Macro Attributes

The #[typestate] macro exposes some extra features through attribute parameters. This chapter introduces them and provides simple examples.

enumerate

The enumerate parameter will generate an additional enum containing all states; this is useful when dealing with anything that requires a more "general" concept of state.

Consider the file examples/light_bulb.rs:

#![allow(unused)]
fn main() {
#[typestate(enumerate = "LightBulbStates")]
mod light_bulb {
    #[state] struct On;
    #[state] struct Off;
    // ...
}
}

Using the enumerate attribute will add the following enum to the expansion:

#![allow(unused)]
fn main() {
pub enum LightBulbStates {
    Off(LightBulb<Off>),
    On(LightBulb<On>),
}
}

state_constructors

The state_constructors parameter will generate additional constructors for each state with fields; this is useful when declaring states inside the automaton.

Consider the following example state:

#![allow(unused)]
fn main() {
#[typestate(state_constructors = "new_state")]
mod light_bulb {
    #[state] struct On {
        color: [u8; 3]
    }
    // ...
}
}

When compiled, the following constructor is generated:

#![allow(unused)]
fn main() {
impl On {
    pub fn new_state(color: [u8; 3]) -> Self {
        Self { color }
    }
}
}