A fsm you can serialize with serde only on some state

main.rs

use std::marker::PhantomData;

use serde::{Deserialize, Serialize};

#[derive(Debug, Deserialize)]
struct A;
#[derive(Debug, Serialize)]
struct B;

#[derive(Debug, Clone, Default, Serialize, Deserialize)]
#[serde(deny_unknown_fields, rename_all = "camelCase", bound(serialize = "T: Serialize", deserialize = "T: Deserialize<'static>"))]
pub struct Fsm<T> {
    pub field: String,

    #[serde(skip)]
    pub _kind: PhantomData<T>,
}

impl Fsm<A> {
    pub fn into_b(self) -> Fsm<B> {
        Fsm {
            field: self.field,
            _kind: PhantomData::default(),
        }
    }
}

fn main() {
    let data = r#"{ "field": "hello" }"#;
    let fsm: Fsm<A> = serde_json::from_str(data).unwrap();

    // does not compile
    // let fsm: Fsm<B> = serde_json::from_str(data).unwrap();

    // does not compile
    // let res = serde_json::to_string_pretty(&fsm);

    let res = serde_json::to_string_pretty(&fsm.into_b()).unwrap();
    println!("{}", &res);
}