SM allows you to define a collection of states and events using Rust's type system. Undefined behavior is not an option.
The implementation ensures a zero-sized abstraction that uses Rust's type-system and ownership model to guarantee valid transitions between states using events, and makes sure previous states are no longer usable after transitioning away to another state, unless transitioned back to using any pre-defined state transitions. Rust validates correct usage of the state machine at compile-time, no runtime checking occurs when using the library.
The library exposes two traits, State, and Event, but primarily provides the
macro sm!, which allows you to declaratively build the state machine.
```rust let stile = sm!{ TurnStile { Locked }
states { Locked, Unlocked }
coin { Locked => Unlocked Unlocked => Unlocked }
push { Locked => Locked Unlocked => Locked } };
stile.state() // => Locked
let newstile = stile.event(Invalid); // won't compile
let newstile = stile.event(Coin); // => TurnStile
stile.state() // won't compile new_stile.state() // => Unlocked ```