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+//! "Fallible" iterators.
+//!
+//! The iterator APIs in the Rust standard library do not support iteration
+//! that can fail in a first class manner. These iterators are typically modeled
+//! as iterating over `Result<T, E>` values; for example, the `Lines` iterator
+//! returns `io::Result<String>`s. When simply iterating over these types, the
+//! value being iterated over must be unwrapped in some way before it can be
+//! used:
+//!
+//! ```ignore
+//! for line in reader.lines() {
+//! let line = line?;
+//! // work with line
+//! }
+//! ```
+//!
+//! In addition, many of the additional methods on the `Iterator` trait will
+//! not behave properly in the presence of errors when working with these kinds
+//! of iterators. For example, if one wanted to count the number of lines of
+//! text in a `Read`er, this might be a way to go about it:
+//!
+//! ```ignore
+//! let count = reader.lines().count();
+//! ```
+//!
+//! This will return the proper value when the reader operates successfully, but
+//! if it encounters an IO error, the result will either be slightly higher than
+//! expected if the error is transient, or it may run forever if the error is
+//! returned repeatedly!
+//!
+//! In contrast, a fallible iterator is built around the concept that a call to
+//! `next` can fail. The trait has an additional `Error` associated type in
+//! addition to the `Item` type, and `next` returns `Result<Option<Self::Item>,
+//! Self::Error>` rather than `Option<Self::Item>`. Methods like `count` return
+//! `Result`s as well.
+//!
+//! This does mean that fallible iterators are incompatible with Rust's `for`
+//! loop syntax, but `while let` loops offer a similar level of ergonomics:
+//!
+//! ```ignore
+//! while let Some(item) = iter.next()? {
+//! // work with item
+//! }
+//! ```
+//!
+//! ## Fallible closure arguments
+//!
+//! Like `Iterator`, many `FallibleIterator` methods take closures as arguments.
+//! These use the same signatures as their `Iterator` counterparts, except that
+//! `FallibleIterator` expects the closures to be fallible: they return
+//! `Result<T, Self::Error>` instead of simply `T`.
+//!
+//! For example, the standard library's `Iterator::filter` adapter method
+//! filters the underlying iterator according to a predicate provided by the
+//! user, whose return type is `bool`. In `FallibleIterator::filter`, however,
+//! the predicate returns `Result<bool, Self::Error>`:
+//!
+//! ```
+//! # use std::error::Error;
+//! # use std::str::FromStr;
+//! # use fallible_iterator::{convert, FallibleIterator};
+//! let numbers = convert("100\n200\nfern\n400".lines().map(Ok::<&str, Box<Error>>));
+//! let big_numbers = numbers.filter(|n| Ok(u64::from_str(n)? > 100));
+//! assert!(big_numbers.count().is_err());
+//! ```
+#![doc(html_root_url = "https://docs.rs/fallible-iterator/0.2")]
+#![warn(missing_docs)]
+#![cfg_attr(feature = "alloc", feature(alloc))]
+#![no_std]
+
+use core::cmp::{self, Ordering};
+use core::iter;
+
+#[cfg(all(feature = "alloc", not(feature = "std")))]
+#[cfg_attr(test, macro_use)]
+extern crate alloc;
+
+#[cfg(all(feature = "alloc", not(feature = "std")))]
+mod imports {
+ pub use alloc::boxed::Box;
+ pub use alloc::collections::btree_map::BTreeMap;
+ pub use alloc::collections::btree_set::BTreeSet;
+ pub use alloc::vec::Vec;
+}
+
+#[cfg(feature = "std")]
+#[cfg_attr(test, macro_use)]
+extern crate std;
+
+#[cfg(feature = "std")]
+mod imports {
+ pub use std::collections::{BTreeMap, BTreeSet, HashMap, HashSet};
+ pub use std::hash::{BuildHasher, Hash};
+ pub use std::prelude::v1::*;
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+use crate::imports::*;
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+#[cfg(test)]
+mod test;
+
+enum FoldStop<T, E> {
+ Break(T),
+ Err(E),
+}
+
+impl<T, E> From<E> for FoldStop<T, E> {
+ #[inline]
+ fn from(e: E) -> FoldStop<T, E> {
+ FoldStop::Err(e)
+ }
+}
+
+trait ResultExt<T, E> {
+ fn unpack_fold(self) -> Result<T, E>;
+}
+
+impl<T, E> ResultExt<T, E> for Result<T, FoldStop<T, E>> {
+ #[inline]
+ fn unpack_fold(self) -> Result<T, E> {
+ match self {
+ Ok(v) => Ok(v),
+ Err(FoldStop::Break(v)) => Ok(v),
+ Err(FoldStop::Err(e)) => Err(e),
+ }
+ }
+}
+
+/// An `Iterator`-like trait that allows for calculation of items to fail.
+pub trait FallibleIterator {
+ /// The type being iterated over.
+ type Item;
+
+ /// The error type.
+ type Error;
+
+ /// Advances the iterator and returns the next value.
+ ///
+ /// Returns `Ok(None)` when iteration is finished.
+ ///
+ /// The behavior of calling this method after a previous call has returned
+ /// `Ok(None)` or `Err` is implemenetation defined.
+ fn next(&mut self) -> Result<Option<Self::Item>, Self::Error>;
+
+ /// Returns bounds on the remaining length of the iterator.
+ ///
+ /// Specifically, the first half of the returned tuple is a lower bound and
+ /// the second half is an upper bound.
+ ///
+ /// For the upper bound, `None` indicates that the upper bound is either
+ /// unknown or larger than can be represented as a `usize`.
+ ///
+ /// Both bounds assume that all remaining calls to `next` succeed. That is,
+ /// `next` could return an `Err` in fewer calls than specified by the lower
+ /// bound.
+ ///
+ /// The default implementation returns `(0, None)`, which is correct for
+ /// any iterator.
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ (0, None)
+ }
+
+ /// Consumes the iterator, returning the number of remaining items.
+ #[inline]
+ fn count(self) -> Result<usize, Self::Error>
+ where
+ Self: Sized,
+ {
+ self.fold(0, |n, _| Ok(n + 1))
+ }
+
+ /// Returns the last element of the iterator.
+ #[inline]
+ fn last(self) -> Result<Option<Self::Item>, Self::Error>
+ where
+ Self: Sized,
+ {
+ self.fold(None, |_, v| Ok(Some(v)))
+ }
+
+ /// Returns the `n`th element of the iterator.
+ #[inline]
+ fn nth(&mut self, mut n: usize) -> Result<Option<Self::Item>, Self::Error> {
+ while let Some(e) = self.next()? {
+ if n == 0 {
+ return Ok(Some(e));
+ }
+ n -= 1;
+ }
+ Ok(None)
+ }
+
+ /// Returns an iterator starting at the same point, but stepping by the given amount at each iteration.
+ ///
+ /// # Panics
+ ///
+ /// Panics if `step` is 0.
+ #[inline]
+ fn step_by(self, step: usize) -> StepBy<Self>
+ where
+ Self: Sized,
+ {
+ assert!(step != 0);
+ StepBy {
+ it: self,
+ step: step - 1,
+ first_take: true,
+ }
+ }
+
+ /// Returns an iterator which yields the elements of this iterator followed
+ /// by another.
+ #[inline]
+ fn chain<I>(self, it: I) -> Chain<Self, I>
+ where
+ I: IntoFallibleIterator<Item = Self::Item, Error = Self::Error>,
+ Self: Sized,
+ {
+ Chain {
+ front: self,
+ back: it,
+ state: ChainState::Both,
+ }
+ }
+
+ /// Returns an iterator that yields pairs of this iterator's and another
+ /// iterator's values.
+ #[inline]
+ fn zip<I>(self, o: I) -> Zip<Self, I::IntoFallibleIter>
+ where
+ Self: Sized,
+ I: IntoFallibleIterator<Error = Self::Error>,
+ {
+ Zip(self, o.into_fallible_iter())
+ }
+
+ /// Returns an iterator which applies a fallible transform to the elements
+ /// of the underlying iterator.
+ #[inline]
+ fn map<F, B>(self, f: F) -> Map<Self, F>
+ where
+ Self: Sized,
+ F: FnMut(Self::Item) -> Result<B, Self::Error>,
+ {
+ Map { it: self, f: f }
+ }
+
+ /// Calls a fallible closure on each element of an iterator.
+ #[inline]
+ fn for_each<F>(self, mut f: F) -> Result<(), Self::Error>
+ where
+ Self: Sized,
+ F: FnMut(Self::Item) -> Result<(), Self::Error>,
+ {
+ self.fold((), move |(), item| f(item))
+ }
+
+ /// Returns an iterator which uses a predicate to determine which values
+ /// should be yielded. The predicate may fail; such failures are passed to
+ /// the caller.
+ #[inline]
+ fn filter<F>(self, f: F) -> Filter<Self, F>
+ where
+ Self: Sized,
+ F: FnMut(&Self::Item) -> Result<bool, Self::Error>,
+ {
+ Filter { it: self, f: f }
+ }
+
+ /// Returns an iterator which both filters and maps. The closure may fail;
+ /// such failures are passed along to the consumer.
