From: Slark <slark@...>
Date: 2008-03-19T21:54:55+09:00
Subject: Re: Undefined method '<' for nil:NilClasse

Roberto Casadei wrote:
> This is the code:
> class StringScanner
>   @str = ""
>   @kounter = 0
>   def initialize(str)
>     @str = str
>   end
>   def scan(arg)
>     res = @str.scan(arg)
>     return nil unless @kounter<res.length
>     @kounter=@kounter+1
>     res[@kounter-1]
>   end
> end
> 
> str = "Watch how I soar!"
> ss = StringScanner.new(str)
> loop do
>   word = ss.scan(/\w+/)    # Grab a word at a time
>   break if word.nil?
>   puts word
>   sep = ss.scan(/\W+/)     # Grab next non-word piece
>   break if sep.nil?
> end
> 
> And this is the result:
> C:/Documents and Settings/Roby/Desktop/Apps/Ruby/prova2.rb:9:in `scan':
> undefined method `<' for nil:NilClass (NoMethodError)
>         from C:/Documents and
> Settings/Roby/Desktop/Apps/Ruby/prova2.rb:18
>         from C:/Documents and
> Settings/Roby/Desktop/Apps/Ruby/prova2.rb:17:in `loop'
>         from C:/Documents and
> Settings/Roby/Desktop/Apps/Ruby/prova2.rb:17
> 
> Help.

A simple way to understand how scoping (and naming convention) is 
working in ruby is to try the following 3 examples and note their 
output/errors:

1....
class C
   str = "Hello"
   def look
     puts str.class
   end
end
c = C.new
c.look

2....
class C
   @str = "Hello"
   def look
     puts @str.class
   end
end
c = C.new
c.look

3...
class C
   @@str = "Hello"
   def look
     puts @@str.class
   end
end
c = C.new
c.look

Graham