1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
//! Parallel iterator types for [strings][std::str]
//!
//! You will rarely need to interact with this module directly unless you need
//! to name one of the iterator types.
//!
//! Note: [`ParallelString::par_split()`] and [`par_split_terminator()`]
//! reference a `Pattern` trait which is not visible outside this crate.
//! This trait is intentionally kept private, for use only by Rayon itself.
//! It is implemented for `char` and any `F: Fn(char) -> bool + Sync + Send`.
//!
//! [`ParallelString::par_split()`]: trait.ParallelString.html#method.par_split
//! [`par_split_terminator()`]: trait.ParallelString.html#method.par_split_terminator
//!
//! [std::str]: https://doc.rust-lang.org/stable/std/str/

use crate::iter::plumbing::*;
use crate::iter::*;
use crate::split_producer::*;

/// Test if a byte is the start of a UTF-8 character.
/// (extracted from `str::is_char_boundary`)
#[inline]
fn is_char_boundary(b: u8) -> bool {
    // This is bit magic equivalent to: b < 128 || b >= 192
    (b as i8) >= -0x40
}

/// Find the index of a character boundary near the midpoint.
#[inline]
fn find_char_midpoint(chars: &str) -> usize {
    let mid = chars.len() / 2;

    // We want to split near the midpoint, but we need to find an actual
    // character boundary.  So we look at the raw bytes, first scanning
    // forward from the midpoint for a boundary, then trying backward.
    let (left, right) = chars.as_bytes().split_at(mid);
    match right.iter().cloned().position(is_char_boundary) {
        Some(i) => mid + i,
        None => left
            .iter()
            .cloned()
            .rposition(is_char_boundary)
            .unwrap_or(0),
    }
}

/// Try to split a string near the midpoint.
#[inline]
fn split(chars: &str) -> Option<(&str, &str)> {
    let index = find_char_midpoint(chars);
    if index > 0 {
        Some(chars.split_at(index))
    } else {
        None
    }
}

/// Parallel extensions for strings.
pub trait ParallelString {
    /// Returns a plain string slice, which is used to implement the rest of
    /// the parallel methods.
    fn as_parallel_string(&self) -> &str;

    /// Returns a parallel iterator over the characters of a string.
    ///
    /// # Examples
    ///
    /// ```
    /// use rayon::prelude::*;
    /// let max = "hello".par_chars().max_by_key(|c| *c as i32);
    /// assert_eq!(Some('o'), max);
    /// ```
    fn par_chars(&self) -> Chars<'_> {
        Chars {
            chars: self.as_parallel_string(),
        }
    }

    /// Returns a parallel iterator over the characters of a string, with their positions.
    ///
    /// # Examples
    ///
    /// ```
    /// use rayon::prelude::*;
    /// let min = "hello".par_char_indices().min_by_key(|&(_i, c)| c as i32);
    /// assert_eq!(Some((1, 'e')), min);
    /// ```
    fn par_char_indices(&self) -> CharIndices<'_> {
        CharIndices {
            chars: self.as_parallel_string(),
        }
    }

    /// Returns a parallel iterator over the bytes of a string.
    ///
    /// Note that multi-byte sequences (for code points greater than `U+007F`)
    /// are produced as separate items, but will not be split across threads.
    /// If you would prefer an indexed iterator without that guarantee, consider
    /// `string.as_bytes().par_iter().cloned()` instead.
    ///
    /// # Examples
    ///
    /// ```
    /// use rayon::prelude::*;
    /// let max = "hello".par_bytes().max();
    /// assert_eq!(Some(b'o'), max);
    /// ```
    fn par_bytes(&self) -> Bytes<'_> {
        Bytes {
            chars: self.as_parallel_string(),
        }
    }

    /// Returns a parallel iterator over a string encoded as UTF-16.
    ///
    /// Note that surrogate pairs (for code points greater than `U+FFFF`) are
    /// produced as separate items, but will not be split across threads.
    ///
    /// # Examples
    ///
    /// ```
    /// use rayon::prelude::*;
    ///
    /// let max = "hello".par_encode_utf16().max();
    /// assert_eq!(Some(b'o' as u16), max);
    ///
    /// let text = "Zażółć gęślą jaźń";
    /// let utf8_len = text.len();
    /// let utf16_len = text.par_encode_utf16().count();
    /// assert!(utf16_len <= utf8_len);
    /// ```
    fn par_encode_utf16(&self) -> EncodeUtf16<'_> {
        EncodeUtf16 {
            chars: self.as_parallel_string(),
        }
    }

