[Python-Dev] Inline and SWIG (original) (raw)

David Beazley beazley@cs.uchicago.edu
Wed, 22 Aug 2001 21:16:02 -0500 (CDT)

It isn't as trivial as you think. It is essentially a superset of SWIG's Python-related functionality. Don't forget that an important part of it is trying to autodetect types. It quickly gets into figuring out structs and then classes and then templates and then madness ensues. Obviously you have to decide how much you are going to support and just require "compliant" wrappers for the rest. Using SWIG might allow you to offload a bunch of that effort for PyInline::C.

I've looked briefly at Inline and agree that it's a pretty nifty approach. However, usability aside, it's got a number of pretty major limitations once you start getting into structure wrapping, C++ classes, and other advanced types of extension wrapping. I think a common misconception about wrapper generation tools in general is that it's just a matter of hacking up a quick parser and throwing something together in a couple of days. The real problem IMHO is actually trying to figure out how to properly handle all of the facets of the C/C++ type system (pointers, references, qualifiers, classes, templates, typedef, inheritance, multiple inheritance, member pointers, pass by value, etc.) and how that's supposed to hook into Python. What's worse, if you get ANY part of the type system wrong, everything becomes a hellish nightmare later (and I can speak from personal experience on this :-).

We've been working on an upcoming major new SWIG release for quite some time now and about 80% of that work has been related to redesigning the internal type system. Maybe this sort of thing is obvious to everyone else and I'm missing some trivial point, but I sure haven't found the C++ type system to be this totally trivial thing I could just hack up in a few days and stick in a code generator!

In any case, I think the coolest thing about Inline is the ability to add small little bits of C code on-the-fly without having to restart the interpreter. That's a pretty neat trick that would probably be useful in the context of working with larger C extensions. I'm not sure I'd want to build a huge 400 function C extension module with that kind of approach, but something like that would definitely be useful for prototyping and adding code on the fly. I almost wonder if something like SWIG could be used behind the scenes to do code generation for something like that.

Cheers,

Dave