[toml::date] Make use of custom type caster support from pybind11

chaitan94 commented 4 years ago

pybind11 has support for custom type casters. Check this for example on how to use: https://github.com/pybind/pybind11/blob/master/include/pybind11/chrono.h#L98

This PR, while it can be used directly in the current state, is more like a proof of concept for making use of this support. I implemented this only for casting toml::date objects - from/to python. @bobfang1992, @EpicWink If you guys like this approach, maybe we can start using it for other types as well. Let me know your thoughts.

Why this approach?

Although right now it's not apparent, once this approach is used for other types, the code in pytomlpp.hpp will become much simpler, as we can just have generic logic there using C++ templates.
Better organization of code IMO - for any given type the load (C++ to Python) and cast (Python to C++) functions will always be found together.
This would make it more idiomatic pybind11 code as we can make use of its native features without adding unnecessary complications or reinventing anything.

bobfang1992 commented 4 years ago

Hi, this is great. Do you plan to apply this to time and datetime etc in the same PR or that will be separate PRs? Thanks!

chaitan94 commented 4 years ago

I think let's have separate PRs for each so as to not make this a big change. That way we can have incremental changes. I will send in two other PRs one for time and one for datetime.

bobfang1992 commented 4 years ago

LGTM. I will merge it now if that's okay with you @chaitan94

chaitan94 commented 4 years ago

Sure, go ahead.

bobfang1992 / pytomlpp

[toml::date] Make use of custom type caster support from pybind11 #26

Why this approach?