    /// Returns a parallel iterator over substrings separated by a
    /// given character or predicate, similar to `str::split`.
    ///
    /// Note: the `Pattern` trait is private, for use only by Rayon itself.
    /// It is implemented for `char` and any `F: Fn(char) -> bool + Sync + Send`.
    ///
    /// # Examples
    ///
    /// ```
    /// use rayon::prelude::*;
    /// let total = "1, 2, buckle, 3, 4, door"
    ///    .par_split(',')
    ///    .filter_map(|s| s.trim().parse::<i32>().ok())
    ///    .sum();
    /// assert_eq!(10, total);
    /// ```
    fn par_split<P: Pattern>(&self, separator: P) -> Split<'_, P> {
        Split::new(self.as_parallel_string(), separator)
    }

    /// Returns a parallel iterator over substrings terminated by a
    /// given character or predicate, similar to `str::split_terminator`.
    /// It's equivalent to `par_split`, except it doesn't produce an empty
    /// substring after a trailing terminator.
    ///
    /// Note: the `Pattern` trait is private, for use only by Rayon itself.
    /// It is implemented for `char` and any `F: Fn(char) -> bool + Sync + Send`.
    ///
    /// # Examples
    ///
    /// ```
    /// use rayon::prelude::*;
    /// let parts: Vec<_> = "((1 + 3) * 2)"
    ///     .par_split_terminator(|c| c == '(' || c == ')')
    ///     .collect();
    /// assert_eq!(vec!["", "", "1 + 3", " * 2"], parts);
    /// ```
    fn par_split_terminator<P: Pattern>(&self, terminator: P) -> SplitTerminator<'_, P> {
        SplitTerminator::new(self.as_parallel_string(), terminator)
    }

    /// Returns a parallel iterator over the lines of a string, ending with an
    /// optional carriage return and with a newline (`\r\n` or just `\n`).
    /// The final line ending is optional, and line endings are not included in
    /// the output strings.
    ///
    /// # Examples
    ///
    /// ```
    /// use rayon::prelude::*;
    /// let lengths: Vec<_> = "hello world\nfizbuzz"
    ///     .par_lines()
    ///     .map(|l| l.len())
    ///     .collect();
    /// assert_eq!(vec![11, 7], lengths);
    /// ```
    fn par_lines(&self) -> Lines<'_> {
        Lines(self.as_parallel_string())
    }

    /// Returns a parallel iterator over the sub-slices of a string that are
    /// separated by any amount of whitespace.
    ///
    /// As with `str::split_whitespace`, 'whitespace' is defined according to
    /// the terms of the Unicode Derived Core Property `White_Space`.
    ///
    /// # Examples
    ///
    /// ```
    /// use rayon::prelude::*;
    /// let longest = "which is the longest word?"
    ///     .par_split_whitespace()
    ///     .max_by_key(|word| word.len());
    /// assert_eq!(Some("longest"), longest);
    /// ```
    fn par_split_whitespace(&self) -> SplitWhitespace<'_> {
        SplitWhitespace(self.as_parallel_string())
    }

    /// Returns a parallel iterator over substrings that match a
    /// given character or predicate, similar to `str::matches`.
    ///
    /// Note: the `Pattern` trait is private, for use only by Rayon itself.
    /// It is implemented for `char` and any `F: Fn(char) -> bool + Sync + Send`.
    ///
    /// # Examples
    ///
    /// ```
    /// use rayon::prelude::*;
    /// let total = "1, 2, buckle, 3, 4, door"
    ///    .par_matches(char::is_numeric)
    ///    .map(|s| s.parse::<i32>().expect("digit"))
    ///    .sum();
    /// assert_eq!(10, total);
    /// ```
    fn par_matches<P: Pattern>(&self, pattern: P) -> Matches<'_, P> {
        Matches {
            chars: self.as_parallel_string(),
            pattern,
        }
    }