+ #[inline]
+ fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F>
+ where
+ Self: Sized,
+ F: FnMut(Self::Item) -> Result<Option<B>, Self::Error>,
+ {
+ FilterMap { it: self, f: f }
+ }
+
+ /// Returns an iterator which yields the current iteration count as well
+ /// as the value.
+ #[inline]
+ fn enumerate(self) -> Enumerate<Self>
+ where
+ Self: Sized,
+ {
+ Enumerate { it: self, n: 0 }
+ }
+
+ /// Returns an iterator that can peek at the next element without consuming
+ /// it.
+ #[inline]
+ fn peekable(self) -> Peekable<Self>
+ where
+ Self: Sized,
+ {
+ Peekable {
+ it: self,
+ next: None,
+ }
+ }
+
+ /// Returns an iterator that skips elements based on a predicate.
+ #[inline]
+ fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P>
+ where
+ Self: Sized,
+ P: FnMut(&Self::Item) -> Result<bool, Self::Error>,
+ {
+ SkipWhile {
+ it: self,
+ flag: false,
+ predicate,
+ }
+ }
+
+ /// Returns an iterator that yields elements based on a predicate.
+ #[inline]
+ fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P>
+ where
+ Self: Sized,
+ P: FnMut(&Self::Item) -> Result<bool, Self::Error>,
+ {
+ TakeWhile {
+ it: self,
+ flag: false,
+ predicate,
+ }
+ }
+
+ /// Returns an iterator which skips the first `n` values of this iterator.
+ #[inline]
+ fn skip(self, n: usize) -> Skip<Self>
+ where
+ Self: Sized,
+ {
+ Skip { it: self, n }
+ }
+
+ /// Returns an iterator that yields only the first `n` values of this
+ /// iterator.
+ #[inline]
+ fn take(self, n: usize) -> Take<Self>
+ where
+ Self: Sized,
+ {
+ Take {
+ it: self,
+ remaining: n,
+ }
+ }
+
+ /// Returns an iterator which applies a stateful map to values of this
+ /// iterator.
+ #[inline]
+ fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F>
+ where
+ Self: Sized,
+ F: FnMut(&mut St, Self::Item) -> Result<Option<B>, Self::Error>,
+ {
+ Scan {
+ it: self,
+ f,
+ state: initial_state,
+ }
+ }
+
+ /// Returns an iterator which maps this iterator's elements to iterators, yielding those iterators' values.
+ #[inline]
+ fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F>
+ where
+ Self: Sized,
+ U: IntoFallibleIterator<Error = Self::Error>,
+ F: FnMut(Self::Item) -> Result<U, Self::Error>,
+ {
+ FlatMap {
+ it: self.map(f),
+ cur: None,
+ }
+ }
+
+ /// Returns an iterator which flattens an iterator of iterators, yielding those iterators' values.
+ #[inline]
+ fn flatten(self) -> Flatten<Self>
+ where
+ Self: Sized,
+ Self::Item: IntoFallibleIterator<Error = Self::Error>,
+ {
+ Flatten {
+ it: self,
+ cur: None,
+ }
+ }
+
+ /// Returns an iterator which yields this iterator's elements and ends after
+ /// the first `Ok(None)`.
+ ///
+ /// The behavior of calling `next` after it has previously returned
+ /// `Ok(None)` is normally unspecified. The iterator returned by this method
+ /// guarantees that `Ok(None)` will always be returned.
+ #[inline]
+ fn fuse(self) -> Fuse<Self>
+ where
+ Self: Sized,
+ {
+ Fuse {
+ it: self,
+ done: false,
+ }
+ }
+
+ /// Returns an iterator which passes each element to a closure before returning it.
+ #[inline]
+ fn inspect<F>(self, f: F) -> Inspect<Self, F>
+ where
+ Self: Sized,
+ F: FnMut(&Self::Item) -> Result<(), Self::Error>,
+ {
+ Inspect { it: self, f }
+ }
+
+ /// Borrow an iterator rather than consuming it.
+ ///
+ /// This is useful to allow the use of iterator adaptors that would
+ /// otherwise consume the value.
+ #[inline]
+ fn by_ref(&mut self) -> &mut Self
+ where
+ Self: Sized,
+ {
+ self
+ }
+
+ /// Transforms the iterator into a collection.
+ ///
+ /// An `Err` will be returned if any invocation of `next` returns `Err`.
+ #[inline]
+ fn collect<T>(self) -> Result<T, Self::Error>
+ where
+ T: FromFallibleIterator<Self::Item>,
+ Self: Sized,
+ {
+ T::from_fallible_iter(self)
+ }
+
+ /// Transforms the iterator into two collections, partitioning elements by a closure.
+ #[inline]
+ fn partition<B, F>(self, mut f: F) -> Result<(B, B), Self::Error>
+ where
+ Self: Sized,
+ B: Default + Extend<Self::Item>,
+ F: FnMut(&Self::Item) -> Result<bool, Self::Error>,
+ {
+ let mut a = B::default();
+ let mut b = B::default();
+
+ self.for_each(|i| {
+ if f(&i)? {
+ a.extend(Some(i));
+ } else {
+ b.extend(Some(i));
+ }
+ Ok(())
+ })?;
+
+ Ok((a, b))
+ }
+
+ /// Applies a function over the elements of the iterator, producing a single
+ /// final value.
+ #[inline]
+ fn fold<B, F>(mut self, init: B, f: F) -> Result<B, Self::Error>
+ where
+ Self: Sized,
+ F: FnMut(B, Self::Item) -> Result<B, Self::Error>,
+ {
+ self.try_fold(init, f)
+ }
+
+ /// Applies a function over the elements of the iterator, producing a single final value.
+ ///
+ /// This is used as the "base" of many methods on `FallibleIterator`.
+ #[inline]
+ fn try_fold<B, E, F>(&mut self, mut init: B, mut f: F) -> Result<B, E>
+ where
+ Self: Sized,
+ E: From<Self::Error>,
+ F: FnMut(B, Self::Item) -> Result<B, E>,
+ {
+ while let Some(v) = self.next()? {
+ init = f(init, v)?;
+ }
+ Ok(init)
+ }
+
+ /// Determines if all elements of this iterator match a predicate.
+ #[inline]
+ fn all<F>(&mut self, mut f: F) -> Result<bool, Self::Error>
+ where
+ Self: Sized,
+ F: FnMut(Self::Item) -> Result<bool, Self::Error>,
+ {
+ self.try_fold((), |(), v| {
+ if !f(v)? {
+ return Err(FoldStop::Break(false));
+ }
+ Ok(())
+ })
+ .map(|()| true)
+ .unpack_fold()
+ }
+
+ /// Determines if any element of this iterator matches a predicate.
+ #[inline]
+ fn any<F>(&mut self, mut f: F) -> Result<bool, Self::Error>
+ where
+ Self: Sized,
+ F: FnMut(Self::Item) -> Result<bool, Self::Error>,
+ {
+ self.try_fold((), |(), v| {
+ if f(v)? {
+ return Err(FoldStop::Break(true));
+ }
+ Ok(())
+ })
+ .map(|()| false)
+ .unpack_fold()
+ }
+
+ /// Returns the first element of the iterator that matches a predicate.
+ #[inline]
+ fn find<F>(&mut self, mut f: F) -> Result<Option<Self::Item>, Self::Error>
+ where
+ Self: Sized,
+ F: FnMut(&Self::Item) -> Result<bool, Self::Error>,
+ {
+ self.try_fold((), |(), v| {
+ if f(&v)? {
+ return Err(FoldStop::Break(Some(v)));
+ }
+ Ok(())
+ })
+ .map(|()| None)
+ .unpack_fold()
+ }
+
+ /// Applies a function to the elements of the iterator, returning the first non-`None` result.
+ #[inline]
+ fn find_map<B, F>(&mut self, f: F) -> Result<Option<B>, Self::Error>
+ where
+ Self: Sized,
+ F: FnMut(Self::Item) -> Result<Option<B>, Self::Error>,
+ {
+ self.filter_map(f).next()
+ }
+
+ /// Returns the position of the first element of this iterator that matches
+ /// a predicate. The predicate may fail; such failures are returned to the
+ /// caller.
+ #[inline]
+ fn position<F>(&mut self, mut f: F) -> Result<Option<usize>, Self::Error>
+ where
+ Self: Sized,
+ F: FnMut(Self::Item) -> Result<bool, Self::Error>,
+ {
+ self.try_fold(0, |n, v| {
+ if f(v)? {
+ return Err(FoldStop::Break(Some(n)));
+ }
+ Ok(n + 1)
+ })
+ .map(|_| None)
+ .unpack_fold()
+ }
+
+ /// Returns the maximal element of the iterator.
+ #[inline]
+ fn max(self) -> Result<Option<Self::Item>, Self::Error>
+ where
+ Self: Sized,
+ Self::Item: Ord,
+ {
+ self.max_by(|a, b| Ok(a.cmp(b)))
+ }
+
+ /// Returns the element of the iterator which gives the maximum value from
+ /// the function.
