Joel Galenson | b593e25 | 2021-06-21 13:15:57 -0700 | [diff] [blame] | 1 | use crate::size_hint; |
| 2 | use std::{ |
| 3 | fmt, |
| 4 | iter::{DoubleEndedIterator, FusedIterator}, |
| 5 | }; |
| 6 | |
| 7 | pub fn flatten_ok<I, T, E>(iter: I) -> FlattenOk<I, T, E> |
| 8 | where |
| 9 | I: Iterator<Item = Result<T, E>>, |
| 10 | T: IntoIterator, |
| 11 | { |
| 12 | FlattenOk { |
| 13 | iter, |
| 14 | inner_front: None, |
| 15 | inner_back: None, |
| 16 | } |
| 17 | } |
| 18 | |
| 19 | /// An iterator adaptor that flattens `Result::Ok` values and |
| 20 | /// allows `Result::Err` values through unchanged. |
| 21 | /// |
| 22 | /// See [`.flatten_ok()`](crate::Itertools::flatten_ok) for more information. |
| 23 | #[must_use = "iterator adaptors are lazy and do nothing unless consumed"] |
| 24 | pub struct FlattenOk<I, T, E> |
| 25 | where |
| 26 | I: Iterator<Item = Result<T, E>>, |
| 27 | T: IntoIterator, |
| 28 | { |
| 29 | iter: I, |
| 30 | inner_front: Option<T::IntoIter>, |
| 31 | inner_back: Option<T::IntoIter>, |
| 32 | } |
| 33 | |
| 34 | impl<I, T, E> Iterator for FlattenOk<I, T, E> |
| 35 | where |
| 36 | I: Iterator<Item = Result<T, E>>, |
| 37 | T: IntoIterator, |
| 38 | { |
| 39 | type Item = Result<T::Item, E>; |
| 40 | |
| 41 | fn next(&mut self) -> Option<Self::Item> { |
| 42 | loop { |
| 43 | // Handle the front inner iterator. |
| 44 | if let Some(inner) = &mut self.inner_front { |
| 45 | if let Some(item) = inner.next() { |
| 46 | return Some(Ok(item)); |
| 47 | } else { |
| 48 | // This is necessary for the iterator to implement `FusedIterator` |
| 49 | // with only the orginal iterator being fused. |
| 50 | self.inner_front = None; |
| 51 | } |
| 52 | } |
| 53 | |
| 54 | match self.iter.next() { |
| 55 | Some(Ok(ok)) => self.inner_front = Some(ok.into_iter()), |
| 56 | Some(Err(e)) => return Some(Err(e)), |
| 57 | None => { |
| 58 | // Handle the back inner iterator. |
| 59 | if let Some(inner) = &mut self.inner_back { |
| 60 | if let Some(item) = inner.next() { |
| 61 | return Some(Ok(item)); |
| 62 | } else { |
| 63 | // This is necessary for the iterator to implement `FusedIterator` |
| 64 | // with only the orginal iterator being fused. |
| 65 | self.inner_back = None; |
| 66 | } |
| 67 | } else { |
| 68 | return None; |
| 69 | } |
| 70 | } |
| 71 | } |
| 72 | } |
| 73 | } |
| 74 | |
| 75 | fn size_hint(&self) -> (usize, Option<usize>) { |
| 76 | let inner_hint = |inner: &Option<T::IntoIter>| { |
| 77 | inner |
| 78 | .as_ref() |
| 79 | .map(Iterator::size_hint) |
| 80 | .unwrap_or((0, Some(0))) |
| 81 | }; |
| 82 | let inner_front = inner_hint(&self.inner_front); |
| 83 | let inner_back = inner_hint(&self.inner_back); |
| 84 | // The outer iterator `Ok` case could be (0, None) as we don't know its size_hint yet. |
| 85 | let outer = match self.iter.size_hint() { |
| 86 | (0, Some(0)) => (0, Some(0)), |
| 87 | _ => (0, None), |
| 88 | }; |
| 89 | |
| 90 | size_hint::add(size_hint::add(inner_front, inner_back), outer) |
| 91 | } |
| 92 | } |
| 93 | |
| 94 | impl<I, T, E> DoubleEndedIterator for FlattenOk<I, T, E> |
| 95 | where |
| 96 | I: DoubleEndedIterator<Item = Result<T, E>>, |
| 97 | T: IntoIterator, |
| 98 | T::IntoIter: DoubleEndedIterator, |
| 99 | { |
| 100 | fn next_back(&mut self) -> Option<Self::Item> { |
| 101 | loop { |
| 102 | // Handle the back inner iterator. |
| 103 | if let Some(inner) = &mut self.inner_back { |
| 104 | if let Some(item) = inner.next_back() { |
| 105 | return Some(Ok(item)); |
| 106 | } else { |
| 107 | // This is necessary for the iterator to implement `FusedIterator` |
| 108 | // with only the orginal iterator being fused. |
| 109 | self.inner_back = None; |
| 110 | } |
| 111 | } |
| 112 | |
| 113 | match self.iter.next_back() { |
| 114 | Some(Ok(ok)) => self.inner_back = Some(ok.into_iter()), |
| 115 | Some(Err(e)) => return Some(Err(e)), |
| 116 | None => { |
| 117 | // Handle the front inner iterator. |
| 118 | if let Some(inner) = &mut self.inner_front { |
| 119 | if let Some(item) = inner.next_back() { |
| 120 | return Some(Ok(item)); |
| 121 | } else { |
| 122 | // This is necessary for the iterator to implement `FusedIterator` |
| 123 | // with only the orginal iterator being fused. |
| 124 | self.inner_front = None; |
| 125 | } |
| 126 | } else { |
| 127 | return None; |
| 128 | } |
| 129 | } |
| 130 | } |
| 131 | } |
| 132 | } |
| 133 | } |
| 134 | |
| 135 | impl<I, T, E> Clone for FlattenOk<I, T, E> |
| 136 | where |
| 137 | I: Iterator<Item = Result<T, E>> + Clone, |
| 138 | T: IntoIterator, |
| 139 | T::IntoIter: Clone, |
| 140 | { |
| 141 | #[inline] |
| 142 | clone_fields!(iter, inner_front, inner_back); |
| 143 | } |
| 144 | |
| 145 | impl<I, T, E> fmt::Debug for FlattenOk<I, T, E> |
| 146 | where |
| 147 | I: Iterator<Item = Result<T, E>> + fmt::Debug, |
| 148 | T: IntoIterator, |
| 149 | T::IntoIter: fmt::Debug, |
| 150 | { |
| 151 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
| 152 | f.debug_struct("FlattenOk") |
| 153 | .field("iter", &self.iter) |
| 154 | .field("inner_front", &self.inner_front) |
| 155 | .field("inner_back", &self.inner_back) |
| 156 | .finish() |
| 157 | } |
| 158 | } |
| 159 | |
| 160 | /// Only the iterator being flattened needs to implement [`FusedIterator`]. |
| 161 | impl<I, T, E> FusedIterator for FlattenOk<I, T, E> |
| 162 | where |
| 163 | I: FusedIterator<Item = Result<T, E>>, |
| 164 | T: IntoIterator, |
| 165 | { |
| 166 | } |