main.rs

extern crate serde;
#[macro_use]
extern crate serde_derive;
extern crate serde_json;

use std::fs::File;
use std::io::Write;

#[derive(Serialize)]
struct Foo {
    bar: &'static str,
}

fn main() {
    let foo = Foo { bar: "lol" };

    let mut file = File::create("foo.json").unwrap();
    file.write_all(&serde_json::to_vec(&foo).unwrap()).unwrap();
}