update libcore to 2016-04-29 nightly

1 files changed, 2111 insertions, 0 deletions

diff --git a/libcore/iter/iterator.rs b/libcore/iter/iterator.rs
new file mode 100644
index 0000000..2033ae5
--- /dev/null
+++ b/libcore/iter/iterator.rs
@@ -0,0 +1,2111 @@
+// Copyright 2013-2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use clone::Clone;
+use cmp::{Ord, PartialOrd, PartialEq, Ordering};
+use default::Default;
+use marker;
+use num::{Zero, One};
+use ops::{Add, FnMut, Mul};
+use option::Option::{self, Some, None};
+use marker::Sized;
+
+use super::{Chain, Cycle, Cloned, Enumerate, Filter, FilterMap, FlatMap, Fuse,
+            Inspect, Map, Peekable, Scan, Skip, SkipWhile, Take, TakeWhile, Rev,
+            Zip};
+use super::ChainState;
+use super::{DoubleEndedIterator, ExactSizeIterator, Extend, FromIterator,
+            IntoIterator};
+
+fn _assert_is_object_safe(_: &Iterator<Item=()>) {}
+
+/// An interface for dealing with iterators.
+///
+/// This is the main iterator trait. For more about the concept of iterators
+/// generally, please see the [module-level documentation]. In particular, you
+/// may want to know how to [implement `Iterator`][impl].
+///
+/// [module-level documentation]: index.html
+/// [impl]: index.html#implementing-iterator
+#[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_on_unimplemented = "`{Self}` is not an iterator; maybe try calling \
+                            `.iter()` or a similar method"]
+pub trait Iterator {
+    /// The type of the elements being iterated over.
+    #[stable(feature = "rust1", since = "1.0.0")]
+    type Item;
+
+    /// Advances the iterator and returns the next value.
+    ///
+    /// Returns `None` when iteration is finished. Individual iterator
+    /// implementations may choose to resume iteration, and so calling `next()`
+    /// again may or may not eventually start returning `Some(Item)` again at some
+    /// point.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// let mut iter = a.iter();
+    ///
+    /// // A call to next() returns the next value...
+    /// assert_eq!(Some(&1), iter.next());
+    /// assert_eq!(Some(&2), iter.next());
+    /// assert_eq!(Some(&3), iter.next());
+    ///
+    /// // ... and then None once it's over.
+    /// assert_eq!(None, iter.next());
+    ///
+    /// // More calls may or may not return None. Here, they always will.
+    /// assert_eq!(None, iter.next());
+    /// assert_eq!(None, iter.next());
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn next(&mut self) -> Option<Self::Item>;
+
+    /// Returns the bounds on the remaining length of the iterator.
+    ///
+    /// Specifically, `size_hint()` returns a tuple where the first element
+    /// is the lower bound, and the second element is the upper bound.
+    ///
+    /// The second half of the tuple that is returned is an `Option<usize>`. A
+    /// `None` here means that either there is no known upper bound, or the
+    /// upper bound is larger than `usize`.
+    ///
+    /// # Implementation notes
+    ///
+    /// It is not enforced that an iterator implementation yields the declared
+    /// number of elements. A buggy iterator may yield less than the lower bound
+    /// or more than the upper bound of elements.
+    ///
+    /// `size_hint()` is primarily intended to be used for optimizations such as
+    /// reserving space for the elements of the iterator, but must not be
+    /// trusted to e.g. omit bounds checks in unsafe code. An incorrect
+    /// implementation of `size_hint()` should not lead to memory safety
+    /// violations.
+    ///
+    /// That said, the implementation should provide a correct estimation,
+    /// because otherwise it would be a violation of the trait's protocol.
+    ///
+    /// The default implementation returns `(0, None)` which is correct for any
+    /// iterator.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    /// let iter = a.iter();
+    ///
+    /// assert_eq!((3, Some(3)), iter.size_hint());
+    /// ```
+    ///
+    /// A more complex example:
+    ///
+    /// ```
+    /// // The even numbers from zero to ten.