    /// Returns a parallel iterator over substrings that match a given character
    /// or predicate, with their positions, similar to `str::match_indices`.
    ///
    /// Note: the `Pattern` trait is private, for use only by Rayon itself.
    /// It is implemented for `char` and any `F: Fn(char) -> bool + Sync + Send`.
    ///
    /// # Examples
    ///
    /// ```
    /// use rayon::prelude::*;
    /// let digits: Vec<_> = "1, 2, buckle, 3, 4, door"
    ///    .par_match_indices(char::is_numeric)
    ///    .collect();
    /// assert_eq!(digits, vec![(0, "1"), (3, "2"), (14, "3"), (17, "4")]);
    /// ```
    fn par_match_indices<P: Pattern>(&self, pattern: P) -> MatchIndices<'_, P> {
        MatchIndices {
            chars: self.as_parallel_string(),
            pattern,
        }
    }
}

impl ParallelString for str {
    #[inline]
    fn as_parallel_string(&self) -> &str {
        self
    }
}

// /////////////////////////////////////////////////////////////////////////

/// We hide the `Pattern` trait in a private module, as its API is not meant
/// for general consumption.  If we could have privacy on trait items, then it
/// would be nicer to have its basic existence and implementors public while
/// keeping all of the methods private.
mod private {
    use crate::iter::plumbing::Folder;

    /// Pattern-matching trait for `ParallelString`, somewhat like a mix of
    /// `std::str::pattern::{Pattern, Searcher}`.
    ///
    /// Implementing this trait is not permitted outside of `rayon`.
    pub trait Pattern: Sized + Sync + Send {
        private_decl! {}
        fn find_in(&self, haystack: &str) -> Option<usize>;
        fn rfind_in(&self, haystack: &str) -> Option<usize>;
        fn is_suffix_of(&self, haystack: &str) -> bool;
        fn fold_splits<'ch, F>(&self, haystack: &'ch str, folder: F, skip_last: bool) -> F
        where
            F: Folder<&'ch str>;
        fn fold_matches<'ch, F>(&self, haystack: &'ch str, folder: F) -> F
        where
            F: Folder<&'ch str>;
        fn fold_match_indices<'ch, F>(&self, haystack: &'ch str, folder: F, base: usize) -> F
        where
            F: Folder<(usize, &'ch str)>;
    }
}
use self::private::Pattern;

#[inline]
fn offset<T>(base: usize) -> impl Fn((usize, T)) -> (usize, T) {
    move |(i, x)| (base + i, x)
}

impl Pattern for char {
    private_impl! {}

    #[inline]
    fn find_in(&self, chars: &str) -> Option<usize> {
        chars.find(*self)
    }

    #[inline]
    fn rfind_in(&self, chars: &str) -> Option<usize> {
        chars.rfind(*self)
    }

    #[inline]
    fn is_suffix_of(&self, chars: &str) -> bool {
        chars.ends_with(*self)
    }

    fn fold_splits<'ch, F>(&self, chars: &'ch str, folder: F, skip_last: bool) -> F
    where
        F: Folder<&'ch str>,
    {
        let mut split = chars.split(*self);
        if skip_last {
            split.next_back();
        }
        folder.consume_iter(split)
    }

    fn fold_matches<'ch, F>(&self, chars: &'ch str, folder: F) -> F
    where
        F: Folder<&'ch str>,
    {
        folder.consume_iter(chars.matches(*self))
    }

    fn fold_match_indices<'ch, F>(&self, chars: &'ch str, folder: F, base: usize) -> F
    where
        F: Folder<(usize, &'ch str)>,
    {
        folder.consume_iter(chars.match_indices(*self).map(offset(base)))
    }
}

impl<FN: Sync + Send + Fn(char) -> bool> Pattern for FN {
    private_impl! {}

    fn find_in(&self, chars: &str) -> Option<usize> {
        chars.find(self)
    }

    fn rfind_in(&self, chars: &str) -> Option<usize> {
        chars.rfind(self)
    }

    fn is_suffix_of(&self, chars: &str) -> bool {
        chars.ends_with(self)
    }

    fn fold_splits<'ch, F>(&self, chars: &'ch str, folder: F, skip_last: bool) -> F
    where
        F: Folder<&'ch str>,
    {
        let mut split = chars.split(self);
        if skip_last {
            split.next_back();
        }
        folder.consume_iter(split)
    }

    fn fold_matches<'ch, F>(&self, chars: &'ch str, folder: F) -> F
    where
        F: Folder<&'ch str>,
    {
        folder.consume_iter(chars.matches(self))
    }

    fn fold_match_indices<'ch, F>(&self, chars: &'ch str, folder: F, base: usize) -> F
    where
        F: Folder<(usize, &'ch str)>,
    {
        folder.consume_iter(chars.match_indices(self).map(offset(base)))
    }
}

