1//! "Fallible" iterators.
2//!
3//! The iterator APIs in the Rust standard library do not support iteration
4//! that can fail in a first class manner. These iterators are typically modeled
5//! as iterating over `Result<T, E>` values; for example, the `Lines` iterator
6//! returns `io::Result<String>`s. When simply iterating over these types, the
7//! value being iterated over must be unwrapped in some way before it can be
8//! used:
9//!
10//! ```ignore
11//! for line in reader.lines() {
12//! let line = line?;
13//! // work with line
14//! }
15//! ```
16//!
17//! In addition, many of the additional methods on the `Iterator` trait will
18//! not behave properly in the presence of errors when working with these kinds
19//! of iterators. For example, if one wanted to count the number of lines of
20//! text in a `Read`er, this might be a way to go about it:
21//!
22//! ```ignore
23//! let count = reader.lines().count();
24//! ```
25//!
26//! This will return the proper value when the reader operates successfully, but
27//! if it encounters an IO error, the result will either be slightly higher than
28//! expected if the error is transient, or it may run forever if the error is
29//! returned repeatedly!
30//!
31//! In contrast, a fallible iterator is built around the concept that a call to
32//! `next` can fail. The trait has an additional `Error` associated type in
33//! addition to the `Item` type, and `next` returns `Result<Option<Self::Item>,
34//! Self::Error>` rather than `Option<Self::Item>`. Methods like `count` return
35//! `Result`s as well.
36//!
37//! This does mean that fallible iterators are incompatible with Rust's `for`
38//! loop syntax, but `while let` loops offer a similar level of ergonomics:
39//!
40//! ```ignore
41//! while let Some(item) = iter.next()? {
42//! // work with item
43//! }
44//! ```
45//!
46//! ## Fallible closure arguments
47//!
48//! Like `Iterator`, many `FallibleIterator` methods take closures as arguments.
49//! These use the same signatures as their `Iterator` counterparts, except that
50//! `FallibleIterator` expects the closures to be fallible: they return
51//! `Result<T, Self::Error>` instead of simply `T`.
52//!
53//! For example, the standard library's `Iterator::filter` adapter method
54//! filters the underlying iterator according to a predicate provided by the
55//! user, whose return type is `bool`. In `FallibleIterator::filter`, however,
56//! the predicate returns `Result<bool, Self::Error>`:
57//!
58//! ```
59//! # use std::error::Error;
60//! # use std::str::FromStr;
61//! # use fallible_iterator::{convert, FallibleIterator};
62//! let numbers = convert("100\n200\nfern\n400".lines().map(Ok::<&str, Box<Error>>));
63//! let big_numbers = numbers.filter(|n| Ok(u64::from_str(n)? > 100));
64//! assert!(big_numbers.count().is_err());
65//! ```
66#![doc(html_root_url = "https://docs.rs/fallible-iterator/0.2")]
67#![warn(missing_docs)]
68#![no_std]
69
70use core::cmp::{self, Ordering};
71use core::convert::Infallible;
72use core::iter;
73use core::marker::PhantomData;
74
75#[cfg(feature = "alloc")]
76extern crate alloc;
77
78#[cfg(feature = "alloc")]
79use alloc::boxed::Box;
80
81#[cfg(all(test, feature = "alloc"))]
82mod test;
83
84enum FoldStop<T, E> {
85 Break(T),
86 Err(E),
87}
88
89impl<T, E> From<E> for FoldStop<T, E> {
90 #[inline]
91 fn from(e: E) -> FoldStop<T, E> {
92 FoldStop::Err(e)
93 }
94}
95
96trait ResultExt<T, E> {
97 fn unpack_fold(self) -> Result<T, E>;
98}
99
100impl<T, E> ResultExt<T, E> for Result<T, FoldStop<T, E>> {
101 #[inline]
102 fn unpack_fold(self) -> Result<T, E> {
103 match self {
104 Ok(v: T) => Ok(v),
105 Err(FoldStop::Break(v: T)) => Ok(v),
106 Err(FoldStop::Err(e: E)) => Err(e),
107 }
108 }
109}
110
111/// An `Iterator`-like trait that allows for calculation of items to fail.
112pub trait FallibleIterator {
113 /// The type being iterated over.
114 type Item;
115
116 /// The error type.
117 type Error;
118
119 /// Advances the iterator and returns the next value.
120 ///
121 /// Returns `Ok(None)` when iteration is finished.
122 ///
123 /// The behavior of calling this method after a previous call has returned
124 /// `Ok(None)` or `Err` is implementation defined.
125 fn next(&mut self) -> Result<Option<Self::Item>, Self::Error>;
126
127 /// Returns bounds on the remaining length of the iterator.
128 ///
129 /// Specifically, the first half of the returned tuple is a lower bound and
130 /// the second half is an upper bound.
131 ///
132 /// For the upper bound, `None` indicates that the upper bound is either
133 /// unknown or larger than can be represented as a `usize`.
134 ///
135 /// Both bounds assume that all remaining calls to `next` succeed. That is,
136 /// `next` could return an `Err` in fewer calls than specified by the lower
137 /// bound.
138 ///
139 /// The default implementation returns `(0, None)`, which is correct for
140 /// any iterator.
141 #[inline]
142 fn size_hint(&self) -> (usize, Option<usize>) {
143 (0, None)
144 }
145
146 /// Consumes the iterator, returning the number of remaining items.
147 #[inline]
148 fn count(self) -> Result<usize, Self::Error>
149 where
150 Self: Sized,
151 {
152 self.fold(0, |n, _| Ok(n + 1))
153 }
154
155 /// Returns the last element of the iterator.
156 #[inline]
157 fn last(self) -> Result<Option<Self::Item>, Self::Error>
158 where
159 Self: Sized,
160 {
161 self.fold(None, |_, v| Ok(Some(v)))
162 }
163
164 /// Returns the `n`th element of the iterator.
165 #[inline]
166 fn nth(&mut self, mut n: usize) -> Result<Option<Self::Item>, Self::Error> {
167 while let Some(e) = self.next()? {
168 if n == 0 {
169 return Ok(Some(e));
170 }
171 n -= 1;
172 }
173 Ok(None)
174 }
175
176 /// Returns an iterator starting at the same point, but stepping by the given amount at each iteration.
177 ///
178 /// # Panics
179 ///
180 /// Panics if `step` is 0.
181 #[inline]
182 fn step_by(self, step: usize) -> StepBy<Self>
183 where
184 Self: Sized,
185 {
186 assert!(step != 0);
187 StepBy {
188 it: self,
189 step: step - 1,
190 first_take: true,
191 }
192 }
193
194 /// Returns an iterator which yields the elements of this iterator followed
195 /// by another.
196 #[inline]
197 fn chain<I>(self, it: I) -> Chain<Self, I>
198 where
199 I: IntoFallibleIterator<Item = Self::Item, Error = Self::Error>,
200 Self: Sized,
201 {
202 Chain {
203 front: self,
204 back: it,
205 state: ChainState::Both,
206 }
207 }
208
209 /// Returns an iterator that yields pairs of this iterator's and another
210 /// iterator's values.
211 #[inline]
212 fn zip<I>(self, o: I) -> Zip<Self, I::IntoFallibleIter>
213 where
214 Self: Sized,
215 I: IntoFallibleIterator<Error = Self::Error>,
216 {
217 Zip(self, o.into_fallible_iter())
218 }
219
220 /// Returns an iterator which applies a fallible transform to the elements
221 /// of the underlying iterator.
222 #[inline]
223 fn map<F, B>(self, f: F) -> Map<Self, F>
224 where
225 Self: Sized,
226 F: FnMut(Self::Item) -> Result<B, Self::Error>,
227 {
228 Map { it: self, f }
229 }
230
231 /// Calls a fallible closure on each element of an iterator.
232 #[inline]
233 fn for_each<F>(self, mut f: F) -> Result<(), Self::Error>
234 where
235 Self: Sized,
236 F: FnMut(Self::Item) -> Result<(), Self::Error>,
237 {
238 self.fold((), move |(), item| f(item))
239 }
240
241 /// Returns an iterator which uses a predicate to determine which values
242 /// should be yielded. The predicate may fail; such failures are passed to
243 /// the caller.
244 #[inline]
245 fn filter<F>(self, f: F) -> Filter<Self, F>
246 where
247 Self: Sized,
248 F: FnMut(&Self::Item) -> Result<bool, Self::Error>,
249 {
250 Filter { it: self, f }
251 }
252
253 /// Returns an iterator which both filters and maps. The closure may fail;
254 /// such failures are passed along to the consumer.
255 #[inline]
256 fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F>
257 where
258 Self: Sized,
259 F: FnMut(Self::Item) -> Result<Option<B>, Self::Error>,
260 {
261 FilterMap { it: self, f }
262 }
263
264 /// Returns an iterator which yields the current iteration count as well
265 /// as the value.
266 #[inline]
267 fn enumerate(self) -> Enumerate<Self>
268 where
269 Self: Sized,
270 {
271 Enumerate { it: self, n: 0 }
272 }
273
274 /// Returns an iterator that can peek at the next element without consuming
275 /// it.
276 #[inline]
277 fn peekable(self) -> Peekable<Self>
278 where
279 Self: Sized,
280 {
281 Peekable {
282 it: self,
283 next: None,
284 }
285 }
286
287 /// Returns an iterator that skips elements based on a predicate.
288 #[inline]
289 fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P>
290 where
291 Self: Sized,
292 P: FnMut(&Self::Item) -> Result<bool, Self::Error>,
293 {
294 SkipWhile {
295 it: self,
296 flag: false,
297 predicate,
298 }
299 }
300
301 /// Returns an iterator that yields elements based on a predicate.
302 #[inline]
303 fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P>
304 where
305 Self: Sized,
306 P: FnMut(&Self::Item) -> Result<bool, Self::Error>,
307 {
308 TakeWhile {
309 it: self,
310 flag: false,
311 predicate,
312 }
313 }
314
315 /// Returns an iterator which skips the first `n` values of this iterator.
316 #[inline]
317 fn skip(self, n: usize) -> Skip<Self>
318 where
319 Self: Sized,
320 {
321 Skip { it: self, n }
322 }
323
324 /// Returns an iterator that yields only the first `n` values of this
325 /// iterator.
326 #[inline]
327 fn take(self, n: usize) -> Take<Self>
328 where
329 Self: Sized,
330 {
331 Take {
332 it: self,
333 remaining: n,
334 }
335 }
336
337 /// Returns an iterator which applies a stateful map to values of this
338 /// iterator.
339 #[inline]
340 fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F>
341 where
342 Self: Sized,
343 F: FnMut(&mut St, Self::Item) -> Result<Option<B>, Self::Error>,
344 {
345 Scan {
346 it: self,
347 f,
348 state: initial_state,
349 }
350 }
351
352 /// Returns an iterator which maps this iterator's elements to iterators, yielding those iterators' values.
