Swift - Classes

Classes in Swift are building blocks of flexible constructs. Similar to constants, variables and functions the user can define class properties and methods. Swift provides us with the functionality that while declaring classes the users need not create interfaces or implementation files. Swift allows us to create classes as a single file and the external interfaces will be created by default once the classes are initialized.

Benefits of having Classes

Inheritance acquires the properties of one class to another class.
Type casting enables the user to check class type at run time.
Deinitializers take care of releasing memory resources.
Reference counting allows the class instance to have more than one reference.

Common Characteristics of Classes and Structures

Properties are defined to store values
Subscripts are defined as providing access to values
Methods are initialized to improve functionality
Initial states are defined by initializers
Functionality is expanded beyond default values
Confirming protocol functionality standards

Definition of a Class in Swift

In Swift, a class is defined using a class keyword along with the name of the class and curly braces({}). The name of the class always starts with a capital letter such as Employee, not employee and the curly braces contain an initializer, properties methods of the class.

Properties − The constants and variables associated with the class are known as the properties of the structure. They are commonly used to define the characteristics of the class. A class can have multiple properties.
Methods − Functions associated with the class are known as the methods of the class. They are commonly used to define behaviour associated with the class. They can have parameters and return values. A single class can have multiple methods.
Initializer − It is a special method associated with a class. An initializer is used to set up the initial state of a class instance. It is defined using the init keyword. It is called when we create an instance of the class. It can have parameters and default values.

Syntax

Following is the syntax of the class −

class nameClass { 
   // Properties
   Property 1 : Type
   Property 2 : Type

   // Initializer
   init(){
      // statement
   }

   // Methods
   func functionName(){
      // Statement
   } 
}

Example

In the following Swift example, we create a class named markStruct with three properties such as studname of String type, mark and mark2 of Int type.

class student{
   var studname: String
   var mark: Int 
   var mark2: Int 
}

Swift Class Object

An object is known as the instance of the class. It is created according to the blueprint defined by the class. A single class can have multiple objects and they are independent of each other, which means if we modify one instance that doesn't affect other instances. We can create an object of the class by calling the class initializer. Using this initializer, we can initialize each property by passing the initial value along with the name of the property.

Syntax

Following is the syntax of the class instance −

var objectName = ClassName(propertyName1: Value, propertyName2: value)

Example

In the following Swift example, we will create an instance of Marks.

class Marks {
   var mark1: Int
   var mark2: Int
   var mark3: Int
}
// Creating a class object using an initializer
var myObj = Marks(mark1: 10, mark2: 20, mark3: 30)

Accessing the Properties of the Class in Swift

To access the properties of the class we can use a class object followed by a dot(.) and the name of the property. We can also modify the values of the properties with the help of dot(.) syntax.

Syntax

Following is the syntax for accessing the properties of the class −

classObjectName.PropertyName

Following is the syntax for modifying the properties of the class −

classObjectName.PropertyName = value

Example

Swift program to access and modify the properties of a class.

// Defining a class 
struct Employee {
   var name: String
   var department: String
   var salary: Int
    
   // Initializer
   init(name: String, department: String, salary: Int){
      self.name = name
      self.department = department
      self.salary = salary
   }
}

// Creating an instance of the Employee class
var emp = Employee(name: "Suman", department: "Designing", salary: 33000)

// Accessing the values of the properties using dot notation
print("Employee Details:")
print("Name: \(emp.name)")
print("Department: \(emp.department)")
print("Salary: \(emp.salary)")

// Modifying the values of the properties using dot notation
emp.salary = 40000

// Displaying the updated values
print("\nUpdated Value:")
print("Salary: \(emp.salary)")

Output

It will produce the following output −

Employee Details:
Name: Suman
Department: Designing
Salary: 33000

Updated Value:
Salary: 40000

Accessing the Methods of the Class in Swift

To access the methods of the class we can use dot notation. Here a class instance is followed by a dot(.) and a method name to access methods.

Syntax

Following is the syntax for accessing the method of the class −

classInstanceName.methodName

Example

Swift program to access the methods of the class.

// Defining a class 
class Parallelogram {

   // Properties of class
   var base: Double
   var height: Double
    
   // Initializer
   init(base: Double, height: Double){
      self.base = base
      self.height = height
   }
    
   // Method to calculate the area of the Parallelogram
   func calculateParallelogramArea() -> Double {
      return base * height
   }
}

// Create an instance of the Parallelogram class
var myObj = Parallelogram(base: 10.0, height: 9.0)

// Calling the calculateParallelogramArea() method
let area = myObj.calculateParallelogramArea()
print("Area of the Parallelogram: \(area)")

Output

It will produce the following output −

Area of the Parallelogram: 90.0

Class as a Reference Type in Swift

In Swift, classes are reference types, which means that when we assign a class to a structure or constant or pass it to a function as a parameter, a reference of the existing object will used. So, when we make changes to one instance will reflect in all the references of that instance.

Example

Swift program to demonstrate class as a reference type.

// Defining a class
class Student {

   // Properties
   var name: String
   var age: Int
    
   // Initializer    
   init(name: String, age: Int){
      self.name = name
      self.age = age
   }
}

// Creating an instance of the Student class 
var stud = Student(name: "Kunal", age: 22)

// Assigning stud to details
// Here details have the reference of stud object
var details = stud

// Modifying the values of the properties
// Here the modification will affect the stud instance 
// because it passed as a reference-type 
details.name = "Mohina"
details.age = 40

print("student 1: name-\(stud.name) and age-\(stud.age)")
print("student 2: name-\(details.name) and age-\(details.age)")

Output

It will produce the following output −

student 1: name-Mohina and age-40
student 2: name-Mohina and age-40

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