CGAL users discussion list

[Efi Fogel <>]

I think that you are correct on both counts.

It should be symmetric and I'd pick the first order.

We will fix it.

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On 2 March 2017 at 06:56, Ch'Gans <> wrote:

When inserting a (isolated) segment:
- Before create vertex
- After create vertex
- Before create vertex
- After create vertex
- Before create Edge
- After create edge

When removing a (isolated) segment:
- Before remove edge
- Before remove vertex
- After remove vertex
- Before remove vertex
- After remove vertex
- After remove edge


As you can see inserting and removing edges lead to a non symetrical
notification ordering, which I think is a bug.

I think that the notification ordering when inserting the edge is
correct, you start by inserting the first vertex, then the second, and
finally you *can* insert the edge since the 2 vertices are "fully"
inserted.
And so, the notification ordering when removing an edge is bogus, the
notifications should be: remove the edge, then remove a vertex (since
it is not used by any edge), then remove the other vertex.

I'm using the observer to maintain a (Qt) tree model of edges,
vertices and faces.
With Qt model/view, you *cannot* say:
- i'm about to remove something somewhere
- i'm about to remove something else somewhere else
- i'm have removed something somewhere
- i'm have removed something else somewhere else

Actually the above could work if 'something else' was a child of
'something', which is not my case, since my root items have 2
children:
- an Edge list node, whith Edge children
- a Vertex list node, with vertex children

Now, you might say that it is not because the CGAL ArrangementObserver
doesn't behave in a friendly way for my use-case (QAbstractItemModel),
that it is broken.
True. Nonetheless, I tend to consider non-symetrical behaviour as
design errors. In SW design, it usually doesn't make sense to
construct something following an order and dis-construct it using a
completely different order.

What do you guys think?

Chris

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