in page 23,
Using Swift requires much more typing. In addition, when stopping the debugger out of the blue, or on Objective-C code, LLDB will default to Objective-C.
and page 74,
You stopped the debugger out of the blue! Remember, LLDB will default to Objective-C; you’ll need to use the -l option to stay in the Swift context:
I don’t understand what is the “out of the blue”
How can i check this in Xcode?