extern crate serde; // 1.0.78
#[macro_use]
extern crate serde_derive; // 1.0.78
extern crate serde_json; // 1.0.27

#[derive(Serialize, Deserialize, Clone, Eq, PartialEq, Debug)]
#[serde(untagged)]
#[serde(rename_all = "camelCase")]
pub enum A {
    Ok {
        status_code: u16,
    },
    Err {
        error_message: String,
    }
}

#[derive(Serialize, Deserialize, Clone, Eq, PartialEq, Debug)]
#[serde(rename_all = "camelCase")]
pub struct B {
    status_code: u16,
}

fn main() {
    let a = A::Ok{ status_code: 0 };
    println!("{:?}", ::serde_json::to_string(&a)); // -> Ok("{\"status_code\":0}")
    let b = B{ status_code: 0 };
    println!("{:?}", ::serde_json::to_string(&b)); // -> Ok("{\"statusCode\":0}")
}