Result alias

main.rs

enum ReadingError {
    OutOfBounds,
    InvalidBuffer
}

trait InsteadOfThis {
    fn next_char() -> Result<u8, ReadingError>;
    fn next_line() -> Result<String, ReadingError>;
    fn char_at(pos: usize) -> Result<u8, ReadingError>;
}

// new result declaring the error just once
type ReadingResult<T> = Result<T, ReadingError>;

trait YouCanDoThis {
    fn next_char() -> ReadingResult<u8>;
    fn next_line() -> ReadingResult<String>;
    fn char_at(pos: usize) -> ReadingResult<u8>;
}

fn get_first(buffer: &[u8]) -> ReadingResult<String> {
    if buffer.len() > 0 {
        Ok(buffer[0].to_string())
    } else {
        Err(ReadingError::OutOfBounds)
    }
}

fn main() {
    if let Ok(first) = get_first(&"foo".as_bytes()) {
        println!("The first char is {}", first)
    }
}