Is it possible to change a C++ object's class after instantiation?

Question

I have a bunch of classes which all inherit the same attributes from a common base class. The base class implements some virtual functions that work in general cases, whilst eac

Answer 1

I would consider regularizing your type.

class Base {
public:
  virtual void whoami() { std::cout << "Base\n"; }
  std::unique_ptr clone() const {
    return std::make_unique(*this);
  }
  virtual ~Base() {}
};
class Derived: public Base {
  virtual void whoami() overload {
    std::cout << "Derived\n";
  };
  std::unique_ptr clone() const override {
    return std::make_unique(*this);
  }
public:
  ~Derived() {}
};
struct Base_Value {
private:
  std::unique_ptr pImpl;
public:
  void whoami () {
    pImpl->whoami();
  }
  template
  void emplace( Args&&...args ) {
    pImpl = std::make_unique(std::forward(args)...);
  }
  Base_Value()=default;
  Base_Value(Base_Value&&)=default;
  Base_Value& operator=(Base_Value&&)=default;
  Base_Value(Base_Value const&o) {
    if (o.pImpl) pImpl = o.pImpl->clone();
  }
  Base_Value& operator=(Base_Value&& o) {
    auto tmp = std::move(o);
    swap( pImpl, tmp.pImpl );
    return *this;
  }
};

Now a Base_Value is semantically a value-type that behaves polymorphically.

Base_Value object;
object.emplace();
object.whoami();

object.emplace();
object.whoami();

You could wrap a Base_Value instance in a smart pointer, but I wouldn't bother.