+ #[inline]
+ fn max_by_key<B, F>(mut self, mut f: F) -> Result<Option<Self::Item>, Self::Error>
+ where
+ Self: Sized,
+ B: Ord,
+ F: FnMut(&Self::Item) -> Result<B, Self::Error>,
+ {
+ let max = match self.next()? {
+ Some(v) => (f(&v)?, v),
+ None => return Ok(None),
+ };
+
+ self.fold(max, |(key, max), v| {
+ let new_key = f(&v)?;
+ if key > new_key {
+ Ok((key, max))
+ } else {
+ Ok((new_key, v))
+ }
+ })
+ .map(|v| Some(v.1))
+ }
+
+ /// Returns the element that gives the maximum value with respect to the function.
+ #[inline]
+ fn max_by<F>(mut self, mut f: F) -> Result<Option<Self::Item>, Self::Error>
+ where
+ Self: Sized,
+ F: FnMut(&Self::Item, &Self::Item) -> Result<Ordering, Self::Error>,
+ {
+ let max = match self.next()? {
+ Some(v) => v,
+ None => return Ok(None),
+ };
+
+ self.fold(max, |max, v| {
+ if f(&max, &v)? == Ordering::Greater {
+ Ok(max)
+ } else {
+ Ok(v)
+ }
+ })
+ .map(Some)
+ }
+
+ /// Returns the minimal element of the iterator.
+ #[inline]
+ fn min(self) -> Result<Option<Self::Item>, Self::Error>
+ where
+ Self: Sized,
+ Self::Item: Ord,
+ {
+ self.min_by(|a, b| Ok(a.cmp(b)))
+ }
+
+ /// Returns the element of the iterator which gives the minimum value from
+ /// the function.
+ #[inline]
+ fn min_by_key<B, F>(mut self, mut f: F) -> Result<Option<Self::Item>, Self::Error>
+ where
+ Self: Sized,
+ B: Ord,
+ F: FnMut(&Self::Item) -> Result<B, Self::Error>,
+ {
+ let min = match self.next()? {
+ Some(v) => (f(&v)?, v),
+ None => return Ok(None),
+ };
+
+ self.fold(min, |(key, min), v| {
+ let new_key = f(&v)?;
+ if key < new_key {
+ Ok((key, min))
+ } else {
+ Ok((new_key, v))
+ }
+ })
+ .map(|v| Some(v.1))
+ }
+
+ /// Returns the element that gives the minimum value with respect to the function.
+ #[inline]
+ fn min_by<F>(mut self, mut f: F) -> Result<Option<Self::Item>, Self::Error>
+ where
+ Self: Sized,
+ F: FnMut(&Self::Item, &Self::Item) -> Result<Ordering, Self::Error>,
+ {
+ let min = match self.next()? {
+ Some(v) => v,
+ None => return Ok(None),
+ };
+
+ self.fold(min, |min, v| {
+ if f(&min, &v)? == Ordering::Less {
+ Ok(min)
+ } else {
+ Ok(v)
+ }
+ })
+ .map(Some)
+ }
+
+ /// Returns an iterator that yields this iterator's items in the opposite
+ /// order.
+ #[inline]
+ fn rev(self) -> Rev<Self>
+ where
+ Self: Sized + DoubleEndedFallibleIterator,
+ {
+ Rev(self)
+ }
+
+ /// Converts an iterator of pairs into a pair of containers.
+ #[inline]
+ fn unzip<A, B, FromA, FromB>(self) -> Result<(FromA, FromB), Self::Error>
+ where
+ Self: Sized + FallibleIterator<Item = (A, B)>,
+ FromA: Default + Extend<A>,
+ FromB: Default + Extend<B>,
+ {
+ let mut from_a = FromA::default();
+ let mut from_b = FromB::default();
+
+ self.for_each(|(a, b)| {
+ from_a.extend(Some(a));
+ from_b.extend(Some(b));
+ Ok(())
+ })?;
+
+ Ok((from_a, from_b))
+ }
+
+ /// Returns an iterator which clones all of its elements.
+ #[inline]
+ fn cloned<'a, T>(self) -> Cloned<Self>
+ where
+ Self: Sized + FallibleIterator<Item = &'a T>,
+ T: 'a + Clone,
+ {
+ Cloned(self)
+ }
+
+ /// Returns an iterator which repeas this iterator endlessly.
+ #[inline]
+ fn cycle(self) -> Cycle<Self>
+ where
+ Self: Sized + Clone,
+ {
+ Cycle {
+ it: self.clone(),
+ cur: self,
+ }
+ }
+
+ /// Lexicographically compares the elements of this iterator to that of
+ /// another.
+ #[inline]
+ fn cmp<I>(mut self, other: I) -> Result<Ordering, Self::Error>
+ where
+ Self: Sized,
+ I: IntoFallibleIterator<Item = Self::Item, Error = Self::Error>,
+ Self::Item: Ord,
+ {
+ let mut other = other.into_fallible_iter();
+
+ loop {
+ match (self.next()?, other.next()?) {
+ (None, None) => return Ok(Ordering::Equal),
+ (None, _) => return Ok(Ordering::Less),
+ (_, None) => return Ok(Ordering::Greater),
+ (Some(x), Some(y)) => match x.cmp(&y) {
+ Ordering::Equal => {}
+ o => return Ok(o),
+ },
+ }
+ }
+ }
+
+ /// Lexicographically compares the elements of this iterator to that of
+ /// another.
+ #[inline]
+ fn partial_cmp<I>(mut self, other: I) -> Result<Option<Ordering>, Self::Error>
+ where
+ Self: Sized,
+ I: IntoFallibleIterator<Error = Self::Error>,
+ Self::Item: PartialOrd<I::Item>,
+ {
+ let mut other = other.into_fallible_iter();
+
+ loop {
+ match (self.next()?, other.next()?) {
+ (None, None) => return Ok(Some(Ordering::Equal)),
+ (None, _) => return Ok(Some(Ordering::Less)),
+ (_, None) => return Ok(Some(Ordering::Greater)),
+ (Some(x), Some(y)) => match x.partial_cmp(&y) {
+ Some(Ordering::Equal) => {}
+ o => return Ok(o),
+ },
+ }
+ }
+ }
+
+ /// Determines if the elements of this iterator are equal to those of
+ /// another.
+ #[inline]
+ fn eq<I>(mut self, other: I) -> Result<bool, Self::Error>
+ where
+ Self: Sized,
+ I: IntoFallibleIterator<Error = Self::Error>,
+ Self::Item: PartialEq<I::Item>,
+ {
+ let mut other = other.into_fallible_iter();
+
+ loop {
+ match (self.next()?, other.next()?) {
+ (None, None) => return Ok(true),
+ (None, _) | (_, None) => return Ok(false),
+ (Some(x), Some(y)) => {
+ if x != y {
+ return Ok(false);
+ }
+ }
+ }
+ }
+ }
+
+ /// Determines if the elements of this iterator are not equal to those of
+ /// another.
+ #[inline]
+ fn ne<I>(mut self, other: I) -> Result<bool, Self::Error>
+ where
+ Self: Sized,
+ I: IntoFallibleIterator<Error = Self::Error>,
+ Self::Item: PartialEq<I::Item>,
+ {
+ let mut other = other.into_fallible_iter();
+
+ loop {
+ match (self.next()?, other.next()?) {
+ (None, None) => return Ok(false),
+ (None, _) | (_, None) => return Ok(true),
+ (Some(x), Some(y)) => {
+ if x != y {
+ return Ok(true);
+ }
+ }
+ }
+ }
+ }
+
+ /// Determines if the elements of this iterator are lexicographically less
+ /// than those of another.
+ #[inline]
+ fn lt<I>(mut self, other: I) -> Result<bool, Self::Error>
+ where
+ Self: Sized,
+ I: IntoFallibleIterator<Error = Self::Error>,
+ Self::Item: PartialOrd<I::Item>,
+ {
+ let mut other = other.into_fallible_iter();
+
+ loop {
+ match (self.next()?, other.next()?) {
+ (None, None) => return Ok(false),
+ (None, _) => return Ok(true),
+ (_, None) => return Ok(false),
+ (Some(x), Some(y)) => match x.partial_cmp(&y) {
+ Some(Ordering::Less) => return Ok(true),
+ Some(Ordering::Equal) => {}
+ Some(Ordering::Greater) => return Ok(false),
+ None => return Ok(false),
+ },
+ }
+ }
+ }
+
+ /// Determines if the elements of this iterator are lexicographically less
+ /// than or equal to those of another.
+ #[inline]
+ fn le<I>(mut self, other: I) -> Result<bool, Self::Error>
+ where
+ Self: Sized,
+ I: IntoFallibleIterator<Error = Self::Error>,
+ Self::Item: PartialOrd<I::Item>,
+ {
+ let mut other = other.into_fallible_iter();
+
+ loop {
+ match (self.next()?, other.next()?) {
+ (None, None) => return Ok(true),
+ (None, _) => return Ok(true),
+ (_, None) => return Ok(false),
+ (Some(x), Some(y)) => match x.partial_cmp(&y) {
+ Some(Ordering::Less) => return Ok(true),
+ Some(Ordering::Equal) => {}
+ Some(Ordering::Greater) => return Ok(false),
+ None => return Ok(false),
+ },
+ }
+ }
+ }
+
+ /// Determines if the elements of this iterator are lexicographically
+ /// greater than those of another.
