From: Rob Biedenharn <Rob@...>
Date: 2010-04-14T08:31:33+09:00
Subject: Re: I thought spaces didn't matter around operators


On Apr 13, 2010, at 7:24 PM, Sarah Allen wrote:

> I had understood that operators, like minus (-), had special  
> "syntactic
> sugar" that allowed me to include or omit spaces around them like  
> this:
>
>>> 1-1
> => 0
>>> 1 -1
> => 0
>>> 1 - 1
> => 0
>>> 1- 1
> => 0
>
> However, in some cases, spaces seem to matter:
>
>>> t = Time.now
> => Tue Apr 13 13:40:24 -0700 2010
>>> Time.now -t
> NoMethodError: undefined method `-@' for Tue Apr 13 13:40:24 -0700
> 2010:Time
>  from (irb):6
>>> Time.now - t
> => 6.895787
>
> Can someone explain what "undefined method `-@'" refers to?
>
> Here's my version of Ruby if it matters:
> $ ruby -v
> ruby 1.8.7 (2008-08-11 patchlevel 72) [universal-darwin10.0]
>
> Thanks,
> Sarah
> http://www.ultrasarus.com
> -- 
> Posted via http://www.ruby-forum.com/.
>


irb> t=Time.now
=> Tue Apr 13 19:27:43 -0400 2010
irb> Time.now() -t
=> 5.824652
irb> Time.now -t
NoMethodError: undefined method `-@' for Tue Apr 13 19:27:43 -0400  
2010:Time
	from (irb):5
	from :0
irb> -t
NoMethodError: undefined method `-@' for Tue Apr 13 19:27:43 -0400  
2010:Time
	from (irb):6
	from :0

The flexible syntax also lets you omit parentheses and in this case,  
the "-t" is parsed as an argument to the Time.now method.  Putting the  
explicit (and empty) argument list on the call removes this ambiguity.

The '-@' method is the unary minus method.  The error message is  
because there is no method that negates a Time instance.

-Rob

Rob Biedenharn
http://agileconsultingllc.com
	Rob@AgileConsultingLLC.com
http://gaslightsoftware.com
	Rob@GaslightSoftware.com