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Subject: Re: [boost] Geometry and spatial indexes, my opinion
From: Simonson, Lucanus J (lucanus.j.simonson_at_[hidden])
Date: 2008-10-09 15:36:09

--Michael Fawcett
>Boost.Typeof. Boost.Units also handles this gracefully, but I'm not
>sure how they ended up solving it. Regardless, this is not something
>the end-user cares how it works, just that it works. It's doable by
>the library writer, so should be done.
>This type of conversion is handled automatically by the compiler in
>much simpler expressions:

First off, relying on auto casting is a great way to write template code
that only works when the template parameters are built-in types and
doesn't even compile when user defined data types are used instead.
Moreover, compiler always auto-casts built-in to user defined regardless
of what your intention, and believe me, the user does care. The
compiler doesn't always do the right thing by default.

The rationale that something is possible, therefore it should be done is
no rationale at all. Heterogeneous coordinates in the interfaces and
internals of algorithms is incompatible with runtime accessors to
coordinates and high order constructs. I don't see any value in
carrying the individual coordinate data types through the interface into
the algorithms. Why not cast them up front in the user-provided
accessor functions and let the user who knows and cares what casting
they want to get control that. Having one coordinate data type within
the algorithms *does* make the implementation of those algorithms
simpler and simpler is usually something worth pursuing.


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