// for example, for debugging messages in `ViewController.swift`

#if DEBUG
private let log = OSLog(subsystem: Bundle.main.bundleIdentifier!, category: "ViewController")
#else
private let log = OSLog.disabled
#endif

// and then:
//
// 1. Use `.debug` log for debugging messages, only shown if configuration is set to show debugging messages
//    (and it's a memory-only log, by default).
//
// 2. Use `%{public}@" for strings that should be logged, but omit the `{public}` if not.

func foo(message: String) {
    os_log(.debug, log: log, "%{public}@ message: %@", #function, message)
}