Statum: Zero-Boilerplate Compile-Time State Machines in Rust

Great question! If i understood you correctly, you’re asking about creating a `Vec` of state machines and operating on them. With the type-state pattern, this can be tricky because each state is a distinct type (`Light<Off>` and `Light<On>`), and `Vec` requires all elements to have the same type.

To directly manage a `Vec` of state machines, you’d need dynamic dispatch (e.g., `Box<dyn ...>`), but as you mentioned, dynamic dispatch can be a giant pain in the ass.

Instead of directly managing a `Vec` of state machines (`Vec<Light<Box<dyn ...>>>`), my approach is to work with a dynamic collection of raw data (e.g., `Vec<DbData>`) and reconstruct state machines on the fly using the `to_machine` method generated by `#[validators]`.

Why?

1. You don’t need to store state machines directly in a collection.

2. The `to_machine` method dynamically reconstructs the appropriate state machine from raw data at runtime.

3.You still retain `Statum`’s compile-time guarantees for state transitions once the machine is reconstructed.

Here’s what i mean:

    use statum::{machine, state, validators};

    #[state]
    pub enum LightState {
        Off,
        On,
    }

    #[machine]
    pub struct LightMachine<S: LightState> {
        name: String,
    }

    impl LightMachine<Off> {
        pub fn switch_on(self) -> LightMachine<On> {
            self.transition()
        }
    }

    impl LightMachine<On> {
        pub fn switch_off(self) -> LightMachine<Off> {
            self.transition()
        }
    }

    // Represents dynamic data
    #[derive(Clone)]
    pub struct DbData {
        id: String,
        state: String,
    }

    #[validators(state = LightState, machine = LightMachine)]
    impl DbData {
        fn is_off(&self) -> Result<(), statum::Error> {
            if self.state == "off" {
                Ok(())
            } else {
                Err(statum::Error::InvalidState)
            }
        }

        fn is_on(&self) -> Result<(), statum::Error> {
            if self.state == "on" {
                Ok(())
            } else {
                Err(statum::Error::InvalidState)
            }
        }
    }

    fn main() {
        // raw data collection
        let db_data = vec![
            DbData {
                id: "1".to_owned(),
                state: "off".to_owned(),
            },
            DbData {
                id: "2".to_owned(),
                state: "on".to_owned(),
            },
        ];

        // do stuff with vec

        // dynamically reconstruct and operate on state machines
        for data in db_data {
            let machine = data
                .to_machine("Light".to_owned()) // Pass shared data here
                .unwrap(); // Handle errors if needed

            match machine {
                LightMachineState::Off(light) => handle_off_light(light),
                LightMachineState::On(light) => handle_on_light(light),
            }
        }
    }

    fn handle_off_light(light: LightMachine<Off>) {
        println!("Turning light on: {}", light.name);
    }

    fn handle_on_light(light: LightMachine<On>) {
        println!("Turning light offf: {}", light.name);
    }

This approach is kind of indirect but it solves the underlying need: operating on many state machines dynamically without sacrificing `Statum`’s type safety.

Did this address your question? If so, I’ll add it to the README—this is a great point worth documenting!