From: David Alan Black <dblack@...>
Date: 2001-11-05T04:36:02+09:00
Subject: [ruby-talk:24341] block/yield puzzle

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.


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav