[geos-devel] Interface consistency

Frank Warmerdam warmerdam at pobox.com
Tue Jun 15 10:15:31 EDT 2004

strk wrote:
> Before releasing next GEOS I'd like to fix interface inconsistencies.
> Namely some geometry constructors take ownership over passed
> components:
> 	o Polygon::Polygon(LinearRing *shell, vector<Geoemtry *> *holes)
> 		will not copy shell and holes, and destroy it at
> 		polygon destruction time.
> 	o GeometryCollection::GeometryCollection(const vector<Geometry *>*geoms)
> 		will copy vector, but not geoms, which it will destroy
> 		at GeometryCollection destruction time.
> 	o MultiGEOM::MultiGEOM(const vector<GEOM *>*geoms)
> 		see GeoemtryCollection constructor
> Other geometry constructors all copy their arguments. I think this needs
> to be fixed to "all-constructors-copy-arguments". This will break existing
> applications, but if we make the change now I don't think there will be
> so much applications involved.


I ran up against a similar issue in GDAL and ended up having two forms of
some of the "attach" methods.  For instance, I have an addRing() method on
the OGRPolygon as well as an addRingDirectly().  The "directly" method takes
ownership of the passed geometry and can save alot of clone/delete overhead
in many common situations.

I gather that the only way to attach the subgeometries to a GEOS geometry
is during the constructor, is that right?  That is, the geometries are
essentially immutable after creation?   This makes it harder to have explicit
means to create attach the geometry with different rules via different named

I would suggest adding a "bool takeOwnership" argument to the constructors
which is defaulted to false. This allows code that wants to avoid the
clone/delete overhead to explicitly control ownership but returns the default
to a consistent approach.

I would add that behavioural changes like this are an awful source of bugs.
All code written against GEOS so far will need careful review to see if this
behavioural change affects them.  The sooner a change such as this is made,
the better.

PS. My integration of GEOS into OGR is going very well.

Best regards,
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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