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Error handling (recoverable (Result<T, E> (unwrap (fn main() { …

Error handling

recoverable

Result<T, E>

enum Result<T, E> {
    Ok(T),
    Err(E),
}

fn main() {
    let f = file::open("test.txt");

    let f = match f {
        Ok(file) => file,
        Err(error) {
            println!("the error is {:?}", error)
        },
    };
}

expect

fn main() {
    let f = file::open("test.txt").expect("can't open the file.");
}

propagate error

fn read_username_from_file() -> Result<String, io::Error> {
    let f = file::open("user.txt");

    let mut f = match f {
        Ok(file) => file,
        Err(error) => return Err(error),
    };

    let s = String::new();

    match f.read_to_string(&s) {
        Ok(_) => Ok(s),
        Err(e) => Err(e),
    }
}

? operator

fn read_username_from_file() -> Result<String, io::Error> {
    let f = file::open("user.txt")?;
    let s = String::new();
    f.read_to_string(&s);
    Ok(s)
}

fn read_username_from_file() -> Result<String, io::Error> {
    let s = String::new();

    let f = file::open("user.txt")?.read_to_string(&s)?;
    Ok(s)
}