--- /dev/null
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+
--- /dev/null
+//! Fallible, streaming iteration.
+//!
+//! `FallibleStreamingIterator` differs from the standard library's `Iterator` trait in two ways:
+//! iteration can fail, resulting in an error, and only one element of the iteration is available at
+//! any time.
+//!
+//! While these iterators cannot be used with Rust `for` loops, `while let` loops offer a similar
+//! level of ergonomics:
+//!
+//! ```ignore
+//! while let Some(value) = it.next()? {
+//! // use value
+//! }
+//! ```
+#![doc(html_root_url = "https://docs.rs/fallible-streaming-iterator/0.1")]
+#![warn(missing_docs)]
+#![cfg_attr(not(feature = "std"), no_std)]
+
+#[cfg(feature = "std")]
+extern crate core;
+
+use core::cmp;
+use core::marker::PhantomData;
+
+/// A fallible, streaming iterator.
+pub trait FallibleStreamingIterator {
+ /// The type being iterated over.
+ type Item: ?Sized;
+
+ /// The error type of iteration.
+ type Error;
+
+ /// Advances the iterator to the next position.
+ ///
+ /// Iterators start just before the first item, so this method should be called before `get`
+ /// when iterating.
+ ///
+ /// The behavior of calling this method after `get` has returned `None`, or after this method
+ /// has returned an error is unspecified.
+ fn advance(&mut self) -> Result<(), Self::Error>;
+
+ /// Returns the current element.
+ ///
+ /// The behavior of calling this method before any calls to `advance` is unspecified.
+ fn get(&self) -> Option<&Self::Item>;
+
+ /// Advances the iterator, returning the next element.
+ ///
+ /// The default implementation simply calls `advance` followed by `get`.
+ #[inline]
+ fn next(&mut self) -> Result<Option<&Self::Item>, Self::Error> {
+ self.advance()?;
+ Ok((*self).get())
+ }
+
+ /// Returns bounds on the number of remaining elements in the iterator.
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ (0, None)
+ }
+
+ /// Determines if all elements of the iterator satisfy a predicate.
+ #[inline]
+ fn all<F>(&mut self, mut f: F) -> Result<bool, Self::Error>
+ where
+ Self: Sized,
+ F: FnMut(&Self::Item) -> bool,
+ {
+ while let Some(e) = self.next()? {
+ if !f(e) {
+ return Ok(false);
+ }
+ }
+ Ok(true)
+ }
+
+ /// Determines if any elements of the iterator satisfy a predicate.
+ #[inline]
+ fn any<F>(&mut self, mut f: F) -> Result<bool, Self::Error>
+ where
+ Self: Sized,
+ F: FnMut(&Self::Item) -> bool,
+ {
+ self.all(|e| !f(e)).map(|r| !r)
+ }
+
+ /// Borrows an iterator, rather than consuming it.
+ ///
+ /// This is useful to allow the application of iterator adaptors while still retaining ownership
+ /// of the original adaptor.
+ #[inline]
+ fn by_ref(&mut self) -> &mut Self
+ where
+ Self: Sized,
+ {
+ self
+ }
+
+ /// Returns the number of remaining elements in the iterator.
+ #[inline]
+ fn count(mut self) -> Result<usize, Self::Error>
+ where
+ Self: Sized,
+ {
+ let mut count = 0;
+ while let Some(_) = self.next()? {
+ count += 1;
+ }
+ Ok(count)
+ }
+
+ /// Returns an iterator which filters elements by a predicate.
+ #[inline]
+ fn filter<F>(self, f: F) -> Filter<Self, F>
+ where
+ Self: Sized,
+ F: FnMut(&Self::Item) -> bool,
+ {
+ Filter { it: self, f: f }
+ }
+
+ /// Returns the first element of the iterator which satisfies a predicate.
+ #[inline]
+ fn find<F>(&mut self, mut f: F) -> Result<Option<&Self::Item>, Self::Error>
+ where
+ Self: Sized,
+ F: FnMut(&Self::Item) -> bool,
+ {
+ loop {
+ self.advance()?;
+ match self.get() {
+ Some(v) => {
+ if f(v) {
+ break;
+ }
+ }
+ None => break,
+ }
+ }
+ Ok((*self).get())
+ }
+
+ /// Calls a closure on each element of an iterator.
+ #[inline]
+ fn for_each<F>(mut self, mut f: F) -> Result<(), Self::Error>
+ where
+ Self: Sized,
+ F: FnMut(&Self::Item),
+ {
+ while let Some(value) = self.next()? {
+ f(value);
+ }
+ Ok(())
+ }
+
+ /// Returns an iterator which is well-behaved at the beginning and end of iteration.
