std.option
Optional values.
The Optional value represents an optional value. An Option is either a
Some, indicating the presence of a value, or a None, indicating the lack
of a value.
Optional values differ from nullable/nilable types in that they can be nested.
That is, Option[Option[T]] and Option[T] are two different types, but
T | null and T | null | null are the same.
Types
| Option | An optional value. |