To customize or not smart pointers?

[andre-caldas]

In my C++ code, I do use std::shared_ptr a lot. But not directly... I have created a custom SharedPtr class.

My SharedPtr is a "convenience subclass". It simply privately inherits from std::shared_ptr. It does not add any new member variables. It re-implements some methods, like operator *, in order to check for invalid pointers and throwing if needed. So, SharedPtr can be safely sliced to a shared_ptr, and it can also be constructed from one.

My methods return and accept SharedPtr all over. But there is a catch! I have disabled the ability to instantiate it from a raw pointer. I would like to keep it just like that, if possible. However, pybind does demand that a HOLDER_TYPE must take a raw pointer on construction.

For that reason,

PYBIND11_DECLARE_HOLDER_TYPE(T, SharedPtr<T>);

gives a compiler error that complains about SharedPtr<T> not having a constructor that takes a T*.

So, my question is:

Is there a nice "pybindonic" way to have the regular std::shared_ptr as my HOLDER_TYPE and at the same time, have my C++ functions taking and returning SharedPtr?

[andre-caldas]

I found out that probably the simplest solution is to:

1. Implement a private constructor that takes a pointer.
2. Make template<...> class pybind11::class_ a friend class.

private:
  SharedPtr(T* ptr) : std::shared_ptr<T>(ptr) {}
  template <typename type_, typename... options>
  friend class pybind11::class_;