+ #[inline]
+ fn fuse(self) -> Fuse<Self>
+ where
+ Self: Sized,
+ {
+ Fuse {
+ it: self,
+ state: FuseState::Start,
+ }
+ }
+
+ /// Returns an iterator which applies a transform to elements.
+ #[inline]
+ fn map<F, B>(self, f: F) -> Map<Self, F, B>
+ where
+ Self: Sized,
+ F: FnMut(&Self::Item) -> B,
+ {
+ Map {
+ it: self,
+ f: f,
+ value: None,
+ }
+ }
+
+ /// Returns an iterator which applies a transform to elements.
+ ///
+ /// Unlike `map`, the the closure provided to this method returns a reference into the original
+ /// value.
+ #[inline]
+ fn map_ref<F, B: ?Sized>(self, f: F) -> MapRef<Self, F>
+ where
+ Self: Sized,
+ F: Fn(&Self::Item) -> &B,
+ {
+ MapRef { it: self, f: f }
+ }
+
+ /// Returns an iterator that applies a transform to errors.
+ #[inline]
+ fn map_err<F, B>(self, f: F) -> MapErr<Self, F>
+ where
+ Self: Sized,
+ F: Fn(Self::Error) -> B,
+ {
+ MapErr { it: self, f: f }
+ }
+
+ /// Returns the `nth` element of the iterator.
+ #[inline]
+ fn nth(&mut self, n: usize) -> Result<Option<&Self::Item>, Self::Error> {
+ for _ in 0..n {
+ self.advance()?;
+ if let None = self.get() {
+ return Ok(None);
+ }
+ }
+ self.next()
+ }
+
+ /// Returns the position of the first element matching a predicate.
+ #[inline]
+ fn position<F>(&mut self, mut f: F) -> Result<Option<usize>, Self::Error>
+ where
+ Self: Sized,
+ F: FnMut(&Self::Item) -> bool,
+ {
+ let mut pos = 0;
+ while let Some(v) = self.next()? {
+ if f(v) {
+ return Ok(Some(pos));
+ }
+ pos += 1;
+ }
+ Ok(None)
+ }
+
+ /// Returns an iterator which skips the first `n` elements.
+ #[inline]
+ fn skip(self, n: usize) -> Skip<Self>
+ where
+ Self: Sized,
+ {
+ Skip { it: self, n: n }
+ }
+
+ /// Returns an iterator which skips the first sequence of elements matching a predicate.
+ #[inline]
+ fn skip_while<F>(self, f: F) -> SkipWhile<Self, F>
+ where
+ Self: Sized,
+ F: FnMut(&Self::Item) -> bool,
+ {
+ SkipWhile {
+ it: self,
+ f: f,
+ done: false,
+ }
+ }
+
+ /// Returns an iterator which only returns the first `n` elements.
+ #[inline]
+ fn take(self, n: usize) -> Take<Self>
+ where
+ Self: Sized,
+ {
+ Take {
+ it: self,
+ n: n,
+ done: false,
+ }
+ }
+
+ /// Returns an iterator which only returns the first sequence of elements matching a predicate.
+ #[inline]
+ fn take_while<F>(self, f: F) -> TakeWhile<Self, F>
+ where
+ Self: Sized,
+ F: FnMut(&Self::Item) -> bool,
+ {
+ TakeWhile {
+ it: self,
+ f: f,
+ done: false,
+ }
+ }
+}
+
+/// A fallible, streaming iterator which can be advanced from either end.
+pub trait DoubleEndedFallibleStreamingIterator: FallibleStreamingIterator {
+ /// Advances the state of the iterator to the next item from the end.
+ ///
+ /// Iterators start just after the last item, so this method should be called before `get`
+ /// when iterating.
+ ///
+ /// The behavior of calling this method after `get` has returned `None`, or after this method
+ /// or `advance` has returned an error is unspecified.
+ fn advance_back(&mut self) -> Result<(), Self::Error>;
+
+ /// Advances the back of the iterator, returning the last element.
+ ///
+ /// The default implementation simply calls `advance_back` followed by `get`.
