Optionals

Optionals are one of Swift's most important safety features. An optional represents a value that might be absent. This lesson covers optional types, unwrapping techniques, and best practices.

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What Are Optionals?

An optional is a type that can hold either a value or nil (no value):

var name: String? = "Alice"   // has a value
var age: Int? = nil           // no value

// Without the ?, the type cannot be nil
// var greeting: String = nil  // Error: 'nil' cannot be assigned to type 'String'

Under the hood, Optional<T> is an enum:

enum Optional<Wrapped> {
    case none       // nil
    case some(Wrapped)  // a value
}

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Why Optionals Matter

In many languages, any reference can be null, leading to runtime crashes. Swift makes the possibility of absence explicit in the type system: