C++模拟Java“内部”类

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代码思路来自Thinking in C++ 10.13.1内部类方法。类似多重继承，但是类型转换是单向的：Outer支持“向上”转型，但是不能“向下”转型回Outer。

#include <iostream>

#include <string>

using namespace std;

class Interface1

{

public:

  virtual void function1() = ;

};

void CallInterface1(Interface1& if1)

{

  if1.function1();

}

class Interface2

{

public:

  virtual void function2() = ;

};

void CallInterface2(Interface2& if2)

{

  if2.function2();

}

// Multiple Inheritance

class Derived : public Interface1,

                public Interface2

{

public:

  Derived(const string& nm) : name(nm) {}

  virtual void function1()

  {

    cout << "Call " << name << "'s " << __func__ << endl;

  }

  virtual void function2()

  {

    cout << "Call " << name << "'s " << __func__ << endl;

  }

private:

  string name;

};

// Mock Inner Class

class Outer {

public:

  Outer(const string& nm) : name(nm), inner1(this), inner2(this) {}

  operator Interface1&() {return inner1;}

  operator Interface2&() {return inner2;}

private:

  string name;

  class Inner1;

  friend class Outer::Inner1;

  class Inner1 : public Interface1

  {

  public:

    Inner1(Outer* p) : parent(p) {}

    virtual void function1()

    {

      cout << "Call " << parent->name << "'s function1" << endl;

    }

  private:

    Outer* parent;

  } inner1;

  class Inner2;

  friend class Outer::Inner2;

  class Inner2 : public Interface2

  {

  public:

    Inner2(Outer* p) : parent(p) {}

    virtual void function2()

    {

      cout << "Call " << parent->name << "'s function2" << endl;

    }

  private:

    Outer* parent;

  } inner2;

};

int main() {

  Derived d("Derived Class");

  CallInterface1(d);

  CallInterface2(d);

  Outer o("Outer Class");

  CallInterface1(o);

  CallInterface2(o);

  return ;

}