From: Markus <markus@...>
Date: 2004-10-14T01:26:58+09:00
Subject: Re: "nan".to_f ?

That should have been:

>        class String
>             def to_f
>                   Float(self) rescue 0.0/0.0
>                   end
>             end

...I really shouldn't post before caffeination, esp. after being up half
the night chasing my son's imaginary tigers out of the house.

-- Markus

On Wed, 2004-10-13 at 09:20, Markus wrote:
> On Wed, 2004-10-13 at 05:38, Yukihiro Matsumoto wrote:
> > Hi,
> > 
> > In message "Re: "nan".to_f ?"
> >     on Wed, 13 Oct 2004 21:18:38 +0900, Markus <markus@reality.com> writes:
> > 
> > |> It's not valid string representation of a float.
> > |
> > |      Then why does:
> > |
> > |x = 0.0/0.0
> > |x.class      #Float
> > |x.to_s	     #NaN
> > |
> > |      If "NaN" is not the valid string representation of a Float, why
> > |does calling Float#to_s return it?
> > 
> > Although we can tell whether a float value is NaN by using isnan(),
> > but as far as I know there's no portably way to generate NaN.  I think
> > it's not guaranteed that 0.0/0.0 generate NaN.
> > 
> > If I'm wrong, feel free to correct me.
> 
>      No, so far as I know you are correct (at as far as math operations
> go).  There was another sub-thread on this topic regarding the
> assumption that 0.0/0.0 could be PosInf, NegInf, Inf, or NaN.
> 
>      I believe there are defined binary representation of IEEE NaNs, so
> one could be constructed.  (See, for example 
> 
> http://www.psc.edu/general/software/packages/ieee/ieee.html
> 
> ), which I suspect is how the libs do it.
> 
>      If we could count on 0.0/0.0 to always produce NaN, I believe the
> original poster's goal could be met by writing something like:
> 
>         class String
>             def to_i
>                  Integer(self) rescue 0.0/0.0
>                  end
>             end
>         
> ...although this may not be as general as he needed.
> 
> -- Markus
> 
>