From: "Stephan Kämper" <Stephan.Kaemper@...>
Date: 2004-10-13T22:24:33+09:00
Subject: Re: "nan".to_f ?

Hi,

Markus wrote:
> 
>      The problem with this (in addition to some of my other contrived
> examples, e.g. the non-convergent infinite series) is that we may want
> to convert values to text and back (e.g., making XML) and would like to
> be able to get something resembling the original values back.
>      Admittedly, it would be possible for users who wanted this to do it
> themselves, but the performance consequences could be considerable.
> 
>      -- Markus

I think there's not even a problem (or an SEP). You could easily

- Add NaN as a constant to class Float
- Implement String#to_f slightly bot not entirely different
   so as to return NaN if the string begins with NaN

Something like this:

class Float
   NaN = 0.0 / 0.0
end

class String
   alias old_to_f to_f

   def to_f
     ( self =~ /^nan/i ) ? Float::NaN : self.old_to_f
   end
end

strings = [ "NaN1234", "nan", "nand is locical", "Nantucket? 70�07'W 
41�18'N", "234234.234NaN",  "1.0e23" ]

strings.each { | s |
   puts "#{'%26s' % s}  -> #{ s.to_f }"
}

Apparently this processing doesn't make sense for all Strings...


Happy rubying


Stephan