353 #[inline]
354 fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F>
355 where
356 Self: Sized,
357 U: IntoFallibleIterator<Error = Self::Error>,
358 F: FnMut(Self::Item) -> Result<U, Self::Error>,
359 {
360 FlatMap {
361 it: self.map(f),
362 cur: None,
363 }
364 }
365
366 /// Returns an iterator which flattens an iterator of iterators, yielding those iterators' values.
367 #[inline]
368 fn flatten(self) -> Flatten<Self>
369 where
370 Self: Sized,
371 Self::Item: IntoFallibleIterator<Error = Self::Error>,
372 {
373 Flatten {
374 it: self,
375 cur: None,
376 }
377 }
378
379 /// Returns an iterator which yields this iterator's elements and ends after
380 /// the first `Ok(None)`.
381 ///
382 /// The behavior of calling `next` after it has previously returned
383 /// `Ok(None)` is normally unspecified. The iterator returned by this method
384 /// guarantees that `Ok(None)` will always be returned.
385 #[inline]
386 fn fuse(self) -> Fuse<Self>
387 where
388 Self: Sized,
389 {
390 Fuse {
391 it: self,
392 done: false,
393 }
394 }
395
396 /// Returns an iterator which passes each element to a closure before returning it.
397 #[inline]
398 fn inspect<F>(self, f: F) -> Inspect<Self, F>
399 where
400 Self: Sized,
401 F: FnMut(&Self::Item) -> Result<(), Self::Error>,
402 {
403 Inspect { it: self, f }
404 }
405
406 /// Borrow an iterator rather than consuming it.
407 ///
408 /// This is useful to allow the use of iterator adaptors that would
409 /// otherwise consume the value.
410 #[inline]
411 fn by_ref(&mut self) -> &mut Self
412 where
413 Self: Sized,
414 {
415 self
416 }
417
418 /// Transforms the iterator into a collection.
419 ///
420 /// An `Err` will be returned if any invocation of `next` returns `Err`.
421 #[inline]
422 fn collect<T>(self) -> Result<T, Self::Error>
423 where
424 T: iter::FromIterator<Self::Item>,
425 Self: Sized,
426 {
427 self.iterator().collect()
428 }
429
430 /// Transforms the iterator into two collections, partitioning elements by a closure.
431 #[inline]
432 fn partition<B, F>(self, mut f: F) -> Result<(B, B), Self::Error>
433 where
434 Self: Sized,
435 B: Default + Extend<Self::Item>,
436 F: FnMut(&Self::Item) -> Result<bool, Self::Error>,
437 {
438 let mut a = B::default();
439 let mut b = B::default();
440
441 self.for_each(|i| {
442 if f(&i)? {
443 a.extend(Some(i));
444 } else {
445 b.extend(Some(i));
446 }
447 Ok(())
448 })?;
449
450 Ok((a, b))
451 }
452
453 /// Applies a function over the elements of the iterator, producing a single
454 /// final value.
455 #[inline]
456 fn fold<B, F>(mut self, init: B, f: F) -> Result<B, Self::Error>
457 where
458 Self: Sized,
459 F: FnMut(B, Self::Item) -> Result<B, Self::Error>,
460 {
461 self.try_fold(init, f)
462 }
463
464 /// Applies a function over the elements of the iterator, producing a single final value.
465 ///
466 /// This is used as the "base" of many methods on `FallibleIterator`.
467 #[inline]
468 fn try_fold<B, E, F>(&mut self, mut init: B, mut f: F) -> Result<B, E>
469 where
470 Self: Sized,
471 E: From<Self::Error>,
472 F: FnMut(B, Self::Item) -> Result<B, E>,
473 {
474 while let Some(v) = self.next()? {
475 init = f(init, v)?;
476 }
477 Ok(init)
478 }
479
480 /// Determines if all elements of this iterator match a predicate.
481 #[inline]
482 fn all<F>(&mut self, mut f: F) -> Result<bool, Self::Error>
483 where
484 Self: Sized,
485 F: FnMut(Self::Item) -> Result<bool, Self::Error>,
486 {
487 self.try_fold((), |(), v| {
488 if !f(v)? {
489 return Err(FoldStop::Break(false));
490 }
491 Ok(())
492 })
493 .map(|()| true)
494 .unpack_fold()
495 }
496
497 /// Determines if any element of this iterator matches a predicate.
498 #[inline]
499 fn any<F>(&mut self, mut f: F) -> Result<bool, Self::Error>
500 where
501 Self: Sized,
502 F: FnMut(Self::Item) -> Result<bool, Self::Error>,
503 {
504 self.try_fold((), |(), v| {
505 if f(v)? {
506 return Err(FoldStop::Break(true));
507 }
508 Ok(())
509 })
510 .map(|()| false)
511 .unpack_fold()
512 }
513
514 /// Returns the first element of the iterator that matches a predicate.
515 #[inline]
516 fn find<F>(&mut self, mut f: F) -> Result<Option<Self::Item>, Self::Error>
517 where
518 Self: Sized,
519 F: FnMut(&Self::Item) -> Result<bool, Self::Error>,
520 {
521 self.try_fold((), |(), v| {
522 if f(&v)? {
523 return Err(FoldStop::Break(Some(v)));
524 }
525 Ok(())
526 })
527 .map(|()| None)
528 .unpack_fold()
529 }
530
531 /// Applies a function to the elements of the iterator, returning the first non-`None` result.
532 #[inline]
533 fn find_map<B, F>(&mut self, f: F) -> Result<Option<B>, Self::Error>
534 where
535 Self: Sized,
536 F: FnMut(Self::Item) -> Result<Option<B>, Self::Error>,
537 {
538 self.filter_map(f).next()
539 }
540
541 /// Returns the position of the first element of this iterator that matches
542 /// a predicate. The predicate may fail; such failures are returned to the
543 /// caller.
544 #[inline]
545 fn position<F>(&mut self, mut f: F) -> Result<Option<usize>, Self::Error>
546 where
547 Self: Sized,
548 F: FnMut(Self::Item) -> Result<bool, Self::Error>,
549 {
550 self.try_fold(0, |n, v| {
551 if f(v)? {
552 return Err(FoldStop::Break(Some(n)));
553 }
554 Ok(n + 1)
555 })
556 .map(|_| None)
557 .unpack_fold()
558 }
559
560 /// Returns the maximal element of the iterator.
561 #[inline]
562 fn max(self) -> Result<Option<Self::Item>, Self::Error>
563 where
564 Self: Sized,
565 Self::Item: Ord,
566 {
567 self.max_by(|a, b| Ok(a.cmp(b)))
568 }
569
570 /// Returns the element of the iterator which gives the maximum value from
571 /// the function.
572 #[inline]
573 fn max_by_key<B, F>(mut self, mut f: F) -> Result<Option<Self::Item>, Self::Error>
574 where
575 Self: Sized,
576 B: Ord,
577 F: FnMut(&Self::Item) -> Result<B, Self::Error>,
578 {
579 let max = match self.next()? {
580 Some(v) => (f(&v)?, v),
581 None => return Ok(None),
582 };
583
584 self.fold(max, |(key, max), v| {
585 let new_key = f(&v)?;
586 if key > new_key {
587 Ok((key, max))
588 } else {
589 Ok((new_key, v))
590 }
591 })
592 .map(|v| Some(v.1))
593 }
594
595 /// Returns the element that gives the maximum value with respect to the function.
596 #[inline]
597 fn max_by<F>(mut self, mut f: F) -> Result<Option<Self::Item>, Self::Error>
598 where
599 Self: Sized,
600 F: FnMut(&Self::Item, &Self::Item) -> Result<Ordering, Self::Error>,
601 {
602 let max = match self.next()? {
603 Some(v) => v,
604 None => return Ok(None),
605 };
606
607 self.fold(max, |max, v| {
608 if f(&max, &v)? == Ordering::Greater {
609 Ok(max)
610 } else {
611 Ok(v)
612 }
613 })
614 .map(Some)
615 }
616
617 /// Returns the minimal element of the iterator.
618 #[inline]
619 fn min(self) -> Result<Option<Self::Item>, Self::Error>
620 where
621 Self: Sized,
622 Self::Item: Ord,
623 {
624 self.min_by(|a, b| Ok(a.cmp(b)))
625 }
626
627 /// Returns the element of the iterator which gives the minimum value from
628 /// the function.
629 #[inline]
630 fn min_by_key<B, F>(mut self, mut f: F) -> Result<Option<Self::Item>, Self::Error>
631 where
632 Self: Sized,
633 B: Ord,
634 F: FnMut(&Self::Item) -> Result<B, Self::Error>,
635 {
636 let min = match self.next()? {
637 Some(v) => (f(&v)?, v),
638 None => return Ok(None),
639 };
640
641 self.fold(min, |(key, min), v| {
642 let new_key = f(&v)?;
643 if key < new_key {
644 Ok((key, min))
645 } else {
646 Ok((new_key, v))
647 }
648 })
649 .map(|v| Some(v.1))
650 }
651
652 /// Returns the element that gives the minimum value with respect to the function.
653 #[inline]
654 fn min_by<F>(mut self, mut f: F) -> Result<Option<Self::Item>, Self::Error>
655 where
656 Self: Sized,
657 F: FnMut(&Self::Item, &Self::Item) -> Result<Ordering, Self::Error>,
658 {
659 let min = match self.next()? {
660 Some(v) => v,
661 None => return Ok(None),
662 };
663
664 self.fold(min, |min, v| {
665 if f(&min, &v)? == Ordering::Less {
666 Ok(min)
667 } else {
668 Ok(v)
669 }
670 })
671 .map(Some)
672 }
673
674 /// Returns an iterator that yields this iterator's items in the opposite
675 /// order.
676 #[inline]
677 fn rev(self) -> Rev<Self>
678 where
679 Self: Sized + DoubleEndedFallibleIterator,
680 {
681 Rev(self)
682 }
683
684 /// Converts an iterator of pairs into a pair of containers.
685 #[inline]
686 fn unzip<A, B, FromA, FromB>(self) -> Result<(FromA, FromB), Self::Error>
687 where
688 Self: Sized + FallibleIterator<Item = (A, B)>,
689 FromA: Default + Extend<A>,
690 FromB: Default + Extend<B>,
691 {
692 let mut from_a = FromA::default();
693 let mut from_b = FromB::default();
694
695 self.for_each(|(a, b)| {
696 from_a.extend(Some(a));
697 from_b.extend(Some(b));
698 Ok(())
699 })?;
700
701 Ok((from_a, from_b))
702 }
703
704 /// Returns an iterator which clones all of its elements.
705 #[inline]
706 fn cloned<'a, T>(self) -> Cloned<Self>
707 where
708 Self: Sized + FallibleIterator<Item = &'a T>,
709 T: 'a + Clone,
710 {
711 Cloned(self)
712 }
713
714 /// Returns an iterator which repeats this iterator endlessly.
715 #[inline]
716 fn cycle(self) -> Cycle<Self>
717 where
718 Self: Sized + Clone,
719 {
720 Cycle {
721 it: self.clone(),
722 cur: self,
723 }
724 }
725
726 /// Lexicographically compares the elements of this iterator to that of
727 /// another.