+    /// let iter = (0..10).filter(|x| x % 2 == 0);
+    ///
+    /// // We might iterate from zero to ten times. Knowing that it's five
+    /// // exactly wouldn't be possible without executing filter().
+    /// assert_eq!((0, Some(10)), iter.size_hint());
+    ///
+    /// // Let's add one five more numbers with chain()
+    /// let iter = (0..10).filter(|x| x % 2 == 0).chain(15..20);
+    ///
+    /// // now both bounds are increased by five
+    /// assert_eq!((5, Some(15)), iter.size_hint());
+    /// ```
+    ///
+    /// Returning `None` for an upper bound:
+    ///
+    /// ```
+    /// // an infinite iterator has no upper bound
+    /// let iter = 0..;
+    ///
+    /// assert_eq!((0, None), iter.size_hint());
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn size_hint(&self) -> (usize, Option<usize>) { (0, None) }
+
+    /// Consumes the iterator, counting the number of iterations and returning it.
+    ///
+    /// This method will evaluate the iterator until its [`next()`] returns
+    /// `None`. Once `None` is encountered, `count()` returns the number of
+    /// times it called [`next()`].
+    ///
+    /// [`next()`]: #tymethod.next
+    ///
+    /// # Overflow Behavior
+    ///
+    /// The method does no guarding against overflows, so counting elements of
+    /// an iterator with more than `usize::MAX` elements either produces the
+    /// wrong result or panics. If debug assertions are enabled, a panic is
+    /// guaranteed.
+    ///
+    /// # Panics
+    ///
+    /// This function might panic if the iterator has more than `usize::MAX`
+    /// elements.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    /// assert_eq!(a.iter().count(), 3);
+    ///
+    /// let a = [1, 2, 3, 4, 5];
+    /// assert_eq!(a.iter().count(), 5);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn count(self) -> usize where Self: Sized {
+        // Might overflow.
+        self.fold(0, |cnt, _| cnt + 1)
+    }
+
+    /// Consumes the iterator, returning the last element.
+    ///
+    /// This method will evaluate the iterator until it returns `None`. While
+    /// doing so, it keeps track of the current element. After `None` is
+    /// returned, `last()` will then return the last element it saw.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    /// assert_eq!(a.iter().last(), Some(&3));
+    ///
+    /// let a = [1, 2, 3, 4, 5];
+    /// assert_eq!(a.iter().last(), Some(&5));
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn last(self) -> Option<Self::Item> where Self: Sized {
+        let mut last = None;
+        for x in self { last = Some(x); }
+        last
+    }
+
+    /// Consumes the `n` first elements of the iterator, then returns the
+    /// `next()` one.
+    ///
+    /// This method will evaluate the iterator `n` times, discarding those elements.
+    /// After it does so, it will call [`next()`] and return its value.
+    ///
+    /// [`next()`]: #tymethod.next
+    ///
+    /// Like most indexing operations, the count starts from zero, so `nth(0)`
+    /// returns the first value, `nth(1)` the second, and so on.
+    ///
+    /// `nth()` will return `None` if `n` is larger than the length of the
+    /// iterator.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    /// assert_eq!(a.iter().nth(1), Some(&2));
+    /// ```
+    ///
+    /// Calling `nth()` multiple times doesn't rewind the iterator:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// let mut iter = a.iter();
+    ///
+    /// assert_eq!(iter.nth(1), Some(&2));
+    /// assert_eq!(iter.nth(1), None);
+    /// ```
+    ///
+    /// Returning `None` if there are less than `n` elements:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    /// assert_eq!(a.iter().nth(10), None);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn nth(&mut self, mut n: usize) -> Option<Self::Item> where Self: Sized {
+        for x in self {
+            if n == 0 { return Some(x) }
+            n -= 1;
+        }
+        None
+    }
+
+    /// Takes two iterators and creates a new iterator over both in sequence.
+    ///
+    /// `chain()` will return a new iterator which will first iterate over
+    /// values from the first iterator and then over values from the second
+    /// iterator.
