From: furufuru@... (Ryo Furue)
Date: 2004-10-16T05:54:36+09:00
Subject: Re: "nan".to_f ?

Yukihiro Matsumoto <matz@ruby-lang.org> wrote in message news:<1097623876.470219.23507.nullmailer@x31.priv.netlab.jp>...
> Hi,
> 
> In message "Re: "nan".to_f ?"
>     on Wed, 13 Oct 2004 05:22:00 +0900, Thomas Fini Hansen <beast@system-tnt.dk> writes:
> 
> |I would say that 'NaN' is a the string representation of a float, so
> |logically it should be parsed to such, that's why I'm wondering why
> |this behaviour was *removed*.
> 
> It's not valid string representation of a float.
[...]

Maybe I'm too late to jump in to this old thread
(three-days old is old enough for people to forget about
 a thread :).  Anyway, . . .

I think that symmetry is important, or if not important, it's nice
to have.  So, *if*

   x = 0.0/0.0  #=> NaN
   x.to_s       #=> "NaN"

*then*

   y = "NaN".to_f  # y *should* be NaN.

In other words, I'd expect (x.to_s).to_f to be an identity
operation (apart from potential truncation associated with to_s)
for a Float x.

I'm not saying that 0.0/0.0 *should* evaluate to NaN.  That depends
on the platform.  What I'm saying is that whatever x.to_s evaluates
to, (x.to_s).to_f "should" recover the (more-or-less) original value.
By "should", I mean "I wish".

Same goes for "Inf" and "-Inf".

Cheers,
Ryo