[vtk-developers] Nested structs and python wrapping

[David Gobbi]

Hi David,

I've identified the bug in the wrappers.  They are trying to wrap the
out-of-line
definition of vtkTextRenderer::Metrics as a class named
"vtkRenderer::Metrics"
in the global namespace (almost as if the "::" was actually part of the
identifier).
This is something that I'll fix as soon as I have time to do so (probably
not today).

If you put the definition of "Metrics" inline, i.e. within vtkTextRender,
then the
wrappers will have no problem.  They will automatically exclude Metrics, and
any methods that use it, from wrapping.

 - David

On Wed, Jan 14, 2015 at 9:00 AM, David Gobbi <david.gobbi at gmail.com> wrote:

> Hi David,
>
> This suggests a bug in the wrappers, because the wrappers should be
> excluding
> these methods automatically. The use of "#ifndef __WRAP__" should be
> avoided,
> if there is an option to instead fix the wrappers themselves. I'll take a
> look at the
> code sometime today in the hope that there is a simple fix.
>
> The wrappers cannot wrap nested classes or structs yet, because they use a
> flat
> global namespace for object types.  I did a bunch of work to fix this
> three years ago,
> but never finished because the "flat namespace" assumption worked well for
> VTK.
> I've always wanted an excuse to go back and finish this code.
>
>  - David
>
>
> On Wed, Jan 14, 2015 at 8:24 AM, David Lonie <david.lonie at kitware.com>
> wrote:
>
>> Hi folks,
>>
>> I'm looking for some advice on getting a patch to play nicely with the
>> wrappers.
>>
>> I have a vtkObject derived class that contains a nested struct:
>>
>> class EXPORT_MACRO vtkTextRenderer : public vtkObject
>> {
>> public:
>>   struct Metrics;
>>
>>   ...
>>
>>   bool GetMetrics(..., Metrics &);
>> }
>>
>> struct vtkTextRenderer::Metrics
>> {
>>   ...
>> }
>>
>> It looks like the python wrappers aren't happy about this, see:
>>
>> https://open.cdash.org/viewBuildError.php?buildid=3651284
>>
>> Ben pointed out that I can use the __WRAP__ define to exclude these, but
>> I'm interested in hearing more options. I see a couple of paths forward:
>>
>> 1) Exclude all usages of Metrics with __WRAP__
>>
>> Cons: Functionality can't be used from wrapped languages. Maintenance
>> would be a chore, as the Metrics struct is used in a number of text
>> rendering related headers.
>>
>> 2) Change Metrics to a stand-alone vtkObject derived class.
>>
>> Cons: It's a really lightweight object, I'd like to avoid having the
>> overhead of vtkObject enter into this.
>>
>> 3) Special wrapping for the metrics class.
>>
>> Cons: Work. Also, maintenance would be a headache as I expect this struct
>> to have new members added over time.
>>
>> Any options I'm missing? I'm leaning towards 2, but a more lightweight
>> solution would be great, if it exists!
>>
>> Thanks,
>> Dave
>>
>>
>
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