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Struct vs. Class: Understanding the Differences in Swift

Updated: Mar 25, 2023

Guide to Structs and Classes in Swift


As a Swift developer, understanding the differences between Structs and Classes is crucial to building efficient and maintainable code.

In this article, we’ll explore the differences between Structs and Classes in Swift, and provide a beginner-friendly guide to help you understand which one to use in different situations.


So, grab a cup of coffee and let’s dive in!



  1. What are Structs and Classes?

In Swift, Structs and Classes are two different types of value types that can be used to define objects. They both have properties and methods, but there are some key differences between them.


Structs are value types, which means that they are copied when they are assigned to a new variable or passed to a function. Classes, on the other hand, are reference types, which means that they are passed by reference.


2. When to Use Structs


Structs are a good choice for small and simple data types, such as simple data structures, mathematical calculations, and basic types like Integers, Strings, and Booleans.


Structs are also a good choice when you need to pass a value type to a function or return it from a function, as they are copied and don’t affect the original value.


Here’s an example of a simple Struct:

struct Rectangle {
    var width: Double
    var height: Double
    
    var area: Double {
        return width * height
    }
}

In this example, we’re defining a Rectangle Struct that has two properties: width and height. We’re also defining a computed property called area that calculates the area of the rectangle.


This Struct is a good example of a simple data type that can be easily copied and passed around as a value.




3. When to Use Classes


Classes are a good choice for more complex data types that require inheritance, reference semantics, or dynamic dispatch. Classes are also a good choice when you need to share data between multiple objects, as they are passed by reference and changes made to the object are reflected in all instances.


Here’s an example of a simple Class:

class Person {
    var name: String
    var age: Int
    
    init(name: String, age: Int) {
        self.name = name
        self.age = age
    }
    
    func celebrateBirthday() {
        age += 1
        print("Happy birthday, \(name)! You are now \(age) years old!")
    }
}

In this example, we’re defining a Person Class that has two properties: name and age. We’re also defining an initializer that sets the initial values of these properties, and a method called celebrateBirthday that increments the age property and prints a birthday message to the console.


This Class is a good example of a more complex data type that requires inheritance and dynamic dispatch.

  1. The Pros and Cons of Structs and Classes

As with any programming concept, there are pros and cons to using Structs and Classes. Here are a few to consider:


Pros of Structs:

  • They are lightweight and efficient

  • They are easy to copy and pass as values

  • They are suitable for small and simple data types

Cons of Structs:

  • They cannot inherit from other types

  • They cannot be used with Objective-C APIs

  • They are limited in terms of functionality compared to Classes

Pros of Classes:

  • They support inheritance and polymorphism

  • They can be used with Objective-C APIs

  • They are suitable for complex data types

Cons of Classes:

  • They are more complex and heavier than Structs

  • They are passed by reference, which can cause unexpected behavior in some situations


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