+ #[inline]
+ fn gt<I>(mut self, other: I) -> Result<bool, Self::Error>
+ where
+ Self: Sized,
+ I: IntoFallibleIterator<Error = Self::Error>,
+ Self::Item: PartialOrd<I::Item>,
+ {
+ let mut other = other.into_fallible_iter();
+
+ loop {
+ match (self.next()?, other.next()?) {
+ (None, None) => return Ok(false),
+ (None, _) => return Ok(false),
+ (_, None) => return Ok(true),
+ (Some(x), Some(y)) => match x.partial_cmp(&y) {
+ Some(Ordering::Less) => return Ok(false),
+ Some(Ordering::Equal) => {}
+ Some(Ordering::Greater) => return Ok(true),
+ None => return Ok(false),
+ },
+ }
+ }
+ }
+
+ /// Determines if the elements of this iterator are lexicographically
+ /// greater than or equal to those of another.
+ #[inline]
+ fn ge<I>(mut self, other: I) -> Result<bool, Self::Error>
+ where
+ Self: Sized,
+ I: IntoFallibleIterator<Error = Self::Error>,
+ Self::Item: PartialOrd<I::Item>,
+ {
+ let mut other = other.into_fallible_iter();
+
+ loop {
+ match (self.next()?, other.next()?) {
+ (None, None) => return Ok(true),
+ (None, _) => return Ok(false),
+ (_, None) => return Ok(true),
+ (Some(x), Some(y)) => match x.partial_cmp(&y) {
+ Some(Ordering::Less) => return Ok(false),
+ Some(Ordering::Equal) => {}
+ Some(Ordering::Greater) => return Ok(true),
+ None => return Ok(false),
+ },
+ }
+ }
+ }
+
+ /// Returns a normal (non-fallible) iterator over `Result<Item, Error>`.
+ #[inline]
+ fn iterator(self) -> Iterator<Self>
+ where
+ Self: Sized,
+ {
+ Iterator(self)
+ }
+
+ /// Returns an iterator which applies a transform to the errors of the
+ /// underlying iterator.
+ #[inline]
+ fn map_err<B, F>(self, f: F) -> MapErr<Self, F>
+ where
+ F: FnMut(Self::Error) -> B,
+ Self: Sized,
+ {
+ MapErr { it: self, f: f }
+ }
+}
+
+impl<I: FallibleIterator + ?Sized> FallibleIterator for &mut I {
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
+ (**self).next()
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ (**self).size_hint()
+ }
+
+ #[inline]
+ fn nth(&mut self, n: usize) -> Result<Option<I::Item>, I::Error> {
+ (**self).nth(n)
+ }
+}
+
+impl<I: DoubleEndedFallibleIterator + ?Sized> DoubleEndedFallibleIterator for &mut I {
+ #[inline]
+ fn next_back(&mut self) -> Result<Option<I::Item>, I::Error> {
+ (**self).next_back()
+ }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<I: FallibleIterator + ?Sized> FallibleIterator for Box<I> {
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
+ (**self).next()
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ (**self).size_hint()
+ }
+
+ #[inline]
+ fn nth(&mut self, n: usize) -> Result<Option<I::Item>, I::Error> {
+ (**self).nth(n)
+ }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<I: DoubleEndedFallibleIterator + ?Sized> DoubleEndedFallibleIterator for Box<I> {
+ #[inline]
+ fn next_back(&mut self) -> Result<Option<I::Item>, I::Error> {
+ (**self).next_back()
+ }
+}
+
+/// A fallible iterator able to yield elements from both ends.
+pub trait DoubleEndedFallibleIterator: FallibleIterator {
+ /// Advances the end of the iterator, returning the last value.
+ fn next_back(&mut self) -> Result<Option<Self::Item>, Self::Error>;
+
+ /// Applies a function over the elements of the iterator in reverse order, producing a single final value.
+ #[inline]
+ fn rfold<B, F>(mut self, init: B, f: F) -> Result<B, Self::Error>
+ where
+ Self: Sized,
+ F: FnMut(B, Self::Item) -> Result<B, Self::Error>,
+ {
+ self.try_rfold(init, f)
+ }
+
+ /// Applies a function over the elements of the iterator in reverse, producing a single final value.
+ ///
+ /// This is used as the "base" of many methods on `DoubleEndedFallibleIterator`.
+ #[inline]
+ fn try_rfold<B, E, F>(&mut self, mut init: B, mut f: F) -> Result<B, E>
+ where
+ Self: Sized,
+ E: From<Self::Error>,
+ F: FnMut(B, Self::Item) -> Result<B, E>,
+ {
+ while let Some(v) = self.next_back()? {
+ init = f(init, v)?;
+ }
+ Ok(init)
+ }
+}
+
+/// Conversion from a fallible iterator.
+pub trait FromFallibleIterator<T>: Sized {
+ /// Creates a value from a fallible iterator.
+ fn from_fallible_iter<I>(it: I) -> Result<Self, I::Error>
+ where
+ I: IntoFallibleIterator<Item = T>;
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<T> FromFallibleIterator<T> for Vec<T> {
+ #[inline]
+ fn from_fallible_iter<I>(it: I) -> Result<Vec<T>, I::Error>
+ where
+ I: IntoFallibleIterator<Item = T>,
+ {
+ let it = it.into_fallible_iter();
+ let mut vec = Vec::with_capacity(it.size_hint().0);
+ it.for_each(|v| Ok(vec.push(v)))?;
+ Ok(vec)
+ }
+}
+
+#[cfg(feature = "std")]
+impl<T, S> FromFallibleIterator<T> for HashSet<T, S>
+where
+ T: Hash + Eq,
+ S: BuildHasher + Default,
+{
+ #[inline]
+ fn from_fallible_iter<I>(it: I) -> Result<HashSet<T, S>, I::Error>
+ where
+ I: IntoFallibleIterator<Item = T>,
+ {
+ let it = it.into_fallible_iter();
+ let mut set = HashSet::default();
+ set.reserve(it.size_hint().0);
+ it.for_each(|v| {
+ set.insert(v);
+ Ok(())
+ })?;
+ Ok(set)
+ }
+}
+
+#[cfg(feature = "std")]
+impl<K, V, S> FromFallibleIterator<(K, V)> for HashMap<K, V, S>
+where
+ K: Hash + Eq,
+ S: BuildHasher + Default,
+{
+ #[inline]
+ fn from_fallible_iter<I>(it: I) -> Result<HashMap<K, V, S>, I::Error>
+ where
+ I: IntoFallibleIterator<Item = (K, V)>,
+ {
+ let it = it.into_fallible_iter();
+ let mut map = HashMap::default();
+ map.reserve(it.size_hint().0);
+ it.for_each(|(k, v)| {
+ map.insert(k, v);
+ Ok(())
+ })?;
+ Ok(map)
+ }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<T> FromFallibleIterator<T> for BTreeSet<T>
+where
+ T: Ord,
+{
+ #[inline]
+ fn from_fallible_iter<I>(it: I) -> Result<BTreeSet<T>, I::Error>
+ where
+ I: IntoFallibleIterator<Item = T>,
+ {
+ let it = it.into_fallible_iter();
+ let mut set = BTreeSet::new();
+ it.for_each(|v| {
+ set.insert(v);
+ Ok(())
+ })?;
+ Ok(set)
+ }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl<K, V> FromFallibleIterator<(K, V)> for BTreeMap<K, V>
+where
+ K: Ord,
+{
+ #[inline]
+ fn from_fallible_iter<I>(it: I) -> Result<BTreeMap<K, V>, I::Error>
+ where
+ I: IntoFallibleIterator<Item = (K, V)>,
+ {
+ let it = it.into_fallible_iter();
+ let mut map = BTreeMap::new();
+ it.for_each(|(k, v)| {
+ map.insert(k, v);
+ Ok(())
+ })?;
+ Ok(map)
+ }
+}
+
+/// Conversion into a `FallibleIterator`.
+pub trait IntoFallibleIterator {
+ /// The elements of the iterator.
+ type Item;
+
+ /// The error value of the iterator.
+ type Error;
+
+ /// The iterator.
+ type IntoFallibleIter: FallibleIterator<Item = Self::Item, Error = Self::Error>;
+
+ /// Creates a fallible iterator from a value.
+ fn into_fallible_iter(self) -> Self::IntoFallibleIter;
+}
+
+impl<I> IntoFallibleIterator for I
+where
+ I: FallibleIterator,
+{
+ type Item = I::Item;
+ type Error = I::Error;
+ type IntoFallibleIter = I;
+
+ #[inline]
+ fn into_fallible_iter(self) -> I {
+ self
+ }
+}
+
+/// An iterator which applies a fallible transform to the elements of the
+/// underlying iterator.