728 #[inline]
729 fn cmp<I>(mut self, other: I) -> Result<Ordering, Self::Error>
730 where
731 Self: Sized,
732 I: IntoFallibleIterator<Item = Self::Item, Error = Self::Error>,
733 Self::Item: Ord,
734 {
735 let mut other = other.into_fallible_iter();
736
737 loop {
738 match (self.next()?, other.next()?) {
739 (None, None) => return Ok(Ordering::Equal),
740 (None, _) => return Ok(Ordering::Less),
741 (_, None) => return Ok(Ordering::Greater),
742 (Some(x), Some(y)) => match x.cmp(&y) {
743 Ordering::Equal => {}
744 o => return Ok(o),
745 },
746 }
747 }
748 }
749
750 /// Lexicographically compares the elements of this iterator to that of
751 /// another.
752 #[inline]
753 fn partial_cmp<I>(mut self, other: I) -> Result<Option<Ordering>, Self::Error>
754 where
755 Self: Sized,
756 I: IntoFallibleIterator<Error = Self::Error>,
757 Self::Item: PartialOrd<I::Item>,
758 {
759 let mut other = other.into_fallible_iter();
760
761 loop {
762 match (self.next()?, other.next()?) {
763 (None, None) => return Ok(Some(Ordering::Equal)),
764 (None, _) => return Ok(Some(Ordering::Less)),
765 (_, None) => return Ok(Some(Ordering::Greater)),
766 (Some(x), Some(y)) => match x.partial_cmp(&y) {
767 Some(Ordering::Equal) => {}
768 o => return Ok(o),
769 },
770 }
771 }
772 }
773
774 /// Determines if the elements of this iterator are equal to those of
775 /// another.
776 #[inline]
777 fn eq<I>(mut self, other: I) -> Result<bool, Self::Error>
778 where
779 Self: Sized,
780 I: IntoFallibleIterator<Error = Self::Error>,
781 Self::Item: PartialEq<I::Item>,
782 {
783 let mut other = other.into_fallible_iter();
784
785 loop {
786 match (self.next()?, other.next()?) {
787 (None, None) => return Ok(true),
788 (None, _) | (_, None) => return Ok(false),
789 (Some(x), Some(y)) => {
790 if x != y {
791 return Ok(false);
792 }
793 }
794 }
795 }
796 }
797
798 /// Determines if the elements of this iterator are not equal to those of
799 /// another.
800 #[inline]
801 fn ne<I>(mut self, other: I) -> Result<bool, Self::Error>
802 where
803 Self: Sized,
804 I: IntoFallibleIterator<Error = Self::Error>,
805 Self::Item: PartialEq<I::Item>,
806 {
807 let mut other = other.into_fallible_iter();
808
809 loop {
810 match (self.next()?, other.next()?) {
811 (None, None) => return Ok(false),
812 (None, _) | (_, None) => return Ok(true),
813 (Some(x), Some(y)) => {
814 if x != y {
815 return Ok(true);
816 }
817 }
818 }
819 }
820 }
821
822 /// Determines if the elements of this iterator are lexicographically less
823 /// than those of another.
824 #[inline]
825 fn lt<I>(mut self, other: I) -> Result<bool, Self::Error>
826 where
827 Self: Sized,
828 I: IntoFallibleIterator<Error = Self::Error>,
829 Self::Item: PartialOrd<I::Item>,
830 {
831 let mut other = other.into_fallible_iter();
832
833 loop {
834 match (self.next()?, other.next()?) {
835 (None, None) => return Ok(false),
836 (None, _) => return Ok(true),
837 (_, None) => return Ok(false),
838 (Some(x), Some(y)) => match x.partial_cmp(&y) {
839 Some(Ordering::Less) => return Ok(true),
840 Some(Ordering::Equal) => {}
841 Some(Ordering::Greater) => return Ok(false),
842 None => return Ok(false),
843 },
844 }
845 }
846 }
847
848 /// Determines if the elements of this iterator are lexicographically less
849 /// than or equal to those of another.
850 #[inline]
851 fn le<I>(mut self, other: I) -> Result<bool, Self::Error>
852 where
853 Self: Sized,
854 I: IntoFallibleIterator<Error = Self::Error>,
855 Self::Item: PartialOrd<I::Item>,
856 {
857 let mut other = other.into_fallible_iter();
858
859 loop {
860 match (self.next()?, other.next()?) {
861 (None, None) => return Ok(true),
862 (None, _) => return Ok(true),
863 (_, None) => return Ok(false),
864 (Some(x), Some(y)) => match x.partial_cmp(&y) {
865 Some(Ordering::Less) => return Ok(true),
866 Some(Ordering::Equal) => {}
867 Some(Ordering::Greater) => return Ok(false),
868 None => return Ok(false),
869 },
870 }
871 }
872 }
873
874 /// Determines if the elements of this iterator are lexicographically
875 /// greater than those of another.
876 #[inline]
877 fn gt<I>(mut self, other: I) -> Result<bool, Self::Error>
878 where
879 Self: Sized,
880 I: IntoFallibleIterator<Error = Self::Error>,
881 Self::Item: PartialOrd<I::Item>,
882 {
883 let mut other = other.into_fallible_iter();
884
885 loop {
886 match (self.next()?, other.next()?) {
887 (None, None) => return Ok(false),
888 (None, _) => return Ok(false),
889 (_, None) => return Ok(true),
890 (Some(x), Some(y)) => match x.partial_cmp(&y) {
891 Some(Ordering::Less) => return Ok(false),
892 Some(Ordering::Equal) => {}
893 Some(Ordering::Greater) => return Ok(true),
894 None => return Ok(false),
895 },
896 }
897 }
898 }
899
900 /// Determines if the elements of this iterator are lexicographically
901 /// greater than or equal to those of another.
902 #[inline]
903 fn ge<I>(mut self, other: I) -> Result<bool, Self::Error>
904 where
905 Self: Sized,
906 I: IntoFallibleIterator<Error = Self::Error>,
907 Self::Item: PartialOrd<I::Item>,
908 {
909 let mut other = other.into_fallible_iter();
910
911 loop {
912 match (self.next()?, other.next()?) {
913 (None, None) => return Ok(true),
914 (None, _) => return Ok(false),
915 (_, None) => return Ok(true),
916 (Some(x), Some(y)) => match x.partial_cmp(&y) {
917 Some(Ordering::Less) => return Ok(false),
918 Some(Ordering::Equal) => {}
919 Some(Ordering::Greater) => return Ok(true),
920 None => return Ok(false),
921 },
922 }
923 }
924 }
925
926 /// Returns a normal (non-fallible) iterator over `Result<Item, Error>`.
927 #[inline]
928 fn iterator(self) -> Iterator<Self>
929 where
930 Self: Sized,
931 {
932 Iterator(self)
933 }
934
935 /// Returns an iterator which applies a transform to the errors of the
936 /// underlying iterator.
937 #[inline]
938 fn map_err<B, F>(self, f: F) -> MapErr<Self, F>
939 where
940 F: FnMut(Self::Error) -> B,
941 Self: Sized,
942 {
943 MapErr { it: self, f }
944 }
945
946 /// Returns an iterator which unwraps all of its elements.
947 #[inline]
948 fn unwrap<T>(self) -> Unwrap<Self>
949 where
950 Self: Sized + FallibleIterator<Item = T>,
951 Self::Error: core::fmt::Debug,
952 {
953 Unwrap(self)
954 }
955}
956
957impl<I: FallibleIterator + ?Sized> FallibleIterator for &mut I {
958 type Item = I::Item;
959 type Error = I::Error;
960
961 #[inline]
962 fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
963 (**self).next()
964 }
965
966 #[inline]
967 fn size_hint(&self) -> (usize, Option<usize>) {
968 (**self).size_hint()
969 }
970
971 #[inline]
972 fn nth(&mut self, n: usize) -> Result<Option<I::Item>, I::Error> {
973 (**self).nth(n)
974 }
975}
976
977impl<I: DoubleEndedFallibleIterator + ?Sized> DoubleEndedFallibleIterator for &mut I {
978 #[inline]
979 fn next_back(&mut self) -> Result<Option<I::Item>, I::Error> {
980 (**self).next_back()
981 }
982}
983
984#[cfg(feature = "alloc")]
985impl<I: FallibleIterator + ?Sized> FallibleIterator for Box<I> {
986 type Item = I::Item;
987 type Error = I::Error;
988
989 #[inline]
990 fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
991 (**self).next()
992 }
993
994 #[inline]
995 fn size_hint(&self) -> (usize, Option<usize>) {
996 (**self).size_hint()
997 }
998
999 #[inline]
1000 fn nth(&mut self, n: usize) -> Result<Option<I::Item>, I::Error> {
1001 (**self).nth(n)
1002 }
1003}
1004
1005#[cfg(feature = "alloc")]
1006impl<I: DoubleEndedFallibleIterator + ?Sized> DoubleEndedFallibleIterator for Box<I> {
1007 #[inline]
1008 fn next_back(&mut self) -> Result<Option<I::Item>, I::Error> {
1009 (**self).next_back()
1010 }
1011}
1012
1013/// A fallible iterator able to yield elements from both ends.
1014pub trait DoubleEndedFallibleIterator: FallibleIterator {
1015 /// Advances the end of the iterator, returning the last value.
1016 fn next_back(&mut self) -> Result<Option<Self::Item>, Self::Error>;
1017
1018 /// Applies a function over the elements of the iterator in reverse order, producing a single final value.
1019 #[inline]
1020 fn rfold<B, F>(mut self, init: B, f: F) -> Result<B, Self::Error>
1021 where
1022 Self: Sized,
1023 F: FnMut(B, Self::Item) -> Result<B, Self::Error>,
1024 {
1025 self.try_rfold(init, f)
1026 }
1027
1028 /// Applies a function over the elements of the iterator in reverse, producing a single final value.
1029 ///
1030 /// This is used as the "base" of many methods on `DoubleEndedFallibleIterator`.
1031 #[inline]
1032 fn try_rfold<B, E, F>(&mut self, mut init: B, mut f: F) -> Result<B, E>
1033 where
1034 Self: Sized,
1035 E: From<Self::Error>,
1036 F: FnMut(B, Self::Item) -> Result<B, E>,
1037 {
1038 while let Some(v) = self.next_back()? {
1039 init = f(init, v)?;
1040 }
1041 Ok(init)
1042 }
1043}
1044
1045/// Conversion into a `FallibleIterator`.
1046pub trait IntoFallibleIterator {
1047 /// The elements of the iterator.
1048 type Item;
1049
1050 /// The error value of the iterator.
1051 type Error;
1052
1053 /// The iterator.
1054 type IntoFallibleIter: FallibleIterator<Item = Self::Item, Error = Self::Error>;
1055
1056 /// Creates a fallible iterator from a value.
