Swift Kick

Game of Phones, part 1 (or: Arrays in the Swift programming language) [Updated]

Update, July 24, 2014: I’ve updated this article to match the updates made to Swift with the release of Xcode beta 4. Gotta love languages in beta!

ios 8 is coming

swift kick

Welcome to another installment of Swift Kick, the series of articles on Global Nerdy covering programming in Apple’s new Swift programming language. Fell free to follow along and fire up your Xcode 6 beta, copy the examples, and experiment on your own! You can find earlier articles in this series by clicking on the Swift Kick logo to the right.

Spoiler alert! This article uses the events from the TV series Game of Thrones as a framework. You don’t need to have watched the series to understand this article, but it will reveal some plot points from the first three seasons.

Game of Thrones is popular among the sort of people who like programming, and given that the show often adds and (very brutally) deletes characters, I thought it would be a fun basis for an article on arrays in Swift.

Here are the Starks, the first family that we’re introduced to in the series:


In this article, we’re going to be working with an array representing the Stark Family. As you might expect, it’s called starkFamily, and here’s its visual representation:

The Stark Family
Parents Children
Ned Catelyn Robb Jon Sansa Arya Bran Rickon

Here’s code to define the array and then display its contents:

Here’s the output of that code:

While most statements in Swift end at the end of a line, there are certain exceptions. One such exception is made for array literals, which you can write over several lines as shown below. I prefer defining longer arrays this way, as I find them easier to read:

If you’ve programmed in Python or Ruby, you’re familiar with this sort of thing, where the interpreter (or in Swift’s case, the compiler) “knows” that arrays and dictionaries can extend beyond a single line.

Getting individual array elements

stark family array notation

If you’re familiar with programming languages like C#, Java, JavaScript, Lua, Objective-C (more modern versions, anyway), PHP, Python and Ruby, you’ll find Swift’s basic array notation familiar — it’s good ol’ reliable arrayName[index], where arrayName is the name of the array, and index is an integer specifying which element of the array we want to retrieve. As with most programming languages, the first element of an array with n elements is at index 0, the second is at index 1, the third is at index 2, and so on up until the last element, which is at index n-1.

In the code snippet below, we want to access the 3rd and 6th elements of the starkFamily array. Put another way, we want the starkFamily elements at indices 2 and 5:

Here’s the output of that code:

Setting individual array elements

The same array notation can be used to set array elements. In the code below, we want to change the contents of the element at index 0 from “Ned”, which is a nickname, to his proper name, “Eddard”:

Here’s the output:

Is the array empty, and if not, how many elements are in the array?

empty fuel gauge

Swift’s Array type has two handy methods that answer these questions:

  • The isEmpty method returns true if the array has no elements, false otherwise
  • The count method returns the number of elements in the array. If the array is empty (that is, if isEmpty returns true), then count returns 0.

For the code snippet below:

the resulting output is:

Getting ranges of array elements

Swift lets you get sub-arrays of an array by specifying a range of elements. This is one of those things that’s easier to show first, then tell afterwards, so I’ll let this picture do the talking first:

selecting sub-arrays using ranges

  • starkFamily[0..<3] (with 2 dots and a <, also known as the half-open range operator) specifies an array made of the elements of starkFamily starting at index 0, and up to but NOT including the element at index 3. If you’re mathematically inclined, you can think of 2 dots as defining a left-closed, right-open interval, which you write as [0, 3).
  • starkFamily[0...3] (with 3 dots, also known as the closed range operator) specifies an array made of the elements of starkFamily starting at index 0, and up to and including the element at index 3. If you’re mathematically inclined, you can think of 3 dots as defining a closed interval, which you’d write as [0, 3].

Here some code showing array ranges in action. Let’s say we want to pull a couple of arrays out of starkFamily:

  1. An array consisting of only the parents (elements 0 and 1).
  2. An array consisting of only the children (elements 2 and beyond).

Here’s the output:

The half-open range operator is useful for when you want to retrieve a range of array elements starting at some given index, and going on for the rest of the array. You use it in conjunction with the count property, like so:

Remember, in an array of n elements, the index of the last item is n – 1. Of course, you can always get an equivalent result with a 3-dot range…

…but in my opinion, that makes things more complicated than they need to be.

Adding elements to an array

Adding to the end of an array, part 1: The append method


Let’s add some elements to the end of the array.

