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Learning Swift
Learning Swift

Learning Swift: Build a solid foundation in Swift to develop smart and robust iOS and OS X applications

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Learning Swift

Chapter 2. Building Blocks – Variables, Collections, and Flow Control

One of the coolest things about programming is the way its concepts build on each other. If you've never programmed anything before, even the most basic app can seem very complex. The reality is that if you analyze everything going on in an app down to the ones and zeroes flowing through the processor, it is incredibly complex. However, every aspect of using a computer is an abstraction. When you use an app, the complexity of the programming is abstracted away for you. Learning to program is just a way of going one level deeper to make a computer work for you.

As you learn the basic concepts behind programming, they will become your second nature and this will free your mind to comprehend even more complex concepts. Just as when you first learn to read, sounding out each word is challenging. However, at some point, you reach a level where you glance at a word and you know the meaning instantaneously...

Core Swift types

Every programming language needs the ability to name a piece of information to be referenced later. This is the fundamental way that a collection of code remains readable after it is written. Swift provides a number of core types that help you represent your information in a very comprehensible way.

Constants and variables

Swift provides two types of information: a constant and a variable:

// Constant
let pi = 3.14
   
// Variable
var name = "Sarah"

All constants are defined using the let keyword followed by a name, and all variables are defined using the var keyword. Both the constants and variables in Swift must contain a value before they are used. This means that when you define a new constant or variable, you will most likely give it an initial value. You do so using the assignment operator (=) followed by a value.

The only difference between the two is that a constant can never be changed, while a variable can be. In the previous example, the code defines a...

Swift's type system

Swift is a strongly typed language, which means that every constant and variable is defined with a specific type. Only values of a matching type can be assigned to them. So far, we have been taking advantage of a feature of Swift called type inference. This makes it such that the code does not have to explicitly declare a type if it can be inferred from the value assigned to it during declaration.

Without the type inference, the name variable declaration from before would be written as:

var name: String = "Sarah"

This code explicitly declares name as the type String with the value "Sarah". A constant or variable's type can be specified by adding a colon (:) and a type after its name.

A String type is defined by a series of characters. This is perfect for storing text like our name example. The reason that we don't actually need to specify the type is that "Sarah" is a String literal. The text surrounded by quotation marks is a...

Printing on the console

It can be very useful to write output to a log so that you can trace the behavior of some code. As a code base grows in complexity, it can be hard to reason about the order in which things happen and exactly what the data looks like as it flows through the code. Playgrounds can help a lot with this, but this is not always enough.

In Swift, this process is called printing to the console. To do this, you use something called println, which is short for print line. It is used by writing println followed by some text surrounded by parenthesis. For example, to print Hello World! to the console, the code would look like this:

println("Hello World!")

If you put that code into a playground, you will see "Hello World!" written in the results pane. However, this is not truly the console. To view the console, you can go to View | Assistant Editor | Assistant Editor. A new view will appear to the right of the results pane and it will have a section called Console...

Control flow

A program wouldn't be very useful if it were a single fixed list of commands that always did the same thing. With a single code path, a calculator app would only be able to perform one operation. To make an app more powerful, there are a number of ways in which we can use the data to make decisions as to what to do next.

Conditionals

The most basic way to control the flow of a program is to specify certain code that should only be executed if a certain condition is met. In Swift, we do that with an if statement. Let's look at an example:

if invitees.count > 20 {
   println("Too many people invited")
}

Semantically, the preceding code reads, "If the number of invitees is greater than 20, print Too many people invited. This example only executes one line of code if the condition is true, but you can put as much code as you like within the curly brackets ({}).

Anything that can be evaluated as either true or false can be used in an if statement. You can...

Functions

All of the code we have explored so far is very linear down the file. Each line is processed one at a time and then, the program moves onto the next. This is one of the great things about programming: everything the program does can be predicted by mentally stepping through the program yourself, one line at a time.

However, as your program gets larger, you will notice that there are many places that reuse very similar or identical code that you cannot reuse using loops. Also, the more code you write, the harder it will become to reason in your head about what it is doing. Code comments can help with that, but there is an even better solution to both of these problems and they're called functions. A function is essentially a named collection of code that can be executed and reused by name.

There are various types of functions but each builds on the previous type.

Basic functions

The most basic type of function simply has a name with some static code to be executed later. Let&apos...

Core Swift types


Every programming language needs the ability to name a piece of information to be referenced later. This is the fundamental way that a collection of code remains readable after it is written. Swift provides a number of core types that help you represent your information in a very comprehensible way.

Constants and variables

Swift provides two types of information: a constant and a variable:

// Constant
let pi = 3.14
   
// Variable
var name = "Sarah"

All constants are defined using the let keyword followed by a name, and all variables are defined using the var keyword. Both the constants and variables in Swift must contain a value before they are used. This means that when you define a new constant or variable, you will most likely give it an initial value. You do so using the assignment operator (=) followed by a value.

The only difference between the two is that a constant can never be changed, while a variable can be. In the previous example, the code defines a constant called...

Swift's type system


Swift is a strongly typed language, which means that every constant and variable is defined with a specific type. Only values of a matching type can be assigned to them. So far, we have been taking advantage of a feature of Swift called type inference. This makes it such that the code does not have to explicitly declare a type if it can be inferred from the value assigned to it during declaration.

Without the type inference, the name variable declaration from before would be written as:

var name: String = "Sarah"

This code explicitly declares name as the type String with the value "Sarah". A constant or variable's type can be specified by adding a colon (:) and a type after its name.