1057 fn into_fallible_iter(self) -> Self::IntoFallibleIter;
1058}
1059
1060impl<I> IntoFallibleIterator for I
1061where
1062 I: FallibleIterator,
1063{
1064 type Item = I::Item;
1065 type Error = I::Error;
1066 type IntoFallibleIter = I;
1067
1068 #[inline]
1069 fn into_fallible_iter(self) -> I {
1070 self
1071 }
1072}
1073
1074/// An iterator which applies a fallible transform to the elements of the
1075/// underlying iterator.
1076#[derive(Clone)]
1077pub struct Map<T, F> {
1078 it: T,
1079 f: F,
1080}
1081
1082impl<I: core::fmt::Debug, F> core::fmt::Debug for Map<I, F> {
1083 fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
1084 f.debug_struct("Map").field(name:"iter", &self.it).finish()
1085 }
1086}
1087
1088impl<T, F, B> FallibleIterator for Map<T, F>
1089where
1090 T: FallibleIterator,
1091 F: FnMut(T::Item) -> Result<B, T::Error>,
1092{
1093 type Item = B;
1094 type Error = T::Error;
1095
1096 #[inline]
1097 fn next(&mut self) -> Result<Option<B>, T::Error> {
1098 match self.it.next() {
1099 Ok(Some(v)) => Ok(Some((self.f)(v)?)),
1100 Ok(None) => Ok(None),
1101 Err(e) => Err(e),
1102 }
1103 }
1104
1105 #[inline]
1106 fn size_hint(&self) -> (usize, Option<usize>) {
1107 self.it.size_hint()
1108 }
1109
1110 #[inline]
1111 fn try_fold<C, E, G>(&mut self, init: C, mut f: G) -> Result<C, E>
1112 where
1113 E: From<T::Error>,
1114 G: FnMut(C, B) -> Result<C, E>,
1115 {
1116 let map = &mut self.f;
1117 self.it.try_fold(init, |b, v| f(b, map(v)?))
1118 }
1119}
1120
1121impl<B, F, I> DoubleEndedFallibleIterator for Map<I, F>
1122where
1123 I: DoubleEndedFallibleIterator,
1124 F: FnMut(I::Item) -> Result<B, I::Error>,
1125{
1126 #[inline]
1127 fn next_back(&mut self) -> Result<Option<B>, I::Error> {
1128 match self.it.next_back() {
1129 Ok(Some(v: ::Item)) => Ok(Some((self.f)(v)?)),
1130 Ok(None) => Ok(None),
1131 Err(e: ::Error) => Err(e),
1132 }
1133 }
1134
1135 #[inline]
1136 fn try_rfold<C, E, G>(&mut self, init: C, mut f: G) -> Result<C, E>
1137 where
1138 E: From<I::Error>,
1139 G: FnMut(C, B) -> Result<C, E>,
1140 {
1141 let map: &mut F = &mut self.f;
1142 self.it.try_rfold(init, |acc: C, v: ::Item| f(acc, map(v)?))
1143 }
1144}
1145
1146#[derive(Clone, Debug)]
1147enum ChainState {
1148 Both,
1149 Front,
1150 Back,
1151}
1152
1153/// An iterator which yields the elements of one iterator followed by another.
1154#[derive(Clone, Debug)]
1155pub struct Chain<T, U> {
1156 front: T,
1157 back: U,
1158 state: ChainState,
1159}
1160
1161impl<T, U> FallibleIterator for Chain<T, U>
1162where
1163 T: FallibleIterator,
1164 U: FallibleIterator<Item = T::Item, Error = T::Error>,
1165{
1166 type Item = T::Item;
1167 type Error = T::Error;
1168
1169 #[inline]
1170 fn next(&mut self) -> Result<Option<T::Item>, T::Error> {
1171 match self.state {
1172 ChainState::Both => match self.front.next()? {
1173 Some(e) => Ok(Some(e)),
1174 None => {
1175 self.state = ChainState::Back;
1176 self.back.next()
1177 }
1178 },
1179 ChainState::Front => self.front.next(),
1180 ChainState::Back => self.back.next(),
1181 }
1182 }
1183
1184 #[inline]
1185 fn size_hint(&self) -> (usize, Option<usize>) {
1186 let front_hint = self.front.size_hint();
1187 let back_hint = self.back.size_hint();
1188
1189 let low = front_hint.0.saturating_add(back_hint.0);
1190 let high = match (front_hint.1, back_hint.1) {
1191 (Some(f), Some(b)) => f.checked_add(b),
1192 _ => None,
1193 };
1194
1195 (low, high)
1196 }
1197
1198 #[inline]
1199 fn count(self) -> Result<usize, T::Error> {
1200 match self.state {
1201 ChainState::Both => Ok(self.front.count()? + self.back.count()?),
1202 ChainState::Front => self.front.count(),
1203 ChainState::Back => self.back.count(),
1204 }
1205 }
1206
1207 #[inline]
1208 fn try_fold<B, E, F>(&mut self, init: B, mut f: F) -> Result<B, E>
1209 where
1210 E: From<T::Error>,
1211 F: FnMut(B, T::Item) -> Result<B, E>,
1212 {
1213 match self.state {
1214 ChainState::Both => {
1215 let init = self.front.try_fold(init, &mut f)?;
1216 self.state = ChainState::Back;
1217 self.back.try_fold(init, f)
1218 }
1219 ChainState::Front => self.front.try_fold(init, f),
1220 ChainState::Back => self.back.try_fold(init, f),
1221 }
1222 }
1223
1224 #[inline]
1225 fn find<F>(&mut self, mut f: F) -> Result<Option<T::Item>, T::Error>
1226 where
1227 F: FnMut(&T::Item) -> Result<bool, T::Error>,
1228 {
1229 match self.state {
1230 ChainState::Both => match self.front.find(&mut f)? {
1231 Some(v) => Ok(Some(v)),
1232 None => {
1233 self.state = ChainState::Back;
1234 self.back.find(f)
1235 }
1236 },
1237 ChainState::Front => self.front.find(f),
1238 ChainState::Back => self.back.find(f),
1239 }
1240 }
1241
1242 #[inline]
1243 fn last(self) -> Result<Option<T::Item>, T::Error> {
1244 match self.state {
1245 ChainState::Both => {
1246 self.front.last()?;
1247 self.back.last()
1248 }
1249 ChainState::Front => self.front.last(),
1250 ChainState::Back => self.back.last(),
1251 }
1252 }
1253}
1254
1255impl<T, U> DoubleEndedFallibleIterator for Chain<T, U>
1256where
1257 T: DoubleEndedFallibleIterator,
1258 U: DoubleEndedFallibleIterator<Item = T::Item, Error = T::Error>,
1259{
1260 #[inline]
1261 fn next_back(&mut self) -> Result<Option<T::Item>, T::Error> {
1262 match self.state {
1263 ChainState::Both => match self.back.next_back()? {
1264 Some(e) => Ok(Some(e)),
1265 None => {
1266 self.state = ChainState::Front;
1267 self.front.next_back()
1268 }
1269 },
1270 ChainState::Front => self.front.next_back(),
1271 ChainState::Back => self.back.next_back(),
1272 }
1273 }
1274
1275 #[inline]
1276 fn try_rfold<B, E, F>(&mut self, init: B, mut f: F) -> Result<B, E>
1277 where
1278 E: From<T::Error>,
1279 F: FnMut(B, T::Item) -> Result<B, E>,
1280 {
1281 match self.state {
1282 ChainState::Both => {
1283 let init = self.back.try_rfold(init, &mut f)?;
1284 self.state = ChainState::Front;
1285 self.front.try_rfold(init, f)
1286 }
1287 ChainState::Front => self.front.try_rfold(init, f),
1288 ChainState::Back => self.back.try_rfold(init, f),
1289 }
1290 }
1291}
1292
1293/// An iterator which clones the elements of the underlying iterator.
1294#[derive(Clone, Debug)]
1295pub struct Cloned<I>(I);
1296
1297impl<'a, T, I> FallibleIterator for Cloned<I>
1298where
1299 I: FallibleIterator<Item = &'a T>,
1300 T: 'a + Clone,
1301{
1302 type Item = T;
1303 type Error = I::Error;
1304
1305 #[inline]
1306 fn next(&mut self) -> Result<Option<T>, I::Error> {
1307 self.0.next().map(|o: Option<&'a T>| o.cloned())
1308 }
1309
1310 #[inline]
1311 fn size_hint(&self) -> (usize, Option<usize>) {
1312 self.0.size_hint()
1313 }
1314
1315 #[inline]
1316 fn try_fold<B, E, F>(&mut self, init: B, mut f: F) -> Result<B, E>
1317 where
1318 E: From<I::Error>,
1319 F: FnMut(B, T) -> Result<B, E>,
1320 {
1321 self.0.try_fold(init, |acc: B, v: &'a T| f(acc, v.clone()))
1322 }
1323}
1324
1325impl<'a, T, I> DoubleEndedFallibleIterator for Cloned<I>
1326where
1327 I: DoubleEndedFallibleIterator<Item = &'a T>,
1328 T: 'a + Clone,
1329{
1330 #[inline]
1331 fn next_back(&mut self) -> Result<Option<T>, I::Error> {
1332 self.0.next_back().map(|o: Option<&'a T>| o.cloned())
1333 }
1334
1335 #[inline]
1336 fn try_rfold<B, E, F>(&mut self, init: B, mut f: F) -> Result<B, E>
1337 where
1338 E: From<I::Error>,
1339 F: FnMut(B, T) -> Result<B, E>,
1340 {
1341 self.0.try_rfold(init, |acc: B, v: &'a T| f(acc, v.clone()))
1342 }
1343}
1344
1345/// Converts an `Iterator<Item = Result<T, E>>` into a `FallibleIterator<Item = T, Error = E>`.
1346#[inline]
1347pub fn convert<T, E, I>(it: I) -> Convert<I>
1348where
1349 I: iter::Iterator<Item = Result<T, E>>,
1350{
1351 Convert(it)
1352}
1353
1354/// A fallible iterator that wraps a normal iterator over `Result`s.
1355#[derive(Clone, Debug)]
1356pub struct Convert<I>(I);
1357
1358impl<T, E, I> FallibleIterator for Convert<I>
1359where
1360 I: iter::Iterator<Item = Result<T, E>>,
1361{
1362 type Item = T;
1363 type Error = E;
1364
1365 #[inline]
1366 fn next(&mut self) -> Result<Option<T>, E> {
1367 match self.0.next() {
1368 Some(Ok(i)) => Ok(Some(i)),
1369 Some(Err(e)) => Err(e),
1370 None => Ok(None),
1371 }
1372 }
1373
1374 #[inline]
1375 fn size_hint(&self) -> (usize, Option<usize>) {
1376 self.0.size_hint()
1377 }
1378
1379 #[inline]
1380 fn try_fold<B, E2, F>(&mut self, init: B, mut f: F) -> Result<B, E2>
1381 where
1382 E2: From<E>,
1383 F: FnMut(B, T) -> Result<B, E2>,
1384 {
1385 self.0.try_fold(init, |acc, v| f(acc, v?))
