json_decode.rs

extern crate rustc_serialize;

use rustc_serialize::{Decodable, Encodable, json};
use rustc_serialize::json::Json;

#[derive(RustcDecodable, RustcEncodable, Debug)]
pub enum Message {
    First {msg: FirstMsg},
    Second {msg: SecondMsg}
}

#[derive(RustcDecodable, RustcEncodable, Debug)]
pub struct FirstMsg {
    pub a_string: String,
    pub a_int: i64
}

#[derive(RustcDecodable, RustcEncodable, Debug)]
pub struct SecondMsg {
    pub a_float: f32
}

fn encode(msg: &Message) -> String {
    json::encode(msg).unwrap()
}

fn decode(text: &str) -> Message {
    json::decode(text).unwrap()
}

fn process(msg: Message) {
    match msg {
        Message::First{ msg } => println!("First {} {}", msg.a_string, msg.a_int),
        Message::Second{ msg } => println!("Second {}", msg.a_float),
    }
}


fn main() {
    let first = Message::First{ msg: FirstMsg { a_string: "anne".to_string(), a_int: 42 } };
    let second = Message::Second{ msg: SecondMsg { a_float: 42.0 } };

    println!("First: '{:?}', Second: '{:?}'", first, second);

    let encoded_first = encode(&first);
    let encoded_second = encode(&second);

    println!("First: '{}', Second: '{}'", encoded_first, encoded_second);

    let first_copy = decode(&encoded_first);
    let second_copy = decode(&encoded_second);

    println!("First: '{:?}', Second: '{:?}'", first_copy, second_copy);

    process(first_copy);
    process(second_copy);
}