Re: [Boost-users] Template specialization for Boost.Polygon

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Bjorn Reese

26 Aug 2019 26 Aug '19

5:01 p.m.

On 8/26/19 5:39 PM, Phil Endecott via Boost-users wrote:

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Can anyone suggest how I can write my specialisations so that they are unambiguous?

By adding another level of indirection. Create your own trait template. Let both the generalization and your specialization redirect to polygon_traits. Something like this (warning untested code ahead) template struct my_polygon_traits : public polygon_traits { }; template struct my_polygon_traits> : public polygon_traits> { };

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Phil Endecott

27 Aug 27 Aug

12:39 p.m.

New subject: Template specialization for Boost.Polygon

Hi Bjorn, Bjorn Reese wrote:

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Can anyone suggest how I can write my specialisations so that they are unambiguous?

By adding another level of indirection. Create your own trait template. Let both the generalization and your specialization redirect to polygon_traits.

Something like this (warning untested code ahead)

template struct my_polygon_traits : public polygon_traits { };

template struct my_polygon_traits> : public polygon_traits> { };

Forgive me if I have misunderstood, but how can that cause Boost.Polygon to see my specialisation when it looks up polygon_traits> ? Regards, Phil.

Patrick J. LoPresti

28 Aug 28 Aug

4:16 p.m.

New subject: Template specialization for Boost.Polygon

"Phil Endecott" writes:

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Forgive me if I have misunderstood, but how can that cause Boost.Polygon to see my specialisation when it looks up polygon_traits> ?

I had a similar problem. As it turns out, Boost.Polygon already uses a level of indirection internally. You can specialize boost_polygon_traits_general (instead of boost_polygon_traits). This is undocumented, but it was the only way I found to get it working. I would argue this is a bug, or at least a deficiency. Not sure if the right fix is to change the documentation or the implementation. - Pat

Phil Endecott

9:19 p.m.

New subject: Template specialization for Boost.Polygon

Patrick J. LoPresti wrote:

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"Phil Endecott" writes:

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Forgive me if I have misunderstood, but how can that cause Boost.Polygon to see my specialisation when it looks up polygon_traits> ?

I had a similar problem.

As it turns out, Boost.Polygon already uses a level of indirection internally. You can specialize boost_polygon_traits_general (instead of boost_polygon_traits).

THANKS! Yes, that works. It's a hack but I've done worse...

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This is undocumented, but it was the only way I found to get it working.

I would argue this is a bug, or at least a deficiency. Not sure if the right fix is to change the documentation or the implementation.

It's clearly a misfeature. Regarding fixing it, I have the impression that Boost.Polygon is essentially abandoned. Are you actively using it? Anyone else out there? Regards, Phil.

Glen Fernandes

10:35 p.m.

New subject: Template specialization for Boost.Polygon

On Wed, Aug 28, 2019 at 5:19 PM Phil Endecott wrote:

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It's clearly a misfeature. Regarding fixing it, I have the impression that Boost.Polygon is essentially abandoned. Are you actively using it? Anyone else out there?

It has a semi active maintainer who is also a co-author (Andrii Sydorchuk). It does have active users; some submit pull requests too. Glen

Bjorn Reese

27 Aug 27 Aug

3:42 p.m.

New subject: Template specialization for Boost.Polygon

On 8/27/19 2:39 PM, Phil Endecott via Boost-users wrote:

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Forgive me if I have misunderstood, but how can that cause Boost.Polygon to see my specialisation when it looks up polygon_traits> ?

Sorry, I did not look into your particular details, but simply described a general way of avoiding ambiguities.

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Bjorn Reese
Glen Fernandes
Patrick J. LoPresti
Phil Endecott