class A {
 public:
  class B {public: bool value;};
 
  A() {}
  B b_;
  void DoStuff(B& b);
 private:
  virtual void DoStuffImpl(B& b) = 0;
};
 
class X : public A {
 public:
  X() {}
  void Trigger();
 private:
  virtual void DoStuffImpl(B& b);
};
 
void A::DoStuff(B& b) {
     DoStuffImpl(b);
}
 
void X::Trigger() {
    DoStuff(b_);
}
void X::DoStuffImpl(B& b) {
    b.value = true;
}
 
int main(){
    X x;
    x.Trigger();
    return x.b_.value;
}

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