// /////////////////////////////////////////////////////////////////////////

/// Parallel iterator over the characters of a string
#[derive(Debug, Clone)]
pub struct Chars<'ch> {
    chars: &'ch str,
}

struct CharsProducer<'ch> {
    chars: &'ch str,
}

impl<'ch> ParallelIterator for Chars<'ch> {
    type Item = char;

    fn drive_unindexed<C>(self, consumer: C) -> C::Result
    where
        C: UnindexedConsumer<Self::Item>,
    {
        bridge_unindexed(CharsProducer { chars: self.chars }, consumer)
    }
}

impl<'ch> UnindexedProducer for CharsProducer<'ch> {
    type Item = char;

    fn split(self) -> (Self, Option<Self>) {
        match split(self.chars) {
            Some((left, right)) => (
                CharsProducer { chars: left },
                Some(CharsProducer { chars: right }),
            ),
            None => (self, None),
        }
    }

    fn fold_with<F>(self, folder: F) -> F
    where
        F: Folder<Self::Item>,
    {
        folder.consume_iter(self.chars.chars())
    }
}

// /////////////////////////////////////////////////////////////////////////

/// Parallel iterator over the characters of a string, with their positions
#[derive(Debug, Clone)]
pub struct CharIndices<'ch> {
    chars: &'ch str,
}

struct CharIndicesProducer<'ch> {
    index: usize,
    chars: &'ch str,
}

impl<'ch> ParallelIterator for CharIndices<'ch> {
    type Item = (usize, char);

    fn drive_unindexed<C>(self, consumer: C) -> C::Result
    where
        C: UnindexedConsumer<Self::Item>,
    {
        let producer = CharIndicesProducer {
            index: 0,
            chars: self.chars,
        };
        bridge_unindexed(producer, consumer)
    }
}

impl<'ch> UnindexedProducer for CharIndicesProducer<'ch> {
    type Item = (usize, char);

    fn split(self) -> (Self, Option<Self>) {
        match split(self.chars) {
            Some((left, right)) => (
                CharIndicesProducer {
                    chars: left,
                    ..self
                },
                Some(CharIndicesProducer {
                    chars: right,
                    index: self.index + left.len(),
                }),
            ),
            None => (self, None),
        }
    }

    fn fold_with<F>(self, folder: F) -> F
    where
        F: Folder<Self::Item>,
    {
        let base = self.index;
        folder.consume_iter(self.chars.char_indices().map(offset(base)))
    }
}

// /////////////////////////////////////////////////////////////////////////

/// Parallel iterator over the bytes of a string
#[derive(Debug, Clone)]
pub struct Bytes<'ch> {
    chars: &'ch str,
}

struct BytesProducer<'ch> {
    chars: &'ch str,
}

impl<'ch> ParallelIterator for Bytes<'ch> {
    type Item = u8;

    fn drive_unindexed<C>(self, consumer: C) -> C::Result
    where
        C: UnindexedConsumer<Self::Item>,
    {
        bridge_unindexed(BytesProducer { chars: self.chars }, consumer)
    }
}

impl<'ch> UnindexedProducer for BytesProducer<'ch> {
    type Item = u8;

    fn split(self) -> (Self, Option<Self>) {
        match split(self.chars) {
            Some((left, right)) => (
                BytesProducer { chars: left },
                Some(BytesProducer { chars: right }),
            ),
            None => (self, None),
        }
    }

    fn fold_with<F>(self, folder: F) -> F
    where
        F: Folder<Self::Item>,
    {
        folder.consume_iter(self.chars.bytes())
    }
}

// /////////////////////////////////////////////////////////////////////////

/// Parallel iterator over a string encoded as UTF-16
#[derive(Debug, Clone)]
pub struct EncodeUtf16<'ch> {
    chars: &'ch str,
}

struct EncodeUtf16Producer<'ch> {
    chars: &'ch str,
}

impl<'ch> ParallelIterator for EncodeUtf16<'ch> {
    type Item = u16;

    fn drive_unindexed<C>(self, consumer: C) -> C::Result
    where
        C: UnindexedConsumer<Self::Item>,
    {
        bridge_unindexed(EncodeUtf16Producer { chars: self.chars }, consumer)
    }
}

impl<'ch> UnindexedProducer for EncodeUtf16Producer<'ch> {
    type Item = u16;

    fn split(self) -> (Self, Option<Self>) {
        match split(self.chars) {
            Some((left, right)) => (
                EncodeUtf16Producer { chars: left },
                Some(EncodeUtf16Producer { chars: right }),
            ),
            None => (self, None),
        }
    }

    fn fold_with<F>(self, folder: F) -> F
    where
        F: Folder<Self::Item>,
    {
        folder.consume_iter(self.chars.encode_utf16())
    }
}

