Logging for inexperienced persons in Swift

Fundamental output in Swift utilizing print

The very first methodology I would like to indicate you is the print perform. It will probably write the textual illustration of the given objects to the usual output. In different phrases we will merely say that it may possibly print textual content to the display. A lot of the howdy phrase packages make the most of this methodology to show the well-known “Good day world!” message. In Swift, print is sort of a strong methodology, since you possibly can cross round a number of objects for printing out plus you possibly can specify a separator string and a terminator parameter. 🤔

print("Good day World!")

The snippet above will show the Good day World! textual content adopted by a newline character (n), it is because the default terminator is at all times a newline. You possibly can override this conduct by offering your personal terminator string.

print("Good day World!", terminator: "")

When you run this instance utilizing Xcode it is 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 “Good day World!” sentence. When you run this system utilizing a Terminal utility, a % character be current as a substitute 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 objects to the print perform, 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 too can customise the separator character via an argument. So when you want a coma character (adopted by an area) in between the weather, you possibly can write one thing like this:

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

Effectively, in my earlier article you could have seen the way to assemble varied strings utilizing literals and interpolation, you need to use all these variables to print out stuff to the console.

print("""
            __
           / _)
    .-^^^-/ /
 __/       /
<__.|_|-|_|
""")

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

Debugging and print

Generally it might be cool to know just a bit bit of additional information in regards to the printed variable, that is when debugPrint will help you. The principle distinction between print and debugPrint is that whereas print merely converts every part to string, debug print offers you a quick debug information in regards to the given objects. The debugPrint methodology 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.

print(1) 
debugPrint(1) 

print("foo") 
debugPrint("foo") 

print(1...5) 
debugPrint(1...5) 

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

Debugging utilizing dump

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

dump(1)
dump(3.14)
dump("foo")
dump(1...5)

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

By the best way, 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 perform. 🤷‍♂️

Dump has a number of extra perform arguments you can configure:

dump("take a look at", 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 complete contents. Be at liberty to play with these parameters for some time. 😉

As you possibly can see dump is sort of a strong methodology, 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 perform

In case you have ever labored with Goal-C try to be accustomed to the NS prefixes. The NSLog perform can log an error message to the Apple System Log facility console. It is not a part of the Swift commonplace library, however you need to import the Basis framework so as to use NSLog.

import Basis

NSLog("I am a dinosaur.")

It’s best to know that NSLog will print the present date & time first, then it’s going to show the title of the working 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 beneficial logging resolution anymore. Additionally it is very gradual and that may trigger some points when 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 a number of years in the past there was no higher built-in various 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’s best to undoubtedly examine the OSLog and Unified Logging beneficial by Apple article if you wish to be taught extra about this subject it is an awesome 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 resolution will not give you the results you want…

SwiftLog – A Logging API bundle for Swift

This open supply bundle may be simply built-in into your Swift tasks by way of the Swift Bundle Supervisor. You simply need to set it up as a dependency within the Bundle.swift manifest file or you possibly can hook it utilizing Xcode underneath the File > Swift Packages menu as an SPM dependency.

import PackageDescription

let bundle = Bundle(
    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 admittedly simple. First you need to import the Logging framework, then you definitely create a logger and you employ that logger occasion to print out varied log messages.

import Logging

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

logger.information("Good day World!")

The next log ranges are supported:

• hint
• debug
• information
• discover
• warning
• error
• vital

You too can connect further logging metadata to the logger, it is best to examine the readme for more information about this selection. SwiftLog is utilized in many real-world tasks, equivalent to Vapor 4 (a server aspect Swift framework), this additionally signifies that it really works nice on Linux working programs. 🐧

Conclusion

If it involves logging, there are a number of good choices to select from. It solely depends upon your wants which one is the perfect, however basically we will 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 is best to think about using the SwiftLog library, which can also be offered by Apple.

Alternatively in case you are simply scratching the floor and you do not want that many choices or log ranges you possibly can merely keep on with print and dump statements. It is completely fantastic to debug utilizing these easy strategies at first. Mastering one thing takes time and debuggers may be fairly horrifying at first sight. Use print as a lot as you want, however at all times attempt to enhance your instruments & information over time, I hope this text offers you a greater view of the accessible logging instruments. 🤓