Import fallible-streaming-iterator-0.1.9

Change-Id: I18258bfb568c3392af54cd4fcc8481ae99b8e9ef

8 files changed, 1222 insertions, 0 deletions

diff --git a/.circleci/config.yml b/.circleci/config.yml
new file mode 100644
index 0000000..f64c742
--- /dev/null
+++ b/.circleci/config.yml
@@ -0,0 +1,38 @@
+restore_registry: &RESTORE_REGISTRY
+  restore_cache:
+    key: registry
+save_registry: &SAVE_REGISTRY
+  save_cache:
+    key: registry-{{ .BuildNum }}
+    paths:
+    - /usr/local/cargo/registry/index
+deps_key: &DEPS_KEY
+  key: deps-{{ checksum "~/rust-version" }}-{{ checksum "Cargo.lock" }}
+restore_deps: &RESTORE_DEPS
+  restore_cache:
+    <<: *DEPS_KEY
+save_deps: &SAVE_DEPS
+  save_cache:
+    <<: *DEPS_KEY
+    paths:
+    - target
+    - /usr/local/cargo/registry/cache
+
+version: 2
+jobs:
+  build:
+    working_directory: ~/build
+    docker:
+      - image: rust:1.19.0
+        environment:
+          RUSTFLAGS: -D warnings
+    steps:
+      - checkout
+      - *RESTORE_REGISTRY
+      - run: cargo generate-lockfile
+      - *SAVE_REGISTRY
+      - run: rustc --version > ~/rust-version
+      - *RESTORE_DEPS
+      - run: cargo test
+      - run: cargo test --features std
+      - *SAVE_DEPS
diff --git a/.gitignore b/.gitignore
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--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,4 @@
+target
+Cargo.lock
+.idea
+*.iml
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..b086cdb
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,25 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g. crates.io) dependencies
+#
+# If you believe there's an error in this file please file an
+# issue against the rust-lang/cargo repository. If you're
+# editing this file be aware that the upstream Cargo.toml
+# will likely look very different (and much more reasonable)
+
+[package]
+name = "fallible-streaming-iterator"
+version = "0.1.9"
+authors = ["Steven Fackler <sfackler@gmail.com>"]
+description = "Fallible streaming iteration"
+readme = "README.md"
+license = "MIT/Apache-2.0"
+repository = "https://github.com/sfackler/fallible-streaming-iterator"
+
+[dependencies]
+
+[features]
+std = []
diff --git a/Cargo.toml.orig b/Cargo.toml.orig
new file mode 100644
index 0000000..4675edb
--- /dev/null
+++ b/Cargo.toml.orig
@@ -0,0 +1,13 @@
+[package]
+name = "fallible-streaming-iterator"
+version = "0.1.9"
+authors = ["Steven Fackler <sfackler@gmail.com>"]
+description = "Fallible streaming iteration"
+license = "MIT/Apache-2.0"
+repository = "https://github.com/sfackler/fallible-streaming-iterator"
+readme = "README.md"
+
+[features]
+std = []
+
+[dependencies]
diff --git a/LICENSE-APACHE b/LICENSE-APACHE
new file mode 100644
index 0000000..8f71f43
--- /dev/null
+++ b/LICENSE-APACHE
@@ -0,0 +1,202 @@
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diff --git a/LICENSE-MIT b/LICENSE-MIT
new file mode 100644
index 0000000..41aaea3
--- /dev/null
+++ b/LICENSE-MIT
@@ -0,0 +1,19 @@
+Copyright (c) 2016 The fallible-streaming-iterator Developers
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
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+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..f085402
--- /dev/null
+++ b/README.md
@@ -0,0 +1,22 @@
+# fallible-streaming-iterator
+[![CircleCI](https://circleci.com/gh/sfackler/fallible-streaming-iterator.svg?style=shield)](https://circleci.com/gh/sfackler/fallible-streaming-iterator)
+
+[Documentation](https://docs.rs/fallible-streaming-iterator)
+
+Fallible, streaming iteration
+
+## License
+
+Licensed under either of
+
+ * Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
+ * MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
+
+at your option.
+
+### Contribution
+
+Unless you explicitly state otherwise, any contribution intentionally
+submitted for inclusion in the work by you, as defined in the Apache-2.0
+license, shall be dual licensed as above, without any additional terms or
+conditions.
diff --git a/src/lib.rs b/src/lib.rs
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index 0000000..69262d6
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,899 @@
+//! 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 = ()>) {}
+}