Appendix F - Newest Features

This appendix documents features that have been added to stable Rust since the main part of the book was completed.

Field init shorthand

We can initialize a data structure (struct, enum, union) with named fields, by writing fieldname as a shorthand for fieldname: fieldname. This allows a compact syntax for initialization, with less duplication:

struct Person {
    name: String,
    age: u8,

fn main() {
    let name = String::from("Peter");
    let age = 27;

    // Using full syntax:
    let peter = Person { name: name, age: age };

    let name = String::from("Portia");
    let age = 27;

    // Using field init shorthand:
    let portia = Person { name, age };

    println!("{:?}", portia);

Returning from loops

One of the uses of a loop is to retry an operation you know can fail, such as checking if a thread completed its job. However, you might need to pass the result of that operation to the rest of your code. If you add it to the break expression you use to stop the loop, it will be returned by the broken loop:

fn main() {
    let mut counter = 0;

    let result = loop {
        counter += 1;

        if counter == 10 {
            break counter * 2;

    assert_eq!(result, 20);