+#[derive(Clone, Debug)]
+pub struct Map<T, F> {
+ it: T,
+ f: F,
+}
+
+impl<T, F, B> FallibleIterator for Map<T, F>
+where
+ T: FallibleIterator,
+ F: FnMut(T::Item) -> Result<B, T::Error>,
+{
+ type Item = B;
+ type Error = T::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<B>, T::Error> {
+ match self.it.next() {
+ Ok(Some(v)) => Ok(Some((self.f)(v)?)),
+ Ok(None) => Ok(None),
+ Err(e) => Err(e),
+ }
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ self.it.size_hint()
+ }
+
+ #[inline]
+ fn try_fold<C, E, G>(&mut self, init: C, mut f: G) -> Result<C, E>
+ where
+ E: From<T::Error>,
+ G: FnMut(C, B) -> Result<C, E>,
+ {
+ let map = &mut self.f;
+ self.it.try_fold(init, |b, v| f(b, map(v)?))
+ }
+}
+
+impl<B, F, I> DoubleEndedFallibleIterator for Map<I, F>
+where
+ I: DoubleEndedFallibleIterator,
+ F: FnMut(I::Item) -> Result<B, I::Error>,
+{
+ #[inline]
+ fn next_back(&mut self) -> Result<Option<B>, I::Error> {
+ match self.it.next_back() {
+ Ok(Some(v)) => Ok(Some((self.f)(v)?)),
+ Ok(None) => Ok(None),
+ Err(e) => Err(e),
+ }
+ }
+
+ #[inline]
+ fn try_rfold<C, E, G>(&mut self, init: C, mut f: G) -> Result<C, E>
+ where
+ E: From<I::Error>,
+ G: FnMut(C, B) -> Result<C, E>,
+ {
+ let map = &mut self.f;
+ self.it.try_rfold(init, |acc, v| f(acc, map(v)?))
+ }
+}
+
+#[derive(Clone, Debug)]
+enum ChainState {
+ Both,
+ Front,
+ Back,
+}
+
+/// An iterator which yields the elements of one iterator followed by another.
+#[derive(Clone, Debug)]
+pub struct Chain<T, U> {
+ front: T,
+ back: U,
+ state: ChainState,
+}
+
+impl<T, U> FallibleIterator for Chain<T, U>
+where
+ T: FallibleIterator,
+ U: FallibleIterator<Item = T::Item, Error = T::Error>,
+{
+ type Item = T::Item;
+ type Error = T::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<T::Item>, T::Error> {
+ match self.state {
+ ChainState::Both => match self.front.next()? {
+ Some(e) => Ok(Some(e)),
+ None => {
+ self.state = ChainState::Back;
+ self.back.next()
+ }
+ },
+ ChainState::Front => self.front.next(),
+ ChainState::Back => self.back.next(),
+ }
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ let front_hint = self.front.size_hint();
+ let back_hint = self.back.size_hint();
+
+ let low = front_hint.0.saturating_add(back_hint.0);
+ let high = match (front_hint.1, back_hint.1) {
+ (Some(f), Some(b)) => f.checked_add(b),
+ _ => None,
+ };
+
+ (low, high)
+ }
+
+ #[inline]
+ fn count(self) -> Result<usize, T::Error> {
+ match self.state {
+ ChainState::Both => Ok(self.front.count()? + self.back.count()?),
+ ChainState::Front => self.front.count(),
+ ChainState::Back => self.back.count(),
+ }
+ }
+
+ #[inline]
+ fn try_fold<B, E, F>(&mut self, init: B, mut f: F) -> Result<B, E>
+ where
+ E: From<T::Error>,
+ F: FnMut(B, T::Item) -> Result<B, E>,
+ {
+ match self.state {
+ ChainState::Both => {
+ let init = self.front.try_fold(init, &mut f)?;
+ self.state = ChainState::Back;
+ self.back.try_fold(init, f)
+ }
+ ChainState::Front => self.front.try_fold(init, f),
+ ChainState::Back => self.back.try_fold(init, f),
+ }
+ }
+
+ #[inline]
+ fn find<F>(&mut self, mut f: F) -> Result<Option<T::Item>, T::Error>
+ where
+ F: FnMut(&T::Item) -> Result<bool, T::Error>,
+ {
+ match self.state {
+ ChainState::Both => match self.front.find(&mut f)? {
+ Some(v) => Ok(Some(v)),
+ None => {
+ self.state = ChainState::Back;
+ self.back.find(f)
+ }
+ },
+ ChainState::Front => self.front.find(f),
+ ChainState::Back => self.back.find(f),
+ }
+ }
+
+ #[inline]
+ fn last(self) -> Result<Option<T::Item>, T::Error> {
+ match self.state {
+ ChainState::Both => {
+ self.front.last()?;
+ self.back.last()
+ }
+ ChainState::Front => self.front.last(),
+ ChainState::Back => self.back.last(),
+ }
+ }
+}
+
+impl<T, U> DoubleEndedFallibleIterator for Chain<T, U>
+where
+ T: DoubleEndedFallibleIterator,
+ U: DoubleEndedFallibleIterator<Item = T::Item, Error = T::Error>,
+{
+ #[inline]
+ fn next_back(&mut self) -> Result<Option<T::Item>, T::Error> {
+ match self.state {
+ ChainState::Both => match self.back.next_back()? {
+ Some(e) => Ok(Some(e)),
+ None => {
+ self.state = ChainState::Front;
+ self.front.next_back()
+ }
+ },
+ ChainState::Front => self.front.next_back(),
+ ChainState::Back => self.back.next_back(),
+ }
+ }
+
+ #[inline]
+ fn try_rfold<B, E, F>(&mut self, init: B, mut f: F) -> Result<B, E>
+ where
+ E: From<T::Error>,
+ F: FnMut(B, T::Item) -> Result<B, E>,
+ {
+ match self.state {
+ ChainState::Both => {
+ let init = self.back.try_rfold(init, &mut f)?;
+ self.state = ChainState::Front;
+ self.front.try_rfold(init, f)
+ }
+ ChainState::Front => self.front.try_rfold(init, f),
+ ChainState::Back => self.back.try_rfold(init, f),
+ }
+ }
+}
+
+/// An iterator which clones the elements of the underlying iterator.
+#[derive(Clone, Debug)]
+pub struct Cloned<I>(I);
+
+impl<'a, T, I> FallibleIterator for Cloned<I>
+where
+ I: FallibleIterator<Item = &'a T>,
+ T: 'a + Clone,
+{
+ type Item = T;
+ type Error = I::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<T>, I::Error> {
+ self.0.next().map(|o| o.cloned())
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ self.0.size_hint()
+ }
+
+ #[inline]
+ fn try_fold<B, E, F>(&mut self, init: B, mut f: F) -> Result<B, E>
+ where
+ E: From<I::Error>,
+ F: FnMut(B, T) -> Result<B, E>,
+ {
+ self.0.try_fold(init, |acc, v| f(acc, v.clone()))
+ }
+}
+
+impl<'a, T, I> DoubleEndedFallibleIterator for Cloned<I>
+where
+ I: DoubleEndedFallibleIterator<Item = &'a T>,
+ T: 'a + Clone,
+{
+ #[inline]
+ fn next_back(&mut self) -> Result<Option<T>, I::Error> {
+ self.0.next_back().map(|o| o.cloned())
+ }
+
+ #[inline]
+ fn try_rfold<B, E, F>(&mut self, init: B, mut f: F) -> Result<B, E>
+ where
+ E: From<I::Error>,
+ F: FnMut(B, T) -> Result<B, E>,
+ {
+ self.0.try_rfold(init, |acc, v| f(acc, v.clone()))
+ }
+}
+
+/// Converts an `Iterator<Item = Result<T, E>>` into a `FallibleIterator<Item = T, Error = E>`.
+#[inline]
+pub fn convert<T, E, I>(it: I) -> Convert<I>
+where
+ I: iter::Iterator<Item = Result<T, E>>,
+{
+ Convert(it)
+}
+
+/// A fallible iterator that wraps a normal iterator over `Result`s.
+#[derive(Clone, Debug)]
+pub struct Convert<I>(I);
+
+impl<T, E, I> FallibleIterator for Convert<I>
+where
+ I: iter::Iterator<Item = Result<T, E>>,
+{
+ type Item = T;
+ type Error = E;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<T>, E> {
+ match self.0.next() {
+ Some(Ok(i)) => Ok(Some(i)),
+ Some(Err(e)) => Err(e),
+ None => Ok(None),
+ }
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ self.0.size_hint()
+ }
+
+ #[inline]
+ fn try_fold<B, E2, F>(&mut self, init: B, mut f: F) -> Result<B, E2>
+ where
+ E2: From<E>,
+ F: FnMut(B, T) -> Result<B, E2>,
+ {
+ self.0.try_fold(init, |acc, v| f(acc, v?))
