Optional Type

Optional is a built-in type layer written as T?.

Basic Usage

Int? maybe = 123;
_ same = maybe;

Bar? bar = Bar { x: 1, y: 2 }
_ field = bar?.x;

Optional Chaining

Use ?. to access a field only when the receiver is not null:

_ value = user?.profile?.name;

Conditional Unwrapping

Use is some:

if maybe is some value {
    print(value);
} else {
    print(0);
}

Explicit inferred and mutable bindings:

if maybe is some _ value {
    print(value);
}

if maybe is some _! value {
    value = value + 1;
}

??

?? provides a fallback value when the optional is empty:

Int value = maybe ?? 42;
Int other = maybe ?? fallback();

The left side must be optional. Use guard for early-exit control flow.

guard

() print_value(Int? maybe) {
    guard maybe is some value else {
        return ();
    }

    print(value);
    return ();
}

The else block must be non-empty and end in return, break, continue, or throw.

Force Unwrap

optional$.some() force unwraps an optional through the implicit operation layer:

Int value = maybe$.some();

Ordinary code should prefer is some, guard, or ??.