Re: [boost] Geometry and spatial indexes, my opinion

Subject: Re: [boost] Geometry and spatial indexes, my opinion
From: Michael Fawcett (michael.fawcett_at_[hidden])
Date: 2008-10-09 15:47:55

On Thu, Oct 9, 2008 at 3:36 PM, Simonson, Lucanus J
<lucanus.j.simonson_at_[hidden]> wrote:
> --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.

No, it doesn't only work with built-in types.  It works with any type
that has the correct operators defined.  If the user does care, he can
cast obviously.  The algorithm shouldn't do the casting or require it
though.

> The rationale that something is possible, therefore it should be done is
> no rationale at all.

This is a gross misrepresentation of what I said.  I said the end-user
cares, *and* it's doable, so it should be done.  You only took half of
what I said.

> Heterogeneous coordinates in the interfaces and
> internals of algorithms is incompatible with runtime accessors to
> coordinates and high order constructs.

Algorithms that need runtime indexing should require that concept.

> I don't see any value in
> carrying the individual coordinate data types through the interface into
> the algorithms.

They're already present at compile-time.  No extra work required.

> 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.

Because the casting and the temporaries it creates is not free,
neither in terms of speed or storage.

--Michael Fawcett