From: Tim Hunter <TimHunter@...>
Date: 2007-06-24T01:37:32+09:00
Subject: Re: Beginner's question on methods

Peter Vanderhaden wrote:
> I'm new to Ruby, having worked with Perl the past couple of years.  I'm
> having trouble calling a method to increment a counter, and I'm assuming
> that the problem is with the scope of the variables?
>
> I'm getting the following error message:
> P:/PETERV2/scripts/vlog2.rb:25:in `test_meth1': undefined method `+' for
> nil:NilClass (NoMethodError)
>   from P:/PETERV2/scripts/vlog2.rb:47
>   from P:/PETERV2/scripts/vlog2.rb:36:in `each'
>   from P:/PETERV2/scripts/vlog2.rb:36
>   from P:/PETERV2/scripts/vlog2.rb:7:in `open'
>   from P:/PETERV2/scripts/vlog2.rb:7
>
> This is the method I'm trying to call:
> def test_meth1
>    counter = counter + 1
>    return counter
> end
>
> This is the call:
>
>           case typrec                             # case statement
> example.
>              when "TR001"
>                  cntr = test_meth1
>                  puts cntr  # Here I want to print the counter value.
>              when "AB001"
>                 ab001 += 1
>              when "AI001"
>                 ai001 += 1
>              else
>                 puts "Invalid message type"
>           end
>
> I assume that there's a really simple mistake I'm making, so any help
> would be greatly appreciated.
>
>   
You never initialize the 'counter' variable so it's default value is 
nil. Ruby is telling you that there is no "+" method for a nil object, 
that is, you can't add 1 to nil.

If "test_meth1" were in a class,  you could make counter be an instance 
variable and initialize it in the initialize method. Since it's not, 
it'll  have to be a global variable. Global variable names start with $.

$counter = 0
def test
   $counter = $counter + 1
   return $counter
end


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