Optional Types ?T

Syntax

?T represents a value that may be absent:

fn find(name: string): ?i32
{
    if (name == "key") { return Some(42) }
    return None
}

Using match

match find("key")
{
    Some(v) -> print("found:", v)
    None -> print("not found")
}

Optional References ?ref T

v0.3.0 supports optional references:

fn maybe_ref(flag: i32, value: ref i32): ?ref i32
{
    if (flag == 0) { return None }
    return Some(value)
}

Implementation

?T is implemented using ADT Some/None constructors with pointer semantics.