In object-oriented programming, we cannot create an object without a blueprint that tells the application what properties and methods to expect from the object. In most object- oriented languages, this blueprint comes in the form of a class. A class is a construct that allows us to encapsulate the properties, methods, and initializers of an object into a single type. Classes can also include other items, such as subscripts; however, we are going to focus on the basic items that make up classes not only in Swift, but in other languages as well.

Let's look at how we would use a class in Swift:

class MyClass { 
  var oneProperty: String 
 
  init(oneProperty: String) { 
    self.oneProperty = oneProperty 
  } 
 
  func oneFunction() { 
 
  } 
} 

An instance of a class is typically called an object. However, in Swift, structures and classes have many of the same functionalities; therefore, we will use the term instance when referring to instances of either type.

Anyone who has used object...

Apple has said that Swift developers should prefer value types over reference types, and it seems that they have also taken that philosophy to heart. If we look at the Swift standard library (http://swiftdoc.org), we will see that the majority of types are implemented using structures. The reason Apple is able to implement the majority of Swift's standard library with structures is that, in Swift, structures have many of the same functionalities as classes. There are, however, some fundamental differences between classes and structures, and we will be looking at these differences later in this chapter.

In Swift, a structure is a construct that allows us to encapsulate the properties, methods, and initializers of an instance into a single type. They can also include other items, such as subscripts. However, we are going to focus on the basic items that make up a structure. This description may sound a lot like how we described classes in the last section. This is because classes...

Access controls allow us to restrict the access to, and visibility of, parts of our code. This allows us to hide implementation details and only expose the interfaces we want the external code to access. We can assign specific access levels to both classes and structures. We can also assign specific access levels to properties, methods, and initializers that belong to our classes and structures.

In Swift, there are five access levels:

In most languages, enumerations are little more than a data type consisting of a set of named values called elements. In Swift, however, enumerations have been supercharged to give them significantly more power. Enumerations in Swift are a lot closer in functionality to classes and structures; however, they can still be used like enumerations in other languages.

Before we see how enumerations are supercharged in Swift, let's see how we can use them as standard enumerations. The following code defines an enumeration called Devices:

enum Devices 
{  
  case IPod  
  case IPhone  
  case IPad 
} 

In the Devices enumeration, we defined three possible values: IPod, IPhone, and IPad. One of the reasons why enumerations are different in Swift as compared to other languages is that they can be prepopulated with values known as raw values. As shown in the following example, we could redefine our Devices enumeration to be prepopulated with String values:

enum Devices: String {  
  case IPod...

In Swift, a tuple is a finite, ordered, comma-separated list of elements. While there are tuples in other languages that I have used, I never really took advantage of them. To be honest, I was only vaguely aware that they actually existed in those other languages. In Swift, tuples are more prominent than they are in other languages, which forced me to take a closer look at them. What I found is that they are extremely useful. In my opinion, tuples are one of the most underutilized types in Swift and, as we go through this book (especially in the case study section), I will point out some cases where the tuple type can be used.

We can create a tuple and access the information within it, as shown in the following example:

let mathGrade1 = ("Jon", 100)  
let (name, score) = mathGrade1  
print("\(name) - \(score)") 

In the previous code, we grouped a String and an Integer into a single tuple type. We then decomposed the tuple using pattern matching, which places the values into the name...

To some, it may seem surprising that protocols are considered a type since we cannot actually create an instance of them; however, we can use them as a type. What this statement means is that, when we define the type for a variable, constant, tuple, or collection, we can use a protocol for that type.

We are not going to cover protocols in depth in this section since we have already covered them in Chapter 1,Starting with the Protocol, however, it is important to understand that they are considered a type.

Each type that we have discussed so far is either a value or a reference type; however, a protocol is neither because we are not able to create an instance of them.

It is really important to have a complete understanding of the differences between value and reference types in Swift, so let's compare the two.

There are some very fundamental differences between value types (structures, enumerations, and tuples) and reference types (classes). The primary difference is how the instances of value and reference types are passed. When we pass an instance of a value type, we are actually passing a copy of the original instance. This means that the changes made to one instance are not reflected back to the others. When we pass an instance of a reference type, we are passing a reference to the original instance. This means that both references point to the same instance; therefore, a change made to one reference will reflect in the others.

The explanation in the previous paragraph is a pretty straightforward explanation; however, it is a very important concept that you must understand. In this section, we are going to examine the differences between value and reference types so that we know the advantages of each, as well as the pitfalls to avoid when using them.

Let's begin by...

A recursive data type is a type that contains other values of the same type as a property for the type. Recursive data types are used when we want to define dynamic data structures, such as lists and trees. The size of these dynamic data structures can grow or shrink depending on our runtime requirements.

Linked lists are perfect examples of a dynamic data structure that we would implement using a recursive data type. A linked list is a group of nodes that are linked together and where, in its simplest form, each node maintains a link to the next node in the list. The following diagram shows how a very basic linked list works:

Each node in the list contains some value or data, and it also contains the link to the next node in the list. If one of the nodes within the list loses the reference to the next node, the remainder of the list will be lost because each node is only aware of the next node. Some linked lists maintain a link to both the previous...