1386 }
1387}
1388
1389impl<T, E, I> DoubleEndedFallibleIterator for Convert<I>
1390where
1391 I: DoubleEndedIterator<Item = Result<T, E>>,
1392{
1393 #[inline]
1394 fn next_back(&mut self) -> Result<Option<T>, E> {
1395 match self.0.next_back() {
1396 Some(Ok(i: T)) => Ok(Some(i)),
1397 Some(Err(e: E)) => Err(e),
1398 None => Ok(None),
1399 }
1400 }
1401
1402 #[inline]
1403 fn try_rfold<B, E2, F>(&mut self, init: B, mut f: F) -> Result<B, E2>
1404 where
1405 E2: From<E>,
1406 F: FnMut(B, T) -> Result<B, E2>,
1407 {
1408 self.0.try_rfold(init, |acc: B, v: Result| f(acc, v?))
1409 }
1410}
1411
1412/// A fallible iterator that wraps a normal iterator over `Result`s.
1413#[derive(Clone, Debug)]
1414pub struct IntoFallible<I>(I);
1415
1416impl<T, I> FallibleIterator for IntoFallible<I>
1417where
1418 I: iter::Iterator<Item = T>,
1419{
1420 type Item = T;
1421 type Error = Infallible;
1422
1423 #[inline]
1424 fn next(&mut self) -> Result<Option<T>, Self::Error> {
1425 Ok(self.0.next())
1426 }
1427
1428 #[inline]
1429 fn size_hint(&self) -> (usize, Option<usize>) {
1430 self.0.size_hint()
1431 }
1432
1433 #[inline]
1434 fn try_fold<B, E2, F>(&mut self, init: B, f: F) -> Result<B, E2>
1435 where
1436 E2: From<Infallible>,
1437 F: FnMut(B, T) -> Result<B, E2>,
1438 {
1439 self.0.try_fold(init, f)
1440 }
1441}
1442
1443impl<T, I: iter::Iterator<Item = T>> From<I> for IntoFallible<I> {
1444 fn from(value: I) -> Self {
1445 Self(value)
1446 }
1447}
1448
1449impl<T, I> DoubleEndedFallibleIterator for IntoFallible<I>
1450where
1451 I: DoubleEndedIterator<Item = T>,
1452{
1453 #[inline]
1454 fn next_back(&mut self) -> Result<Option<T>, Infallible> {
1455 Ok(self.0.next_back())
1456 }
1457
1458 #[inline]
1459 fn try_rfold<B, E2, F>(&mut self, init: B, f: F) -> Result<B, E2>
1460 where
1461 E2: From<Infallible>,
1462 F: FnMut(B, T) -> Result<B, E2>,
1463 {
1464 self.0.try_rfold(init, f)
1465 }
1466}
1467
1468/// An iterator that yields the iteration count as well as the values of the
1469/// underlying iterator.
1470#[derive(Clone, Debug)]
1471pub struct Enumerate<I> {
1472 it: I,
1473 n: usize,
1474}
1475
1476impl<I> FallibleIterator for Enumerate<I>
1477where
1478 I: FallibleIterator,
1479{
1480 type Item = (usize, I::Item);
1481 type Error = I::Error;
1482
1483 #[inline]
1484 fn next(&mut self) -> Result<Option<(usize, I::Item)>, I::Error> {
1485 self.it.next().map(|o| {
1486 o.map(|e| {
1487 let i = self.n;
1488 self.n += 1;
1489 (i, e)
1490 })
1491 })
1492 }
1493
1494 #[inline]
1495 fn size_hint(&self) -> (usize, Option<usize>) {
1496 self.it.size_hint()
1497 }
1498
1499 #[inline]
1500 fn count(self) -> Result<usize, I::Error> {
1501 self.it.count()
1502 }
1503
1504 #[inline]
1505 fn nth(&mut self, n: usize) -> Result<Option<(usize, I::Item)>, I::Error> {
1506 match self.it.nth(n)? {
1507 Some(v) => {
1508 let i = self.n + n;
1509 self.n = i + 1;
1510 Ok(Some((i, v)))
1511 }
1512 None => Ok(None),
1513 }
1514 }
1515
1516 #[inline]
1517 fn try_fold<B, E, F>(&mut self, init: B, mut f: F) -> Result<B, E>
1518 where
1519 E: From<I::Error>,
1520 F: FnMut(B, (usize, I::Item)) -> Result<B, E>,
1521 {
1522 let n = &mut self.n;
1523 self.it.try_fold(init, |acc, v| {
1524 let i = *n;
1525 *n += 1;
1526 f(acc, (i, v))
1527 })
1528 }
1529}
1530
1531/// An iterator which uses a fallible predicate to determine which values of the
1532/// underlying iterator should be yielded.
1533#[derive(Clone, Debug)]
1534pub struct Filter<I, F> {
1535 it: I,
1536 f: F,
1537}
1538
1539impl<I, F> FallibleIterator for Filter<I, F>
1540where
1541 I: FallibleIterator,
1542 F: FnMut(&I::Item) -> Result<bool, I::Error>,
1543{
1544 type Item = I::Item;
1545 type Error = I::Error;
1546
1547 #[inline]
1548 fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
1549 let filter = &mut self.f;
1550 self.it
1551 .try_fold((), |(), v| {
1552 if filter(&v)? {
1553 return Err(FoldStop::Break(Some(v)));
1554 }
1555 Ok(())
1556 })
1557 .map(|()| None)
1558 .unpack_fold()
1559 }
1560
1561 #[inline]
1562 fn size_hint(&self) -> (usize, Option<usize>) {
1563 (0, self.it.size_hint().1)
1564 }
1565
1566 #[inline]
1567 fn try_fold<B, E, G>(&mut self, init: B, mut f: G) -> Result<B, E>
1568 where
1569 E: From<I::Error>,
1570 G: FnMut(B, I::Item) -> Result<B, E>,
1571 {
1572 let predicate = &mut self.f;
1573 self.it.try_fold(
1574 init,
1575 |acc, v| {
1576 if predicate(&v)? {
1577 f(acc, v)
1578 } else {
1579 Ok(acc)
1580 }
1581 },
1582 )
1583 }
1584}
1585
1586impl<I, F> DoubleEndedFallibleIterator for Filter<I, F>
1587where
1588 I: DoubleEndedFallibleIterator,
1589 F: FnMut(&I::Item) -> Result<bool, I::Error>,
1590{
1591 #[inline]
1592 fn next_back(&mut self) -> Result<Option<I::Item>, I::Error> {
1593 let filter = &mut self.f;
1594 self.it
1595 .try_rfold((), |(), v| {
1596 if filter(&v)? {
1597 return Err(FoldStop::Break(Some(v)));
1598 }
1599 Ok(())
1600 })
1601 .map(|()| None)
1602 .unpack_fold()
1603 }
1604
1605 #[inline]
1606 fn try_rfold<B, E, G>(&mut self, init: B, mut f: G) -> Result<B, E>
1607 where
1608 E: From<I::Error>,
1609 G: FnMut(B, I::Item) -> Result<B, E>,
1610 {
1611 let predicate = &mut self.f;
1612 self.it.try_rfold(
1613 init,
1614 |acc, v| {
1615 if predicate(&v)? {
1616 f(acc, v)
1617 } else {
1618 Ok(acc)
1619 }
1620 },
1621 )
1622 }
1623}
1624
1625/// An iterator which both filters and maps the values of the underlying
1626/// iterator.
1627#[derive(Clone, Debug)]
1628pub struct FilterMap<I, F> {
1629 it: I,
1630 f: F,
1631}
1632
1633impl<B, I, F> FallibleIterator for FilterMap<I, F>
1634where
1635 I: FallibleIterator,
1636 F: FnMut(I::Item) -> Result<Option<B>, I::Error>,
1637{
1638 type Item = B;
1639 type Error = I::Error;
1640
1641 #[inline]
1642 fn next(&mut self) -> Result<Option<B>, I::Error> {
1643 let map = &mut self.f;
1644 self.it
1645 .try_fold((), |(), v| match map(v)? {
1646 Some(v) => Err(FoldStop::Break(Some(v))),
1647 None => Ok(()),
1648 })
1649 .map(|()| None)
1650 .unpack_fold()
1651 }
1652
1653 #[inline]
1654 fn size_hint(&self) -> (usize, Option<usize>) {
1655 (0, self.it.size_hint().1)
1656 }
1657
1658 #[inline]
1659 fn try_fold<C, E, G>(&mut self, init: C, mut f: G) -> Result<C, E>
1660 where
1661 E: From<I::Error>,
1662 G: FnMut(C, B) -> Result<C, E>,
1663 {
1664 let map = &mut self.f;
1665 self.it.try_fold(init, |acc, v| match map(v)? {
1666 Some(v) => f(acc, v),
1667 None => Ok(acc),
1668 })
1669 }
1670}
1671
1672impl<B, I, F> DoubleEndedFallibleIterator for FilterMap<I, F>
1673where
1674 I: DoubleEndedFallibleIterator,
1675 F: FnMut(I::Item) -> Result<Option<B>, I::Error>,
1676{
1677 #[inline]
1678 fn next_back(&mut self) -> Result<Option<B>, I::Error> {
1679 let map = &mut self.f;
1680 self.it
1681 .try_rfold((), |(), v| match map(v)? {
1682 Some(v) => Err(FoldStop::Break(Some(v))),
1683 None => Ok(()),
1684 })
1685 .map(|()| None)
1686 .unpack_fold()
1687 }
1688
1689 #[inline]
1690 fn try_rfold<C, E, G>(&mut self, init: C, mut f: G) -> Result<C, E>
1691 where
1692 E: From<I::Error>,
1693 G: FnMut(C, B) -> Result<C, E>,
1694 {
1695 let map = &mut self.f;
1696 self.it.try_rfold(init, |acc, v| match map(v)? {
1697 Some(v) => f(acc, v),
1698 None => Ok(acc),
1699 })
1700 }
1701}
1702
1703/// An iterator which maps each element to another iterator, yielding those iterator's elements.
1704#[derive(Clone, Debug)]
1705pub struct FlatMap<I, U, F>
1706where
1707 U: IntoFallibleIterator,
1708{
1709 it: Map<I, F>,
1710 cur: Option<U::IntoFallibleIter>,
1711}
1712
1713impl<I, U, F> FallibleIterator for FlatMap<I, U, F>
1714where
1715 I: FallibleIterator,
1716 U: IntoFallibleIterator<Error = I::Error>,
1717 F: FnMut(I::Item) -> Result<U, I::Error>,
1718{
1719 type Item = U::Item;
1720 type Error = U::Error;
1721
1722 #[inline]
1723 fn next(&mut self) -> Result<Option<U::Item>, U::Error> {
1724 loop {
1725 if let Some(it) = &mut self.cur {
1726 if let Some(v) = it.next()? {
1727 return Ok(Some(v));
1728 }
1729 }
1730 match self.it.next()? {
1731 Some(it) => self.cur = Some(it.into_fallible_iter()),
1732 None => return Ok(None),
1733 }
1734 }
1735 }
1736
1737 #[inline]
1738 fn try_fold<B, E, G>(&mut self, init: B, mut f: G) -> Result<B, E>
1739 where
1740 E: From<U::Error>,
1741 G: FnMut(B, U::Item) -> Result<B, E>,
1742 {
1743 let mut acc = init;
1744 if let Some(cur) = &mut self.cur {
1745 acc = cur.try_fold(acc, &mut f)?;
1746 self.cur = None;
1747 }
1748
1749 let cur = &mut self.cur;
1750 self.it.try_fold(acc, |acc, v| {
1751 let mut it = v.into_fallible_iter();
1752 match it.try_fold(acc, &mut f) {
1753 Ok(acc) => Ok(acc),
1754 Err(e) => {
1755 *cur = Some(it);
1756 Err(e)
1757 }
1758 }
1759 })
1760 }
1761}
1762
1763/// An iterator which flattens an iterator of iterators, yielding those iterators' elements.
