--- Simon Buchan wrote:
David Abrahams wrote:
my_rational<x,1> can be an integral constant *at compile time*. I'm not sure it's useful, but it's not insane.
If you for some reason still think this, why not eagerly evaluate template<typename Num> rational<Num,1> to Num, since we are already eagerly normalising?
It's possible to do so, but I see three concerns. One, we need to be careful where to do it. Putting this capability directly in the definition of rational makes expressions like rational<int_<4> > rather useless. Employing downcasting on the result of each rational operation leads us to the second concern: performance. Computationally heavy numeric metafunctions (e.g. exponential, sine) are going to pay extra at each step checking for an event that may never occur. And even if downcasting occurs half the time, if there are just as many regular casts back to rational, we end up overpaying twice as much. We could give users the ability to explicitly downcast any numeric constant. This leads us to the final concern: usefulness. For the moment, I don't see any need beyond rounding; the library provides a numeric metafunction called whole_part if you want truncation. If anybody needs either downcasting or rounding, we'd like to hear from you. Cromwell D. Enage __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com