While Hodor doesn’t provide much in the way of conversation — the only thing he can say is his own name — he’s practically part of the Stark family. Let’s add him to the end of the starkFamily array with the append method. Here’s a representation of what that would look like:

add hodor

Here’s the code:

and here’s the output:

Adding to the end of an array, part 2: Adding single elements with the += operator


Later in the series, Osha the wildling is taken prisoner and agrees to work for the Starks as a nanny, so she too is practically part of the family. Let’s add her to the starkFamily array, but using the += operator instead. Here’s the visualization of that operation:

add osha

Here’s the code:

And here’s the output:

Adding to the end of an array, part 3: Adding arrays with the += operator

stark direwolves

In the very first episode of Game of Thrones, the Starks come across a dead direwolf and several surviving pups. Each of the pups — eventually named Grey Wind, Lady, Numeria, Summer, Shaggydog, and Ghost — is taken by the Stark children as a pet, making them practically part of the family. Let’s put the direwolves’ names into an array, and then add that array to starkFamily. Here’s the visualization:

add direwolves

The corresponding code:

And the output:

Inserting new elements at a specified position


What if we want to add elements to the array, but somewhere other than the end?

After his father’s failed rebellion against the Starks, Theon became a hostage and ward of the Stark family, who raised him as one of their own. Let’s add him to the family, between the two elder brothers, Robb and Jon, using the insert method:

add theon

The output:

Want to add an element at the beginning of an array? Just use the insert method to insert the new element at index 0.

Deleting elements from an array

Deleting elements from a specified position

The advice given to people new to Game of Thrones is to not get too attached to a character, because anyone — even a lead character — could die. This happened in season 1 when Ned was falsely accused and found guilty of treason:


…and then Catelyn and Robb (and a good chunk of the army of the North) were killed at the “Red Wedding”, which got this sort of reaction from viewers:

Let’s reflect these deaths by deleting them from the starkFamily array. Here’s the visualization:

killing off characters

Here’s the code:

And here’s the output:

There’s a reason I removed element 2, then element 1, then element 0 rather than starting with element 0 and worked my way up. I’m going to leave it to you to figure why I did it that way.

Deleting the last element of an array

Suppose we want to get rid of the last element in starkFamily. One way to do it is to use the count property of the array to get the array’s size, then subtract 1 from it to get the last index of the array. Then, you’d use the removeAtIndex method to remove that element. It’s done in a single line of code:

While it’s simple, there’s an even simpler way that doesn’t require you to calculate the last index of the array. It’s the removeLast method, and it removes the last element of the array. Here’s the visualization:


Here’s the code:

The output:

Replacing ranges of array elements

Replacing a range of array elements with an array of equal size

don and betty draper
Let’s cross over to another popular show that airs on Sunday nights: Mad Men. As ill-advised as many of the choices made by the heads of the Stark family were, chances are those choices might by much worse if they were made by Don and Betty Draper. Still, people who make good choices don’t make good drama, so let’s go ahead and replace Ned and Catelyn with Don and Sally.

We could perform the replacement element by element:

But we can reduce this operation to a single line by specifying a range in our array, and assigning a replacement array:

replace range equal size

For this code:

We get this output:

Replacing a range of array elements with a smaller array

In season 4 of Mad Men, Betty had divorced Don and his second bachelorhood is in full swing. Let’s represent this with an array containing only Don, and let’s use this array to replace the range in starkFamily containing Ned and Catelyn. Here’s a visualization of the result:

replace range smaller

Here’s the code:

And here’s the output:

Replacing a range of array elements with a larger array

Later in the Mad Men series, Don marries his second wife, Megan. Let’s treat Don, Betty, and Megan as an array of parents and use them to replace Ned and Catelyn in starkFamily. Here’s the visualization of that arrangement:

replace range larger

Here’s the code:

And here’s the output:

Replacing a range of array elements with an empty array

Earlier in this article, we represented the deaths of Ned, Catelyn, and Robb by deleting them from the starkFamily array one at a time. Since Ned’s, Catelyn’s, and Rob’s elements are all in a row in the range [0...2], we can delete them in a single action by replacing that range with an empty array. Here’s the visualization:

replace range empty

Here’s the code:

And here’s the output:

Want to find out more about arrays in Swift?

There’s more in the Collections Types chapter of Apple’s The Swift Programming Language, and I’ll cover more in part 2 as well.

Swift Kick

Swift Kick: Need more Swift programming examples? Go to Github!

swift projects on github

Click the image to see Swift language projects on GitHub.

swift kickApple’s documentation, The Swift Programming Language, is a pretty decent read, but its examples are geared around showing individual language features and not around building full-blown apps. With Swift having been released to registered Apple developers a mere three days ago and the NDA preventing the posting of screenshots of iOS 8 and Xcode 6 until their general release, we’re going to be short on books and detailed tutorials for the next few months. So how’s a developer to learn about Swift and still play within the rules of their developer agreement with Apple?

The answer: Github. More accurately, Swift projects on Github. And there are more of them than you might think.

As I write this (10:00 a.m. EDT, June 5, 2014), even though it’s been less than 72 hours since the beta of Xcode 6 (and therefore Swift) was made available for download, there are already about 350 repos on Github marked as being done in Swift. There may be more by the time you read this.

