From: Brent Roman <brent@...>
Date: 2009-03-07T15:07:33+09:00
Subject: [ruby-core:22713] Re: suggestions for float


How about this:

# return true if other (Numeric) is approximately equal
#eps is chosen such that =~ indicates whether self.to_s == other.to_s
#however, this is at least 30 times faster than comparing the results of
to_s
#if one were to code it in 'C', I suspect it would be >1000 times faster.

class Float
  @@eps = 5e-15
  def =~ other
    (self-other).abs < (@@eps*self).abs
  end
end

It works well for me.  Test it and see if it behaves as you would expect.

  f =~ g 

is similar enough to the standard "approximately equal" math symbol that I
hope many people would understand it at first glance. 

- brent


Roger Pack wrote:
> 
>> A variant of the float to string conversion that tries to preserve all
>> the
>> binary information would certainly be useful, but not as the default to_s
>> method.  That is, unless you think that:
>>
>> irb>  2.1 - 3.0
>> -0.8999999999999999
>>
>> would not be "surprising"!  (well, at least annoying)
> 
> At least users would be able to understand this:
>>> 2.1 - 3.0
> => -0.9
>>> (2.1-3.0) == -0.9
> => false
> 
> Since it would become
>>> 2.1 - 3.0
> => -0.8999999999999
>>> (2.1-3.0) == -0.9
> => false
> 
> I'd prefer the second--at least I'm reminded as to what's going on and
> don't have to constantly pester ruby talk with questions like "is this
> normal?" :)
> 
> However, this would seem surprising
>>> 0.9
> =>  0.90000000000000002
> 
> It seems slightly more annoying and verbose but more honest.
> That being said, as someone above mentioned, the current float default
> output is to "prettify" by stripping the ending few bits [I guess].
> Perhaps we should keep this around as a new method name.  Like
> to_human_string or something [?]
> 
> -=r
> 
> 
> 

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