[Qgis-developer] Object owner design in QgsGraphBuilder

[Tim Sutton]

Hi

On Fri, Aug 24, 2012 at 9:32 AM, Matthias Kuhn <matthias.kuhn at gmx.ch> wrote:
> Just figured out that the sip option /Factory/ tells python that it
> takes ownership of this object. So there won't be any memory loss. I'd
> still say this should be changed and if not at least stated in the API
> so anybody using this in C++ will be aware of this without reading the
> code.
>

Patches to the code that document things better will be welome.

Regards

Tim

> On Thu, 2012-08-23 at 12:47 +0000, Kuhn Matthias, Vermessung wrote:
>> Hi
>>
>> I've recently been working with the network analysis library.
>>
>> When I had a look at the code I noticed the following:
>>
>> In the constructor a new QgsGraph() mGraph is instantiated
>> In the destructor mGraph is deleted if not null
>> In the method graph() mGraph is returned and set to null
>>
>> This leads to the effect, that if I request the graph() from the QgsGraphBuilder ( and I normally will, as that's the only purpose of using the QgsGraphBuilder ) I get the full ownership and have to delete the graph-object, when I'm finished with it. But this is not stated in the API. So without looking at the code there is no way to know this.
>>
>> - How does python handle this? Does the following code delete this object?
>>
>> graph = graphBuilder.graph()
>> graph = null
>>
>> - In my opinion, this is a wrong design. I would rather pass a graph-object to the graphbuilder in the constructor and let it fill this object. Then I know, that is my responsibility to delete it afterwards.
>>
>> I would provide a patch to change this if there are no good reasons to keep it the way it is.
>>
>> Regards,
>> Matthias
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>
>
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