From: Christophe Grandsire <christophe.grandsire@...>
Date: 2005-11-24T05:57:40+09:00
Subject: Re: syntax error warning: useless use of a variable in void context

Selon Tom Reilly :
> class Tl
>    def initialize(a,b)
>        @a = a
>        @b = b
>    end
>       def to_s
>        "#{@a}    #{@b}"
>    end
>       def <=>(tlr)
>        if @a > tlr.@a
                  ^^^^^^

>            1
>        elsif
>            @a == tlr.@a
                    ^^^^^^
>                0
>        else
>            -1
>        end
>    end
>    end
> 
> aa = Tl.new("tom","reilly")
> ab = Tl.new("jack","charity")
> 
> r = aa <=> ab
> p r
> 
> --------------------------
>  >ruby -cw tmp.rb
> tmp.rb:12: syntax error
> tmp.rb:12: warning: useless use of a variable in void context
> tmp.rb:14: syntax error
> tmp.rb:15: syntax error
> tmp.rb:15: warning: useless use of a variable in void context
> tmp.rb:19: warning: else without rescue is useless
> tmp.rb:22: syntax error
>  >Exit code: 1
> 
> 
> Considering I've been using Ruby for a couple of years, I've been 
> totally frustrated
> making this bit of code work.
> 

Instance variables are completely private by default in Ruby, and you 
can only make them accessible by adding accessor methods (what the 
attr_* methods do for you). You can't access the private instance 
variable of a different object, even if they have the same class, so 
your "tlr.@a" simply won't work.

The only ways to make this work is:
- to make the instance variable @a readable with "attr_reader :a" and 
replace "tlr.@a" with "tlr.a"
- to bypass encapsulation by replacing "tlr.@a" with 
"tlr.instance_variable_get(:@a)".
-- 
Christophe Grandsire.

http://rainbow.conlang.free.fr

You need a straight mind to invent a twisted conlang.