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master
src/repeatn.rs
83 строки
2 KB
Philippe-Cholet
`RepeatN`: implement `PeekingNext`
18 янв 2024, 18:08
18 янв 2024, 18:08
272aa21
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use std::iter::FusedIterator; /// An iterator that produces *n* repetitions of an element. /// /// See [`repeat_n()`](crate::repeat_n) for more information. #[must_use = "iterators are lazy and do nothing unless consumed"] #[derive(Clone, Debug)] pub struct RepeatN<A> { pub(crate) elt: Option<A>, n: usize, } /// Create an iterator that produces `n` repetitions of `element`. pub fn repeat_n<A>(element: A, n: usize) -> RepeatN<A> where A: Clone, { if n == 0 { RepeatN { elt: None, n } } else { RepeatN { elt: Some(element), n, } } } impl<A> Iterator for RepeatN<A> where A: Clone, { type Item = A; fn next(&mut self) -> Option<Self::Item> { if self.n > 1 { self.n -= 1; self.elt.as_ref().cloned() } else { self.n = 0; self.elt.take() } } fn size_hint(&self) -> (usize, Option<usize>) { (self.n, Some(self.n)) } fn fold<B, F>(self, mut init: B, mut f: F) -> B where F: FnMut(B, Self::Item) -> B, { match self { Self { elt: Some(elt), n } => { debug_assert!(n > 0); init = (1..n).map(|_| elt.clone()).fold(init, &mut f); f(init, elt) } _ => init, } } } impl<A> DoubleEndedIterator for RepeatN<A> where A: Clone, { #[inline] fn next_back(&mut self) -> Option<Self::Item> { self.next() } #[inline] fn rfold<B, F>(self, init: B, f: F) -> B where F: FnMut(B, Self::Item) -> B, { self.fold(init, f) } } impl<A> ExactSizeIterator for RepeatN<A> where A: Clone {} impl<A> FusedIterator for RepeatN<A> where A: Clone {}