#include <iostream>
 
// source1.h
class A {
public:
    class B;
 
public:
    explicit A(B &);
 
    void use_b();
 
private:
    B & b;
};
 
// source2.h
class A::B {
public:
    B();
    void do_something();
};
 
// source3.cpp
 
A::A(B & pB) : b(pB) { }
 
void A::use_b()
{
    b.do_something();
}
 
// source4.cpp
 
A::B::B() { }
 
void A::B::do_something()
{
    std::cout << "Did something." << std::endl;
}
 
// main
 
int main()
{
    A::B b;
    A a(b);
 
    a.use_b();
}
 

I2luY2x1ZGUgPGlvc3RyZWFtPgoKLy8gc291cmNlMS5oCmNsYXNzIEEgewpwdWJsaWM6CiAgICBjbGFzcyBCOwoKcHVibGljOgogICAgZXhwbGljaXQgQShCICYpOwoKICAgIHZvaWQgdXNlX2IoKTsKCnByaXZhdGU6CiAgICBCICYgYjsKfTsKCi8vIHNvdXJjZTIuaApjbGFzcyBBOjpCIHsKcHVibGljOgogICAgQigpOwogICAgdm9pZCBkb19zb21ldGhpbmcoKTsKfTsKCi8vIHNvdXJjZTMuY3BwCgpBOjpBKEIgJiBwQikgOiBiKHBCKSB7IH0KCnZvaWQgQTo6dXNlX2IoKQp7CiAgICBiLmRvX3NvbWV0aGluZygpOwp9CgovLyBzb3VyY2U0LmNwcAoKQTo6Qjo6QigpIHsgfQoKdm9pZCBBOjpCOjpkb19zb21ldGhpbmcoKQp7CiAgICBzdGQ6OmNvdXQgPDwgIkRpZCBzb21ldGhpbmcuIiA8PCBzdGQ6OmVuZGw7Cn0KCi8vIG1haW4KCmludCBtYWluKCkKewogICAgQTo6QiBiOwogICAgQSBhKGIpOwoKICAgIGEudXNlX2IoKTsKfQo=