的 xxxx 和 derived 中的 yyyy 访问说明符应该是什么来实现这一点？

#include <iostream>

class AbstractBase {
 xxxx: <-- // protected/private/public?
  std::string baseprivate1;

 public:
  virtual void set_privates() = 0;
  void print() { std::cout << baseprivate1 << std::endl; }
  void foo() { // some definition here }
};

class Derived : yyyy AbstractBase {  <--- //public/protected/private? 
 private:
  std::string derivedprivate1;

 public:
  void set_privates() {
    // I want this baseprivate1 to be private in derived class as well.
    // When I choose xxxx as protected and yyyy as public, the baseprivate1 is protected. 
    this->baseprivate1 = "Base private1";
    this->derivedprivate1 = "Derived private1";
  }
  void print() {
    AbstractBase::print();
    std::cout << this->derivedprivate1;
  }
  // When I choose xxxx as protected and yyyy as protected
  // foo becomes protected and unable to call from outside
  // I want the foo of abstract base to be public here as well. 
};

int main(int argc, char *argv[]){
    Derived d;
    d.set_privates();
    d.print();
    d.foo(); // I should be able to call foo of abstract base class
}

它可能与 Difference between private, public, and protected inheritance 的拷贝混淆.如果您将 xxxx 保持为 protected 状态并将 yyyy 保持为公开状态，则 baseprivate1 将在 Derived 中受到保护并且不再是私有(private)的。或者，如果 xxxx 是公共(public)的/ protected 并且 yyyy 是私有(private)的，则 derived 中的函数变为私有(private)。

Answer 1

完成所需内容的一种方法是在派生类上使用 AbstractBase 的私有(private)继承。然后，您可以在 Derived 类的公共(public)访问说明符下使用 using 声明公开一些 AbstractBase 的方法。

#include <iostream>

class AbstractBase {
    public:
        std::string baseprivate1;

        virtual void set_privates() = 0;
        void print() { std::cout << baseprivate1 << std::endl; }
        void foo() { /* some definition here */ }
};

class Derived : private AbstractBase { // use private inheritance on AbstractBase
    private:
        std::string derivedprivate1;

    public:
        // expose AbstractBase's methods with using-declarations
        using AbstractBase::foo;
        using AbstractBase::print;

        void set_privates() {
            this->baseprivate1 = "Base private1";
            this->derivedprivate1 = "Derived private1";
        }

        void print() {
            AbstractBase::print();
            std::cout << this->derivedprivate1 << std::endl;;
        }
};

int main(int argc, char *argv[]){
    Derived d;
    d.set_privates();
    d.print();
    d.foo();
    return 0;
}