1//! Common splitter for strings and slices
2//!
3//! This module is private, so these items are effectively `pub(super)`
4
5use crate::iter::plumbing::{Folder, UnindexedProducer};
6
7/// Common producer for splitting on a predicate.
8pub(super) struct SplitProducer<'p, P, V> {
9 data: V,
10 separator: &'p P,
11
12 /// Marks the endpoint beyond which we've already found no separators.
13 tail: usize,
14}
15
16/// Helper trait so `&str`, `&[T]`, and `&mut [T]` can share `SplitProducer`.
17pub(super) trait Fissile<P>: Sized {
18 fn length(&self) -> usize;
19 fn midpoint(&self, end: usize) -> usize;
20 fn find(&self, separator: &P, start: usize, end: usize) -> Option<usize>;
21 fn rfind(&self, separator: &P, end: usize) -> Option<usize>;
22 fn split_once(self, index: usize) -> (Self, Self);
23 fn fold_splits<F>(self, separator: &P, folder: F, skip_last: bool) -> F
24 where
25 F: Folder<Self>,
26 Self: Send;
27}
28
29impl<'p, P, V> SplitProducer<'p, P, V>
30where
31 V: Fissile<P> + Send,
32{
33 pub(super) fn new(data: V, separator: &'p P) -> Self {
34 SplitProducer {
35 tail: data.length(),
36 data,
37 separator,
38 }
39 }
40
41 /// Common `fold_with` implementation, integrating `SplitTerminator`'s
42 /// need to sometimes skip its final empty item.
43 pub(super) fn fold_with<F>(self, folder: F, skip_last: bool) -> F
44 where
45 F: Folder<V>,
46 {
47 let SplitProducer {
48 data,
49 separator,
50 tail,
51 } = self;
52
53 if tail == data.length() {
54 // No tail section, so just let `fold_splits` handle it.
55 data.fold_splits(separator, folder, skip_last)
56 } else if let Some(index) = data.rfind(separator, tail) {
57 // We found the last separator to complete the tail, so
58 // end with that slice after `fold_splits` finds the rest.
59 let (left, right) = data.split_once(index);
60 let folder = left.fold_splits(separator, folder, false);
61 if skip_last || folder.full() {
62 folder
63 } else {
64 folder.consume(right)
65 }
66 } else {
67 // We know there are no separators at all. Return our whole data.
68 if skip_last {
69 folder
70 } else {
71 folder.consume(data)
72 }
73 }
74 }
75}
76
77impl<'p, P, V> UnindexedProducer for SplitProducer<'p, P, V>
78where
79 V: Fissile<P> + Send,
80 P: Sync,
81{
82 type Item = V;
83
84 fn split(self) -> (Self, Option<Self>) {
85 // Look forward for the separator, and failing that look backward.
86 let mid = self.data.midpoint(self.tail);
87 let index = match self.data.find(self.separator, mid, self.tail) {
88 Some(i) => Some(mid + i),
89 None => self.data.rfind(self.separator, mid),
90 };
91
92 if let Some(index) = index {
93 let len = self.data.length();
94 let (left, right) = self.data.split_once(index);
95
96 let (left_tail, right_tail) = if index < mid {
97 // If we scanned backwards to find the separator, everything in
98 // the right side is exhausted, with no separators left to find.
99 (index, 0)
100 } else {
101 let right_index = len - right.length();
102 (mid, self.tail - right_index)
103 };
104
105 // Create the left split before the separator.
106 let left = SplitProducer {
107 data: left,
108 tail: left_tail,
109 ..self
110 };
111
112 // Create the right split following the separator.
113 let right = SplitProducer {
114 data: right,
115 tail: right_tail,
116 ..self
117 };
118
119 (left, Some(right))
120 } else {
121 // The search is exhausted, no more separators...
122 (SplitProducer { tail: 0, ..self }, None)
123 }
124 }
125
126 fn fold_with<F>(self, folder: F) -> F
127 where
128 F: Folder<Self::Item>,
129 {
130 self.fold_with(folder, false)
131 }
132}
133