Swift: Classes, Structures & Optionals

What you will learn

The difference between structs (value types) and classes (reference types), and how Swift handles optional values safely.

Structures (value types)

struct Person {
    var name: String
    var age: Int
}

var alice = Person(name: "Alice", age: 25)
var bob = alice         // COPY — alice and bob are independent
bob.name = "Bob"
print(alice.name)       // "Alice" — unchanged

Structs are value types: they are copied on assignment. let alice makes the struct immutable.

Classes (reference types)

class Animal {
    var name: String

    init(name: String) {
        self.name = name
    }

    func speak() -> String {
        return "..."
    }
}

let dog = Animal(name: "Rex")  // reference, even with let
let pet = dog                  // same object — both refer to Rex
pet.name = "Max"
print(dog.name)               // "Max" — changed through pet

Classes are reference types: they are shared, not copied. let on a class reference prevents reassignment but the object's properties can still change (if var).

Struct vs Class — when to use what

Optionals (no null pointers)

Swift has no nil for regular types. Use Optionals to represent the absence of a value:

var name: String? = nil      // Optional<String>, can be nil
name = "Alice"

// Optional binding — safe unwrapping
if let unwrapped = name {
    print("Hello, \(unwrapped)!")
}

// Guard let — early exit
guard let name = name else { return }
print(name)  // name is now a regular String

Common mistakes

• Forcing an optional with ! when you haven't checked for nil — causes a runtime crash
• Using a class when a struct would be more efficient and safer
• Forgetting that let on a class reference does not make the object immutable

Quick check below!