🐦 Swift

Structs & Enums

Lesson 3 of 5 ~6 min

Structs and Enums are the building blocks of data modeling in Swift. Structs group related properties and behavior together, while enums define a group of related values.

Swift uses structs as its primary data type — even String, Int, and Array are structs under the hood.

Structs

A struct defines a blueprint for a custom data type with properties (data) and methods (behavior). Structs are value types — when you assign one to another variable, you get an independent copy.

Editor

Swift

// Struct definition
struct Recipe {
  var name: String
  var ingredients: [String]
  var cookTime: Int

  func describe() -> String {
    return "\(name) — \(ingredients.count) ingredients, \(cookTime) min"
  }
}

// Creating an instance
let pasta = Recipe(
  name: "Pasta Carbonara",
  ingredients: ["spaghetti", "eggs", "pancetta", "parmesan"],
  cookTime: 20
)

print(pasta.describe())
print("First ingredient: \(pasta.ingredients[0])")

// Value type — copy is independent
var quickPasta = pasta
quickPasta.cookTime = 10
print("Original: \(pasta.cookTime) min")
print("Copy: \(quickPasta.cookTime) min")

Output

Try it

Add a new property to the Recipe struct and update the describe() method to include it.

Enums

Enums define a type with a fixed set of related values. They can have raw values (like strings or integers) and associated values (custom data per case).

// Basic enum
enum Direction {
  case north, south, east, west
}

// Enum with raw values
enum Planet: Int {
  case mercury = 1
  case venus = 2
  case earth = 3
}

// Using switch
let direction = Direction.north
switch direction {
case .north: print("Going up")
case .south: print("Going down")
case .east:  print("Going right")
case .west:  print("Going left")
}

// Raw value access
let earthNumber = Planet.earth.rawValue  // 3

Value Types vs Reference Types

→ Structs are value types — assigning copies the data. Each variable holds its own independent version.
→ Classes are reference types — assigning shares the same instance. Changes in one affect the other.
→ Swift favors structs for most data modeling because value semantics are safer and easier to reason about.

Quiz

Are structs value types or reference types in Swift?

Challenge

Create a struct for a Recipe with name and ingredients properties, then create an instance and print its details.

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Optionals

Closures