+ #[inline]
+ fn next_back(&mut self) -> Result<Option<&Self::Item>, Self::Error> {
+ self.advance_back()?;
+ Ok((*self).get())
+ }
+}
+
+impl<'a, I: ?Sized> FallibleStreamingIterator for &'a mut I
+where
+ I: FallibleStreamingIterator,
+{
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn advance(&mut self) -> Result<(), I::Error> {
+ (**self).advance()
+ }
+
+ #[inline]
+ fn get(&self) -> Option<&I::Item> {
+ (**self).get()
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ (**self).size_hint()
+ }
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<&I::Item>, I::Error> {
+ (**self).next()
+ }
+}
+
+#[cfg(feature = "std")]
+impl<I: ?Sized> FallibleStreamingIterator for Box<I>
+where
+ I: FallibleStreamingIterator,
+{
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn advance(&mut self) -> Result<(), I::Error> {
+ (**self).advance()
+ }
+
+ #[inline]
+ fn get(&self) -> Option<&I::Item> {
+ (**self).get()
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ (**self).size_hint()
+ }
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<&I::Item>, I::Error> {
+ (**self).next()
+ }
+}
+
+/// Converts a normal `Iterator` over `Results` of references into a
+/// `FallibleStreamingIterator`.
+pub fn convert<'a, I, T, E>(it: I) -> Convert<'a, I, T>
+where
+ I: Iterator<Item = Result<&'a T, E>>,
+{
+ Convert { it: it, item: None }
+}
+
+/// An iterator which wraps a normal `Iterator`.
+pub struct Convert<'a, I, T: 'a> {
+ it: I,
+ item: Option<&'a T>,
+}
+
+impl<'a, I, T, E> FallibleStreamingIterator for Convert<'a, I, T>
+where
+ I: Iterator<Item = Result<&'a T, E>>,
+{
+ type Item = T;
+ type Error = E;
+
+ #[inline]
+ fn advance(&mut self) -> Result<(), E> {
+ self.item = match self.it.next() {
+ Some(Ok(v)) => Some(v),
+ Some(Err(e)) => return Err(e),
+ None => None,
+ };
+ Ok(())
+ }
+
+ #[inline]
+ fn get(&self) -> Option<&T> {
+ self.item
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ self.it.size_hint()
+ }
+}
+
+impl<'a, I, T, E> DoubleEndedFallibleStreamingIterator for Convert<'a, I, T>
+where
+ I: DoubleEndedIterator<Item = Result<&'a T, E>>,
+{
+ #[inline]
+ fn advance_back(&mut self) -> Result<(), E> {
+ self.item = match self.it.next_back() {
+ Some(Ok(v)) => Some(v),
+ Some(Err(e)) => return Err(e),
+ None => None,
+ };
+ Ok(())
+ }
+}
+
+/// Returns an iterator over no items.
+pub fn empty<T, E>() -> Empty<T, E> {
+ Empty(PhantomData)
+}
+
+/// An iterator over no items.
+pub struct Empty<T, E>(PhantomData<(T, E)>);
+
+impl<T, E> FallibleStreamingIterator for Empty<T, E> {
+ type Item = T;
+ type Error = E;
+
+ #[inline]
+ fn advance(&mut self) -> Result<(), E> {
+ Ok(())
+ }
+
+ #[inline]
+ fn get(&self) -> Option<&T> {
+ None
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ (0, Some(0))
+ }
+}
+
+impl<T, E> DoubleEndedFallibleStreamingIterator for Empty<T, E> {
+ #[inline]
+ fn advance_back(&mut self) -> Result<(), E> {
+ Ok(())
+ }
+}
+
+/// An iterator which filters elements with a predicate.
+pub struct Filter<I, F> {
+ it: I,
+ f: F,
+}
+
+impl<I, F> FallibleStreamingIterator for Filter<I, F>
+where
+ I: FallibleStreamingIterator,
+ F: FnMut(&I::Item) -> bool,
+{
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn advance(&mut self) -> Result<(), I::Error> {
+ while let Some(i) = self.it.next()? {
+ if (self.f)(i) {
+ break;
+ }
+ }
+ Ok(())
+ }
+
+ #[inline]
+ fn get(&self) -> Option<&I::Item> {
+ self.it.get()
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ (0, self.it.size_hint().1)
+ }
+}
+
+#[derive(Copy, Clone)]
+enum FuseState {
+ Start,
+ Middle,
+ End,
+}
+
+/// An iterator which is well-behaved at the beginning and end of iteration.
