From: Brian Candler <B.Candler@...>
Date: 2007-04-05T14:33:57+09:00
Subject: Re: nil? and non-existent objects

On Thu, Apr 05, 2007 at 06:56:46AM +0900, Jamal Soueidan wrote:
> Fran�ois Montel wrote:
> > Why is it that the nil? method can sometimes be called on an object that
> > doesn't exist, and other times will return an error. Under what
> > circumstances can you call the nil? method on a non-existent object?
> > 
> > Consider:
> > 
> >>> puts x = 1 if x.nil?
> > => 1
> >>> puts ???z is not defined??? if z.nil?
> > => NameError: undefined local variable or method ???z???
> > 
> > Someone mentioned that = has higher precedence than if, so it could be
> > that in the first statement x is assigned 1 before the conditional
> > statement is run. However, x.nil? would then always return false.
> 
> You could also fix it this way :)
> 
> ----------------------------------------------
> 
> def x
>   @x
> end
> 
> def x=(val)
>    @x = val
> end
> 
> puts x=1 if x.nil?
> 
> ----------------------------------------------
> 
> This would output: 1

I think you should check your work before posting (I do)

Run this:

def x
  puts "calling main.x"
  @x
end

def x=(val)
  puts "calling main.x="
  @x = val
end

puts x=1 if x.nil?

You'll see that your two methods are never called, so they don't make any
difference.