Hi list!
I am using some time to learn more about the relationships between
Python, C++, SIP, the QGIS API and everything in-between.
And currently I am confused why this Python snippet leads to a segfault:
from qgis.core import QgsGeometry
g = QgsGeometry.fromWkt("POINT (1 2)")
g_geom = g.get()
del g
print(g_geom.asWkt())
I understand that deleting wrapped objects can lead to unexpected
deletions of related objects (e. g. if I delete a PyQt parent object and
then try to use an existing reference/"variablename" to a child of it)
but at least from the documentation this does not seem related to that.
https://github.com/qgis/QGIS/blob/dc73608a60229c9960ee65e308cfaba5f32566ec/src/core/geometry/qgsgeometry.h#L196
says about QgsGeometry.get():
> Returns a modifiable (non-const) reference to the underlying abstract
geometry primitive. This method can be slow to call, as it may trigger a
detachment of the geometry and a deep copy. Where possible, use
constGet() instead.
I do not understand anything in the detach() function itself
https://github.com/qgis/QGIS/blob/dc73608a60229c9960ee65e308cfaba5f32566ec/src/core/geometry/qgsgeometry.cpp#L102
:o)
Would my small snippet lead to a reference to the C++ object's geometry?
Then I'd understand the segfault (although not why it would not trigger
one of the usual "wrapped C/C++ object of type [...] has been deleted"
errors) if I try to access it after the whole QgsGeometry might have
been destroyed.
Or does it get a "detached deep copy"? In that case it sounds like an
independent object to me but I might be completely wrong.
Are there any C++ or SIP terms you could throw my way for further reading?
Thanks for your help!
Cheers, Hannes
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