From: Roger Pack <rogerpack2005@...>
Date: 2009-06-14T05:10:36+09:00
Subject: Re: a few thoughts for ruby...

> Doing a quick bit of testing suggested that using  "%f" % float
> might be better than using float.to_s because in some cases
> the former preserves information that is actually in the float
> which the latter uses. In fact, I was going to suggest you propose
> to use  "%f" % self  in Float#to_d instead of  self.to_s.
> But after some more thought and a bit of testing, I found that
> for me in IRB  "%f" % float  only gives results to 6 decimal places
> but  float.to_s  seems to give results to 14 or 15 significant figures
> so overall using  float.to_s  for the conversion seems better.

The good news is that with current ruby trunk I believe that Float#to_s 
is as accurate as doing a ("%f" % self) [it no longer loses accuracy].


> If we want a BigDecimal method (and in view of  BigDecimal( float.to_s )
> I don't think we do - but  BigDecimal( float.to_s )  should perhaps
> be mentioned prominently in BigDecimal documentation)
> how about something like (not tested):
>   def BigDecimal.from_f( f )
>     if f.kind_of?( Float ) then BigDecimal( f.to_s )
>     else raise "BigDecimal.from_f: argument must be a Float"
>     end
>   end

That would be nice, though the way you suggested earlier (require 
'bigdecimal/util'; 3.3.to_d) works for me :)
-=
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