Swift Classes

Swift Classes

Classes are one of the fundamental building blocks of object-oriented programming in Swift. A class defines a blueprint for creating objects that encapsulate properties (data) and methods (functions) into a single entity.

Classes in Swift also support features such as inheritance, reference semantics, and initialisers, making them a powerful tool for modelling real-world entities and relationships in code.

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Declaring a Class

Declaring a class in Swift requires the class keyword followed by the class name. The name should start with an uppercase letter by convention. The body of the class is enclosed in curly braces {}, where you define the class’s properties and methods.

Syntax:

class ClassName {
    // Properties
    // Methods
}

Example: main.swift

class Student {
    var name: String
    var age: Int

    init(name: String, age: Int) {
        self.name = name
        self.age = age
    }

    func displayDetails() {
        print("Name: \(name), Age: \(age)")
    }
}

Explanation:

• class: The keyword used to declare a class.
• Student: The name of the class, starting with an uppercase letter.
• Curly braces: Enclose the class’s properties and methods.
• name and age: Properties to store the student’s name and age.
• init: An initializer used to set up properties when a new object is created.
• displayDetails: A method to print the student’s details.

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Properties

Properties in a class are variables or constants that store data. They are declared inside the class body and are typically initialized either directly or through an initializer.

Example: main.swift

class Student {
    var name: String
    var age: Int
}

Properties can be accessed and modified using dot notation, as shown later in this tutorial.

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Methods

Methods are functions that are defined inside a class and operate on its properties. They can perform actions or return values based on the class’s properties.

Example: main.swift

class Student {
    var name: String
    var age: Int

    init(name: String, age: Int) {
        self.name = name
        self.age = age
    }

    func greet() {
        print("Hello, my name is \(name).")
    }
}

Explanation:

• greet: A method that prints a greeting message using the name property.

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Initializers

An initializer is a special method in a class that sets up the initial state of an object by assigning values to its properties. It is defined using the init keyword.

Example: main.swift

class Student {
    var name: String
    var age: Int

    init(name: String, age: Int) {
        self.name = name
        self.age = age
    }
}

Explanation:

• init: The initializer sets the initial values of name and age when a new object is created.

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Creating Objects in Swift

To use a class, you need to create an object (also called an instance). This is done by calling the class name followed by parentheses.

Example: main.swift

class Student {
  var name: String
  var age: Int
  
  init(name: String, age: Int) {
    self.name = name
    self.age = age
  }
  
  func displayDetails() {
    print("Name: \(name), Age: \(age)")
  }
}

let student = Student(name: "Kumar", age: 20)
student.displayDetails()

Explanation:

• Object creation: The Student class is instantiated using the Student(name: "Kumar", age: 20) initializer.
• Method call: The displayDetails method is called using dot notation to print the student’s details.

Output:

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Accessing Properties and Methods

Properties and methods of a class object can be accessed using the dot operator (.). This operator connects the object name to the property or method.

Example: main.swift

class Student {
  var name: String
  var age: Int
  
  init(name: String, age: Int) {
    self.name = name
    self.age = age
  }
  
  func displayDetails() {
    print("Name: \(name), Age: \(age)")
  }
}

let student = Student(name: "Arjun", age: 18)

// Accessing properties
print("Student Name: \(student.name)")
print("Student Age: \(student.age)")

// Accessing methods
student.displayDetails()

Explanation:

• Dot operator: Used to access name and age properties as well as the displayDetails method.
• The name and age properties are printed directly, while the displayDetails method prints them through a formatted message.

Output:

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Classes as Reference Types

In Swift, classes are reference types. This means that when you assign a class object to another variable, both variables refer to the same instance. Any changes made through one variable will affect the other.

Example: main.swift

class Student {
  var name: String
  var age: Int
  
  init(name: String, age: Int) {
    self.name = name
    self.age = age
  }
}

let student1 = Student(name: "Arjun", age: 22)
let student2 = student1

student2.name = "Ram"

print("Student1 Name: \(student1.name)") // Ram
print("Student2 Name: \(student2.name)") // Ram

Explanation:

• Reference type: Both student1 and student2 refer to the same object in memory.
• Changing the name property through student2 also updates it for student1.

Output:

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Conclusion

Classes in Swift provide a powerful way to model real-world entities and their behaviour.