Re: [Swig-user] traits-based access to swig_type_info

[Stefan Z. <sz...@gm...>]

Jim,

Could you provide a concrete example of where you would use this?
>From time to time, I have wished for a function like this, only to
realize that I could get the functionality I needed using the existing
features.

(As an aside, the one case where the existing functionality came up
short was trying to interface two libraries: one had a custom python
wrapper implementation, and I was using SWIG to wrap the other).

Thanks,

Stefan


On Thu, Jan 5, 2012 at 10:54 AM, Jim Bosch <tal...@gm...> wrote:
> I'm trying to wrap a heavily-templated C++ library for Python, and I
> need to use SWIG_NewPointerObj within a template, and that means I need
> a swig_type_info to pass to it.
>
> It seems like the only way to do this is to use preprocessor macros
> instead of templates, stringify the C++ name, and call SWIG_TypeQuery.
>  From reading the comments in the generated code, it looks like that's
> going to do a O(n) search (with a lot of string comparisons) of all the
> types in the module, after first wasting time by assuming that the name
> is mangled.
>
> It'd be so much nicer to be able to do something like:
>
> template <typename T>
> PyObject * convertToPython(T * x) {
>     return SWIG_NewPointerObj(
>         x,
>         SwigTraits<T*>::info(),   // something I'm imagining
>         SWIG_POINTER_OWN
>     );
> }
>
> Note that this would then be used as a utility function in writing
> %extend blocks, not wrapped directly; I'm not concerned with trying to
> declare this to SWIG with %template.
>
> Is something like this already available, and I just didn't find it in
> the docs?  If not, it seems like it'd be pretty easy to implement, by
> having SWIG generate a specialization of SwigTraits<> every time it
> generates a "#define SWIGTYPE_p_Foo" line in the types table, something
> like:
>
> template <typename T> struct SwigTraits;
>
> #define SWIGTYPE_p_Foo swig_types[N];
> template <> struct SwigTraits< Foo * > {
>     swig_type_info* info() { return SWIGTYPE_p_Foo; }
> };
>
> If something like this doesn't already exist, could it be added to SWIG
> in the future?
>
> Thanks!
>
> Jim Bosch
>
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