Rust: What does the `@` (at sign) operator do?

Question

I saw the following line in my code, and I am not sure what it does as I haven't encountered the @ operator before.

if let e@Err(_) = changed {
    ...
}

Can this line be written without the @ operator, what would that look like?

Answer 1

It's a way to bind the matched value of a pattern to a variable(using the syntax: variable @ subpattern).

Example:

let x = 2;

match x {
    e @ 1 ..= 5 => println!("got a range element {}", e),
    _ => println!("anything"),
}