From: Tim Hunter <rmagick@...>
Date: 2008-06-26T01:05:20+09:00
Subject: Re: Question on passing blocks

Ruby Freak wrote:
> In the code below, a block, { x += 1 } is magically passed to
> thrice ?? or something like that.
> I don't understand the usage of  the "thrice { iterator }" using {}
> and why I can't make a normal block syntax work. The thrice method
> doesn't take (normal) parameters, so how does this work?
> 
> Ruby, Have you been messing around behind my back?
> Thanks in advance.
> 
> def thrice
>     yield
>     yield
>     yield
> end
> 
> x = 5
> puts "value of x before: #{x}" #  => 5
> thrice { x += 1 }
> puts "value of x after: #{x}" #  => 8
> 
> # broken from here down
> 
> thrice  { |x| x += 1 }
> 
> thrice do |x|
>   x += 1
> end

In the first case, x in the block refers to the x defined outside the 
block. In the 2nd and 3rd cases, you've used x as an argument so it 
hides the x outside the block. Any changes you make to x-the-argument 
are lost each time the block exits.
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