[swift] why? compiler warnings

defer-do.rst

xcode:	11
target/platform:	iOS 13.1
swift:	5
warning:	'defer' statement before end of scope always executes immediately; replace with 'do' statement to silence this warning
fix-suggest:	Replace 'defer' with 'do'

func doSomething(value: Int?, value2: Int?) {
    guard let value = value else { return }
    defer {
        print(value2 ?? "nil")
    }
}

doSomething(value: nil, value2: 1) // result:
doSomething(value: 1, value2: nil) // result: nil