From: Emmanuel Oga <oga_emmanuel_oga@...>
Date: 2007-04-05T04:46:12+09:00
Subject: Re: nil? and non-existent objects

I think is because of the ruby's analisis on the scope. That is, in:

puts x = 1 if x.nil?

ruby sees x in the scope even if it is never accesed nor asigned, but in

puts ‘z is not defined’ if z.nil?

z is never in scope, because it is present only inside a string, it does 
not appear anywhere before the call of the method "nil?"

you can do:

{ z } if z.nil? => returns nothing of nothings (not nil nor false) ruby 
don't complain because z is seen in the scope

Also works:

"HELLO #{an_unique_var_name}" if an_unique_var_name.nil?

-------------------------------------------------------------------------------

François 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.


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