Optionals in Swift

The maybe-missing value, spelled into the type.

let berths = ["Kestrel": 12, "Sable": 4]

// A dictionary lookup is Optional: the key might not be there.
let kestrelBerth: Int? = berths["Kestrel"]
let ghostBerth: Int? = berths["Osprey"]

// ?? supplies a default; optional chaining stops at nil.
print("Kestrel moors at \(kestrelBerth ?? 0)")
print("Osprey moors at \(ghostBerth ?? 0)")

let radioCall: String? = "Kestrel, Kestrel, race control"
print("Call length: \(radioCall?.count ?? 0)")

How it works

1. A dictionary lookup returns Int? — the key might be absent.
2. ?? 0 supplies the default for the nil case.
3. radioCall?.count chains past nil instead of crashing.

Keywords and builtins used here

• Int
• String
• count
• let
• print

The run, in numbers

Lines

12

Characters to type

444

Tokens

92

Three-star pace

70 tpm

At the three-star pace of 70 tokens a minute, this run takes about 79 seconds.

Type this snippet

Step 1 of 3 in Optionals, step 10 of 27 in Language basics.

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Optionals in other languages

• Zig