Advanced Debugging with Xcode and LLDB

WWDC 2018

“Failed to get module from AST context”

Swift Type Resolution

Advanced Debugging Tips and Tricks

Debug Tab 👍

expression (change a value)

You can test your code without reRun 👍

Symbolic Breakpoint

• symbolic breakpoint → use commands ($arg1, $arg2, etc) for more detail

One shot breakpoint

• Temporary breakpoint that’s automatically deleted
• breakpoint set --one-shot true --name “-[UILabel setText:]”

Instruction Pointer

• With great power comes great responsibility (The riskiest feature)
• It can not guarantee that the application’s state will remain intact, 
  i.e., memory issues

CustomDebugStringConvertible

Watchpoint 👍

• It pauses the debugger the next time the value of that variable is changed.

UIView.recursiveDescription( )

unsafeBitCast(memory address, to: )

LLDB Print Commands

Advanced View Debugging

• You can get an object info and edit a value in debugging.
• po ((NSLayoutConstraint *)memory address)
• e [((NSLayoutConstraint *)memory address setConstant:-30]

All Allocation and Free History

• Allocation backtrack for all selected in the view debugger

Backtrace → Go to code 👍