From: 7stud -- <bbxx789_05ss@...>
Date: 2009-08-25T00:59:12+09:00
Subject: Re: Modules setting values to nil in unprocessed conditional

Nate wrote:
> Hi everyone.  We're noticing some strange behavior when including
> modules in classes.  It seems that even if a conditional block is
> forced to evaluate as false (and presumably not execute), assignments
> in the conditional block are executed and set to nil.  Here is an
> example:
> 
> ==========================
> module Conundrum
>   def riddle
>     @riddle ||= 'mystery'
>   end
> 
>   def riddle=(new_val)
>     puts "Called riddle="
>     @riddle = new_val
>   end
> end
> 
> class Test
>   include Conundrum
> 
>   def test
>     puts "Before: #{riddle}"
>     if true == false


Inside test, self is equal to the Test instance you created here:

> Test.new.test

And this line:

>     puts "Before: #{riddle}"

is equivalent to:

>     puts "Before: #{self.riddle}"

However, when ruby parses this line:

>       riddle = 'solved!'

ruby creates a local variable named riddle.  As a result, when you get 
to this statement:

>     puts "After: #{riddle}"

riddle is no longer equivalent to self.riddle.  Instead riddle is just 
riddle; and riddle is a local variable that hasn't been assigned a 
value.  For local variables that exist but have not been assigned a 
value, ruby returns nil for the value of the variable.  Then the string 
interpolation calls nil.to_s which returns a blank string.

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