1 | use crate::fmt; |
2 | use crate::iter::InPlaceIterable; |
3 | use crate::iter::adapters::SourceIter; |
4 | use crate::num::NonZero; |
5 | use crate::ops::{ControlFlow, Try}; |
6 | |
7 | /// An iterator to maintain state while iterating another iterator. |
8 | /// |
9 | /// This `struct` is created by the [`scan`] method on [`Iterator`]. See its |
10 | /// documentation for more. |
11 | /// |
12 | /// [`scan`]: Iterator::scan |
13 | /// [`Iterator`]: trait.Iterator.html |
14 | #[must_use = "iterators are lazy and do nothing unless consumed" ] |
15 | #[stable (feature = "rust1" , since = "1.0.0" )] |
16 | #[derive (Clone)] |
17 | pub struct Scan<I, St, F> { |
18 | iter: I, |
19 | f: F, |
20 | state: St, |
21 | } |
22 | |
23 | impl<I, St, F> Scan<I, St, F> { |
24 | pub(in crate::iter) fn new(iter: I, state: St, f: F) -> Scan<I, St, F> { |
25 | Scan { iter, state, f } |
26 | } |
27 | } |
28 | |
29 | #[stable (feature = "core_impl_debug" , since = "1.9.0" )] |
30 | impl<I: fmt::Debug, St: fmt::Debug, F> fmt::Debug for Scan<I, St, F> { |
31 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
32 | f.debug_struct("Scan" ).field("iter" , &self.iter).field(name:"state" , &self.state).finish() |
33 | } |
34 | } |
35 | |
36 | #[stable (feature = "rust1" , since = "1.0.0" )] |
37 | impl<B, I, St, F> Iterator for Scan<I, St, F> |
38 | where |
39 | I: Iterator, |
40 | F: FnMut(&mut St, I::Item) -> Option<B>, |
41 | { |
42 | type Item = B; |
43 | |
44 | #[inline ] |
45 | fn next(&mut self) -> Option<B> { |
46 | let a = self.iter.next()?; |
47 | (self.f)(&mut self.state, a) |
48 | } |
49 | |
50 | #[inline ] |
51 | fn size_hint(&self) -> (usize, Option<usize>) { |
52 | let (_, upper) = self.iter.size_hint(); |
53 | (0, upper) // can't know a lower bound, due to the scan function |
54 | } |
55 | |
56 | #[inline ] |
57 | fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R |
58 | where |
59 | Self: Sized, |
60 | Fold: FnMut(Acc, Self::Item) -> R, |
61 | R: Try<Output = Acc>, |
62 | { |
63 | fn scan<'a, T, St, B, Acc, R: Try<Output = Acc>>( |
64 | state: &'a mut St, |
65 | f: &'a mut impl FnMut(&mut St, T) -> Option<B>, |
66 | mut fold: impl FnMut(Acc, B) -> R + 'a, |
67 | ) -> impl FnMut(Acc, T) -> ControlFlow<R, Acc> + 'a { |
68 | move |acc, x| match f(state, x) { |
69 | None => ControlFlow::Break(try { acc }), |
70 | Some(x) => ControlFlow::from_try(fold(acc, x)), |
71 | } |
72 | } |
73 | |
74 | let state = &mut self.state; |
75 | let f = &mut self.f; |
76 | self.iter.try_fold(init, scan(state, f, fold)).into_try() |
77 | } |
78 | |
79 | impl_fold_via_try_fold! { fold -> try_fold } |
80 | } |
81 | |
82 | #[unstable (issue = "none" , feature = "inplace_iteration" )] |
83 | unsafe impl<St, F, I> SourceIter for Scan<I, St, F> |
84 | where |
85 | I: SourceIter, |
86 | { |
87 | type Source = I::Source; |
88 | |
89 | #[inline ] |
90 | unsafe fn as_inner(&mut self) -> &mut I::Source { |
91 | // SAFETY: unsafe function forwarding to unsafe function with the same requirements |
92 | unsafe { SourceIter::as_inner(&mut self.iter) } |
93 | } |
94 | } |
95 | |
96 | #[unstable (issue = "none" , feature = "inplace_iteration" )] |
97 | unsafe impl<St, F, I: InPlaceIterable> InPlaceIterable for Scan<I, St, F> { |
98 | const EXPAND_BY: Option<NonZero<usize>> = I::EXPAND_BY; |
99 | const MERGE_BY: Option<NonZero<usize>> = I::MERGE_BY; |
100 | } |
101 | |