+ }
+}
+
+impl<T, E, I> DoubleEndedFallibleIterator for Convert<I>
+where
+ I: DoubleEndedIterator<Item = Result<T, E>>,
+{
+ #[inline]
+ fn next_back(&mut self) -> Result<Option<T>, E> {
+ match self.0.next_back() {
+ Some(Ok(i)) => Ok(Some(i)),
+ Some(Err(e)) => Err(e),
+ None => Ok(None),
+ }
+ }
+
+ #[inline]
+ fn try_rfold<B, E2, F>(&mut self, init: B, mut f: F) -> Result<B, E2>
+ where
+ E2: From<E>,
+ F: FnMut(B, T) -> Result<B, E2>,
+ {
+ self.0.try_rfold(init, |acc, v| f(acc, v?))
+ }
+}
+
+/// An iterator that yields the iteration count as well as the values of the
+/// underlying iterator.
+#[derive(Clone, Debug)]
+pub struct Enumerate<I> {
+ it: I,
+ n: usize,
+}
+
+impl<I> FallibleIterator for Enumerate<I>
+where
+ I: FallibleIterator,
+{
+ type Item = (usize, I::Item);
+ type Error = I::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<(usize, I::Item)>, I::Error> {
+ self.it.next().map(|o| {
+ o.map(|e| {
+ let i = self.n;
+ self.n += 1;
+ (i, e)
+ })
+ })
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ self.it.size_hint()
+ }
+
+ #[inline]
+ fn count(self) -> Result<usize, I::Error> {
+ self.it.count()
+ }
+
+ #[inline]
+ fn nth(&mut self, n: usize) -> Result<Option<(usize, I::Item)>, I::Error> {
+ match self.it.nth(n)? {
+ Some(v) => {
+ let i = self.n + n;
+ self.n = i + 1;
+ Ok(Some((i, v)))
+ }
+ None => Ok(None),
+ }
+ }
+
+ #[inline]
+ fn try_fold<B, E, F>(&mut self, init: B, mut f: F) -> Result<B, E>
+ where
+ E: From<I::Error>,
+ F: FnMut(B, (usize, I::Item)) -> Result<B, E>,
+ {
+ let n = &mut self.n;
+ self.it.try_fold(init, |acc, v| {
+ let i = *n;
+ *n += 1;
+ f(acc, (i, v))
+ })
+ }
+}
+
+/// An iterator which uses a fallible predicate to determine which values of the
+/// underlying iterator should be yielded.
+#[derive(Clone, Debug)]
+pub struct Filter<I, F> {
+ it: I,
+ f: F,
+}
+
+impl<I, F> FallibleIterator for Filter<I, F>
+where
+ I: FallibleIterator,
+ F: FnMut(&I::Item) -> Result<bool, I::Error>,
+{
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
+ let filter = &mut self.f;
+ self.it
+ .try_fold((), |(), v| {
+ if filter(&v)? {
+ return Err(FoldStop::Break(Some(v)));
+ }
+ Ok(())
+ })
+ .map(|()| None)
+ .unpack_fold()
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ (0, self.it.size_hint().1)
+ }
+
+ #[inline]
+ fn try_fold<B, E, G>(&mut self, init: B, mut f: G) -> Result<B, E>
+ where
+ E: From<I::Error>,
+ G: FnMut(B, I::Item) -> Result<B, E>,
+ {
+ let predicate = &mut self.f;
+ self.it.try_fold(
+ init,
+ |acc, v| {
+ if predicate(&v)? {
+ f(acc, v)
+ } else {
+ Ok(acc)
+ }
+ },
+ )
+ }
+}
+
+impl<I, F> DoubleEndedFallibleIterator for Filter<I, F>
+where
+ I: DoubleEndedFallibleIterator,
+ F: FnMut(&I::Item) -> Result<bool, I::Error>,
+{
+ #[inline]
+ fn next_back(&mut self) -> Result<Option<I::Item>, I::Error> {
+ let filter = &mut self.f;
+ self.it
+ .try_rfold((), |(), v| {
+ if filter(&v)? {
+ return Err(FoldStop::Break(Some(v)));
+ }
+ Ok(())
+ })
+ .map(|()| None)
+ .unpack_fold()
+ }
+
+ #[inline]
+ fn try_rfold<B, E, G>(&mut self, init: B, mut f: G) -> Result<B, E>
+ where
+ E: From<I::Error>,
+ G: FnMut(B, I::Item) -> Result<B, E>,
+ {
+ let predicate = &mut self.f;
+ self.it.try_rfold(
+ init,
+ |acc, v| {
+ if predicate(&v)? {
+ f(acc, v)
+ } else {
+ Ok(acc)
+ }
+ },
+ )
+ }
+}
+
+/// An iterator which both filters and maps the values of the underlying
+/// iterator.
+#[derive(Clone, Debug)]
+pub struct FilterMap<I, F> {
+ it: I,
+ f: F,
+}
+
+impl<B, I, F> FallibleIterator for FilterMap<I, F>
+where
+ I: FallibleIterator,
+ F: FnMut(I::Item) -> Result<Option<B>, I::Error>,
+{
+ type Item = B;
+ type Error = I::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<B>, I::Error> {
+ let map = &mut self.f;
+ self.it
+ .try_fold((), |(), v| match map(v)? {
+ Some(v) => Err(FoldStop::Break(Some(v))),
+ None => Ok(()),
+ })
+ .map(|()| None)
+ .unpack_fold()
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ (0, self.it.size_hint().1)
+ }
+
+ #[inline]
+ fn try_fold<C, E, G>(&mut self, init: C, mut f: G) -> Result<C, E>
+ where
+ E: From<I::Error>,
+ G: FnMut(C, B) -> Result<C, E>,
+ {
+ let map = &mut self.f;
+ self.it.try_fold(init, |acc, v| match map(v)? {
+ Some(v) => f(acc, v),
+ None => Ok(acc),
+ })
+ }
+}
+
+impl<B, I, F> DoubleEndedFallibleIterator for FilterMap<I, F>
+where
+ I: DoubleEndedFallibleIterator,
+ F: FnMut(I::Item) -> Result<Option<B>, I::Error>,
+{
+ #[inline]
+ fn next_back(&mut self) -> Result<Option<B>, I::Error> {
+ let map = &mut self.f;
+ self.it
+ .try_rfold((), |(), v| match map(v)? {
+ Some(v) => Err(FoldStop::Break(Some(v))),
+ None => Ok(()),
+ })
+ .map(|()| None)
+ .unpack_fold()
+ }
+
+ #[inline]
+ fn try_rfold<C, E, G>(&mut self, init: C, mut f: G) -> Result<C, E>
+ where
+ E: From<I::Error>,
+ G: FnMut(C, B) -> Result<C, E>,
+ {
+ let map = &mut self.f;
+ self.it.try_rfold(init, |acc, v| match map(v)? {
+ Some(v) => f(acc, v),
+ None => Ok(acc),
+ })
+ }
+}
+
+/// An iterator which maps each element to another iterator, yielding those iterator's elements.
+#[derive(Clone, Debug)]
+pub struct FlatMap<I, U, F>
+where
+ U: IntoFallibleIterator,
+{
+ it: Map<I, F>,
+ cur: Option<U::IntoFallibleIter>,
+}
+
+impl<I, U, F> FallibleIterator for FlatMap<I, U, F>
+where
+ I: FallibleIterator,
+ U: IntoFallibleIterator<Error = I::Error>,
+ F: FnMut(I::Item) -> Result<U, I::Error>,
+{
+ type Item = U::Item;
+ type Error = U::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<U::Item>, U::Error> {
+ loop {
+ if let Some(it) = &mut self.cur {
+ if let Some(v) = it.next()? {
+ return Ok(Some(v));
+ }
+ }
+ match self.it.next()? {
+ Some(it) => self.cur = Some(it.into_fallible_iter()),
+ None => return Ok(None),
+ }
+ }
+ }
+
+ #[inline]
+ fn try_fold<B, E, G>(&mut self, init: B, mut f: G) -> Result<B, E>
+ where
+ E: From<U::Error>,
+ G: FnMut(B, U::Item) -> Result<B, E>,
+ {
+ let mut acc = init;
+ if let Some(cur) = &mut self.cur {
+ acc = cur.try_fold(acc, &mut f)?;
+ self.cur = None;
+ }
+
+ let cur = &mut self.cur;
+ self.it.try_fold(acc, |acc, v| {
+ let mut it = v.into_fallible_iter();
+ match it.try_fold(acc, &mut f) {
+ Ok(acc) => Ok(acc),
+ Err(e) => {
+ *cur = Some(it);
+ Err(e)
+ }
+ }
+ })
+ }
+}
+
+/// An iterator which flattens an iterator of iterators, yielding those iterators' elements.
