Rust Programming By Example

Composing error types

The last thing we need to do in order to use all the good practices for error types in Rust is to make them easy to compose, because, for now, if we have another error type, such as io::Error, we would need to use the following code every time we have another type:

let val =
    match result {
        Ok(val) => val,
        Err(error) => return Err(Error::Io(error)),
    };

This can quickly become cumbersome. To improve that, we'll implement the From trait for different error types:

impl From<io::Error> for Error {
    fn from(error: io::Error) -> Self {
        Io(error)
    }
}

impl<'a> From<&'a str> for Error {
    fn from(message: &'a str) -> Self {
        Msg(message.to_string())
    }
}

impl From<Utf8Error> for Error {
    fn from(error: Utf8Error) -> Self { Utf8(error) ...