Option
Option[Char] is an enum that represents a Char value that may or may not be present. It is a common way to handle exceptional cases.
Nonemeans the value is missing.Some(e)is a wrapper that contains the valuee.
The [Char] part in the type is a type parameter, which means the value type in Option is Char. We can use Option[String], Option[Double], etc. We will cover generics later.
The type annotation Option[A] can be shortened to A?.
You can use c1.is_empty() to check if the value is missing and c1.unwrap() to get the value.
fn first_char(s : String) -> Option[Char] {
if s.length() == 0 {
None
} else {
Some(s[0])
}
}
fn main {
let c1 : Char? = first_char("hello")
let c2 : Option[Char] = first_char("")
println("\{c1.is_empty()}, \{c1.unwrap()}")
println("\{c2.is_empty()}, \{c2}")
}