+pub struct Flatten<I>
+where
+ I: FallibleIterator,
+ I::Item: IntoFallibleIterator,
+{
+ it: I,
+ cur: Option<<I::Item as IntoFallibleIterator>::IntoFallibleIter>,
+}
+
+impl<I> Clone for Flatten<I>
+where
+ I: FallibleIterator + Clone,
+ I::Item: IntoFallibleIterator,
+ <I::Item as IntoFallibleIterator>::IntoFallibleIter: Clone,
+{
+ #[inline]
+ fn clone(&self) -> Flatten<I> {
+ Flatten {
+ it: self.it.clone(),
+ cur: self.cur.clone(),
+ }
+ }
+}
+
+impl<I> FallibleIterator for Flatten<I>
+where
+ I: FallibleIterator,
+ I::Item: IntoFallibleIterator<Error = I::Error>,
+{
+ type Item = <I::Item as IntoFallibleIterator>::Item;
+ type Error = <I::Item as IntoFallibleIterator>::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<Self::Item>, Self::Error> {
+ loop {
+ if let Some(it) = &mut self.cur {
+ if let Some(v) = it.next()? {
+ return Ok(Some(v));
+ }
+ }
+ match self.it.next()? {
+ Some(it) => self.cur = Some(it.into_fallible_iter()),
+ None => return Ok(None),
+ }
+ }
+ }
+
+ #[inline]
+ fn try_fold<B, E, G>(&mut self, init: B, mut f: G) -> Result<B, E>
+ where
+ E: From<Self::Error>,
+ G: FnMut(B, Self::Item) -> Result<B, E>,
+ {
+ let mut acc = init;
+ if let Some(cur) = &mut self.cur {
+ acc = cur.try_fold(acc, &mut f)?;
+ self.cur = None;
+ }
+
+ let cur = &mut self.cur;
+ self.it.try_fold(acc, |acc, v| {
+ let mut it = v.into_fallible_iter();
+ match it.try_fold(acc, &mut f) {
+ Ok(acc) => Ok(acc),
+ Err(e) => {
+ *cur = Some(it);
+ Err(e)
+ }
+ }
+ })
+ }
+}
+
+/// An iterator that yields `Ok(None)` forever after the underlying iterator
+/// yields `Ok(None)` once.
+#[derive(Clone, Debug)]
+pub struct Fuse<I> {
+ it: I,
+ done: bool,
+}
+
+impl<I> FallibleIterator for Fuse<I>
+where
+ I: FallibleIterator,
+{
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
+ if self.done {
+ return Ok(None);
+ }
+
+ match self.it.next()? {
+ Some(i) => Ok(Some(i)),
+ None => {
+ self.done = true;
+ Ok(None)
+ }
+ }
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ if self.done {
+ (0, Some(0))
+ } else {
+ self.it.size_hint()
+ }
+ }
+
+ #[inline]
+ fn count(self) -> Result<usize, I::Error> {
+ if self.done {
+ Ok(0)
+ } else {
+ self.it.count()
+ }
+ }
+
+ #[inline]
+ fn last(self) -> Result<Option<I::Item>, I::Error> {
+ if self.done {
+ Ok(None)
+ } else {
+ self.it.last()
+ }
+ }
+
+ #[inline]
+ fn nth(&mut self, n: usize) -> Result<Option<I::Item>, I::Error> {
+ if self.done {
+ Ok(None)
+ } else {
+ let v = self.it.nth(n)?;
+ if v.is_none() {
+ self.done = true;
+ }
+ Ok(v)
+ }
+ }
+
+ #[inline]
+ fn try_fold<B, E, F>(&mut self, init: B, f: F) -> Result<B, E>
+ where
+ E: From<I::Error>,
+ F: FnMut(B, I::Item) -> Result<B, E>,
+ {
+ if self.done {
+ Ok(init)
+ } else {
+ self.it.try_fold(init, f)
+ }
+ }
+}
+
+/// An iterator which passes each element to a closure before returning it.
+#[derive(Clone, Debug)]
+pub struct Inspect<I, F> {
+ it: I,
+ f: F,
+}
+
+impl<I, F> FallibleIterator for Inspect<I, F>
+where
+ I: FallibleIterator,
+ F: FnMut(&I::Item) -> Result<(), I::Error>,
+{
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
+ match self.it.next()? {
+ Some(i) => {
+ (self.f)(&i)?;
+ Ok(Some(i))
+ }
+ None => Ok(None),
+ }
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ self.it.size_hint()
+ }
+
+ #[inline]
+ fn try_fold<B, E, G>(&mut self, init: B, mut f: G) -> Result<B, E>
+ where
+ E: From<I::Error>,
+ G: FnMut(B, I::Item) -> Result<B, E>,
+ {
+ let inspect = &mut self.f;
+ self.it.try_fold(init, |acc, v| {
+ inspect(&v)?;
+ f(acc, v)
+ })
+ }
+}
+
+impl<I, F> DoubleEndedFallibleIterator for Inspect<I, F>
+where
+ I: DoubleEndedFallibleIterator,
+ F: FnMut(&I::Item) -> Result<(), I::Error>,
+{
+ #[inline]
+ fn next_back(&mut self) -> Result<Option<I::Item>, I::Error> {
+ match self.it.next_back()? {
+ Some(i) => {
+ (self.f)(&i)?;
+ Ok(Some(i))
+ }
+ None => Ok(None),
+ }
+ }
+
+ #[inline]
+ fn try_rfold<B, E, G>(&mut self, init: B, mut f: G) -> Result<B, E>
+ where
+ E: From<I::Error>,
+ G: FnMut(B, I::Item) -> Result<B, E>,
+ {
+ let inspect = &mut self.f;
+ self.it.try_rfold(init, |acc, v| {
+ inspect(&v)?;
+ f(acc, v)
+ })
+ }
+}
+
+/// A normal (non-fallible) iterator which wraps a fallible iterator.
+#[derive(Clone, Debug)]
+pub struct Iterator<I>(I);
+
+impl<I> iter::Iterator for Iterator<I>
+where
+ I: FallibleIterator,
+{
+ type Item = Result<I::Item, I::Error>;
+
+ #[inline]
+ fn next(&mut self) -> Option<Result<I::Item, I::Error>> {
+ match self.0.next() {
+ Ok(Some(v)) => Some(Ok(v)),
+ Ok(None) => None,
+ Err(e) => Some(Err(e)),
+ }
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ self.0.size_hint()
+ }
+}
+
+impl<I> DoubleEndedIterator for Iterator<I>
+where
+ I: DoubleEndedFallibleIterator,
+{
+ #[inline]
+ fn next_back(&mut self) -> Option<Result<I::Item, I::Error>> {
+ match self.0.next_back() {
+ Ok(Some(v)) => Some(Ok(v)),
+ Ok(None) => None,
+ Err(e) => Some(Err(e)),
+ }
+ }
+}
+
+/// An iterator which applies a transform to the errors of the underlying
+/// iterator.
+#[derive(Clone, Debug)]
+pub struct MapErr<I, F> {
+ it: I,
+ f: F,
+}
+
+impl<B, F, I> FallibleIterator for MapErr<I, F>
+where
+ I: FallibleIterator,
+ F: FnMut(I::Error) -> B,
+{
+ type Item = I::Item;
+ type Error = B;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<I::Item>, B> {
+ self.it.next().map_err(&mut self.f)
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ self.it.size_hint()
+ }
+
+ #[inline]
+ fn count(mut self) -> Result<usize, B> {
+ self.it.count().map_err(&mut self.f)
+ }
+
+ #[inline]
+ fn last(mut self) -> Result<Option<I::Item>, B> {
+ self.it.last().map_err(&mut self.f)
+ }
+
+ #[inline]
+ fn nth(&mut self, n: usize) -> Result<Option<I::Item>, B> {
+ self.it.nth(n).map_err(&mut self.f)
+ }
+
+ #[inline]
+ fn try_fold<C, E, G>(&mut self, init: C, mut f: G) -> Result<C, E>
+ where
+ E: From<B>,
+ G: FnMut(C, I::Item) -> Result<C, E>,
+ {
+ self.it
+ .try_fold(init, |acc, v| f(acc, v).map_err(MappedErr::Fold))
+ .map_err(|e| match e {
+ MappedErr::It(e) => (self.f)(e).into(),
+ MappedErr::Fold(e) => e,
+ })
+ }
+}
+
+impl<B, F, I> DoubleEndedFallibleIterator for MapErr<I, F>
+where
+ I: DoubleEndedFallibleIterator,
+ F: FnMut(I::Error) -> B,
+{
+ #[inline]
+ fn next_back(&mut self) -> Result<Option<I::Item>, B> {
+ self.it.next_back().map_err(&mut self.f)
+ }
+
+ #[inline]
+ fn try_rfold<C, E, G>(&mut self, init: C, mut f: G) -> Result<C, E>
+ where
+ E: From<B>,
+ G: FnMut(C, I::Item) -> Result<C, E>,
+ {
+ self.it
+ .try_rfold(init, |acc, v| f(acc, v).map_err(MappedErr::Fold))
+ .map_err(|e| match e {
+ MappedErr::It(e) => (self.f)(e).into(),
+ MappedErr::Fold(e) => e,
+ })
+ }
+}
+
+enum MappedErr<T, U> {
+ It(T),
+ Fold(U),
+}
+
+impl<T, U> From<T> for MappedErr<T, U> {
+ #[inline]
+ fn from(t: T) -> MappedErr<T, U> {
+ MappedErr::It(t)
+ }
+}
+
+/// An iterator which can look at the next element without consuming it.