+pub struct Fuse<I> {
+ it: I,
+ state: FuseState,
+}
+
+impl<I> FallibleStreamingIterator for Fuse<I>
+where
+ I: FallibleStreamingIterator,
+{
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn advance(&mut self) -> Result<(), I::Error> {
+ match self.state {
+ FuseState::Start => {
+ match self.it.next() {
+ Ok(Some(_)) => self.state = FuseState::Middle,
+ Ok(None) => self.state = FuseState::End,
+ Err(e) => {
+ self.state = FuseState::End;
+ return Err(e);
+ }
+ };
+ }
+ FuseState::Middle => match self.it.next() {
+ Ok(Some(_)) => {}
+ Ok(None) => self.state = FuseState::End,
+ Err(e) => {
+ self.state = FuseState::End;
+ return Err(e);
+ }
+ },
+ FuseState::End => {}
+ }
+ Ok(())
+ }
+
+ #[inline]
+ fn get(&self) -> Option<&I::Item> {
+ match self.state {
+ FuseState::Middle => self.it.get(),
+ FuseState::Start | FuseState::End => None,
+ }
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ self.it.size_hint()
+ }
+
+ #[inline]
+ fn next(&mut self) -> Result<Option<&I::Item>, I::Error> {
+ match self.state {
+ FuseState::Start => match self.it.next() {
+ Ok(Some(v)) => {
+ self.state = FuseState::Middle;
+ Ok(Some(v))
+ }
+ Ok(None) => {
+ self.state = FuseState::End;
+ Ok(None)
+ }
+ Err(e) => {
+ self.state = FuseState::End;
+ Err(e)
+ }
+ },
+ FuseState::Middle => match self.it.next() {
+ Ok(Some(v)) => Ok(Some(v)),
+ Ok(None) => {
+ self.state = FuseState::End;
+ Ok(None)
+ }
+ Err(e) => {
+ self.state = FuseState::End;
+ Err(e)
+ }
+ },
+ FuseState::End => Ok(None),
+ }
+ }
+}
+
+/// An iterator which applies a transform to elements.
+pub struct Map<I, F, B> {
+ it: I,
+ f: F,
+ value: Option<B>,
+}
+
+impl<I, F, B> FallibleStreamingIterator for Map<I, F, B>
+where
+ I: FallibleStreamingIterator,
+ F: FnMut(&I::Item) -> B,
+{
+ type Item = B;
+ type Error = I::Error;
+
+ #[inline]
+ fn advance(&mut self) -> Result<(), I::Error> {
+ self.value = self.it.next()?.map(&mut self.f);
+ Ok(())
+ }
+
+ #[inline]
+ fn get(&self) -> Option<&B> {
+ self.value.as_ref()
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ self.it.size_hint()
+ }
+}
+
+impl<I, F, B> DoubleEndedFallibleStreamingIterator for Map<I, F, B>
+where
+ I: DoubleEndedFallibleStreamingIterator,
+ F: FnMut(&I::Item) -> B,
+{
+ #[inline]
+ fn advance_back(&mut self) -> Result<(), I::Error> {
+ self.value = self.it.next_back()?.map(&mut self.f);
+ Ok(())
+ }
+}
+
+/// An iterator which applies a transform to elements.
+pub struct MapRef<I, F> {
+ it: I,
+ f: F,
+}
+
+impl<I, F, B: ?Sized> FallibleStreamingIterator for MapRef<I, F>
+where
+ I: FallibleStreamingIterator,
+ F: Fn(&I::Item) -> &B,
+{
+ type Item = B;
+ type Error = I::Error;
+
+ #[inline]
+ fn advance(&mut self) -> Result<(), I::Error> {
+ self.it.advance()
+ }
+
+ #[inline]
+ fn get(&self) -> Option<&B> {
+ self.it.get().map(&self.f)
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ self.it.size_hint()
+ }
+}
+
+impl<I, F, B: ?Sized> DoubleEndedFallibleStreamingIterator for MapRef<I, F>
+where
+ I: DoubleEndedFallibleStreamingIterator,
+ F: Fn(&I::Item) -> &B,
+{
+ #[inline]
+ fn advance_back(&mut self) -> Result<(), I::Error> {
+ self.it.advance_back()
+ }
+}
+
+/// An iterator which applies a transform to errors.
