
Boost : 
From: Barend Gehrels (barend_at_[hidden])
Date: 20080327 15:48:42
> > The distance of two integers may result in a floating point value.
> > Therefore distance returns a double. Internally, you will see, often,
> > the same numeric types or better is used as you describe. See
> > select_type_traits and large_type_traits.
>
> I couldn't find one for the instance of distance, perhaps I wasn't looking properly,
> in any case the simplest definition in my opinion could be:
>
> template<typename point_type>
> point_trait<point_type>::value_type distance(const point_type& p1, const point_type& p2);
>
See also the discussions on the other thread about distance and
"distance_result". It turns out to be very useful to have a variant
which is squared, in some cases, for fast comparisons. But not all
pointtypes need that.
Besides that the library as is in preview can compare two types.
But all this, indeed, is not "the simplest definition".
> btw will there be support for base value inputs?
>
> template<typename T>
> T distance(const T& x1,const T& y1, const T& y2,const T& x2);
>
Good idea.
> > Points of different types can be handled.
> > If you use a derived class, you have to provide an appropriate traits
> > class. It is not promoted. At least not in the compilers I use.
> All the compilers I use do it quite easily.
>
> class my_rational
> {
> public:
> my_rational(const int& i);
> my_rational& operator=(const int& i);
> };
>
> void foo(my_rational value){...}
> {
> int i = 123;
> foo(i);
> }
>
> as per the example above if I provided a distance strategy/routine
> using my_rational, then I should not need to do anything
> else in order to be able to pass in a series of integers
> into the routine  the result would of course be my_rational
> but the class my also have a few cast operators to convert
> into the various C++ PODs
>
This is not how I use it in the traits class, but I have to check again
if its promoted there. Thought it was not.
> > Besides that, the library user might choose to specify a strategy.
> Thats great, but consider me a really dumb user, I have 4 values
> I've just read in from a file and i want to compute the euclidian
> distance, I would like to be able to say the following without having
> to worry about strategies or converting my values into point types etc:
>
> dist = boost::geometry::distance(x1,y1,x2,y2);
>
The strategy is optional... Dumb users don't have to use them...
But again, offering a calculation of the distance of four coordinates is
a good idea.
> (snip)
>
> There is so much to this topic, you indeed are very courageous to take
> it on.
>
Thanks.
Barend Gehrels,
Geodan, Amsterdam
Boost list run by bdawes at acm.org, gregod at cs.rpi.edu, cpdaniel at pacbell.net, john at johnmaddock.co.uk