Update: As of 1:45 p.m. EDT, June 5, 2014, there are 370 Swift repos in Github.

Some of these repos are simple experiments with Swift and its syntax, some are tests of interacting with various API using Swift, some are the sort of mini-apps you build when learning a new language, and then there’s this:


That’s right: it’s an implementation of Flappy Bird in Swift. If you’ve always wanted to learn SpriteKit and now want to learn Swift, go to the FlappySwift repo on GitHub and kill two — ahem — birds with one stone.

Keep an eye on Swift projects in Github; I’m sure that their numbers will keep growing. And don’t forget to make your own contribution!


Swift Kick

Swift Kick: Variables, constants, simple functions, and basic types in the Swift programming language

swift kickLet’s dive into Swift! For the next several articles, I’m going to share my observations as I noodle around with Swift on the Xcode 6 beta and try to get a feel for the language.

Keep in mind that Swift is in beta, and given the loose way “beta” is defined in these agile, pivot-happy days, it could be subject to all sorts of changes that may invalidate some of what I cover here.

Example 1: No semicolons, implicitly-typed variables, basic variable types, output, and string interpolation

We’ll start off with a couple of variable declarations, and then we’ll print them out on the console. Here’s the code:

And here’s its output:

No semicolons

Note that unlike Objective-C (or C, or most other languages that borrow its syntax), the lines of code above don’t end in semicolons. Swift is like JavaScript in that a line break is enough to mark the end of a statement, and ending them with semicolons is optional (much to the chagrin of the pro-mandatory-semicolon people in the Great JavaScript Semicolon Debate). You do need to use a semicolon to separate statements if you want to put them on the same line. For example, the following code compiles:

My recommendation: follow the style in Apple’s example code, be like our friends in the Lua, Python, and Ruby worlds, and don’t use semicolons to separate statements.

Implicitly-typed variables

Note that we didn’t have to specify the types of the name and radius variables. All we did was declare them with the var keyword, and then we assigned values to them:

This code is legal JavaScript, but it’s rather different underneath. JavaScript associates types with values, while Swift associates types with variables. The compiler infers the variables’ types from the values assigned to them:

  • name was assigned a string literal, which means that it should be of type String, and
  • radius was assigned a numeric literal with a decimal point, so the compiler assigned it the type Double.

This feature goes by names like type inference and implicit typing. We’ve had this in C# since late 2007, and it’s nice to see it in Swift.

Swift’s basic types

The basic types that I’ve encountered in the documentation so far are:

  • Int
  • Float
  • Double
  • Bool (whose values are true and false as opposed to Objective-C’s YES and NO)
  • String


The println() function sends output to the console. It’s capable of outputting all of Swift’s basic types without your having to convert them to String first. All of the following lines work in Swift:

String interpolation

\() is used for string interpolation, in a manner similar to Ruby’s and CoffeeScript’s #{}.

Example 2: Defining functions, defining constants, and Unicode names

Let’s take our initial code and add a function that calculates the area of a circle, given its radius:

Here’s its output:

Defining functions

Function headers in Swift have the following format… function headers in swift …and they’re bounded by braces — { and } — just like in Objective-C and every other C-like language. The return keyword works as you’d expect it to: it specifies the function’s return value and returns program control to whatever called the function in the first place.

There’s a lot more to function definitions, and I’ll cover than in a later article.

Defining constants

Take a closer look at the definition inside the circleArea function:

Just as var is used to declare variables, let is used to declare constants. As with variables, if there’s enough information in the value you’re assigning to the constant, the compiler will infer its type.

As you might expect, any attempt to redefine a constant results in an error. After all, a redefinable constant is a variable.

Unicode names

In our constant declaration, we used the greek letter π (which you get by typing option-p) instead of pi.Swift’s source files are Unicode, which means that you’re not limited to the Roman character set for naming things. This feature is meant to let people whose native languages with non-Roman alphabets give more meaningful names to their variables, constants, functions, classes, and so on.

As I wrote in an earlier post, it also lets you use emoji, which may be useful for amusing demos or in the event someone declares an Obfuscated Swift programming contest.

Explicitly declaring variable types

There are times when the compiler just doesn’t have enough information to infer the type of a variable. For instance, if you make the following declaration…

…the compiler will assume that someValue‘s type is Double. What if you need someValue to be a Float instead? You’ll need to specify its type, as shown below:

If you need to declare a variable but don’t want to assign a value to it immediately, you’ll also have to specify its type, as the compiler won’t have enough information to infer it:

Example 3: Remember, Swift is a strongly-typed language

Try the following code, but take note: it won’t work!

