extern crate serde;
extern crate serde_derive;
extern crate serde_json;

use serde::Deserialize;

#[derive(Debug, Deserialize)]
struct X {
    x: u32
}

impl Default for X {
    fn default() -> X {
        X { x: 666 }
    }
}

#[derive(Debug, Deserialize)]
struct Derp {
    s: u32,
    #[serde(default = "X::default")]
    x: X,
}

fn main() {
    println!("{:?}",
    serde_json::from_str::<Derp>(r#"{
    "s": 42
    }"#).unwrap());
}