Geometry Boost List: Re: [geometry] Support of C++11 initializer list

Subject: Re: [geometry] Support of C++11 initializer list
From: Barend Gehrels (barend_at_[hidden])
Date: 2015-01-24 06:00:44

Hi Adam,

Adam Wulkiewicz schreef op 24-1-2015 om 3:36:
> Hi,
>
> Some time ago I added an experimental support for C++ initializer 
> lists in geometries to make possible the creation of geometries using 
> uniform initialization, e.g.:
>
> linestring ls = {{0, 0},{1, 1},{2, 2}};
> polygon poly = {{{0, 0},{0, 5},{5, 5},{5, 0},{0, 0}},{{1, 1},{4, 
> 1},{4, 4},{1, 4},{1, 1}}};

Thanks for this, it looks very good.

To draw attention to this (to the list): the polygon contains an 
interior ring, nice.

Do multi-linestrings and multi-polygons (having interior rings too) also 
work and how does it look?

Does a point work and how does it look? I recently changed the 
constructor there to get rid of a warning we had for a long time about 
out of boundary values.

>
> The goal was to support C++11 initializer lists and Boost.Assign in 
> the same time even if Boost.Assign currently doesn't work on all 
> compilers with STL containers. FYI, there is a PR with proposed fix 
> but nobody is willing to merge it.

Hmm... I see no messages on the boost ML, maybe that would help too?

>
> Anyway, to work around it and avoid ambiguity while using Boost.Assign 
> to assign new data to the geometry I implemented only the constructor 
> taking std::initializer_list. This way the compiler prefers the 
> conversion from Boost.Assign generic_list directly into the Geometry 
> because conversion first to std::initializer_list would require 1 more 
> conversion.
>
> It seems that everything is ok on all compilers except the msvc14 CTP, 
> I hope they'll fix it in the final release. See 
> http://www.boost.org/development/tests/develop/developer/geometry.html, the 
> test geometries.
>
> So if you'd like to try it out you have to checkout the develop branch 
> and define BOOST_GEOMETRY_EXPERIMENTAL_ENABLE_INITIALIZER_LIST. Please 
> let me know if it works for you.
>
> The final question is, should we enable it by default in Boost 1.58?

That depends on the consequences for MSVC 14. If they don't fix it, and 
that results in our geometries being unusable, we should not do it. If 
just that feature is unusable, it looks OK to me. What is the case?

If so, we should add a doc-page with examples too.

Regards, Barend