How do I use the box keyword in pattern matching?

Question

This code is shown in The Rust Programming Language:

#![feature(box_syntax, box_patterns)]

fn main() {
    let b = Some(box 5);
    match b {
        Some(b         


        

Answer 1

You are using a #[feature] and those can only be used with a nightly Rust compiler. I don't think it is currently possible to match against a Box in stable Rust, but nightly allows the following way of doing it (like you attempted in the beginning):

#![feature(box_patterns)]

fn main() {
    let b = Some(Box::new(5));
    match b {
        Some(box y) => print!("{:?}", y),
        _ => print!("{:?}", 1),
    }
}