KVSegFault.swift

if context == &FooKVOContext {
    // .CGSizeValue can cause a sneaky segfault here, because it will execute on ALL keyPaths (not just "contentSize")
    if let newContentSize = change?[NSKeyValueChangeNewKey]?.CGSizeValue() where keyPath == "contentSize" {
        // do things
    }
} else {
    super.observeValueForKeyPath(keyPath, ofObject: object, change: change, context: context)
}