You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: lib.rs
    path of file: ./repos/materialize/src/cluster-client/src
    
    the code of the file until where you have to start completion: // Copyright Materialize, Inc. and contributors. All rights reserved.
//
// Use of this soft
    
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let first = s.chars().next();
        let rest = s.get(1..);
        if let (Some(prefix), Some(num)) = (first, rest) {
            let id = num.parse()?;
            match prefix {
                'u' => return Ok(Self::User(id)),
                's' => return Ok(Self::System(id)),
                _ => (),
            }
        }

        bail!("invalid replica ID: {}", s);
    }