From: "Peña, Botp" <botp@...>
Date: 2007-09-04T16:29:34+09:00
Subject: Re: 0.06 == 0.06 returns false in Ruby?

From: Michael Ulm [mailto:michael.ulm@isis-papyrus.com] 
# Daniel Berger wrote:
# > class Float
# >    def ==(other)
# >       self.to_s == other.to_s
# >    end
# > end
# Oh yes, nice one. This fulfills 
# 'from  x==y and y==z follows x==z'
# Unfortunately it does not fulfill some other properties one

w a little help fr bigdecimal, a little goes a long long way

> class Float
>   def to_dec
>      BigDecimal.new(self.to_s)
>   end
> end
=> nil
> class Fixnum
>    def to_dec
>       BigDecimal.new(self.to_s)
>    end
> end
=> nil

> x=0.06.to_dec
> y=0.05.to_dec + 0.01.to_dec
> x==y
=> true
> z=0.02.to_dec+0.04.to_dec
> y==z
=> true
> z==y
=> true
> x==z
=> true
> z==x
=> true

# wants to have; e.g. it violates
# 'from x==y follows x+z==y+z'

> x+z == y+z
=> true
> (x+z).to_s == (y+z).to_s
=> true
> puts (x+z)
0.12E0
=> nil

# for example
# In particular, you don't have
# 
# 'from x==y follows x-y==0'

> x==y
=> true
> x-y == 0
=> true

 
# for example
# 
# > x, y = 0.6, 6 * 0.1
# > x.to_s == y.to_s # => true
# > (x - y).to_s == 0.to_s # => false

> x, y = 0.6.to_dec, 6 * 0.1.to_dec
> (x - y) == 0
=> true
> (x - y) == 0.to_dec
=> true
> (x - y).to_s == 0.to_dec.to_s
=> true

kind regards -botp