Idea: Make Handle_* classes completely transparent

[rainman110]

Using the GetHandle(), GetObject() functions is awkward from a python perspective.

Users should not know the details of reference counted objects, when dealing with pythonocc.

Swig offers typemaps for std::shared_ptr, which wraps them completely transparent. The same can be done for Handle_ classes as well.

Since there is already much code out there, that uses the GetHandle() GetObject() syntax, we don't want to break this code. Therefore, both functions can be added, returning just a self reference and doing no harm.

I created a proof of concept, which shows that this in pricipally possible:
https://github.com/rainman110/swighandles

The file https://github.com/rainman110/swighandles/blob/master/standard.i shows, how easy it would be to wrap the handle classes. The dark magic obviously happens at https://github.com/rainman110/swighandles/blob/master/occ_handle1.i.

Much of the code and ideas are actually borrowed from std_shared_ptr.i from swig!

@jf--- @tpaviot What do you think about this idea?

[jf---]

What do you think about this idea?

That would be a huge deal, in terms of elegance of API, which seems obvious.
But out of my depth to comment on the technical aspects / maintainability.
A thrilling perspective @rainman110 !

[rainman110]

Hi together. I have a first semi-working code. Most of the examples already work.

What currently does not work are the following issues:

• There are no Handle_ classes anymore. This means, that all checks is_instance(obj, Handle_Geom_Curve) do not work. They now have to be is_instance(obj, Geom_Curve). A workaround would be, to simply make an alias from e.g. Handle_Geom_Curve to Geom_Curve in Python.
• I had to disable all Classes that derive from Standard_Transient in the end but which don't have a Handle class defined. Either, we simply create a Handle class for them, or, we find another workaround. This is mostly the case for the AIS package. E.g. AIS_Textured_Shape does not have a handle right now.
• There are yet no downcast methods since I completely removed the Handle_* classes from the interface files. It is principally simple to re-add them though.

[rainman110]

@jf--- Okay... Now I managed to solve all the problems! 😄

All examples are now working, meaning I achieved full backwards compatibilty.

Compared to the old code, one can now implement much more pythonic code like:

• Before, we had to check Handles using the "IsNull()" method.
• Now, you can simply check "is None"
• You don't need any Handle_* classes any more
• You don't need GetObject(), GetHandle() methods anymore

I would create some conda packages, such that you can test it with your code. My adaptions are currently based on pythonocc-core 0.17.2 though.