From: "Erik Bågfors" <erik@...>
Date: 2001-11-05T04:52:18+09:00
Subject: [ruby-talk:24342] Re: block/yield puzzle

On Sun, 2001-11-04 at 20:36, David Alan Black wrote:
> Hello --
> 
> Well, not puzzle in the fun sense -- just something I don't
> understand.
> 
> I've been playing around with ways to generated a default block to
> yield to.  This isn't a particular great way, but I'm stuck on why it
> doesn't at least work.
> 
>   def thing(x, b = proc { puts "default" } )
>     if block_given?
>       yield
>     else
>       thing(x) &b
>     end
>   end
> 
>   thing(1) { puts "associated block" }  #  => "associated block"
>   thing(1)                              #  infinite loop
> 
> 
> Somehow the "x" argument seems to be causing trouble, because this
> version does what I expected:
> 
>   def thing(b = proc { puts "default" } )
>     if block_given?
>       yield
>     else
>       thing &b
>     end
>   end
> 
>   thing{ puts "associated block" }  #  => "associated block"
>   thing                             #  => "default"
> 
> I'm not seeing why the first version hangs.  Enlightenment welcome.
> 

Is there anything wrong with this solution??
def thing(x, b = proc { puts "default" } )
  if block_given?
    yield
  else
    thing(x, &b)
  end
end

thing(1) { puts "associated block" }  #  => "associated block"
thing(1)                              #  => "default"

Works for me.

/Erik

-- 
Erik B�gfors               | erik@bagfors.nu
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