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Subject: Re: [geometry] Using Boost.Geometry with a legacy class hierarchy
From: Mats Taraldsvik (mats.taraldsvik_at_[hidden])
Date: 2012-02-21 06:43:39

Hi Barend,

On 02/20/2012 07:21 PM, Barend Gehrels wrote:
> Hi Mats,
> On 20-2-2012 9:03, Mats Taraldsvik wrote:
>> The object hierarcy is a bit more complex than my current example
>> (also contains 2d, 3d points, curves etc.), and objects are stored in
>> pointer to base/super-containers. Therefore, I can't remove the
>> pointer requirement, I'm afraid. I guess creating separate pointer
>> and non-pointer specializations (e.g. point_type and point_type_ptr)
>> since they are so different, means either a lot of duplicated code,
>> or a very difficult problem...
>> I was also hoping to overcome the pointer-to-base container issue
>> also, but thought it was best to take one step at a time. :)
> OK, so the first solution I mailed is still based on pointers. Does
> that work for you?

After re-reading your email, I realise that I misinterpreted it -- the
version you suggested, using references instead of pointers, should
work, since it does not modify my hierarchy.

However, since I the structure is a bit more complex, and I need to 
worry about casting from base pointers etc. later, I want to use the 
pointer version, as long as it works and behaves correctly.
I managed to fix the issue in QRing, without modifying Boost.Geometry. :)
Basically, I needed to change the ConstRingIterator :
typedef RingIteratorImpl<std::vector<QLineString*>::const_iterator, 
const QPoint*> ConstRingIterator;
typedef RingIteratorImpl<std::vector<QLineString*>::const_iterator, 
QPoint* const> ConstRingIterator;
and then it woked perfectly.
However, I'm not sure if the semantics are right -- shouldn't the QPoint 
be const as well as the pointer (i.e. const QPoint* const)? When 
ConstRingIterator is changed to (const QPoint* const), it does not 
compile (perhaps it is because of lacking specializations (I have 
defined QPoint* and const QPoint*).
I updated my gist with the latest version [1] (a diff userscript is 
available for convenience, if you're not using git [2])
Mats Taraldsvik
> Regards, Barend
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