From: Seebs <usenet-nospam@...>
Date: 2010-04-14T08:50:08+09:00
Subject: Re: I thought spaces didn't matter around operators

On 2010-04-13, Sarah Allen <sarah@ultrasaurus.com> wrote:
> I had understood that operators, like minus (-), had special "syntactic
> sugar" that allowed me to include or omit spaces around them like this:

Often, yes.

> 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

Hmm!

> Can someone explain what "undefined method `-@'" refers to?

Probably "unary -".

As in:
	> x = 3
	> puts (-x)
	-3

But!

	> puts -x
	-3
	> puts - x

	NoMethodError: undefined method `-' for nil:NilClass

Basically, Ruby is interpreting "-x" as a unary minus on x, rather
than as part of a larger expression.  It turns out to be ambiguous
in this case, because Ruby can't tell whether you mean
	(Time.now()) - (t)
or
	(Time.now(-1 * t))

Only unary - isn't necessarily "-1 * t", it's just "whatever you get
calling -@ on t".

-s
-- 
Copyright 2010, all wrongs reversed.  Peter Seebach / usenet-nospam@seebs.net
http://www.seebs.net/log/ <-- lawsuits, religion, and funny pictures
http://en.wikipedia.org/wiki/Fair_Game_(Scientology) <-- get educated!