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Swift Structs vs. Classes: Choosing the Right Data Type

Swift, Structs, Classes2 min read

When working with Swift, you have the flexibility to choose between two fundamental data types: structs and classes. Both structs and classes allow you to define custom types to encapsulate data and behavior. However, they have distinct characteristics that make them suitable for different scenarios. In this article, we will delve into the nuances of Swift structs and classes, exploring their features, use cases, and performance implications.


A struct is a value type in Swift, meaning it is copied when assigned or passed as an argument to a function. Structs are typically used for modeling simple data structures, such as coordinates, sizes, or other small pieces of information. They are immutable by default, but you can define mutable properties using the mutating keyword.

Here's an example of a struct representing a Point:

1struct Point {
2 var x: Double
3 var y: Double

You can create instances of Point and modify its properties:

1var point = Point(x: 1.0, y: 2.0)
2point.x = 3.0

Structs are great for scenarios where immutability and value semantics are desired. They provide thread safety and don't require complex memory management.


On the other hand, classes are reference types in Swift, meaning they are passed by reference rather than copied. Classes are used for more complex object-oriented programming scenarios, where identity and shared state are important. They support inheritance, type casting, and deinitialization.

Let's consider an example of a class representing a Person:

1class Person {
2 var name: String
4 init(name: String) {
5 = name
6 }
8 func sayHello() {
9 print("Hello, my name is \(name).")
10 }

You can create instances of Person and modify its properties or call methods:

1let person = Person(name: "John")

Classes are suitable when you need shared state, identity, or complex behavior. However, it's important to note that classes introduce more memory management concerns, such as retaining and releasing references.

Performance Considerations

When deciding between structs and classes, it's crucial to consider performance implications. Structs are generally more lightweight and efficient due to their value semantics. As they are copied, modifying a struct doesn't affect other copies. On the other hand, classes incur additional overhead due to reference counting and sharing state.

In scenarios where you have small, simple data structures that are frequently created and modified, using structs can offer better performance. However, for larger objects with shared state or complex behavior, classes may be more appropriate.

Choosing the Right Data Type

Now that we have a better understanding of the differences between structs and classes, let's consider some guidelines for choosing the right data type in Swift:

  • Use structs when dealing with simple, immutable data structures.
  • Prefer classes when you require reference semantics or need to model complex behavior.
  • Consider the performance implications and choose structs for small, frequently modified data, and classes for larger objects with shared state.
  • Strive to follow Swift's value semantics principles and use structs by default, unless there is a specific need for class behavior.

By understanding the distinctions between structs and classes and their intended use cases, you can make informed decisions when designing your Swift applications.