Latest 2.0.1
License MIT
Platforms ios 8.0, osx 10.9, watchos 2.0, tvos 9.0

SLF4Swift – Simple Loging Facade for Swift

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Simple Log Facade for Swift serves as a simple facade for logging frameworks allowing the end user to plug in the desired logging framework at deployment time

let myLogger = SLF4Swift.getLogger("loggerName")"my info message")
myLogger.log(.Error, "my error message")

Not already chosen a logging framework? Don’t want to be tied to a specific framework and want to switch (or even combine) easily?
Why not uing a logging facade?

A Simple Logging Facade

  • make your framework or any part of your codes no dependent to a specific logging frameworks ie. reduce the coupling between an application and any particular logging framework
  • allow to log of course with a common interface, avoiding the use of print() or NSLog() or commented debugging print code
  • allow the end user capture the logs and print using his chosen logging frameworks

For framework or any part of codes not linked to a logging framework

Getting Logger

Getting the default one

let myLogger = SLF4Swift.defaultLogger

Get logger using a key or create if not exist

let myLogger = SLF4Swift.createLogger("loggerKey")

Or just get it – here logger could be nil if not already created

if let myLogger = SLF4Swift.getLogger("loggerKey") {..}

A key could be a framework name, a class name, a topic name, ….

If you use a key into a framework, create a public constant to allow the end user to decide according to this key what to do with your logs (see Custom factories and loggers)

Printing like any other log framework

myLogger.log(.Error, "my error message") // basic method
// and some shortcut"my info message")
myLogger.warn("my warn message")
// if message compute in a long period of time
if myLogger.isLoggable(.Verbose) {
    myLogger.log(.Verbose, createLongMessageClosure())
if myLogger.exec(.Verbose) { // or with closure
    myLogger.log(.Verbose, createLongMessageClosure())

There is also macro functions for default logger

SLFLogInfo("info message")
SLFLog(.Verbose, "verbose message")

By declaring typealias Log = SLFLogLevel you can also use default logger like this

Log.Info.message("info message")
Log.Verbose.message("verbose message")
Log.Verbose.trace()// print file, function and line

For the end user

Installing a logger factory

By default is installed a NullLoggerFactory, which disable all logs


To enable log, set your LogFactoryType


or add DEBUG to "Other Swift Flags" into "Swift Compiler – Custom Flags" section
this add by default a SLFLoggerFactory, which use by default print()


Some backend factories are already implemented into backend folder (see setup for pod)


Custom factories and loggers

You can your create your own LogFactoryType and/or LoggerType

  • then return a logger according to the logger key used by one framework or any part of code
class MyCustomLoggerFactory: ProxyLoggerFactory {

    func getLogger(name: LoggerKeyType) -> LoggerType? {
        if name == AFrameWorkKey {
            return NullLogger.instance // deactive log for specifc logger
        else if name == AnOtherFrameWorkKey {
            var logger = super.getLogger(name)
            logger.level = .DEBUG // set a specific log level
            return logger
        return super.getLogger(name)

What you can use

To create a custom LogFactoryType extend

  • SingleLoggerFactory if your factory use only one logger
  • ProxyLoggerFactory if your want to use an another factory and make some adaptations
  • SLFLoggerFactory and override doCreateLogger, if you want to store logger into a Dictionnary by key

Some basic loggers are already implemented into implementation folder (log to a file, using nslog, …)


Don’t hesitate to fork this repository and PR additionnal LogFactoryType for your logging framework



Using cocoapods

Add pod 'SLF4Swift' to your Podfile and run pod install.

Add use_frameworks! to the end of the Podfile.


pod 'SLF4Swift/CocoaLumberjack'

pod 'SLF4Swift/XCGLogger'

pod 'SLF4Swift/SpeedLog'

pod 'SLF4Swift/Loggerithm'

Make your own framework dependent

In podspec

s.dependency 'SLF4Swift'

For additional logger ie. simple implementation

Add pod 'SLF4Swift/Impl' to your Podfile

Using xcode project

  1. Drag the.xcodeproj file to your project/workspace or open it to compile it
  2. Add the framework to your project


  • Protocol or protocol implentations do not allow to give default value for functions parameters, caller context cannot be passed to log message (__FILE__, __LINE__, __FUNCTION__). If there is a way, I am interested to learn it


The MIT License (MIT), see LICENSE file

Latest podspec

    "name": "SLF4Swift",
    "version": "2.0.1",
    "summary": "Simple Log Facade for Swift",
    "description": "Simple Log Facade for Swift serves as a simple facadenfor logging frameworks allowing the end user to plug in the desirednlogging framework at deployment time",
    "homepage": "",
    "license": "MIT",
    "authors": {
        "phimage": "[email protected]"
    "platforms": {
        "ios": "8.0",
        "osx": "10.9",
        "watchos": "2.0",
        "tvos": "9.0"
    "source": {
        "git": "",
        "tag": "2.0.1"
    "default_subspecs": "Core",
    "resources": "logo-128x128.png",
    "subspecs": [
            "name": "Core",
            "source_files": "SLF4Swift/*.swift"
            "name": "Impl",
            "source_files": "SLF4Swift/Implementation/*.swift",
            "dependencies": {
                "SLF4Swift/Core": []
            "name": "CocoaLumberjack",
            "source_files": "Backend/CocoaLumberjack/*.swift",
            "dependencies": {
                "SLF4Swift/Core": [],
                "CocoaLumberjack/Swift": []
            "platforms": {
                "ios": "8.0",
                "osx": "10.10",
                "watchos": "2.0"
            "name": "XCGLogger",
            "source_files": "Backend/XCGLogger/*.swift",
            "dependencies": {
                "SLF4Swift/Core": [],
                "XCGLogger": []
            "platforms": {
                "ios": "8.0",
                "osx": "10.9",
                "watchos": "2.0"

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