How to directly invoke datetime type caster?

[WillAyd]

I am working on a project where I read values into a vector of objects. I have a class structure that looks something like:

class ReadHelper {
public:
  ReadHelper() {}
  virtual ~ReadHelper() {}
  virtual nb::object Read(const hyperapi::Value &value) { return nb::none(); }
};

class IntegralReadHelper : public ReadHelper {
  nb::object Read(const hyperapi::Value &value) {
    if (value.isNull()) {
      return nb::none();
    }
    return nb::int_(value.get<int64_t>());
  }
};

class FloatReadHelper : public ReadHelper {
  nb::object Read(const hyperapi::Value &value) {
    if (value.isNull()) {
      return nb::none();
    }
    return nb::float_(value.get<double>());
  }
};

I am struggling to figure out how to extend this to datetime objects. I see #175 added a built in caster but I don't see how to use that outside of the Python<>C++ bridge. I also noticed nb_types.h has no class for datetime following the idioms used in the code above. Any ideas on how to approach this?

[wjakob]

You would use the types from <chrono> on the C++ side and then let the type caster convert them into their Python analogs at the C++<->Python transition. There currently isn't a wrapper class for datetime objects, you are welcome to propose one in a PR.

Did you see this part of the documentation? -> https://nanobind.readthedocs.io/en/latest/api_extra.html#timestamp-and-duration-conversions

[WillAyd]

I think your response confirms what I need. With the above design I would want the conversion to object to happen before the C++<->Python transition. I'll see what I can do to create that wrapper class in a PR.

Thanks for the quick response and this great library!