// /////////////////////////////////////////////////////////////////////////

/// Parallel iterator over substrings separated by a pattern
#[derive(Debug, Clone)]
pub struct Split<'ch, P: Pattern> {
    chars: &'ch str,
    separator: P,
}

impl<'ch, P: Pattern> Split<'ch, P> {
    fn new(chars: &'ch str, separator: P) -> Self {
        Split { chars, separator }
    }
}

impl<'ch, P: Pattern> ParallelIterator for Split<'ch, P> {
    type Item = &'ch str;

    fn drive_unindexed<C>(self, consumer: C) -> C::Result
    where
        C: UnindexedConsumer<Self::Item>,
    {
        let producer = SplitProducer::new(self.chars, &self.separator);
        bridge_unindexed(producer, consumer)
    }
}

/// Implement support for `SplitProducer`.
impl<'ch, P: Pattern> Fissile<P> for &'ch str {
    fn length(&self) -> usize {
        self.len()
    }

    fn midpoint(&self, end: usize) -> usize {
        // First find a suitable UTF-8 boundary.
        find_char_midpoint(&self[..end])
    }

    fn find(&self, separator: &P, start: usize, end: usize) -> Option<usize> {
        separator.find_in(&self[start..end])
    }

    fn rfind(&self, separator: &P, end: usize) -> Option<usize> {
        separator.rfind_in(&self[..end])
    }

    fn split_once(self, index: usize) -> (Self, Self) {
        let (left, right) = self.split_at(index);
        let mut right_iter = right.chars();
        right_iter.next(); // skip the separator
        (left, right_iter.as_str())
    }

    fn fold_splits<F>(self, separator: &P, folder: F, skip_last: bool) -> F
    where
        F: Folder<Self>,
    {
        separator.fold_splits(self, folder, skip_last)
    }
}

// /////////////////////////////////////////////////////////////////////////

/// Parallel iterator over substrings separated by a terminator pattern
#[derive(Debug, Clone)]
pub struct SplitTerminator<'ch, P: Pattern> {
    chars: &'ch str,
    terminator: P,
}

struct SplitTerminatorProducer<'ch, 'sep, P: Pattern> {
    splitter: SplitProducer<'sep, P, &'ch str>,
    skip_last: bool,
}

impl<'ch, P: Pattern> SplitTerminator<'ch, P> {
    fn new(chars: &'ch str, terminator: P) -> Self {
        SplitTerminator { chars, terminator }
    }
}

impl<'ch, 'sep, P: Pattern + 'sep> SplitTerminatorProducer<'ch, 'sep, P> {
    fn new(chars: &'ch str, terminator: &'sep P) -> Self {
        SplitTerminatorProducer {
            splitter: SplitProducer::new(chars, terminator),
            skip_last: chars.is_empty() || terminator.is_suffix_of(chars),
        }
    }
}

impl<'ch, P: Pattern> ParallelIterator for SplitTerminator<'ch, P> {
    type Item = &'ch str;

    fn drive_unindexed<C>(self, consumer: C) -> C::Result
    where
        C: UnindexedConsumer<Self::Item>,
    {
        let producer = SplitTerminatorProducer::new(self.chars, &self.terminator);
        bridge_unindexed(producer, consumer)
    }
}

impl<'ch, 'sep, P: Pattern + 'sep> UnindexedProducer for SplitTerminatorProducer<'ch, 'sep, P> {
    type Item = &'ch str;

    fn split(mut self) -> (Self, Option<Self>) {
        let (left, right) = self.splitter.split();
        self.splitter = left;
        let right = right.map(|right| {
            let skip_last = self.skip_last;
            self.skip_last = false;
            SplitTerminatorProducer {
                splitter: right,
                skip_last,
            }
        });
        (self, right)
    }

    fn fold_with<F>(self, folder: F) -> F
    where
        F: Folder<Self::Item>,
    {
        self.splitter.fold_with(folder, self.skip_last)
    }
}

