[PROJ] What's the difference between PJ and PJ_OBJ?

[Kristian Evers]

I guess this is mostly for Even but of course anyone is welcome to join the discussion.

I am slowly working my way through the new additions to the C API and the C++ code
that is backing it and once in a while a question pops up. This time regarding the
PJ_OBJ struct. Basically I am struggling to understand how it differs from the PJ struct?
From a user viewpoint that is. I get that it is probably simpler to keep the C++ parts
separated from the C parts as much as possible but is that the only reason why they
are two different datatypes? I’ve noticed that PJ_CONTEXT has got a pointer to an
optional C++ struct (projCppContext), why was this approach not chosen for
PJ/PC_CONTEXT?

/Kristian