A String type is defined by a series of characters. This is perfect for storing text like our name example. The reason that we don't actually need to specify the type is that "Sarah" is a String literal. The text surrounded by quotation marks is a String literal and is inferred to be of the type...

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Description

If you are looking to build iOS or OS X apps using the most modern technology, this book is ideal for you. You will find this book especially useful if you are new to programming or if you have yet to develop for iOS or OS X.

Who is this book for?

If you are looking to build iOS or OS X apps using the most modern technology, this book is ideal for you. You will find this book especially useful if you are new to programming or if you have yet to develop for iOS or OS X.
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Publication date, Length, Edition, Language, ISBN-13
Publication date : Jun 30, 2015
Length: 266 pages
Edition : 1st
Language : English
ISBN-13 : 9781784392505
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Length: 266 pages
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Language : English
ISBN-13 : 9781784392505
Vendor :
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Category :
Languages :

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Table of Contents

12 Chapters
1. Introducing Swift Chevron down icon Chevron up icon
2. Building Blocks – Variables, Collections, and Flow Control Chevron down icon Chevron up icon
3. One Piece at a Time – Types, Scopes, and Projects Chevron down icon Chevron up icon
4. To Be or Not to Be – Optionals Chevron down icon Chevron up icon
5. A Modern Paradigm – Closures and Functional Programming Chevron down icon Chevron up icon
6. Make Swift Work for You – Protocols and Generics Chevron down icon Chevron up icon
7. Everything is Connected – Memory Management Chevron down icon Chevron up icon
8. Writing Code the Swift Way – Design Patterns and Techniques Chevron down icon Chevron up icon
9. Harnessing the Past – Understanding and Translating Objective-C Chevron down icon Chevron up icon
10. A Whole New World – Developing an App Chevron down icon Chevron up icon
11. What's Next? Resources, Advice, and Next Steps Chevron down icon Chevron up icon
Index Chevron down icon Chevron up icon

Customer reviews

Rating distribution
Full star icon Full star icon Full star icon Full star icon Half star icon 4.8
(5 Ratings)
5 star 80%
4 star 20%
3 star 0%
2 star 0%
1 star 0%
Ronnie Pitman Aug 16, 2015
Full star icon Full star icon Full star icon Full star icon Full star icon 5
This is not a huge, thick book, but it is a book packed with information. In the Preface it is written that this book is “especially useful if you are new to programming or….” While it’s true that Chapter 2 does start with the basics—variables, constants, tuples, arrays, dictionaries, etc.—the material moves on quickly. All concepts, throughout the book, are amply demonstrated in Playgrounds, but still, someone new to programming will have to pay close attention and probably reread portions. In at least two chapter summaries, the author himself refers to the material presented as having been dense. It’s good to have a book that deals in depth.Many programming books teach Swift in the context of iOS. This one does not but instead concentrates on Swift language fundamentals. It’s not a tutorial on how to build this or that app, and only in the penultimate chapter does the author address iOS and building an app.Many programming books also jam a great deal of code into one class. This author places a premium on code reuse and flexibility and writes his code accordingly.A note on the book’s code files: at the time I write this, if you download them from the publisher website they download as Learning Swift.zip.html. Unless Packt knows something I don’t know, you have to strip .html off the file name for it to open as a zip file rather than as gibberish.A small error in Chapter 2 (pdf page 13): “View | Assistant Editor | Assistant Editor” should be “View | Assistant Editor | Show Assistant Editor”. Otherwise this book is admirably edited and proofread.
Amazon Verified review Amazon
Aurélien Sep 02, 2015
Full star icon Full star icon Full star icon Full star icon Full star icon 5
What this book is not:This book is not a Bible, it does not deal with countless topics, it is not either a how-to guide to programming your first Iphone app. "Learning Swift" is not packed with information easily googled and deprecated within the next 6 months.What it is:Instead "Learning Swift" focuses on how to understand Swift programming, how the language is structured and how it works.It gives the keys to become a good swift developper by understanding the core concepts, while being concrete at every step of the process.A whole chapter is dedicated to Design Patterns, and even chapter 10 "Developing an App" is full of good advices on how to code properly and how to refactor your code.
Amazon Verified review Amazon
Winston Sep 05, 2015
Full star icon Full star icon Full star icon Full star icon Full star icon 5
The author does a great job of taking the reader through all the intricacies of the swift programing language. Apple is now in Swift 2 and this book will put any novice or experienced developer in the drivers seat to building award winning ios apps. Buy it!
Amazon Verified review Amazon
Sergio Martinez-Losa del Rincon Aug 14, 2015
Full star icon Full star icon Full star icon Full star icon Full star icon 5
This book is a very nice one to learn swift from scratch, it is useful information from easy topic to difficult ones, you can learn many useful thinks like categories, interpolation, infix/postfix, optionals...Patterns chapter is very handy, because you can reuse your programming techniques to create a more easy code. Also I found very useful optionals information.I learn a lot with this book, it deserves a 5-stars.
Amazon Verified review Amazon
Michael Aug 28, 2015
Full star icon Full star icon Full star icon Full star icon Empty star icon 4
I am new to learning Mac and iOS programming. This book is great even though I've only gotten through a couple chapters. It starts out with the basics of types, collections, conditionals and loops and builds on that.One note, this book was written for XCode 6 and Swift 1.2 so it will hopefully be updated for XCode 7 and Swift 2 when they are released since some of the basic functions are changing, for example the println() function is replaced by print(). The beta for XCode 7 does have functionality to convert the 1.2 to 2.0 code. Hopefully that will be in the final build of XCode 7.I look forward to getting deeper into learning Swift.
Amazon Verified review Amazon
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