// https://www.youtube.com/watch?v=nLSm3Haxz0I 

class MyWidget 
{
  void tinker_with(int amount);
public:
  class Tinkerable;
  
  Tinkerable get_tinkerable(){
    return Tinkerable(*this);
  }
};

class MyWidget::Tinkerable
{
  MyWidget& widget_;
  std::scoped_lock<std::mutex> lock_;
  friend MyWidget;
  
  explicit Tinkerable(MyWidget& widget)
    : widget_(widget), lock_(widget_.mutex_) {}

public:
  void tinker_with(int amount){
    widget_.thinker_with(amount);
  }
};

void tinker(MyWidget& widget)
{
  auto tinkerable = widget.get_tinkerable();
  tinkerable.tinker_with(123);
  tinkerable.tinker_with(456);
}