Hey, I was trying to implement a breadth first search where I would mutate the search queue while iterating through it. Simplified, it was something like this: numbers = [1, 2, 3, 4] numbers.each { |number| numbers << (1+number) unless number > 3 puts number } This works fine for arrays that are being made in the MacRuby VM, but if I get an array back from an Objective-C method and try to iterate over that array then I would get an exception (which segfaulted the VM) when I tried to mutate the array during iteration. Simplified, it would be something like this: numbers = NSMutableArray.alloc.init numbers.addObjectsFromArray [1, 2, 3, 4] numbers.each { |number| numbers << (1+number) unless number > 3 puts number } Should both types of arrays work the same way? An instance of NSMutableArray says its class is Array, so I thought that they would. Also, is this type of exception one that should be caught by the VM and propagated as a normal Ruby Exception that I could rescue? Mark Rada mrada@marketcircle.com