OSLog Variadic Arguments

main-multiple-functions.swift

// A version of main.swift that is closer to https://stackoverflow.com/questions/50937765/why-does-wrapping-os-log-cause-doubles-to-not-be-logged-correctly/50942917#50942917, a linked by https://twitter.com/caseyliss/status/1268555666412765184

import Foundation
import os.log
import os

class OSLogWrapper {

    func logDefaultariadicArg(_ message: StaticString, _ args: CVarArg... ) {
        os_log(message, type: .default, args)
    }

    func logDefaultMultiArg(_ message: StaticString, _ arg1: CVarArg) {
        os_log(message, type: .default, arg1)
    }

    func logDefaultMultiArg(_ message: StaticString, _ arg1: CVarArg, _ arg2: CVarArg) {
        os_log(message, type: .default, arg1, arg2)
    }

    func logDefaultMultiArg(_ message: StaticString, _ arg1: CVarArg, _ arg2: CVarArg, _ arg3: CVarArg) {
        os_log(message, type: .default, arg1, arg2, arg3)
    }

    func testWrapper() {
        logDefaultMultiArg("WTF: %f", 1.2345)
        logDefaultMultiArg("WTF: %f, %@, %f", 1.2345, "testing", 6.789)
        logDefaultMultiArg("WTF: %f, %@", 1.2345, 1.2345, "testing")
        logDefaultariadicArg("WTF: %f", 1.2345)
    }
}

OSLogWrapper().testWrapper()

main.swift

import Foundation
import os.log

extension OSLog {

    public private(set) static var tests = OSLog(category: "Tests")

    private convenience init(category: String) {
        self.init(subsystem: "uk.josephduffy.os_log_testing", category: category)
    }

    public func signpost(type: OSSignpostType, name: StaticString, signpostID: OSSignpostID) {
        os_signpost(type, log: self, name: name, signpostID: signpostID)
    }

    public func signpost(type: OSSignpostType, name: StaticString, signpostID: OSSignpostID, format: StaticString, _ args: CVarArg...) {
        signpost(type: type, name: name, signpostID: signpostID, message: format, args: args)
    }

    public func `default`(_ message: StaticString, _ args: CVarArg...) {
        log(message, type: .default, args: args)
    }

    public func info(_ message: StaticString, _ args: CVarArg...) {
        log(message, type: .info, args: args)
    }

    public func debug(_ message: StaticString, _ args: CVarArg...) {
        log(message, type: .debug, args: args)
    }

    public func error(_ message: StaticString, _ args: CVarArg...) {
        log(message, type: .error, args: args)
    }

    public func fault(_ message: StaticString, _ args: CVarArg...) {
        log(message, type: .fault, args: args)
    }

    private func log(_ message: StaticString, type: OSLogType, args: [CVarArg]) {
        switch args.count {
        case 0:
            os_log(message, log: self, type: type)
        case 1:
            os_log(message, log: self, type: type, args[0])
        case 2:
            os_log(message, log: self, type: type, args[0], args[1])
        case 3:
            os_log(message, log: self, type: type, args[0], args[1], args[2])
        default:
            assertionFailure("Too many arguments passed to log. Update this to support this many arguments.")
            os_log(message, log: self, type: type, args[0], args[1], args[2])
        }
    }

    private func signpost(type: OSSignpostType, name: StaticString, signpostID: OSSignpostID, message: StaticString, args: [CVarArg]) {
        switch args.count {
        case 0:
            os_signpost(type, log: self, name: name, signpostID: signpostID)
        case 1:
            os_signpost(type, log: self, name: name, signpostID: signpostID, message, args[0])
        case 2:
            os_signpost(type, log: self, name: name, signpostID: signpostID, message, args[0] ,args[1])
        case 3:
            os_signpost(type, log: self, name: name, signpostID: signpostID, message, args[0], args[1], args[2])
        default:
            assertionFailure("Too many arguments passed to signpost. Update this to support this many arguments.")
            os_signpost(type, log: self, name: name, signpostID: signpostID, message, args[0], args[1], args[2])
        }
    }

}

let signpostID = OSSignpostID(log: OSLog.tests)
OSLog.tests.signpost(type: .begin, name: "Test Event", signpostID: signpostID, format: "%f, %@, %f", 1.2345, "testing start", 6.789)
Thread.sleep(forTimeInterval: 5)
OSLog.tests.signpost(type: .end, name: "Test Event", signpostID: signpostID, format: "%f, %@, %f", 1.2345, "testing end", 6.789)