Swift Enumerations

Enumerations, in simple terms, are a data type that includes only specific, predefined data. They are a collection of data with common characteristics.

Swift's enumerations are similar to those in Objective-C and C. Their functions include:

• They are declared within a class and can be accessed by instantiating the class.
• Enumerations can define initializers to provide an initial member value; they can extend their functionality based on the original implementation.
• They can conform to protocols to provide standard functionality.

Syntax

In Swift, the enum keyword is used to create an enumeration, and its entire definition is enclosed in a pair of braces:

enum enumname {
   // Enumeration definition goes here
}

For example, we define an enumeration to represent days of the week:

import Cocoa

// Define the enumeration
enum DaysofaWeek {
    case Sunday
    case Monday
    case TUESDAY
    case WEDNESDAY
    case THURSDAY
    case FRIDAY
    case Saturday
}

var weekDay = DaysofaWeek.THURSDAY
weekDay = .THURSDAY
switch weekDay {
case .Sunday:
    print("Sunday")
case .Monday:
    print("Monday")
case .TUESDAY:
    print("Tuesday")
case .WEDNESDAY:
    print("Wednesday")
case .THURSDAY:
    print("Thursday")
case .FRIDAY:
    print("Friday")
case .Saturday:
    print("Saturday")
}

The output of the above program is:

Thursday

The values defined in the enumeration (such as Sunday, Monday, ..., and Saturday) are the member values (or members). The case keyword indicates that a new member value is being defined.

Note: Unlike C and Objective-C, Swift's enumeration members are not assigned a default integer value when they are created. In the DaysofaWeek example, Sunday, Monday, ..., and Saturday are not implicitly assigned values 0, 1, ..., and 6. Instead, these enumeration members have fully defined values, which are of the DaysofaWeek type.

var weekDay = DaysofaWeek.THURSDAY

The type of weekDay can be inferred when it is initialized with a possible value of DaysofaWeek. Once weekDay is declared as a DaysofaWeek, you can use a shorthand syntax (.) to set it to another value of DaysofaWeek:

var weekDay = .THURSDAY

When the type of weekDay is known, you can omit the enumeration name when assigning it a new value. Using explicit typed enumeration values improves code readability.

Enumerations can be divided into associated values and raw values.

Differences Between Associated Values and Raw Values

Associated Values

In the following example, we define an enumeration named Student, which can be either a Name string or a Mark with associated values (Int, Int, Int).

import Cocoa

enum Student {
    case Name(String)
    case Mark(Int, Int, Int)
}
var studDetails = Student.Name("tutorialpro")
var studMarks = Student.Mark(98, 97, 95)
switch studMarks {
case .Name(let studName):
    print("Student's name is: \(studName).")
case .Mark(let Mark1, let Mark2, let Mark3):
    print("Student's marks are: \(Mark1), \(Mark2), \(Mark3).")
}

The output of the above program is:

Student's marks are: 98, 97, 95.

Raw Values

Raw values are not covered in the provided text. Raw values can be strings, characters, or any integer or floating-point values. Each raw value must be unique within its enumeration declaration.

When the raw value is an integer enumeration, you do not need to assign a value explicitly to each member; Swift will assign values automatically for you.

import Cocoa

enum Month: Int {
    case January = 1, February, March, April, May, June, July, August, September, October, November, December
}

let yearMonth = Month.May.rawValue
print("The numeric month is: \(yearMonth).")

The output of the above program is:

The numeric month is: 5.