Syntax error warning: useless use of a variable in void cont


#1

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.

Help!
Thanks


#2

Tom R. wrote:

       1

ab = Tl.new(“jack”,“charity”)
tmp.rb:15: warning: useless use of a variable in void context
Thanks
You seem to be having difficulty accessing the variables in the tla
object.
This seems to work:

#!/usr/bin/env ruby

class Tl
attr_reader :a, :b

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


#3

Selon Tom R. :

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
                ^^^^^^

r = aa <=> ab
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 G…

http://rainbow.conlang.free.fr

You need a straight mind to invent a twisted conlang.


#4

Thanks everybody.
I had thought that an @_whatever could be seen anywhere the class was
used.
TR


#5

On Thu, 24 Nov 2005, Tom R. wrote:

class Tl
def initialize(a,b)
@a = a
@b = b
end
def to_s
“#{@a} #{@b}”
end
def <=>(tlr)
if @a > tlr.@a
^
^
^

               you can't do this.

probably you want

attr “a”

tlr.a

hth.

-a


#6

On Nov 23, 2005, at 3:57 PM, Christophe G. wrote:

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)”.

To be pedantic:
a) attr_reader doesn’t make an instance variable readable, it’s a
convenient way to add a method that returns the value of the instance
variable.

b) There are other ways (variations on your latter) such as
tlr.instance_eval{ @a }