Logging & Debugging

The Foundation manager provides a customizable logger utility. You can use the logger in client application development or ignore it.

The logging services are rendered per contract with the Logger protocol. The logging service uses Apple's Unified Logging System (OSLog) as the underlying service provider. The logger service provides useful inline functions for each OSLogLevel in two variations:

• Log function accepting StaticString and variadic CVarArg
• Log function accepting Any typed value

Usage

We recommend you create an OSLog instance providing a subsystem and category, per Apple's naming convention.

static let FLFoundationLog = FLFoundationFactory.logger(
                                    subsystem: "com.quickplay.FLFoundation",
                                    category: "HTTPClient")
FLFoundationLog.logDebug(...)
FLFoundationLog.logInfo(...)
FLFoundationLog.log(...)
FLFoundationLog.logError(...)
FLFoundationLog.logFault(...)

Provide a subsystem value in reverse domain format. You can use the bundle identifier of the framework or app in use. The category value must be a valid and thoughtful name of the module being logged. You can view logs outside Xcode using Console.app. The subsystem and category values are used for filtering log messages, which makes debugging easier.

Make your custom complex types conform to CustomDebugStringConvertible and CustomStringConvertible, and use the wrapper functions to pass your complex type to log them.

Privacy

The unified logging system considers dynamic strings and complex dynamic objects to be private and doesn't collect them automatically. The log messages need to be marked with access modifiers. When you need to capture a dynamic string, explicitly declare the string public using the public keyword. For example, %{public}s.

The wrapper functions accepting Any type value as input with this logger service mark log message arguments as public with DEBUG and private with RELEASE configurations. When using the other log function, it's up to you to mark arguments as public or private. Be careful about what you log. Don't accidentally expose confidential data, that is, secret keys or anything of that sort.

Customize log output

To provide your own custom formatting while logging your custom type, extend it to conform to CustomOSLogMessageConvertible.