Ross Bamford wrote:
>  Normally, n + 1 would end up calling your method because Ruby would have
>  to figure out whether it's a method or variable, but because in this
>  case Ruby has seen a bare assignment to 'n' by that point, it remembers
>  that and assumes 'n' is a local variable.
> 
>  This local variable isn't yet initialized (the n + 1 would be it's
>  initializer), so n + 1 ends up being nil + 1, or (effectively) nil.+(1),
>  hence the "undefined method '+' for nil:NilClass".

Sigh. This reminds me of the rule that I have to use
"this-> method_name( )" when I want call a method of T, parent class,
which is passed as template parameter. Anyway, it's not a perfect
world...

Best,
Minkoo Seo