Re: [boost] Geometry Template Library from Intel

From: Bruno Lalande (bruno.lalande_at_[hidden])
Date: 2008-05-03 07:38:58

>  >As pointed out by John, another advantage of compile-time access is
>  >the ability to have different types for each coordinate. It's
>  >something that has been asked for several times during recent
>  >discussions on this list. I was even wondering the other day if it
>  >wouldn't be better to not require any coordinate_type typedef and have
>  >the algorithms deducing by themselves the type of each coordinate by a
>  >BOOST_TYPEOF on the accessor.
>
>  Can you provide me with a code example of how to do this?  I'm getting
>  really tired of writing typename point_traits<T>::coordinate_type over
>  and over and over again.  I would greatly appreciate a better way.

You can have the type of a coordinate by applying BOOST_TYPEOF on the
expression by which you access this coordinate. For instance, let's
say we have a tuple<float,double> t:

BOOST_TYPEOF(t.get<0>()) x = t.get<0>();
BOOST_TYPEOF(t.get<1>()) y = t.get<1>();

x will be a float and y will be a double. Here you can see that we
ended up writing "t.get<0>()" and "t.get<1>()" twice, once for the
declaration and once for the initialization. BOOST_AUTO can help by
both declaring and assigning at the same time:

BOOST_AUTO(x, t.get<0>());
BOOST_AUTO(y, t.get<1>());

x is a float and receives the value of t.get<0>(), y is a double and
receives the value of t.get<1>().

Bruno