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 ;
}
使用聚合代替继承，时间空间的折衷。