From: Charles Mills <cmills@...>
Date: 2005-09-16T13:21:34+09:00
Subject: Re: "unless" keyword

Neville Burnell wrote:
> "Unless" == "if not"
>
> so
>
> errors.add(:price, "should be positive") unless price.nil? || price >
> 0.0
>
> Is equivalent to
>
> errors.add(:price, "should be positive") if !price.nil? and price > 0.0

I think you mean
errors.add(:price, "should be positive") if not (price.nil? and price >
0.0)
-or-
errors.add(:price, "should be positive") if !price.nil? and price <=
0.0

-Charlie

>
> -----Original Message-----
> From: Mike Novecento [mailto:mike.novecento@gmail.com]
> Sent: Friday, 16 September 2005 1:42 PM
> To: ruby-talk ML
> Subject: "unless" keyword
>
> Ok guys, you convinced me: Ruby is the way to go. I have been reading
> online for a few hours now, and it looks simply fantastic (especially
> with Ruby on Rails).
> I am so excited, I have been programming for years, and never thought it
> could be so fun.
>
> I have a first question. Looking at some code online, I have seen this
> line of code from a the site of pragmatic programmer:
>
> errors.add(:price, "should be positive") unless price.nil? || price >
> 0.0
>
> I understand that it is required to validate that a price is strictly
> positive.
> My question, maybe very easy, is... how does it exactly work?
>
> I thought it should be "ADD ERROR unless NOT NIL AND PRICE > 0.0"...
> why he uses (OR) ||? Maybe I am missing the logic of the keyword
> "unless". I feel dumb :-)
> 
> Thanks in advance,
> Mike.