C++: Example of intentional member function hiding

intentional-hiding.cpp

#include <string>
#include <iostream>

#pragma GCC diagnostic warning "-Woverloaded-virtual"

struct Visitor
{
  virtual void visit(int val) const =0;
  virtual void visit(std::string const &val) const =0;
};

template<class Derived>
struct GenericVisitor : Visitor
{
  virtual void visit(int val) const override
  {
    self().visit(val);
  }
  
  virtual void visit(std::string const &val) const override
  {
    self().visit(val);
  }

private:
  Derived const &self() const
  {
    return static_cast<Derived const&>(*this);
  }
};

template<class Overloads>
struct OverloadVisitor : GenericVisitor<OverloadVisitor<Overloads>>, Overloads
{
  explicit OverloadVisitor(Overloads overloads)
    : GenericVisitor<OverloadVisitor>(), Overloads(std::move(overloads))
  {
  }
  
  template<class T>
  void visit(T&& val) const
  {
    this->operator()(std::forward<T>(val));
  }

// Adding the following (which is suggested in the GCC manual) to silence
// the warning does not work, both with 'private:' and without it.
// With 'private:' the compiler complains about inaccessible members,
// and without 'private:' the code compiles but crashes due to infinite
// recursion.
//private:
//  using GenericVisitor<OverloadVisitor<Overloads>>::visit;
};

void acceptVisitor(const Visitor &visitor)
{
  visitor.visit(42);
  visitor.visit("This was the answer.");
}

int main()
{
  std::cout << "Hello cruel world!" << std::endl;

  OverloadVisitor visitor([](auto &&val) {
    std::cout << "Logging: " << val << std::endl;
  });
  acceptVisitor(visitor);
}