Optional Chaining
Optional chaining lets you safely ask a chain of questions about something that might not exist, stopping quietly at the first "no" instead of crashing.
Syntax
let result = object.optionalProperty?.member
let result = object.optionalProperty?.member ?? defaultValueChaining Through an Optional Property
Using ?. after an optional lets you safely access one of its properties, automatically returning nil if the optional itself is empty.
Example: Chaining Through an Optional Property
// Define a struct `Address`
struct Address {
var city: String
}
// Define a struct `Person`
struct Person {
var address: Address?
}
// Declare a constant `person`, set to `Person(address: Address(city: "Paris"))`
let person = Person(address: Address(city: "Paris"))
// Print `person.address?.city as Any` to the console
print(person.address?.city as Any)
// Declare a constant `personNoAddress`, set to `Person(address: nil)`
let personNoAddress = Person(address: nil)
// Print `personNoAddress.address?.city as Any` to the console
print(personNoAddress.address?.city as Any)Login to try C/C++/Java/PHP code in the editor
Combining Chaining with Nil Coalescing
Optional chaining is often paired with ?? to supply a default value when any part of the chain is missing.
Example: Combining Chaining with Nil Coalescing
// Define a struct `Address`
struct Address {
var city: String
}
// Define a struct `Person`
struct Person {
var address: Address?
}
// Declare a constant `person`, set to `Person(address: nil)`
let person = Person(address: nil)
// Declare a constant `city`, set to `person.address?.city ?? "Unknown city"`
let city = person.address?.city ?? "Unknown city"
// Print `city` to the console
print(city)Login to try C/C++/Java/PHP code in the editor
Related Topics
{# common_mistakes/chapter_summary/browser_support: on Hindi pages the
view already swaps in the hi_ translation fields (or blanks these
out if untranslated), so this renders correctly for both languages
without a lang_code check here. #}
Common Mistakes
- Confusing optional chaining's
?.with force-unwrapping's!-- chaining returnsnilgracefully instead of crashing on a missing link. - Forgetting that the overall result of an optional chain is always itself an optional, even if the final property isn't.
- Trying to chain through a method call that doesn't itself return an optional, and being surprised the whole expression's result is still optional because of an earlier link.
Chapter Summary
?.accesses a property or calls a method only if the optional isn'tnil.- If any link in the chain is
nil, the entire expression short-circuits tonil. - The overall result of a chain is always wrapped in an optional, regardless of the underlying property's type.
- Chaining avoids deeply nested
if letchecks for accessing nested optional structures.
🔒
Chapter Quiz — Complete all 8 topics to unlock
0/8 topics done
Complete these topics first: