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Logging

Set a logging level to dictate priority of events logged

Quick Start

By default, nothing will be logged, so you want to set a logging level during app set-up, before any loggable events. Different logging levels are often set for different build schemes (debug scheme may be .verbose while release might be .warn).

Log.logLevel = .warn

Use the level functions when logging to indicate what type of event has occurred

Log.verbose("Lower priority events will not be logged")
Log.error("Errors are higher priority than .warn, so will be logged")

Log levels (from highest to lowest priority):

  • verbose
  • debug
  • info
  • warn
  • error
  • off

A Trace is similar to a Log, but can be used to measure timing. Traces will also be logged as os_signposts which are viewable in Xcode Instruments.

Trace.begin("App Startup")
...
Trace.end("App Startup")

Trace.event("App moved to background")

Advanced functionality

One or more LogHandlers may be added at both the instance level, or global level. A LogHandler may be used for example to send the log messages to the console, or to an analytics service. There is a OSLogHandler defined globally by default, which will send log output to the console or oslog if running iOS 14 or greater.

public protocol LogHandler {
    func handle(message: Log.Message)
}

// add a handler that will receive messages from ALL log instances.
Log.addGlobalHandler(MyLogHandler())

Log messages may be categorized by defining separate instances of the Log class.

final class Loggers {
    static let userInterface = Log("UI", logLevel: .verbose)
    static let app = Log("App")
    static let network = Log("Network", logLevel: .error)
}

Loggers.userInterface.info("Button Pressed")
Loggers.network.error("Token Expired")
Loggers.app.warn("Out of Memory")

You may also include custom handlers per Log instance. Messages will still be reported to the global handler as well.

Loggers.network.addHandler(MyLogHandler())

Log level can also be represented by emoji instead of strings.

Log.useEmoji = true

Emoji key:

  • .verbose = 📖
  • .debug = 🐝
  • .info = ✏️
  • .warn = ⚠️
  • .error = ⁉️