Continue return never type compile error

1 
        let guess: u32 = match guess.trim().parse() {
            Ok(num) => num,
            Err(_) => continue,
        };

this code is from Advanced Types - The Rust Programming Language

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when i copy this code into rustrover, the ide tells me compile error: "continue can obly be used inside a loop/while block".
WHY?
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2

Uhm. Because you've just copied the code without making sure it is, in fact, inside of a loop or a while block? The snippet in question is from 2-5 (as per "recall the code from Listing 2-5" part):

loop {
    // ...
    match guess.cmp(&secret_number) {
        Ordering::Less => println!("Too small!"),
        Ordering::Greater => println!("Too big!"),
        Ordering::Equal => println!("You win!"),
    }
    // it's here that that the `match guess.trim().parse()` + `continue` goes
}
3

Without a loop to "continue", you can't continue.

"continue" means go back to the start of the loop and run the loop again. If in a "while" loop you go back to the start of loop and check the condition of the "while" before looping.
If you are not in a loop, there is nowhere to continue.

4

This is one of those strange cases where a "match" can have arms that are of different types.

5

Nit: All the arms have the same type. ! has special coercion abilities and coerces to the type of the other arms.

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