From: Colin Bartlett <colinb2r@...>
Date: 2009-12-22T19:48:59+09:00
Subject: Re: Strange behavior of unary +@ for Fixnum?

On Tue, Dec 22, 2009 at 3:45 AM, Caleb Clausen <vikkous@gmail.com> wrote:
> On 12/21/09, Colin Bartlett <colinb2r@googlemail.com> wrote:
>> Ruby parses (-7) as an _integer literal_,
>> unless it's an expression like (-7**2)
>> in which case it's parsed as (-(7**2)), that is (7**2).send( :-@ )
>> By analogy, it seems that the parser is treating (+7) as an integer literal,
>> not as 7.send( :+@ ) ?
>
> This is correct. + or - at the start of an numeric literal is
> tokenized as part of that literal. (Except in the ** case, as you say.)

I think that your post is more correct than mine: when I put that bit
about (-7**2) I was assuming (without trying) that (+7**2)
would behave similarly. Not so, and your comment below
about "+" being eaten up is correct.

> The situation is somewhat better in 1.9, where at least
>  + 7 #with a space in between
> is treated as +@ method applied to the literal 7. But that doesn't
> help in 1.8. Note that in ruby 1.8, any number of leading + signs are
> glommed into the integer literal:
>
>  ++++++++++++++++++++++++++7  #still no method call in 1.8
>
> Having integer literals eat up the leading + or - as part of the
> number token is a common 'optimization' in many languages...

When all else fails, actually try some code.
Which is what I should have done before my first post.
As confirmation of what you say in your post:

# ruby=1.9.1  release-date=2009-07-16  platform=i386-mingw32
class Fixnum
  def +@() ; puts "in +@" ; self ; end
  def -@() ; puts "in -@" ; self * -1 ; end
end
-7     #=> -7
+7     #=> 7
-(7)   #=> in -@   #=> -7
+(7)   #=> in +@   #=> 7
-7**2  #=> in -@   #=> -49
+7**2  #=> 49      # note difference between this and -7**2
---7   #=> in -@   #=> in -@  #=> -7
- 7    #=> in -@   #=> -7
+++7   #=> in +@   #=> in +@  #=> 7
+ 7    #=> in +@   #=> 7

# ruby=1.8.6  release-date=2007-09-24  platform=i386-mswin32
# the only differences are, as you said:
+++7  #=> 7
+ 7   #=> 7