use serde::{Serialize};

#[derive(Serialize, Debug)]
struct A {
    a: String
}

#[derive(Serialize, Debug)]
struct B {
    b: String
}

#[derive(Serialize, Debug)]
enum Foo {
    A(A),
    B(B),
}

fn main() {
    let response = match 1 {
        1 => Foo::A(A { a: "a".to_string() }),
        2 => Foo::B(B { b: "b".to_string() }),
        _ => unreachable!(),
    };

    println!("{}", serde_json::to_string(&response).unwrap());
}