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Logging for newcomers in Swift

Discover ways to print variables to the debug console utilizing completely different capabilities resembling print, dump, NSLog and the unified os.log API.


Primary output in Swift utilizing print

The very first technique I would like to indicate you is the print operate. It might write the textual illustration of the given gadgets to the usual output. In different phrases we are able to merely say that it could print textual content to the display. A lot of the whats up phrase applications make the most of this technique to show the well-known “Howdy world!” message. In Swift, print is kind of a robust technique, since you’ll be able to cross round a number of gadgets for printing out plus you’ll be able to specify a separator string and a terminator parameter. 🤔

print("Howdy World!")

The snippet above will show the Howdy World! textual content adopted by a newline character (n), it’s because the default terminator is at all times a newline. You may override this habits by offering your individual terminator string.

print("Howdy World!", terminator: "")

When you run this instance utilizing Xcode it’s best to see that the “Program ended with exit code: 0” textual content will seem in a newline within the first case, however within the second situation it’s going to be printed out proper after the “Howdy World!” sentence. When you run this system utilizing a Terminal software, a % character be current as an alternative of the brand new line within the second case. 💡

What about printing out a number of variables? It’s doable to offer a number of gadgets to the print operate, they are often actually something, print can deal with strings, integers and all types of different variables. Print underneath the hood will convert the variable into a correct string illustration, so you do not have to fiddle with kind casting on a regular basis, however merely print out something.

print(1, 2, 3, 4, 5)

print(1, "two", 3.14, true)

You may as well customise the separator character by way of an argument. So in case you want a coma character (adopted by an area) in between the weather, you’ll be able to write one thing like this:

print("a", "b", "c", separator: ", ")

Effectively, in my earlier article you will have seen how you can assemble numerous strings utilizing literals and interpolation, you need to use all these variables to print out stuff to the console.

           / _)
    .-^^^-/ /
 __/       /

For instance, here is a cute multi-line ascii artwork dinosaur. 🦕

Debugging and print

Typically it might be cool to know just a bit bit of additional information in regards to the printed variable, that is when debugPrint may also help you. The primary distinction between print and debugPrint is that whereas print merely converts every thing to string, debug print will provide you with a short debug information in regards to the given gadgets. The debugPrint technique will print out numbers similar to print does, it’s going to add double quotes round strings, and it will print some additional information about a lot of the different “advanced” sorts.




Truthfully I’ve virtually by no means used this technique, and I at all times most popular print if I needed to print out one thing to the console, however it’s at all times good to know that there’s such an possibility accessible built-in to the usual library, nevertheless there’s a technique that can provide you far more information… 🧐

Debugging utilizing dump

The dump technique can print out the given object’s content material utilizing its mirror to the usual output. Lengthy story brief, this operate will present you a extra detailed view in regards to the property. For scalar values the dump technique will produce virtually the identical output as debug-print, besides the dump line at all times begins with a touch character, however for extra advanced sorts it’s going to output the underlying construction of the thing. Don’t be concerned, you need not perceive the output of this technique, simply do not forget that it could present you useful information throughout debugging. 🐞


The ClosedRange struct is a built-in kind with a lowerBound and an upperBound property. Whereas the print operate solely returned the outlined vary (1…5), the debugPrint technique additionally revealed the kind of the thing, dump takes this one step additional by displaying us the precise decrease and higher sure properties of the worth. This may be extraordinarily useful when you will have a fancy kind with numerous underlying properties that you simply wish to shortly examine for some purpose. 🔍

By the way in which, debugging is the act of discovering (and resolving) bugs. Bugs are issues in your program code that forestall regular operation. Builders can use debugger instruments to run and examine code step-by-step, line by line or per instruction, however most of them are merely placing print statements into the code to see the present state or results of a given operate. 🤷‍♂️

Dump has just a few extra operate arguments which you could configure:

dump("check", title: "my-variable", indent: 4, maxDepth: 5, maxItems: 5)

You can provide a reputation to every dumped variable, add some additional indentation earlier than the sprint character, specify the utmost depth for descendents and the utmost variety of components for which to jot down the total contents. Be at liberty to play with these parameters for some time. 😉

As you’ll be able to see dump is kind of a robust technique, however nonetheless there are different capabilities for logging functions, let me present you one that’s coming from the Goal-C instances.

NSLog – the legacy logger operate

When you’ve got ever labored with Goal-C you have to be aware of the NS prefixes. The NSLog operate can log an error message to the Apple System Log facility console. It is not a part of the Swift customary library, however it’s a must to import the Basis framework with the intention to use NSLog.

import Basis

NSLog("I am a dinosaur.")

It is best to know that NSLog will print the present date & time first, then it’s going to show the title of the operating program with the method and thread identifiers and solely then it’s going to print your message.

Simply to be clear, NSLog is coming from the Goal-C period, it’s not a really useful logging answer anymore. It’s also very sluggish and that may trigger some points in case you want exactly timed outputs. That is why I do NOT suggest utilizing NSLog in any respect, however you additionally need to know that till just a few years in the past there was no higher built-in different for it, I am not judging, simply saying… 😅

Unified Logging and Exercise Tracing

If you wish to ship log messages on an Apple gadget to the unified logging system, you need to use the OSLog framework. This new software was launched at WWDC 2016 and not too long ago obtained some good API refinements & updates. It is best to positively test the OSLog and Unified Logging really useful by Apple article if you wish to be taught extra about this subject it is an ideal write up.

My solely concern about this logging API is that it’s not that common. It really works nice on Apple platforms, however since Swift is an common language if you wish to add Linux and even Home windows help, this answer will not give you the results you want…

SwiftLog – A Logging API package deal for Swift

This open supply package deal will be simply built-in into your Swift tasks through the Swift Package deal Supervisor. You simply need to set it up as a dependency within the Package deal.swift manifest file or you’ll be able to hook it utilizing Xcode underneath the File > Swift Packages menu as an SPM dependency.

import PackageDescription

let package deal = Package deal(
    title: "myProject",
    dependencies: [
        .package(url: "https://github.com/apple/swift-log.git", from: "1.4.0"),
    targets: [
        .target(name: "myProject", dependencies: [
            .product(name: "Logging", package: "swift-log")

The utilization is basically easy. First it’s a must to import the Logging framework, then you definately create a logger and you employ that logger occasion to print out numerous log messages.

import Logging

let logger = Logger(label: "app-identifier")

logger.information("Howdy World!")

The next log ranges are supported:

  • hint
  • debug
  • information
  • discover
  • warning
  • error
  • essential

You may as well connect further logging metadata to the logger, it’s best to test the readme for more information about this feature. SwiftLog is utilized in many real-world tasks, resembling Vapor 4 (a server facet Swift framework), this additionally implies that it really works nice on Linux working techniques. 🐧


If it involves logging, there are a number of good choices to select from. It solely relies on your wants which one is the perfect, however on the whole we are able to say that it’s time to go away behind NSLog, and time to make use of the brand new OSLog framework. If you’re utilizing Swift on non-Apple platform it’s best to think about using the SwiftLog library, which can be supplied by Apple.

Alternatively if you’re simply scratching the floor and you do not want that many choices or log ranges you’ll be able to merely persist with print and dump statements. It is completely high quality to debug utilizing these easy strategies to start with. Mastering one thing takes time and debuggers will be fairly horrifying at first sight. Use print as a lot as you want, however at all times attempt to enhance your instruments & data over time, I hope this text offers you a greater view of the accessible logging instruments. 🤓



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