Almost. In Rust to use a trait, you have to explicitly import it. That means if you want to run `.to_json()` on something, you need to import trait `ToJson`. Then again if you want to force a type of something (for example an empty hashmap) you need to import the types which are included.

So what in a dynamic language could be:

    a.to_json() if a else {}.to_json()

In rust will start with:

    use rustc_serialize::json::{ToJson,Json};
    use std::collections::BTreeMap;
    ...