标准库中没有这样一个迭代器。
如果您知道迭代器的大小,可以将您的数字乘以迭代器的大小后再take
:
fn cycle_n_times<T: Clone>(slice: &[T], count: usize) -> impl Iterator<Item = &T> {
slice.iter().cycle().take(slice.len() * count)
}
或者您可以编写更通用的自定义代码:
pub struct Ncycles<I> {
orig: I,
iter: I,
count: usize,
}
impl<I: Clone> Ncycles<I> {
fn new(iter: I, count: usize) -> Ncycles<I> {
Ncycles {
orig: iter.clone(),
iter,
count,
}
}
}
impl<I> Iterator for Ncycles<I>
where
I: Clone + Iterator,
{
type Item = <I as Iterator>::Item;
#[inline]
fn next(&mut self) -> Option<<I as Iterator>::Item> {
match self.iter.next() {
None if self.count == 0 => None,
None => {
self.iter = self.orig.clone();
self.count -= 1;
self.iter.next()
}
y => y,
}
}
}
#[test]
fn it_work() {
Ncycles::new(vec![1, 2, 3].iter(), 4).eq(&[1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, 3]);
}