swift logging for iOS >= 8 with os_log and NSLog

Question

I want to write my own logging function using os_log (available for iOS >= 10.0) and NSLog.

I already wrote this code:

static func LogDebug(log: StaticString) {
    if #available(iOS 10.0, *) {
        os_log(log, type: .debug)
    } else {
        NSLog(log)
    }
}

But now I get the exception that StaticString can not be converted to normal String. Do you know how to solve that?

Answer 1

The first argument of both os_log() and NSLog() is a format string, and contains format specifiers (starting with %) which are expanded by the following variable argument list.

To log an arbitrary string, use the %@ format, followed by the string. Otherwise it can crash or produce wrong output if the string contains % characters:

func LogDebug(log: String) {
    if #available(iOS 10.0, macOS 10.12, *) {
        os_log("%@", type: .debug, log)
    } else {
        NSLog("%@", log)
    }
}