I have this function parse to parse a HTTP request string. I declare an uninitialized variable method then later on in the match statement, I assign it the value GET or I return from the function with an error.

I would think that upon returning Ok, the method field would be either populated or the function would return an error before that point, yet the compiler tells me that this is not the case:

error[E0381]: use of possibly-uninitialized variable: `method`
    Ok(HttpRequest { s_addr: s_addr, method, scheme: RequestScheme::HTTP })
                                     ^^^^^^ use of possibly-uninitialized `method`

pub fn parse(request_string: String, s_addr: SocketAddr) -> Result<HttpRequest, HttpError> {
    let mut method: HttpMethod;
    for element in request_string.split(" ") {
        method = match element {
            "GET" => HttpMethod::GET,
            _ => { 
                eprintln!("Couldn't parse word : {}", element); 
                return Err(HttpError::ParseError);
            },
        }
    }
    Ok(HttpRequest { s_addr: s_addr, method, scheme: RequestScheme::HTTP })
}

CodePudding user response：

As @mkrieger1 points out:

What if the for loop has 0 iterations?

String's split function never returns an empty iterator, so consider using an Option<T>, then unwrapping the value.

let mut method: Option<HttpMethod> = None;

for element in request_string.split(" ") {
    if element != "GET" {
        eprintln!("Couldn't parse word : {}", element); 
        return Err(HttpError::ParseError);
    }
    method.insert(HttpMethod::Get);
}

Ok(HttpRequest { s_addr, method: method.unwrap(), scheme: RequestScheme::HTTP})

Or, in your case you can just avoid a variable all together.

for element in request_string.split(" ") {
    if element != "GET" {
        eprintln!("Couldn't parse word : {}", element); 
        return Err(HttpError::ParseError);
    }
}
Ok(HttpRequest { s_addr, method: HttpMethod::Get, scheme: RequestScheme::HTTP})