1use crate::num::NonZeroUsize;
2use crate::ops::{NeverShortCircuit, Try};
3
4/// Like `Iterator::by_ref`, but requiring `Sized` so it can forward generics.
5///
6/// Ideally this will no longer be required, eventually, but as can be seen in
7/// the benchmarks (as of Feb 2022 at least) `by_ref` can have performance cost.
8#[unstable(feature = "std_internals", issue = "none")]
9#[derive(Debug)]
10pub struct ByRefSized<'a, I>(pub &'a mut I);
11
12// The following implementations use UFCS-style, rather than trusting autoderef,
13// to avoid accidentally calling the `&mut Iterator` implementations.
14
15#[unstable(feature = "std_internals", issue = "none")]
16impl<I: Iterator> Iterator for ByRefSized<'_, I> {
17 type Item = I::Item;
18
19 #[inline]
20 fn next(&mut self) -> Option<Self::Item> {
21 I::next(self.0)
22 }
23
24 #[inline]
25 fn size_hint(&self) -> (usize, Option<usize>) {
26 I::size_hint(self.0)
27 }
28
29 #[inline]
30 fn advance_by(&mut self, n: usize) -> Result<(), NonZeroUsize> {
31 I::advance_by(self.0, n)
32 }
33
34 #[inline]
35 fn nth(&mut self, n: usize) -> Option<Self::Item> {
36 I::nth(self.0, n)
37 }
38
39 #[inline]
40 fn fold<B, F>(self, init: B, f: F) -> B
41 where
42 F: FnMut(B, Self::Item) -> B,
43 {
44 // `fold` needs ownership, so this can't forward directly.
45 I::try_fold(self.0, init, NeverShortCircuit::wrap_mut_2(f)).0
46 }
47
48 #[inline]
49 fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R
50 where
51 F: FnMut(B, Self::Item) -> R,
52 R: Try<Output = B>,
53 {
54 I::try_fold(self.0, init, f)
55 }
56}
57
58#[unstable(feature = "std_internals", issue = "none")]
59impl<I: DoubleEndedIterator> DoubleEndedIterator for ByRefSized<'_, I> {
60 #[inline]
61 fn next_back(&mut self) -> Option<Self::Item> {
62 I::next_back(self.0)
63 }
64
65 #[inline]
66 fn advance_back_by(&mut self, n: usize) -> Result<(), NonZeroUsize> {
67 I::advance_back_by(self.0, n)
68 }
69
70 #[inline]
71 fn nth_back(&mut self, n: usize) -> Option<Self::Item> {
72 I::nth_back(self.0, n)
73 }
74
75 #[inline]
76 fn rfold<B, F>(self, init: B, f: F) -> B
77 where
78 F: FnMut(B, Self::Item) -> B,
79 {
80 // `rfold` needs ownership, so this can't forward directly.
81 I::try_rfold(self.0, init, NeverShortCircuit::wrap_mut_2(f)).0
82 }
83
84 #[inline]
85 fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R
86 where
87 F: FnMut(B, Self::Item) -> R,
88 R: Try<Output = B>,
89 {
90 I::try_rfold(self.0, init, f)
91 }
92}
93