borrow-example.rs

extern crate serialize;

use serialize::json;

fn get_string<'a>(data: &'a json::Json, key: &~str) -> Option<&'a str> {
    match *data {
        json::Object(ref map) => {
            match map.find(key) {
                Some(&json::String(ref s)) => {
                    Some(s.as_slice())
                },
                _ => None,
            }
        },
        _ => None,
    }
}

fn main() {
    let data = json::from_str(stringify!(
        {
            "language": "Rust",
            "level"   : 9001
        }
    )).unwrap();

    println!("{}", get_string(&data, &~"language")); // Prints Some("Rust")
    println!("{}", get_string(&data, &~"level"));    // Prints None
}