How To Make a clone method using shared_ptr and inheriting from enable_shared_from_this

Question

I have seen that a useful way to write a clone method that returns a boost::shared_ptr is to do

class A
{
public:
  shared_ptr Clone() const
  {
    ret         


        

Answer 1

Since you are already implementing the public interface covariance yourself via the non-virtual Clone() functions, you may consider abandoning the covariance for the CloneImpl() functions.

If you only need shared_ptr and never the raw pointer, so you could then do:

class X
{
public:
  shared_ptr Clone() const
  {
    return CloneImpl();
  }
private:
  virtual shared_ptr CloneImpl() const
  {
    return(shared_ptr(new X(*this)));
  }
};

class Y : public X
{
public:
  shared_ptr Clone() const
  {
    return(static_pointer_cast(CloneImpl())); // no need for dynamic_pointer_cast
  }
private:
  virtual shared_ptr CloneImpl() const
  {
    return shared_ptr(new Y(*this));
  }
};

CloneImpl() would always return a shared_ptr and now you could register your object inside the B::CloneImpl() function and return the registerd shared_ptr.