loops can now break with a value:

#![allow(unused_variables)]
fn main() {
// old code
let x;

loop {
    x = 7;
    break;
}

// new code
let x = loop { break 7; };
}

Rust has traditionally positioned itself as an “expression oriented language”, that is, most things are expressions that evaluate to a value, rather than statements. loop stuck out as strange in this way, as it was previously a statement.

For now, this only applies to loop, and not things like while or for. It's not clear yet, but we may add this to those in the future.