// /////////////////////////////////////////////////////////////////////////

/// Parallel iterator over lines in a string
#[derive(Debug, Clone)]
pub struct Lines<'ch>(&'ch str);

#[inline]
fn no_carriage_return(line: &str) -> &str {
    if line.ends_with('\r') {
        &line[..line.len() - 1]
    } else {
        line
    }
}

impl<'ch> ParallelIterator for Lines<'ch> {
    type Item = &'ch str;

    fn drive_unindexed<C>(self, consumer: C) -> C::Result
    where
        C: UnindexedConsumer<Self::Item>,
    {
        self.0
            .par_split_terminator('\n')
            .map(no_carriage_return)
            .drive_unindexed(consumer)
    }
}

// /////////////////////////////////////////////////////////////////////////

/// Parallel iterator over substrings separated by whitespace
#[derive(Debug, Clone)]
pub struct SplitWhitespace<'ch>(&'ch str);

#[inline]
fn not_empty(s: &&str) -> bool {
    !s.is_empty()
}

impl<'ch> ParallelIterator for SplitWhitespace<'ch> {
    type Item = &'ch str;

    fn drive_unindexed<C>(self, consumer: C) -> C::Result
    where
        C: UnindexedConsumer<Self::Item>,
    {
        self.0
            .par_split(char::is_whitespace)
            .filter(not_empty)
            .drive_unindexed(consumer)
    }
}

// /////////////////////////////////////////////////////////////////////////

/// Parallel iterator over substrings that match a pattern
#[derive(Debug, Clone)]
pub struct Matches<'ch, P: Pattern> {
    chars: &'ch str,
    pattern: P,
}

struct MatchesProducer<'ch, 'pat, P: Pattern> {
    chars: &'ch str,
    pattern: &'pat P,
}

impl<'ch, P: Pattern> ParallelIterator for Matches<'ch, P> {
    type Item = &'ch str;

    fn drive_unindexed<C>(self, consumer: C) -> C::Result
    where
        C: UnindexedConsumer<Self::Item>,
    {
        let producer = MatchesProducer {
            chars: self.chars,
            pattern: &self.pattern,
        };
        bridge_unindexed(producer, consumer)
    }
}

impl<'ch, 'pat, P: Pattern> UnindexedProducer for MatchesProducer<'ch, 'pat, P> {
    type Item = &'ch str;

    fn split(self) -> (Self, Option<Self>) {
        match split(self.chars) {
            Some((left, right)) => (
                MatchesProducer {
                    chars: left,
                    ..self
                },
                Some(MatchesProducer {
                    chars: right,
                    ..self
                }),
            ),
            None => (self, None),
        }
    }

    fn fold_with<F>(self, folder: F) -> F
    where
        F: Folder<Self::Item>,
    {
        self.pattern.fold_matches(self.chars, folder)
    }
}

// /////////////////////////////////////////////////////////////////////////

/// Parallel iterator over substrings that match a pattern, with their positions
#[derive(Debug, Clone)]
pub struct MatchIndices<'ch, P: Pattern> {
    chars: &'ch str,
    pattern: P,
}

struct MatchIndicesProducer<'ch, 'pat, P: Pattern> {
    index: usize,
    chars: &'ch str,
    pattern: &'pat P,
}

impl<'ch, P: Pattern> ParallelIterator for MatchIndices<'ch, P> {
    type Item = (usize, &'ch str);

    fn drive_unindexed<C>(self, consumer: C) -> C::Result
    where
        C: UnindexedConsumer<Self::Item>,
    {
        let producer = MatchIndicesProducer {
            index: 0,
            chars: self.chars,
            pattern: &self.pattern,
        };
        bridge_unindexed(producer, consumer)
    }
}

impl<'ch, 'pat, P: Pattern> UnindexedProducer for MatchIndicesProducer<'ch, 'pat, P> {
    type Item = (usize, &'ch str);

    fn split(self) -> (Self, Option<Self>) {
        match split(self.chars) {
            Some((left, right)) => (
                MatchIndicesProducer {
                    chars: left,
                    ..self
                },
                Some(MatchIndicesProducer {
                    chars: right,
                    index: self.index + left.len(),
                    ..self
                }),
            ),
            None => (self, None),
        }
    }

    fn fold_with<F>(self, folder: F) -> F
    where
        F: Folder<Self::Item>,
    {
        self.pattern
            .fold_match_indices(self.chars, folder, self.index)
    }
}