public/private API class trick

api.cc

namespace blink {

class RealClass : public RealBase {
 public:
  static RealClass* Create();
  void DoSomething();
 private:
  // members here
};

namespace agent {

class AgentClass : public AgentBase {
 public:
  AgentClass* Create();
  void DoSomething();
  
  // no data members; not a real class
};

AgentClass* AgentClass::Create() {
  ScriptWrappable* self = RealClass::Create();
  return reinterpret_cast<AgentClass*>(self);
}

void AgentClass::DoSomething() {
  RealClass* self = static_cast<RealClass*>(reinterpret_cast<ScriptWrappable*>(this));
  self->DoSomething();
}

}  // namespace agent

}  // namespace blink