Joel Galenson | b593e25 | 2021-06-21 13:15:57 -0700 | [diff] [blame] | 1 | use std::iter::{Fuse, FusedIterator}; |
Jakub Kotur | a425e55 | 2020-12-21 17:28:15 +0100 | [diff] [blame] | 2 | use crate::size_hint; |
| 3 | |
| 4 | /// An iterator adaptor that pads a sequence to a minimum length by filling |
| 5 | /// missing elements using a closure. |
| 6 | /// |
| 7 | /// Iterator element type is `I::Item`. |
| 8 | /// |
Joel Galenson | b593e25 | 2021-06-21 13:15:57 -0700 | [diff] [blame] | 9 | /// See [`.pad_using()`](crate::Itertools::pad_using) for more information. |
Jakub Kotur | a425e55 | 2020-12-21 17:28:15 +0100 | [diff] [blame] | 10 | #[derive(Clone)] |
| 11 | #[must_use = "iterator adaptors are lazy and do nothing unless consumed"] |
| 12 | pub struct PadUsing<I, F> { |
| 13 | iter: Fuse<I>, |
| 14 | min: usize, |
| 15 | pos: usize, |
| 16 | filler: F, |
| 17 | } |
| 18 | |
| 19 | /// Create a new **PadUsing** iterator. |
| 20 | pub fn pad_using<I, F>(iter: I, min: usize, filler: F) -> PadUsing<I, F> |
| 21 | where I: Iterator, |
| 22 | F: FnMut(usize) -> I::Item |
| 23 | { |
| 24 | PadUsing { |
| 25 | iter: iter.fuse(), |
| 26 | min, |
| 27 | pos: 0, |
| 28 | filler, |
| 29 | } |
| 30 | } |
| 31 | |
| 32 | impl<I, F> Iterator for PadUsing<I, F> |
| 33 | where I: Iterator, |
| 34 | F: FnMut(usize) -> I::Item |
| 35 | { |
| 36 | type Item = I::Item; |
| 37 | |
| 38 | #[inline] |
Joel Galenson | 6f79871 | 2021-04-01 17:03:06 -0700 | [diff] [blame] | 39 | fn next(&mut self) -> Option<Self::Item> { |
Jakub Kotur | a425e55 | 2020-12-21 17:28:15 +0100 | [diff] [blame] | 40 | match self.iter.next() { |
| 41 | None => { |
| 42 | if self.pos < self.min { |
| 43 | let e = Some((self.filler)(self.pos)); |
| 44 | self.pos += 1; |
| 45 | e |
| 46 | } else { |
| 47 | None |
| 48 | } |
| 49 | }, |
| 50 | e => { |
| 51 | self.pos += 1; |
| 52 | e |
| 53 | } |
| 54 | } |
| 55 | } |
| 56 | |
| 57 | fn size_hint(&self) -> (usize, Option<usize>) { |
| 58 | let tail = self.min.saturating_sub(self.pos); |
| 59 | size_hint::max(self.iter.size_hint(), (tail, Some(tail))) |
| 60 | } |
| 61 | } |
| 62 | |
| 63 | impl<I, F> DoubleEndedIterator for PadUsing<I, F> |
| 64 | where I: DoubleEndedIterator + ExactSizeIterator, |
| 65 | F: FnMut(usize) -> I::Item |
| 66 | { |
Joel Galenson | 6f79871 | 2021-04-01 17:03:06 -0700 | [diff] [blame] | 67 | fn next_back(&mut self) -> Option<Self::Item> { |
Jakub Kotur | a425e55 | 2020-12-21 17:28:15 +0100 | [diff] [blame] | 68 | if self.min == 0 { |
| 69 | self.iter.next_back() |
| 70 | } else if self.iter.len() >= self.min { |
| 71 | self.min -= 1; |
| 72 | self.iter.next_back() |
| 73 | } else { |
| 74 | self.min -= 1; |
| 75 | Some((self.filler)(self.min)) |
| 76 | } |
| 77 | } |
| 78 | } |
| 79 | |
| 80 | impl<I, F> ExactSizeIterator for PadUsing<I, F> |
| 81 | where I: ExactSizeIterator, |
| 82 | F: FnMut(usize) -> I::Item |
| 83 | {} |
Joel Galenson | b593e25 | 2021-06-21 13:15:57 -0700 | [diff] [blame] | 84 | |
| 85 | |
| 86 | impl<I, F> FusedIterator for PadUsing<I, F> |
| 87 | where I: FusedIterator, |
| 88 | F: FnMut(usize) -> I::Item |
| 89 | {} |