1764pub struct Flatten<I>
1765where
1766 I: FallibleIterator,
1767 I::Item: IntoFallibleIterator,
1768{
1769 it: I,
1770 cur: Option<<I::Item as IntoFallibleIterator>::IntoFallibleIter>,
1771}
1772
1773impl<I> Clone for Flatten<I>
1774where
1775 I: FallibleIterator + Clone,
1776 I::Item: IntoFallibleIterator,
1777 <I::Item as IntoFallibleIterator>::IntoFallibleIter: Clone,
1778{
1779 #[inline]
1780 fn clone(&self) -> Flatten<I> {
1781 Flatten {
1782 it: self.it.clone(),
1783 cur: self.cur.clone(),
1784 }
1785 }
1786}
1787
1788impl<I> FallibleIterator for Flatten<I>
1789where
1790 I: FallibleIterator,
1791 I::Item: IntoFallibleIterator<Error = I::Error>,
1792{
1793 type Item = <I::Item as IntoFallibleIterator>::Item;
1794 type Error = <I::Item as IntoFallibleIterator>::Error;
1795
1796 #[inline]
1797 fn next(&mut self) -> Result<Option<Self::Item>, Self::Error> {
1798 loop {
1799 if let Some(it) = &mut self.cur {
1800 if let Some(v) = it.next()? {
1801 return Ok(Some(v));
1802 }
1803 }
1804 match self.it.next()? {
1805 Some(it) => self.cur = Some(it.into_fallible_iter()),
1806 None => return Ok(None),
1807 }
1808 }
1809 }
1810
1811 #[inline]
1812 fn try_fold<B, E, G>(&mut self, init: B, mut f: G) -> Result<B, E>
1813 where
1814 E: From<Self::Error>,
1815 G: FnMut(B, Self::Item) -> Result<B, E>,
1816 {
1817 let mut acc = init;
1818 if let Some(cur) = &mut self.cur {
1819 acc = cur.try_fold(acc, &mut f)?;
1820 self.cur = None;
1821 }
1822
1823 let cur = &mut self.cur;
1824 self.it.try_fold(acc, |acc, v| {
1825 let mut it = v.into_fallible_iter();
1826 match it.try_fold(acc, &mut f) {
1827 Ok(acc) => Ok(acc),
1828 Err(e) => {
1829 *cur = Some(it);
1830 Err(e)
1831 }
1832 }
1833 })
1834 }
1835}
1836
1837/// Creates an iterator from a fallible function generating values.
1838///
1839/// ```
1840/// # use fallible_iterator::{from_fn, FallibleIterator};
1841/// let mut count = 0;
1842/// let counter = from_fn(move || {
1843/// // Increment our count. This is why we started at zero.
1844/// count += 1;
1845///
1846/// // Check to see if we've finished counting or not.
1847/// if count < 6 {
1848/// Ok(Some(count))
1849/// } else if count < 7 {
1850/// Ok(None)
1851/// } else {
1852/// Err(())
1853/// }
1854/// });
1855/// assert_eq!(&counter.collect::<Vec<_>>().unwrap(), &[1, 2, 3, 4, 5]);
1856/// ```
1857#[inline]
1858pub fn from_fn<I, E, F>(fun: F) -> FromFn<F>
1859where
1860 F: FnMut() -> Result<Option<I>, E>,
1861{
1862 FromFn { fun }
1863}
1864
1865/// An iterator using a function to generate new values.
1866#[derive(Clone, Debug)]
1867pub struct FromFn<F> {
1868 fun: F,
1869}
1870
1871impl<I, E, F> FallibleIterator for FromFn<F>
1872where
1873 F: FnMut() -> Result<Option<I>, E>,
1874{
1875 type Item = I;
1876 type Error = E;
1877
1878 fn next(&mut self) -> Result<Option<I>, E> {
1879 (self.fun)()
1880 }
1881}
1882
1883/// An iterator that yields `Ok(None)` forever after the underlying iterator
1884/// yields `Ok(None)` once.
1885#[derive(Clone, Debug)]
1886pub struct Fuse<I> {
1887 it: I,
1888 done: bool,
1889}
1890
1891impl<I> FallibleIterator for Fuse<I>
1892where
1893 I: FallibleIterator,
1894{
1895 type Item = I::Item;
1896 type Error = I::Error;
1897
1898 #[inline]
1899 fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
1900 if self.done {
1901 return Ok(None);
1902 }
1903
1904 match self.it.next()? {
1905 Some(i) => Ok(Some(i)),
1906 None => {
1907 self.done = true;
1908 Ok(None)
1909 }
1910 }
1911 }
1912
1913 #[inline]
1914 fn size_hint(&self) -> (usize, Option<usize>) {
1915 if self.done {
1916 (0, Some(0))
1917 } else {
1918 self.it.size_hint()
1919 }
1920 }
1921
1922 #[inline]
1923 fn count(self) -> Result<usize, I::Error> {
1924 if self.done {
1925 Ok(0)
1926 } else {
1927 self.it.count()
1928 }
1929 }
1930
1931 #[inline]
1932 fn last(self) -> Result<Option<I::Item>, I::Error> {
1933 if self.done {
1934 Ok(None)
1935 } else {
1936 self.it.last()
1937 }
1938 }
1939
1940 #[inline]
1941 fn nth(&mut self, n: usize) -> Result<Option<I::Item>, I::Error> {
1942 if self.done {
1943 Ok(None)
1944 } else {
1945 let v = self.it.nth(n)?;
1946 if v.is_none() {
1947 self.done = true;
1948 }
1949 Ok(v)
1950 }
1951 }
1952
1953 #[inline]
1954 fn try_fold<B, E, F>(&mut self, init: B, f: F) -> Result<B, E>
1955 where
1956 E: From<I::Error>,
1957 F: FnMut(B, I::Item) -> Result<B, E>,
1958 {
1959 if self.done {
1960 Ok(init)
1961 } else {
1962 self.it.try_fold(init, f)
1963 }
1964 }
1965}
1966
1967/// An iterator which passes each element to a closure before returning it.
1968#[derive(Clone, Debug)]
1969pub struct Inspect<I, F> {
1970 it: I,
1971 f: F,
1972}
1973
1974impl<I, F> FallibleIterator for Inspect<I, F>
1975where
1976 I: FallibleIterator,
1977 F: FnMut(&I::Item) -> Result<(), I::Error>,
1978{
1979 type Item = I::Item;
1980 type Error = I::Error;
1981
1982 #[inline]
1983 fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
1984 match self.it.next()? {
1985 Some(i) => {
1986 (self.f)(&i)?;
1987 Ok(Some(i))
1988 }
1989 None => Ok(None),
1990 }
1991 }
1992
1993 #[inline]
1994 fn size_hint(&self) -> (usize, Option<usize>) {
1995 self.it.size_hint()
1996 }
1997
1998 #[inline]
1999 fn try_fold<B, E, G>(&mut self, init: B, mut f: G) -> Result<B, E>
2000 where
2001 E: From<I::Error>,
2002 G: FnMut(B, I::Item) -> Result<B, E>,
2003 {
2004 let inspect = &mut self.f;
2005 self.it.try_fold(init, |acc, v| {
2006 inspect(&v)?;
2007 f(acc, v)
2008 })
2009 }
2010}
2011
2012impl<I, F> DoubleEndedFallibleIterator for Inspect<I, F>
2013where
2014 I: DoubleEndedFallibleIterator,
2015 F: FnMut(&I::Item) -> Result<(), I::Error>,
2016{
2017 #[inline]
2018 fn next_back(&mut self) -> Result<Option<I::Item>, I::Error> {
2019 match self.it.next_back()? {
2020 Some(i) => {
2021 (self.f)(&i)?;
2022 Ok(Some(i))
2023 }
2024 None => Ok(None),
2025 }
2026 }
2027
2028 #[inline]
2029 fn try_rfold<B, E, G>(&mut self, init: B, mut f: G) -> Result<B, E>
2030 where
2031 E: From<I::Error>,
2032 G: FnMut(B, I::Item) -> Result<B, E>,
2033 {
2034 let inspect = &mut self.f;
2035 self.it.try_rfold(init, |acc, v| {
2036 inspect(&v)?;
2037 f(acc, v)
2038 })
2039 }
2040}
2041
2042/// A normal (non-fallible) iterator which wraps a fallible iterator.
2043#[derive(Clone, Debug)]
2044pub struct Iterator<I>(I);
2045
2046impl<I> iter::Iterator for Iterator<I>
2047where
2048 I: FallibleIterator,
2049{
2050 type Item = Result<I::Item, I::Error>;
2051
2052 #[inline]
2053 fn next(&mut self) -> Option<Result<I::Item, I::Error>> {
2054 match self.0.next() {
2055 Ok(Some(v: ::Item)) => Some(Ok(v)),
2056 Ok(None) => None,
2057 Err(e: ::Error) => Some(Err(e)),
2058 }
2059 }
2060
2061 #[inline]
2062 fn size_hint(&self) -> (usize, Option<usize>) {
2063 self.0.size_hint()
2064 }
2065}
2066
2067impl<I> DoubleEndedIterator for Iterator<I>
2068where
2069 I: DoubleEndedFallibleIterator,
2070{
2071 #[inline]
2072 fn next_back(&mut self) -> Option<Result<I::Item, I::Error>> {
2073 match self.0.next_back() {
2074 Ok(Some(v: ::Item)) => Some(Ok(v)),
2075 Ok(None) => None,
2076 Err(e: ::Error) => Some(Err(e)),
2077 }
2078 }
2079}
2080
2081/// An iterator which applies a transform to the errors of the underlying
2082/// iterator.
