From: Patrick Li <patrickli_2001@...>
Date: 2008-08-29T04:28:35+09:00
Subject: Subtle bug with catch/throw. Am I missing something?

Hi,
I'm having trouble locating this bug that I'm having. I think it's
because I don't completely understand Ruby's throw/catch mechanism.

I'm trying to write a simple example that demonstrates the same problem,
but I can't track down the bug.

Here's my code: Is there any subtleties that may cause throw/catch to
not behave as expected?

  def idle(engine,key)
    catch(:exit) do                       <-- Catch :exit
      while engine.nextFrame(key)
        engine.drawFrame do
          drawInContext(@img, 0, 0, 1)
        end

        @enterEvent.listen do
          @state = method(:active)
          puts "player entered"
          throw :exit                     <-- Throw :exit
        end
      end
    end
  end

Gives me: "in `throw': uncaught throw `exit' (NameError)"

And what's really strange is, the problem goes away after putting in a
print statement.


  def idle(engine,key)
    catch(:exit) do                       <-- Catch :exit
      while engine.nextFrame(key)
        engine.drawFrame do
          drawInContext(@img, 0, 0, 1)
        end

        @enterEvent.listen do
          @state = method(:active)
          puts "player entered"
          throw :exit                     <-- Throw :exit
        end
      end
    end

    puts "end"  <-- This line causes the problem to go away.
  end

Thanks a lot for your help. Any place to start looking would be really
helpful. I'm fresh out of ideas.
  -Patrick

I'm using Ruby 1.8.6 on Windows.
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