Logging for newbies in Swift

Primary output in Swift utilizing print

The very first technique I would like to point out you is the print operate. It might probably write the textual illustration of the given gadgets to the usual output. In different phrases we will merely say that it could possibly print textual content to the display screen. Many of the whats up phrase packages make the most of this technique to show the well-known “Hi there world!” message. In Swift, print is sort of a strong technique, since you possibly can go round a number of gadgets for printing out plus you possibly can specify a separator string and a terminator parameter. 🤔

print("Hi there World!")

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

print("Hi there World!", terminator: "")

Should 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 state of affairs it will be printed out proper after the “Hi there World!” sentence. Should you run this system utilizing a Terminal software, 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 potential to present 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 beneath the hood will convert the variable into a correct string illustration, so you do not have to fiddle with sort casting on a regular basis, however merely print out something.

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


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

You can too customise the separator character by means of an argument. So if you happen to 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: ", ")

Properly, in my earlier article you’ve got seen learn how 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, here is a cute multi-line ascii artwork dinosaur. 🦕

Debugging and print

Generally it will 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 the whole lot to string, debug print provides you with a quick debug information in regards to the given gadgets. The debugPrint technique will print out numbers similar to print does, it will add double quotes round strings, and it will print some additional information about many of the different “advanced” varieties.

print(1) 
debugPrint(1) 

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

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

Actually 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, but it surely’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 may give 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 splash character, however for extra advanced varieties it will output the underlying construction of the article. Don’t be concerned, you needn’t perceive the output of this technique, simply do not forget that it could possibly present you useful information throughout debugging. 🐞

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

The ClosedRange struct is a built-in sort 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 article, dump takes this one step additional by displaying us the precise decrease and higher certain properties of the worth. This may be extraordinarily useful when you’ve got a posh sort with plenty of underlying properties that you just need to rapidly 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 a couple of extra operate arguments you could configure:

dump("take a look at", identify: "my-variable", indent: 4, maxDepth: 5, maxItems: 5)

You may give 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 parts for which to put in writing the complete contents. Be happy to play with these parameters for some time. 😉

As you possibly can see dump is sort of a strong technique, however nonetheless there are different capabilities for logging functions, let me present you one that’s coming from the Goal-C occasions.

NSLog – the legacy logger operate

In case you have ever labored with Goal-C you ought 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 important to import the Basis framework so as to use NSLog.

import Basis

NSLog("I am a dinosaur.")

You need to know that NSLog will print the present date & time first, then it will show the identify of the working program with the method and thread identifiers and solely then it will print your message.

Simply to be clear, NSLog is coming from the Goal-C period, it’s not a beneficial logging answer anymore. It is usually very gradual and that may trigger some points if you happen to want exactly timed outputs. That is why I do NOT suggest utilizing NSLog in any respect, however you additionally should know that till a couple of 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 system to the unified logging system, you need to use the OSLog framework. This new software was launched at WWDC 2016 and just lately acquired some good API refinements & updates. You need to undoubtedly verify the OSLog and Unified Logging beneficial by Apple article if you wish to be taught extra about this matter it is an incredible 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 assist, this answer will not be just right for you…

SwiftLog – A Logging API package deal for Swift

This open supply package deal may be simply built-in into your Swift initiatives by way of the Swift Package deal Supervisor. You simply should set it up as a dependency within the Package deal.swift manifest file or you possibly can hook it utilizing Xcode beneath the File > Swift Packages menu as an SPM dependency.

import PackageDescription

let package deal = Package deal(
    identify: "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 easy. First it’s important to import the Logging framework, you then 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("Hi there World!")

The next log ranges are supported:

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

You can too connect extra logging metadata to the logger, it is best to verify the readme for more information about this feature. SwiftLog is utilized in many real-world initiatives, comparable to Vapor 4 (a server facet Swift framework), this additionally implies that it really works nice on Linux working techniques. 🐧

Conclusion

If it involves logging, there are a number of good choices to select from. It solely is determined by your wants which one is the most effective, however typically 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 be supplied 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 stick to print and dump statements. It is completely high quality to debug utilizing these easy methods 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 & data over time, I hope this text offers you a greater view of the accessible logging instruments. 🤓