Geometry Boost List: Re: [geometry] Report not yet implemented feature at runtime

Subject: Re: [geometry] Report not yet implemented feature at runtime
From: Samuel Debionne (samuel.debionne_at_[hidden])
Date: 2015-03-13 06:52:32

An alternative to Variant could be type erasure.

Before trying out this solution, has someone already try to use
Boost.TypeErasure to implement, for example, any_point<> ?

More generally, if input types can vary at runtime (for example, if they
depend on user input), is there any recommended solution for
Boost.Geometry user ?

Le 09/03/2015 18:58, Samuel Debionne a écrit :
> Hi,
> The rational of this proposed feature is the following (pseudo code) :
> 
> variant<point_xy, point_xyz, polygon_xy, polygon_xyz> geometries_t;
> geometries_t a, b;
> 
> bg::within(a, b);
> 
> With the present implementation this code would not compile since
> within() is not implemented for all the combinations of the bounded
> types of the variant (not_implemented uses MPL_ASSERT to report this
> error at compile time).
> 
> The following proposal introduce an other mechanism to report
> incompatible type (or not yet implemented features) at runtime and is
> prototyped here :
> 
> https://github.com/boostorg/geometry/compare/develop...sdebionne:feature/nyi_runtime_error
> 
> The specifications are :
> 
> - maintain backward compatibility (default to compile time error)
> - specialization on a per algorithm basis and per compile unit (meaning
> that some part of the applications may use compile time errors while
> other part may use runtime errors)
> - should be quite easy to adapt the existing algorithm (see the example
> with within)
> 
> I can't think of a solution to implement this as a pure extension (e.g.
> without modifying the core library). In short, this is what I have in mind :
> 
> An algorithm should be identified by an "algorithm tag" (this could be
> extended to strategies as well) :
> 
> BOOST_GEOMETRY_REGISTER_ALGORITHM(within)
> 
> At the dispatch stage, the algorithm inherit from the new
> not_implemented<> interface that takes the algorithm tag as first
> template parameter :
> 
> template <...>
> struct within
>   : not_implemented<within_tag, Tag1, Tag2>
>   {};
> 
> Finally, in the code that invokes the algorithm, set whether to use
> runtime errors:
> 
> // Enable runtime errors
> BOOST_GEOMETRY_NYI_RUNTIME_ERROR(within_tag)
> 
> try {
>   bg::within(a, b);
> } catch (bg::not_implemented_runtime_error& ex) {
>   std::cerr << ex.what() << " is not yet implemented."
> }
> 
> Is there any interest in this feature?
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