[C++-sig] Type conversion problem -- simplified

[David Abrahams]

David Abrahams <dave at boost-consulting.com> writes:

>> Traceback (most recent call last):
>>   ...
>>   File "osg_to_sgg.py", line 153, in setupGeode
>>     v[0].set( 0, 1, 2 )
>> Boost.Python.ArgumentError: Python argument types in
>>     Vec3Array.__getitem__(Vec3Array, int)
>
> __getitem__ refers to the square brackets operator, so this has
> nothing to do with callability of the Vec3Array object.  
>
>> did not match C++ signature:
>>     __getitem__(osg::TemplateArray<osg::Vec3f, (osg::Array::Type)10, 3, 5126>*, int)
>> Note that the Vec3Array type is identical to the osg::TemplateArray<...>
>> type (via typedef), so the key difference is the extra "*" in the last
>> line.
>
> Interesting; how did you generate that __getitem__ method?  Its first
> parameter should be a reference to a Vec3Array, not a pointer.

Come to think of it, the reason we prefer a reference is that wrapped
C++ functions with pointer parameters will accept a wrapped NULL
pointer, and those accepting a reference parameter will automatically
reject a NULL pointer at the library level, saving the function author
from the NULL check.  So the signature of the function wrapped to
generate that __getitem__ method above is *more* permissive than if it
was built in the usual correct manner.

If you're certain that 

  osg::TemplateArray<osg::Vec3f, (osg::Array::Type)10, 3, 5126>

and 

  Vec3Array

are identical types, then I'm stumped.  I'd like to see the code that
exposes Vec3Array to Python.  But even more than that, I'd like to see
a minimal, reproducible example of your problem.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com