Re: [Boost-users] extending boost::rational to represent infinities

From: me22 (me22.ca_at_[hidden])
Date: 2005-04-03 12:33:22

On Apr 3, 2005 5:08 AM, Jedediah Smith <jedediah_at_[hidden]> wrote:
> I need a type equivelant to rational<int> but supporting two special
> values, +inf and -inf which compare greater and less (respectively) to
> all other values besides themselves. I don't need to perform any
> arithmetic on the inf values so those operations can be undefined.
> 
> What is the best strategy for creating such a type? Would it be better
> to subclass rational or create an underlying integer type with the inf
> values and use rational based on that underlying type? If the former
> option, how exactly would I do it?

I expect that subclassing wouldn't be a good idea since none of the
critical functions are virtual ( for good -- speed -- reason ).  The
way that immediatly jumps to mind is copying rational<> and changing
it to allow a zero denominator to represent infinities, although this
violates OnceAndOnlyOnce, so perhaps a class that has a rational as a
member would be a more maintainable option, but I expect it would be
to run and more annoying to code.

A with_inf<> wrapper for a numeric type seems to me to be the best
option as it would be straight-foreward and usable in other contexts. 
The only problems I see with that is your denominator would also get
overhead from checking for infs ( when it should never have them ) and
that there's no simple way for a rational< with_inf<> > divide-by-zero
to return the appropriate +/- inf value.

- Scott McMurray