Sized问题的动态调度迭代器Rust

因为您知道_state的实际类型，并且它是有大小的，所以您可以go 掉所有的特征对象，只需直接定义它.

struct Pawn {
    _state: std::iter::Cycle<std::array::IntoIter<u8, 10>>
}

impl Pawn {
    fn new() -> Self {
        // as before, but remove Box::new
    }
}

impl Clone for Pawn {

    fn clone(&self) -> Self {
        Self { _state: self._state.clone() }
    }
}

注:如果你不知道_state的确切类型，只知道它是一个产生u8的迭代器，如果你在Pawn中将它的类型参数化，你仍然可以定义克隆.请考虑:

struct Pawn<S>
where
    S: Iterator<Item = u8>,
{
    _state: S,
}

impl Pawn<std::iter::Cycle<std::array::IntoIter<u8, 10>>> {
    const ALL_STATES: [u8; 10] = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

    fn new() -> Self {
        Pawn {
            _state: Self::ALL_STATES.into_iter().cycle(),
        }
    }

    fn tick(&mut self, steps: usize) -> u8 {
        (0..steps - 1).for_each(|_| {
            self._state.next();
        });
        self._state.next().unwrap()
    }
}

// Note the extra trait bound here! S must also be clone
impl<S> Clone for Pawn<S>
where
    S: Iterator<Item = u8> + Clone,
{
    fn clone(&self) -> Self {
        Self {
            _state: self._state.clone(),
        }
    }
}