+#[derive(Clone, Debug)]
+pub struct Peekable<I: FallibleIterator> {
+ it: I,
+ next: Option<I::Item>,
+}
+
+impl<I> Peekable<I>
+where
+ I: FallibleIterator,
+{
+ /// Returns a reference to the next value without advancing the iterator.
+ #[inline]
+ pub fn peek(&mut self) -> Result<Option<&I::Item>, I::Error> {
+ if self.next.is_none() {
+ self.next = self.it.next()?;
+ }
+
+ Ok(self.next.as_ref())
+ }
+}
+
+impl<I> FallibleIterator for Peekable<I>
+where
+ I: FallibleIterator,
+{
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
+ if let Some(next) = self.next.take() {
+ return Ok(Some(next));
+ }
+
+ self.it.next()
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ let mut hint = self.it.size_hint();
+ if self.next.is_some() {
+ hint.0 = hint.0.saturating_add(1);
+ hint.1 = hint.1.and_then(|h| h.checked_add(1));
+ }
+ hint
+ }
+
+ #[inline]
+ fn try_fold<B, E, F>(&mut self, init: B, mut f: F) -> Result<B, E>
+ where
+ E: From<I::Error>,
+ F: FnMut(B, I::Item) -> Result<B, E>,
+ {
+ let mut acc = init;
+ if let Some(v) = self.next.take() {
+ acc = f(acc, v)?;
+ }
+ self.it.try_fold(acc, f)
+ }
+}
+
+/// An iterator which yields elements of the underlying iterator in reverse
+/// order.
+#[derive(Clone, Debug)]
+pub struct Rev<I>(I);
+
+impl<I> FallibleIterator for Rev<I>
+where
+ I: DoubleEndedFallibleIterator,
+{
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
+ self.0.next_back()
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ self.0.size_hint()
+ }
+
+ #[inline]
+ fn count(self) -> Result<usize, I::Error> {
+ self.0.count()
+ }
+
+ #[inline]
+ fn try_fold<B, E, F>(&mut self, init: B, f: F) -> Result<B, E>
+ where
+ E: From<I::Error>,
+ F: FnMut(B, I::Item) -> Result<B, E>,
+ {
+ self.0.try_rfold(init, f)
+ }
+}
+
+impl<I> DoubleEndedFallibleIterator for Rev<I>
+where
+ I: DoubleEndedFallibleIterator,
+{
+ #[inline]
+ fn next_back(&mut self) -> Result<Option<I::Item>, I::Error> {
+ self.0.next()
+ }
+
+ #[inline]
+ fn try_rfold<B, E, F>(&mut self, init: B, f: F) -> Result<B, E>
+ where
+ E: From<I::Error>,
+ F: FnMut(B, I::Item) -> Result<B, E>,
+ {
+ self.0.try_fold(init, f)
+ }
+}
+
+/// An iterator which applies a stateful closure.
+#[derive(Clone, Debug)]
+pub struct Scan<I, St, F> {
+ it: I,
+ f: F,
+ state: St,
+}
+
+impl<B, I, St, F> FallibleIterator for Scan<I, St, F>
+where
+ I: FallibleIterator,
+ F: FnMut(&mut St, I::Item) -> Result<Option<B>, I::Error>,
+{
+ type Item = B;
+ type Error = I::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<B>, I::Error> {
+ match self.it.next()? {
+ Some(v) => (self.f)(&mut self.state, v),
+ None => Ok(None),
+ }
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ let hint = self.it.size_hint();
+ (0, hint.1)
+ }
+}
+
+/// An iterator which skips initial elements.
+#[derive(Clone, Debug)]
+pub struct Skip<I> {
+ it: I,
+ n: usize,
+}
+
+impl<I> FallibleIterator for Skip<I>
+where
+ I: FallibleIterator,
+{
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
+ if self.n == 0 {
+ self.it.next()
+ } else {
+ let n = self.n;
+ self.n = 0;
+ self.it.nth(n)
+ }
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ let hint = self.it.size_hint();
+
+ (
+ hint.0.saturating_sub(self.n),
+ hint.1.map(|x| x.saturating_sub(self.n)),
+ )
+ }
+}
+
+/// An iterator which skips initial elements based on a predicate.
+#[derive(Clone, Debug)]
+pub struct SkipWhile<I, P> {
+ it: I,
+ flag: bool,
+ predicate: P,
+}
+
+impl<I, P> FallibleIterator for SkipWhile<I, P>
+where
+ I: FallibleIterator,
+ P: FnMut(&I::Item) -> Result<bool, I::Error>,
+{
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
+ let flag = &mut self.flag;
+ let pred = &mut self.predicate;
+ self.it.find(move |x| {
+ if *flag || !pred(x)? {
+ *flag = true;
+ Ok(true)
+ } else {
+ Ok(false)
+ }
+ })
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ let hint = self.it.size_hint();
+ if self.flag {
+ hint
+ } else {
+ (0, hint.1)
+ }
+ }
+}
+
+/// An iterator which steps through the elements of the underlying iterator by a certain amount.
+#[derive(Clone, Debug)]
+pub struct StepBy<I> {
+ it: I,
+ step: usize,
+ first_take: bool,
+}
+
+impl<I> FallibleIterator for StepBy<I>
+where
+ I: FallibleIterator,
+{
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
+ if self.first_take {
+ self.first_take = false;
+ self.it.next()
+ } else {
+ self.it.nth(self.step)
+ }
+ }
+
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ let inner_hint = self.it.size_hint();
+
+ if self.first_take {
+ let f = |n| {
+ if n == 0 {
+ 0
+ } else {
+ 1 + (n - 1) / (self.step + 1)
+ }
+ };
+ (f(inner_hint.0), inner_hint.1.map(f))
+ } else {
+ let f = |n| n / (self.step + 1);
+ (f(inner_hint.0), inner_hint.1.map(f))
+ }
+ }
+}
+
+/// An iterator which yields a limited number of elements from the underlying
+/// iterator.
+#[derive(Clone, Debug)]
+pub struct Take<I> {
+ it: I,
+ remaining: usize,
+}
+
+impl<I> FallibleIterator for Take<I>
+where
+ I: FallibleIterator,
+{
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
+ if self.remaining == 0 {
+ return Ok(None);
+ }
+
+ let next = self.it.next();
+ if let Ok(Some(_)) = next {
+ self.remaining -= 1;
+ }
+ next
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ let hint = self.it.size_hint();
+ (
+ cmp::min(hint.0, self.remaining),
+ hint.1.map(|n| cmp::min(n, self.remaining)),
+ )
+ }
+}
+
+/// An iterator which yields elements based on a predicate.
+#[derive(Clone, Debug)]
+pub struct TakeWhile<I, P> {
+ it: I,
+ flag: bool,
+ predicate: P,
+}
+
+impl<I, P> FallibleIterator for TakeWhile<I, P>
+where
+ I: FallibleIterator,
+ P: FnMut(&I::Item) -> Result<bool, I::Error>,
+{
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
+ if self.flag {
+ Ok(None)
+ } else {
+ match self.it.next()? {
+ Some(item) => {
+ if (self.predicate)(&item)? {
+ Ok(Some(item))
+ } else {
+ self.flag = true;
+ Ok(None)
+ }
+ }
+ None => Ok(None),
+ }
+ }
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ if self.flag {
+ (0, Some(0))
+ } else {
+ let hint = self.it.size_hint();
+ (0, hint.1)
+ }
+ }
+}
+
+/// An iterator which cycles another endlessly.
+#[derive(Clone, Debug)]
+pub struct Cycle<I> {
+ it: I,
+ cur: I,
+}
+
+impl<I> FallibleIterator for Cycle<I>
+where
+ I: FallibleIterator + Clone,
+{
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<I::Item>, I::Error> {
+ match self.cur.next()? {
+ None => {
+ self.cur = self.it.clone();
+ self.cur.next()
+ }
+ Some(v) => Ok(Some(v)),
+ }
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ (usize::max_value(), None)
+ }
+}
+
+/// An iterator that yields pairs of this iterator's and another iterator's
+/// values.
+#[derive(Clone, Debug)]
+pub struct Zip<T, U>(T, U);
+
+impl<T, U> FallibleIterator for Zip<T, U>
+where
+ T: FallibleIterator,
+ U: FallibleIterator<Error = T::Error>,
+{
+ type Item = (T::Item, U::Item);
+ type Error = T::Error;
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<(T::Item, U::Item)>, T::Error> {
+ match (self.0.next()?, self.1.next()?) {
+ (Some(a), Some(b)) => Ok(Some((a, b))),
+ _ => Ok(None),
+ }
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ let a = self.0.size_hint();
+ let b = self.1.size_hint();
+
+ let low = cmp::min(a.0, b.0);
+
+ let high = match (a.1, b.1) {
+ (Some(a), Some(b)) => Some(cmp::min(a, b)),
+ (Some(a), None) => Some(a),
+ (None, Some(b)) => Some(b),
+ (None, None) => None,
+ };
+
+ (low, high)
+ }
+}
+
+fn _is_object_safe(_: &dyn DoubleEndedFallibleIterator<Item = (), Error = ()>) {}
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-03 21:36:26 +0000