2083#[derive(Clone, Debug)]
2084pub struct MapErr<I, F> {
2085 it: I,
2086 f: F,
2087}
2088
2089impl<B, F, I> FallibleIterator for MapErr<I, F>
2090where
2091 I: FallibleIterator,
2092 F: FnMut(I::Error) -> B,
2093{
2094 type Item = I::Item;
2095 type Error = B;
2096
2097 #[inline]
2098 fn next(&mut self) -> Result<Option<I::Item>, B> {
2099 self.it.next().map_err(&mut self.f)
2100 }
2101
2102 #[inline]
2103 fn size_hint(&self) -> (usize, Option<usize>) {
2104 self.it.size_hint()
2105 }
2106
2107 #[inline]
2108 fn count(mut self) -> Result<usize, B> {
2109 self.it.count().map_err(&mut self.f)
2110 }
2111
2112 #[inline]
2113 fn last(mut self) -> Result<Option<I::Item>, B> {
2114 self.it.last().map_err(&mut self.f)
2115 }
2116
2117 #[inline]
2118 fn nth(&mut self, n: usize) -> Result<Option<I::Item>, B> {
2119 self.it.nth(n).map_err(&mut self.f)
2120 }
2121
2122 #[inline]
2123 fn try_fold<C, E, G>(&mut self, init: C, mut f: G) -> Result<C, E>
2124 where
2125 E: From<B>,
2126 G: FnMut(C, I::Item) -> Result<C, E>,
2127 {
2128 self.it
2129 .try_fold(init, |acc, v| f(acc, v).map_err(MappedErr::Fold))
2130 .map_err(|e| match e {
2131 MappedErr::It(e) => (self.f)(e).into(),
2132 MappedErr::Fold(e) => e,
2133 })
2134 }
2135}
2136
2137impl<B, F, I> DoubleEndedFallibleIterator for MapErr<I, F>
2138where
2139 I: DoubleEndedFallibleIterator,
2140 F: FnMut(I::Error) -> B,
2141{
2142 #[inline]
2143 fn next_back(&mut self) -> Result<Option<I::Item>, B> {
2144 self.it.next_back().map_err(&mut self.f)
2145 }
2146
2147 #[inline]
2148 fn try_rfold<C, E, G>(&mut self, init: C, mut f: G) -> Result<C, E>
2149 where
2150 E: From<B>,
2151 G: FnMut(C, I::Item) -> Result<C, E>,
2152 {
2153 self.it
2154 .try_rfold(init, |acc, v| f(acc, v).map_err(MappedErr::Fold))
2155 .map_err(|e: MappedErr<::Error, …>| match e {
2156 MappedErr::It(e: ::Error) => (self.f)(e).into(),
2157 MappedErr::Fold(e: E) => e,
2158 })
2159 }
2160}
2161
2162enum MappedErr<T, U> {
2163 It(T),
2164 Fold(U),
2165}
2166
2167impl<T, U> From<T> for MappedErr<T, U> {
2168 #[inline]
2169 fn from(t: T) -> MappedErr<T, U> {
2170 MappedErr::It(t)
2171 }
2172}
2173
2174/// An iterator which can look at the next element without consuming it.
2175#[derive(Clone, Debug)]
2176pub struct Peekable<I: FallibleIterator> {
2177 it: I,
2178 next: Option<I::Item>,
2179}
2180
2181impl<I> Peekable<I>
2182where
2183 I: FallibleIterator,
2184{
2185 /// Returns a reference to the next value without advancing the iterator.
2186 #[inline]
2187 pub fn peek(&mut self) -> Result<Option<&I::Item>, I::Error> {
2188 if self.next.is_none() {
2189 self.next = self.it.next()?;
2190 }
2191
2192 Ok(self.next.as_ref())
2193 }
2194
2195 /// Consume and return the next value of this iterator if a condition is true.
2196 ///
2197 /// If func returns true for the next value of this iterator, consume and return it. Otherwise, return None.
2198 #[inline]
2199 pub fn next_if(&mut self, f: impl Fn(&I::Item) -> bool) -> Result<Option<I::Item>, I::Error> {
2200 match self.peek()? {
2201 Some(item) if f(item) => self.next(),
2202 _ => Ok(None),
2203 }
2204 }
2205
2206 /// Consume and return the next item if it is equal to `expected`.
2207 #[inline]
2208 pub fn next_if_eq<T>(&mut self, expected: &T) -> Result<Option<I::Item>, I::Error>
2209 where
2210 T: ?Sized,
2211 I::Item: PartialEq<T>,
2212 {
2213 self.next_if(|found| found == expected)
2214 }
2215}
2216
2217impl<I> FallibleIterator for Peekable<I>
2218where
2219 I: FallibleIterator,
2220{
2221 type Item = I::Item;
2222 type Error = I::Error;
2223
2224 #[inline]
2225 fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
2226 if let Some(next) = self.next.take() {
2227 return Ok(Some(next));
2228 }
2229
2230 self.it.next()
2231 }
2232
2233 #[inline]
2234 fn size_hint(&self) -> (usize, Option<usize>) {
2235 let mut hint = self.it.size_hint();
2236 if self.next.is_some() {
2237 hint.0 = hint.0.saturating_add(1);
2238 hint.1 = hint.1.and_then(|h| h.checked_add(1));
2239 }
2240 hint
2241 }
2242
2243 #[inline]
2244 fn try_fold<B, E, F>(&mut self, init: B, mut f: F) -> Result<B, E>
2245 where
2246 E: From<I::Error>,
2247 F: FnMut(B, I::Item) -> Result<B, E>,
2248 {
2249 let mut acc = init;
2250 if let Some(v) = self.next.take() {
2251 acc = f(acc, v)?;
2252 }
2253 self.it.try_fold(acc, f)
2254 }
2255}
2256
2257/// An iterator which yields elements of the underlying iterator in reverse
2258/// order.
2259#[derive(Clone, Debug)]
2260pub struct Rev<I>(I);
2261
2262impl<I> FallibleIterator for Rev<I>
2263where
2264 I: DoubleEndedFallibleIterator,
2265{
2266 type Item = I::Item;
2267 type Error = I::Error;
2268
2269 #[inline]
2270 fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
2271 self.0.next_back()
2272 }
2273
2274 #[inline]
2275 fn size_hint(&self) -> (usize, Option<usize>) {
2276 self.0.size_hint()
2277 }
2278
2279 #[inline]
2280 fn count(self) -> Result<usize, I::Error> {
2281 self.0.count()
2282 }
2283
2284 #[inline]
2285 fn try_fold<B, E, F>(&mut self, init: B, f: F) -> Result<B, E>
2286 where
2287 E: From<I::Error>,
2288 F: FnMut(B, I::Item) -> Result<B, E>,
2289 {
2290 self.0.try_rfold(init, f)
2291 }
2292}
2293
2294impl<I> DoubleEndedFallibleIterator for Rev<I>
2295where
2296 I: DoubleEndedFallibleIterator,
2297{
2298 #[inline]
2299 fn next_back(&mut self) -> Result<Option<I::Item>, I::Error> {
2300 self.0.next()
2301 }
2302
2303 #[inline]
2304 fn try_rfold<B, E, F>(&mut self, init: B, f: F) -> Result<B, E>
2305 where
2306 E: From<I::Error>,
2307 F: FnMut(B, I::Item) -> Result<B, E>,
2308 {
2309 self.0.try_fold(init, f)
2310 }
2311}
2312
2313/// An iterator which applies a stateful closure.
2314#[derive(Clone, Debug)]
2315pub struct Scan<I, St, F> {
2316 it: I,
2317 f: F,
2318 state: St,
2319}
2320
2321impl<B, I, St, F> FallibleIterator for Scan<I, St, F>
2322where
2323 I: FallibleIterator,
2324 F: FnMut(&mut St, I::Item) -> Result<Option<B>, I::Error>,
2325{
2326 type Item = B;
2327 type Error = I::Error;
2328
2329 #[inline]
2330 fn next(&mut self) -> Result<Option<B>, I::Error> {
2331 match self.it.next()? {
2332 Some(v: ::Item) => (self.f)(&mut self.state, v),
2333 None => Ok(None),
2334 }
2335 }
2336
2337 #[inline]
2338 fn size_hint(&self) -> (usize, Option<usize>) {
2339 let hint: (usize, Option) = self.it.size_hint();
2340 (0, hint.1)
2341 }
2342}
2343
2344/// An iterator which skips initial elements.
2345#[derive(Clone, Debug)]
2346pub struct Skip<I> {
2347 it: I,
2348 n: usize,
2349}
2350
2351impl<I> FallibleIterator for Skip<I>
2352where
2353 I: FallibleIterator,
2354{
2355 type Item = I::Item;
2356 type Error = I::Error;
2357
2358 #[inline]
2359 fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
2360 if self.n == 0 {
2361 self.it.next()
2362 } else {
2363 let n = self.n;
2364 self.n = 0;
2365 self.it.nth(n)
2366 }
2367 }
2368
2369 #[inline]
2370 fn size_hint(&self) -> (usize, Option<usize>) {
2371 let hint = self.it.size_hint();
2372
2373 (
2374 hint.0.saturating_sub(self.n),
2375 hint.1.map(|x| x.saturating_sub(self.n)),
2376 )
2377 }
2378}
2379
2380/// An iterator which skips initial elements based on a predicate.
2381#[derive(Clone, Debug)]
2382pub struct SkipWhile<I, P> {
2383 it: I,
2384 flag: bool,
2385 predicate: P,
2386}
2387
2388impl<I, P> FallibleIterator for SkipWhile<I, P>
2389where
2390 I: FallibleIterator,
2391 P: FnMut(&I::Item) -> Result<bool, I::Error>,
2392{
2393 type Item = I::Item;
2394 type Error = I::Error;
2395
2396 #[inline]
2397 fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
2398 let flag = &mut self.flag;
2399 let pred = &mut self.predicate;
2400 self.it.find(move |x| {
2401 if *flag || !pred(x)? {
2402 *flag = true;
2403 Ok(true)
2404 } else {
2405 Ok(false)
2406 }
2407 })
2408 }
2409
2410 #[inline]
2411 fn size_hint(&self) -> (usize, Option<usize>) {
2412 let hint = self.it.size_hint();
2413 if self.flag {
2414 hint
2415 } else {
2416 (0, hint.1)
2417 }
2418 }
2419}
2420
2421/// An iterator which steps through the elements of the underlying iterator by a certain amount.
2422#[derive(Clone, Debug)]
2423pub struct StepBy<I> {
2424 it: I,
2425 step: usize,
2426 first_take: bool,
2427}
2428
2429impl<I> FallibleIterator for StepBy<I>
2430where
2431 I: FallibleIterator,
2432{
2433 type Item = I::Item;
2434 type Error = I::Error;
2435
2436 #[inline]
2437 fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
2438 if self.first_take {
2439 self.first_take = false;
2440 self.it.next()
2441 } else {
2442 self.it.nth(self.step)
2443 }
2444 }
2445
2446 fn size_hint(&self) -> (usize, Option<usize>) {
2447 let inner_hint = self.it.size_hint();
2448
2449 if self.first_take {
2450 let f = |n| {
2451 if n == 0 {
2452 0
2453 } else {
2454 1 + (n - 1) / (self.step + 1)
2455 }
2456 };
2457 (f(inner_hint.0), inner_hint.1.map(f))
2458 } else {
2459 let f = |n| n / (self.step + 1);
2460 (f(inner_hint.0), inner_hint.1.map(f))
2461 }
2462 }
2463}
2464
2465/// An iterator which yields a limited number of elements from the underlying
2466/// iterator.
