Structures in Swift

Introduction to Structures in Swift

In Swift, a structure (struct) is a lightweight, efficient way to encapsulate related data and behavior. Unlike classes, structs are value types, meaning they are copied when assigned to a new variable or passed to a function.

Structures are highly optimized for performance and are recommended for most data models in Swift, especially when immutability and safety are priorities.

Why Use Structures in Swift?

Value Semantics: Structs are copied, preventing unintended changes.
Performance: Stored in the stack, making them faster than classes.
Thread Safety: Safer in multithreading since copies are independent.
Immutability: Encourages functional programming when used with let.

Class vs. Struct – Key Differences

Feature	Struct	Class
Type	Value	Reference
Stored In	Stack	Heap
Inheritance	No	Yes
Deinitializer (deinit)	No	Yes
Mutability	Immutable by default	Mutable

Defining a Structure in Swift

struct StructName {
     var property: Type
     func method() {
         // Code here
     }
}

Example 1: Creating and Using a Struct

struct Car {
     var brand: String
     var model: String
     var year: Int

     func details() {
         print("\(brand) \(model) - Year: \(year)")
     }
}

let myCar = Car(brand: "Tesla", model: "Model 3", year: 2024)
myCar.details()

Output

Tesla Model 3 - Year: 2024

Example 2: Mutating a Struct Method

Since structs are immutable by default, use the mutating keyword to modify properties.

struct Counter {
     var count: Int = 0

     mutating func increment() {
         count += 1
     }
}

var myCounter = Counter()
myCounter.increment()
print(myCounter.count) // 1

Output

Example 3: Structs with Computed Properties

struct Rectangle {
     var width: Double
     var height: Double

     var area: Double {
         return width * height
     }
}

let rect = Rectangle(width: 10, height: 5)
print("Area: \(rect.area)")

Output

Area: 50.0

Example 4: Structs with Initializers

Swift structs automatically generate an initializer, but you can define a custom one.

struct Person {
     var name: String
     var age: Int

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

let person1 = Person(name: "Alice", age: 25)
print(person1.name) // Alice

Output

Alice

Example 5: Value Type Behavior of Structs

struct Point {
var x: Int
var y: Int
}

var p1 = Point(x: 10, y: 20)
var p2 = p1 // Copy is created
p2.x = 30

print(p1.x) // 10 (Original remains unchanged)
print(p2.x) // 30 (Copy modified)

Output

10
30

Best Practices for Using Structs

Use structs for simple data models that don’t need inheritance.
Prefer structs over classes for thread-safe, predictable behavior.
Use mutating functions to modify struct properties.
Avoid large structs (over 16 bytes) for performance optimization.
Leverage value semantics to prevent unintended side effects.