From: Eric LIn <ericlin852@...>
Date: 2008-10-02T05:49:09+09:00
Subject: Re: Bug in the money gem?

On Sep 25, 12:04 pm, Michael Guterl <mgut...@gmail.com> wrote:
> On Thu, Sep 25, 2008 at 2:34 PM, Eric LIn <ericlin...@gmail.com> wrote:
> > For anyone of you using the money gem (http://dist.leetsoft.com/api/
> > money/), I noticed today that 0 - 100 does not equal -100, it equals
> > 100 instead (all numbers here represent Money objects).  Do any of you
> > find that odd?
>
> I'm not sure, but it seems a bit strange.  Here is the offending code:
>
>     # File lib/money/money.rb, line 79
> 79:   def -(other_money)
> 80:     return other_money.dup if cents.zero?
> 81:     return dup if other_money.cents.zero?
> 82:
> 83:     if self.cents == 0 or currency == other_money.currency
> 84:       Money.new(cents - other_money.cents, other_money.currency)
> 85:     else
> 86:       Money.new(cents - other_money.exchange_to(currency).cents, currency)
> 87:     end
> 88:   end
>
> I think the first return would make sense if the other_money variable
> had a negative value associated with it, however, other_money's value
> is not negative.
>
> HTH,
> Michael Guterl

Thanks for the response, I figured that's the problem too.  It seems
the author made the mistake unintentionally, when he copies that line
of code from the "+" method.  Thanks for confirming my suspicion; I
was thinking maybe it's something in currency arithmetic that I don't
understand.  I've emailed the author, but so far no response.