2467#[derive(Clone, Debug)]
2468pub struct Take<I> {
2469 it: I,
2470 remaining: usize,
2471}
2472
2473impl<I> FallibleIterator for Take<I>
2474where
2475 I: FallibleIterator,
2476{
2477 type Item = I::Item;
2478 type Error = I::Error;
2479
2480 #[inline]
2481 fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
2482 if self.remaining == 0 {
2483 return Ok(None);
2484 }
2485
2486 let next = self.it.next();
2487 if let Ok(Some(_)) = next {
2488 self.remaining -= 1;
2489 }
2490 next
2491 }
2492
2493 #[inline]
2494 fn size_hint(&self) -> (usize, Option<usize>) {
2495 let hint = self.it.size_hint();
2496 (
2497 cmp::min(hint.0, self.remaining),
2498 hint.1.map(|n| cmp::min(n, self.remaining)),
2499 )
2500 }
2501}
2502
2503/// An iterator which yields elements based on a predicate.
2504#[derive(Clone, Debug)]
2505pub struct TakeWhile<I, P> {
2506 it: I,
2507 flag: bool,
2508 predicate: P,
2509}
2510
2511impl<I, P> FallibleIterator for TakeWhile<I, P>
2512where
2513 I: FallibleIterator,
2514 P: FnMut(&I::Item) -> Result<bool, I::Error>,
2515{
2516 type Item = I::Item;
2517 type Error = I::Error;
2518
2519 #[inline]
2520 fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
2521 if self.flag {
2522 Ok(None)
2523 } else {
2524 match self.it.next()? {
2525 Some(item) => {
2526 if (self.predicate)(&item)? {
2527 Ok(Some(item))
2528 } else {
2529 self.flag = true;
2530 Ok(None)
2531 }
2532 }
2533 None => Ok(None),
2534 }
2535 }
2536 }
2537
2538 #[inline]
2539 fn size_hint(&self) -> (usize, Option<usize>) {
2540 if self.flag {
2541 (0, Some(0))
2542 } else {
2543 let hint = self.it.size_hint();
2544 (0, hint.1)
2545 }
2546 }
2547}
2548
2549/// An iterator which cycles another endlessly.
2550#[derive(Clone, Debug)]
2551pub struct Cycle<I> {
2552 it: I,
2553 cur: I,
2554}
2555
2556impl<I> FallibleIterator for Cycle<I>
2557where
2558 I: FallibleIterator + Clone,
2559{
2560 type Item = I::Item;
2561 type Error = I::Error;
2562
2563 #[inline]
2564 fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
2565 match self.cur.next()? {
2566 None => {
2567 self.cur = self.it.clone();
2568 self.cur.next()
2569 }
2570 Some(v: ::Item) => Ok(Some(v)),
2571 }
2572 }
2573
2574 #[inline]
2575 fn size_hint(&self) -> (usize, Option<usize>) {
2576 (usize::max_value(), None)
2577 }
2578}
2579
2580/// An iterator that yields pairs of this iterator's and another iterator's
2581/// values.
2582#[derive(Clone, Debug)]
2583pub struct Zip<T, U>(T, U);
2584
2585impl<T, U> FallibleIterator for Zip<T, U>
2586where
2587 T: FallibleIterator,
2588 U: FallibleIterator<Error = T::Error>,
2589{
2590 type Item = (T::Item, U::Item);
2591 type Error = T::Error;
2592
2593 #[inline]
2594 fn next(&mut self) -> Result<Option<(T::Item, U::Item)>, T::Error> {
2595 match (self.0.next()?, self.1.next()?) {
2596 (Some(a), Some(b)) => Ok(Some((a, b))),
2597 _ => Ok(None),
2598 }
2599 }
2600
2601 #[inline]
2602 fn size_hint(&self) -> (usize, Option<usize>) {
2603 let a = self.0.size_hint();
2604 let b = self.1.size_hint();
2605
2606 let low = cmp::min(a.0, b.0);
2607
2608 let high = match (a.1, b.1) {
2609 (Some(a), Some(b)) => Some(cmp::min(a, b)),
2610 (Some(a), None) => Some(a),
2611 (None, Some(b)) => Some(b),
2612 (None, None) => None,
2613 };
2614
2615 (low, high)
2616 }
2617}
2618
2619/// An iterator that unwraps every element yielded by the underlying
2620/// FallibleIterator
2621#[derive(Clone, Debug)]
2622pub struct Unwrap<T>(T);
2623
2624impl<T> iter::Iterator for Unwrap<T>
2625where
2626 T: FallibleIterator,
2627 T::Error: core::fmt::Debug,
2628{
2629 type Item = T::Item;
2630
2631 #[inline]
2632 fn next(&mut self) -> Option<T::Item> {
2633 self.0.next().unwrap()
2634 }
2635
2636 #[inline]
2637 fn size_hint(&self) -> (usize, Option<usize>) {
2638 let (_, max: Option) = self.0.size_hint();
2639 (0, max)
2640 }
2641}
2642
2643fn _is_object_safe(_: &dyn DoubleEndedFallibleIterator<Item = (), Error = ()>) {}
2644
2645/// An extnsion-trait with set of useful methods to convert [`core::iter::Iterator`]
2646/// into [`FallibleIterator`]
2647pub trait IteratorExt {
2648 /// Convert an iterator of `Result`s into `FallibleIterator` by transposition
2649 fn transpose_into_fallible<T, E>(self) -> Convert<Self>
2650 where
2651 Self: iter::Iterator<Item = Result<T, E>> + Sized;
2652
2653 /// Convert an iterator of anything into `FallibleIterator` by wrapping
2654 /// into `Result<T, Infallible>` where `Infallible` is an error that can never actually
2655 /// happen.
2656 fn into_fallible<T>(self) -> IntoFallible<Self>
2657 where
2658 Self: iter::Iterator<Item = T> + Sized;
2659}
2660
2661impl<I> IteratorExt for I
2662where
2663 I: iter::Iterator,
2664{
2665 /// Convert an iterator of `Result`s into `FallibleIterator` by transposition
2666 fn transpose_into_fallible<T, E>(self) -> Convert<Self>
2667 where
2668 Self: iter::Iterator<Item = Result<T, E>> + Sized,
2669 {
2670 Convert(self)
2671 }
2672
2673 /// Convert an iterator of anything into `FallibleIterator` by wrapping
2674 /// into `Result<T, Infallible>` where `Infallible` is an error that can never actually
2675 /// happen.
2676 fn into_fallible<T>(self) -> IntoFallible<Self>
2677 where
2678 Self: iter::Iterator<Item = T> + Sized,
2679 {
2680 IntoFallible(self)
2681 }
2682}
2683
2684/// An iterator that yields nothing.
2685#[derive(Clone, Debug)]
2686pub struct Empty<T, E>(PhantomData<T>, PhantomData<E>);
2687
2688impl<T, E> FallibleIterator for Empty<T, E> {
2689 type Item = T;
2690 type Error = E;
2691
2692 #[inline]
2693 fn next(&mut self) -> Result<Option<T>, E> {
2694 Ok(None)
2695 }
2696
2697 #[inline]
2698 fn size_hint(&self) -> (usize, Option<usize>) {
2699 (0, Some(0))
2700 }
2701}
2702
2703/// Creates an iterator that yields nothing.
2704pub fn empty<T, E>() -> Empty<T, E> {
2705 Empty(PhantomData, PhantomData)
2706}
2707
2708/// An iterator that yields something exactly once.
2709#[derive(Clone, Debug)]
2710pub struct Once<T, E>(Option<T>, PhantomData<E>);
2711
2712/// Creates an iterator that yields an element exactly once.
2713pub fn once<T, E>(value: T) -> Once<T, E> {
2714 Once(Some(value), PhantomData)
2715}
2716
2717impl<T, E> FallibleIterator for Once<T, E> {
2718 type Item = T;
2719 type Error = E;
2720
2721 #[inline]
2722 fn next(&mut self) -> Result<Option<Self::Item>, Self::Error> {
2723 Ok(self.0.take())
2724 }
2725
2726 #[inline]
2727 fn size_hint(&self) -> (usize, Option<usize>) {
2728 match self.0 {
2729 Some(_) => (1, Some(1)),
2730 None => (0, Some(0)),
2731 }
2732 }
2733}
2734
2735/// An iterator that fails with a predetermined error exactly once.
2736#[derive(Clone, Debug)]
2737pub struct OnceErr<T, E>(PhantomData<T>, Option<E>);
2738
2739/// Creates an iterator that fails with a predetermined error exactly once.
2740pub fn once_err<T, E>(value: E) -> OnceErr<T, E> {
2741 OnceErr(PhantomData, Some(value))
2742}
2743
2744impl<T, E> FallibleIterator for OnceErr<T, E> {
2745 type Item = T;
2746 type Error = E;
2747
2748 #[inline]
2749 fn next(&mut self) -> Result<Option<Self::Item>, Self::Error> {
2750 match self.1.take() {
2751 Some(value: E) => Err(value),
2752 None => Ok(None),
2753 }
2754 }
2755
2756 #[inline]
2757 fn size_hint(&self) -> (usize, Option<usize>) {
2758 (0, Some(0))
2759 }
2760}
2761
2762/// An iterator that endlessly repeats a single element.
2763#[derive(Clone, Debug)]
2764pub struct Repeat<T: Clone, E>(T, PhantomData<E>);
2765
2766/// Creates an iterator that endlessly repeats a single element.
2767pub fn repeat<T: Clone, E>(value: T) -> Repeat<T, E> {
2768 Repeat(value, PhantomData)
2769}
2770
2771impl<T: Clone, E> FallibleIterator for Repeat<T, E> {
2772 type Item = T;
2773 type Error = E;
2774
2775 #[inline]
2776 fn next(&mut self) -> Result<Option<Self::Item>, Self::Error> {
2777 Ok(Some(self.0.clone()))
2778 }
2779
2780 #[inline]
2781 fn size_hint(&self) -> (usize, Option<usize>) {
2782 (usize::max_value(), None)
2783 }
2784}
2785
2786/// An iterator that endlessly repeats a single error.
2787#[derive(Clone, Debug)]
2788pub struct RepeatErr<T, E: Clone>(PhantomData<T>, E);
2789
2790/// Creates an iterator that endlessly repeats a single error.
2791pub fn repeat_err<T, E: Clone>(value: E) -> RepeatErr<T, E> {
2792 RepeatErr(PhantomData, value)
2793}
2794
2795impl<T, E: Clone> FallibleIterator for RepeatErr<T, E> {
2796 type Item = T;
2797 type Error = E;
2798
2799 #[inline]
2800 fn next(&mut self) -> Result<Option<Self::Item>, Self::Error> {
2801 Err(self.1.clone())
2802 }
2803
2804 #[inline]
2805 fn size_hint(&self) -> (usize, Option<usize>) {
2806 (0, Some(0))
2807 }
2808}
2809