Option

let value = Some(3);

if value.is_some() {
   // Some!!
   let value = value.unwrap();
}

if value.is_none() {
    value.unwrap(); // ERROR!!
}

Some functions have variations with a ? appended to their name that return options instead of throwing errors:

let empty = [];
let fst = empty.first(); // ERROR: list is empty
let fst = empty.first?(); // None

let my_list = [1,2,3];
let fst = my_list.first?; // Some(1)

A list has two pairs of element accessors. get / get? take a non-negative index (a usize); index / index? take a signed integer and wrap negative indices from the end, like the [] operator. The ? variant of each returns None when the index is past the end instead of erroring:

let my_list = [10, 20, 30];

my_list.get(0);     // 10
my_list.get(5);     // ERROR: index 5 is out of bounds
my_list.get?(0);    // Some(10)
my_list.get?(5);    // None
my_list.get?(-1);   // ERROR: a negative index is not a valid usize

my_list.index(-1);  // 30   (wraps from the end)
my_list.index(5);   // ERROR: index out of bounds
my_list.index?(-1); // Some(30)
my_list.index?(5);  // None

unwrap_or extracts the contained value, falling back to a default when the option is None:

[10, 20, 30].get?(1).unwrap_or(0); // 20
[10, 20, 30].get?(9).unwrap_or(0); // 0

Note: unfortunately the language doesn’t support pattern matching on options