F - Newest Features - F - Newest Features - The Rust Programming Language

# 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:

    #[derive(Debug)]
    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);
    }