The problem is that you’re passing a Float to a function that expects a Double parameter. You need to convert floatRadius into a Double first. Luckily that’s pretty simple — all the basic types have conversion functions:

  • Int() takes a numeric or Bool argument and returns its Int equivalent, with the fraction removed (not rounded). The Bool value true is converted to 1, false is converted to 0.
  • Float() takes a numeric argument and returns its Float equivalent. You lose decimal precision if you use Float() on a Double, and gain some if you use it on an Int. The Bool value true is converted to 1.0, false is converted to 0.0.
  • Double() takes a numeric argument and returns its Double equivalent. You gain decimal precision if you use Double() on an Int or Float. The Bool value true is converted to 1.0, false is converted to 0.0.
  • Bool() takes a numeric or String argument and returns its Bool equivalent. As far as I can tell, only 0 equates to false; everything else — even the empty string "" — equates to true. I tried Bool(nil) and got an error.
  • String() takes a numeric argument and returns its String equivalent.

This code works, because we use Float() to convert floatRadius into a Double before passing it to circleArea():

Why all the type fussiness?

swift speed

Craig Federighi talks about Swift’s swiftness.

The payoff for all this fussiness about type is speed. As Matt Galloway writes in his Swift Language Highlights article on

In Swift, the compiler knows much more [than Objective-C] about the types in play in any method call. It knows exactly where [any given function or method] is defined. Because of this, it can optimise certain call sites by jumping directly to the implementation rather than having to go through dynamic dispatch. In other cases, it can use vtable style dispatch, which is far less overhead than dynamic dispatch in Objective-C. This is the kind of dispatch that C++ uses for virtual functions.

Swift Kick

Swift Kick: Resources for getting started with the Swift programming language

swift kickIf you’re a regular reader of this blog, chances are that you’re itching to take Apple’s new programming language, Swift, out for a spin. Global Nerdy’s largely about mobile technology these days, and since I’m looking to make it more about mobile development as well, I thought “Hey, here’s a great opportunity to write about programming and cover something new and exciting. I’ve already got my hands on the Xcode 6 beta and iOS 8, as well as Apple’s Swift programming book, and will be noodling with the language for the next little while. I’ll post my observations here, under the category “Swift Kick”.

(If you think that name is silly, my friend David Janes came up with a worse one: “Tailored Swift”. I may still use that name for a presentation.)

Swift stuff that’s available to the general public

swift site

The Swift site, located at, is open to the general public and the first place you should head. Its landing page gives you a quick overview of the language and provides a number of useful links, including the online edition of the ebook The Swift Programming Language.

swift cheat sheet

There’s a reason is one of the go-to sites for iOS developers: they’ve got great articles, and they’re quick to put out tutorials on how to use the latest iDevelopment tools. They’ve done it again by putting out a cheat sheet and reference card for Swift.

swift stack overflow

And finally, there’s a Swift tag — swift-language — in Stack Overflow, and as of this writing (2:00 pm on Tuesday, June 3, 2014), there are 155 questions with this tag.

Swift stuff that’s available to people with Apple devices

swift ibook

If you have a Mac (necessary if you want to developer for iOS) or an iPhone/iPad/iPod Touch, you can get your hands on the iBook The Swift Programming Language, which is available for free.

Swift stuff that’s available to registered developers

swift xcode

If you’re a registered iOS or OS X developer, you’ll be able to download the betas for Xcode 6 and iOS 8. Remember that this is beta code: don’t build anything that you’re putting on the market with the Xcode beta, and don’t install the iOS beta on a device that’s critical to your work!

What can we talk about? Where does the NDA apply?

Ole Bergmann points out that Apple has eased up on their NDA (non-disclosure agreement) for the iOS 8 / OS X Yosemite releases. He points to this sentence in the agreement from section 10.1, titled Information Deemed Apple Confidential:

Further, Apple agrees that You will not be bound by the foregoing confidentiality terms with regard to technical information about pre-release Apple Software and services disclosed by Apple at WWDC (Apple’s Worldwide Developers Conference), except that You may not post screen shots, write public reviews or redistribute any pre-release Apple Software or services.

It appears to mean that we can talk about material that’s covered in the Swift book, at the very least. Can anyone enlighten us and tell us what else we can talk about?



Swift Kick

Swift fun fact #1: You can use emoji characters in variable, constant, function, and class names

swift kickBy allowing Unicode characters in constant and variable names, Apple’s new Swift programming language will allow programmers whose native languages don’t use the Roman alphabet to write code that makes more sense to them. Since emoji are part of the Unicode set, expect to see amusing code demos and search-and-replace pranks that look like this:

poopy swift code example

(And yes, this code compiles and runs on Swift using the XCode 6 beta.)

Want to see more Swift content?

Click here or on the “Swift Kick” logo near the top of this article to see all the Swift-related articles on Global Nerdy.