+pub struct MapErr<I, F> {
+ it: I,
+ f: F,
+}
+
+impl<I, F, B> FallibleStreamingIterator for MapErr<I, F>
+where
+ I: FallibleStreamingIterator,
+ F: Fn(I::Error) -> B,
+{
+ type Item = I::Item;
+ type Error = B;
+
+ #[inline]
+ fn advance(&mut self) -> Result<(), B> {
+ self.it.advance().map_err(&mut self.f)
+ }
+
+ #[inline]
+ fn get(&self) -> Option<&I::Item> {
+ self.it.get()
+ }
+
+ #[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()
+ }
+}
+
+impl<I, F, B> DoubleEndedFallibleStreamingIterator for MapErr<I, F>
+where
+ I: DoubleEndedFallibleStreamingIterator,
+ F: Fn(I::Error) -> B,
+{
+ #[inline]
+ fn advance_back(&mut self) -> Result<(), B> {
+ self.it.advance_back().map_err(&mut self.f)
+ }
+
+ #[inline]
+ fn next_back(&mut self) -> Result<Option<&I::Item>, B> {
+ self.it.next_back().map_err(&mut self.f)
+ }
+}
+
+/// An iterator which skips a number of initial elements.
+pub struct Skip<I> {
+ it: I,
+ n: usize,
+}
+
+impl<I> FallibleStreamingIterator for Skip<I>
+where
+ I: FallibleStreamingIterator,
+{
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn advance(&mut self) -> Result<(), I::Error> {
+ for _ in 0..self.n {
+ if let None = self.it.next()? {
+ return Ok(());
+ }
+ }
+ self.n = 0;
+ self.advance()
+ }
+
+ #[inline]
+ fn get(&self) -> Option<&I::Item> {
+ self.it.get()
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ let hint = self.it.size_hint();
+ (
+ hint.0.saturating_sub(self.n),
+ hint.1.map(|h| h.saturating_sub(self.n)),
+ )
+ }
+}
+
+/// An iterator which skips initial elements matching a predicate.
+pub struct SkipWhile<I, F> {
+ it: I,
+ f: F,
+ done: bool,
+}
+
+impl<I, F> FallibleStreamingIterator for SkipWhile<I, F>
+where
+ I: FallibleStreamingIterator,
+ F: FnMut(&I::Item) -> bool,
+{
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn advance(&mut self) -> Result<(), I::Error> {
+ if !self.done {
+ self.done = true;
+ let f = &mut self.f;
+ self.it.find(|i| !f(i)).map(|_| ())
+ } else {
+ self.it.advance()
+ }
+ }
+
+ #[inline]
+ fn get(&self) -> Option<&I::Item> {
+ self.it.get()
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ let hint = self.it.size_hint();
+ if self.done {
+ hint
+ } else {
+ (0, hint.1)
+ }
+ }
+}
+
+/// An iterator which only returns a number of initial elements.
+pub struct Take<I> {
+ it: I,
+ n: usize,
+ done: bool,
+}
+
+impl<I> FallibleStreamingIterator for Take<I>
+where
+ I: FallibleStreamingIterator,
+{
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn advance(&mut self) -> Result<(), I::Error> {
+ if self.n != 0 {
+ self.it.advance()?;
+ self.n -= 1;
+ } else {
+ self.done = true;
+ }
+ Ok(())
+ }
+
+ #[inline]
+ fn get(&self) -> Option<&I::Item> {
+ if self.done {
+ None
+ } else {
+ self.it.get()
+ }
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ let (lower, upper) = self.it.size_hint();
+
+ let lower = cmp::min(lower, self.n);
+
+ let upper = match upper {
+ Some(x) if x < self.n => Some(x),
+ _ => Some(self.n)
+ };
+
+ (lower, upper)
+ }
+}
+
+/// An iterator which only returns initial elements matching a predicate.
+pub struct TakeWhile<I, F> {
+ it: I,
+ f: F,
+ done: bool,
+}
+
+impl<I, F> FallibleStreamingIterator for TakeWhile<I, F>
+where
+ I: FallibleStreamingIterator,
+ F: FnMut(&I::Item) -> bool,
+{
+ type Item = I::Item;
+ type Error = I::Error;
+
+ #[inline]
+ fn advance(&mut self) -> Result<(), I::Error> {
+ if let Some(v) = self.it.next()? {
+ if !(self.f)(v) {
+ self.done = true;
+ }
+ }
+ Ok(())
+ }
+
+ #[inline]
+ fn get(&self) -> Option<&I::Item> {
+ if self.done {
+ None
+ } else {
+ self.it.get()
+ }
+ }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ if self.done {
+ (0, Some(0))
+ } else {
+ (0, self.it.size_hint().1)
+ }
+ }
+}
+
+#[cfg(test)]
+mod test {
+ use super::*;
+
+ fn _is_object_safe(_: &FallibleStreamingIterator<Item = (), Error = ()>) {}
+ fn _is_object_safe_double(_: &DoubleEndedFallibleStreamingIterator<Item = (), Error = ()>) {}
+}
projects / platform / upstream / rust-fallible-streaming-iterator.git / commitdiff