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pub trait State: 'static + Send + Sized {}

pub trait Model: 'static + Send + Sync + Sized {
    type State: State;
    fn new_state(&self) -> Self::State;
}

impl Model for () {
    type State = ();
    fn new_state(&self) -> Self::State {}
}

impl<T: 'static + Send + Sized> State for T {}