+    ///
+    /// In other words, it links two iterators together, in a chain. 🔗
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a1 = [1, 2, 3];
+    /// let a2 = [4, 5, 6];
+    ///
+    /// let mut iter = a1.iter().chain(a2.iter());
+    ///
+    /// assert_eq!(iter.next(), Some(&1));
+    /// assert_eq!(iter.next(), Some(&2));
+    /// assert_eq!(iter.next(), Some(&3));
+    /// assert_eq!(iter.next(), Some(&4));
+    /// assert_eq!(iter.next(), Some(&5));
+    /// assert_eq!(iter.next(), Some(&6));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    ///
+    /// Since the argument to `chain()` uses [`IntoIterator`], we can pass
+    /// anything that can be converted into an [`Iterator`], not just an
+    /// [`Iterator`] itself. For example, slices (`&[T]`) implement
+    /// [`IntoIterator`], and so can be passed to `chain()` directly:
+    ///
+    /// [`IntoIterator`]: trait.IntoIterator.html
+    /// [`Iterator`]: trait.Iterator.html
+    ///
+    /// ```
+    /// let s1 = &[1, 2, 3];
+    /// let s2 = &[4, 5, 6];
+    ///
+    /// let mut iter = s1.iter().chain(s2);
+    ///
+    /// assert_eq!(iter.next(), Some(&1));
+    /// assert_eq!(iter.next(), Some(&2));
+    /// assert_eq!(iter.next(), Some(&3));
+    /// assert_eq!(iter.next(), Some(&4));
+    /// assert_eq!(iter.next(), Some(&5));
+    /// assert_eq!(iter.next(), Some(&6));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn chain<U>(self, other: U) -> Chain<Self, U::IntoIter> where
+        Self: Sized, U: IntoIterator<Item=Self::Item>,
+    {
+        Chain{a: self, b: other.into_iter(), state: ChainState::Both}
+    }
+
+    /// 'Zips up' two iterators into a single iterator of pairs.
+    ///
+    /// `zip()` returns a new iterator that will iterate over two other
+    /// iterators, returning a tuple where the first element comes from the
+    /// first iterator, and the second element comes from the second iterator.
+    ///
+    /// In other words, it zips two iterators together, into a single one.
+    ///
+    /// When either iterator returns `None`, all further calls to `next()`
+    /// will return `None`.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a1 = [1, 2, 3];
+    /// let a2 = [4, 5, 6];
+    ///
+    /// let mut iter = a1.iter().zip(a2.iter());
+    ///
+    /// assert_eq!(iter.next(), Some((&1, &4)));
+    /// assert_eq!(iter.next(), Some((&2, &5)));
+    /// assert_eq!(iter.next(), Some((&3, &6)));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    ///
+    /// Since the argument to `zip()` uses [`IntoIterator`], we can pass
+    /// anything that can be converted into an [`Iterator`], not just an
+    /// [`Iterator`] itself. For example, slices (`&[T]`) implement
+    /// [`IntoIterator`], and so can be passed to `zip()` directly:
+    ///
+    /// [`IntoIterator`]: trait.IntoIterator.html
+    /// [`Iterator`]: trait.Iterator.html
+    ///
+    /// ```
+    /// let s1 = &[1, 2, 3];
+    /// let s2 = &[4, 5, 6];
+    ///
+    /// let mut iter = s1.iter().zip(s2);
+    ///
+    /// assert_eq!(iter.next(), Some((&1, &4)));
+    /// assert_eq!(iter.next(), Some((&2, &5)));
+    /// assert_eq!(iter.next(), Some((&3, &6)));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    ///
+    /// `zip()` is often used to zip an infinite iterator to a finite one.
+    /// This works because the finite iterator will eventually return `None`,
+    /// ending the zipper. Zipping with `(0..)` can look a lot like [`enumerate()`]:
+    ///
+    /// ```
+    /// let enumerate: Vec<_> = "foo".chars().enumerate().collect();
+    ///
+    /// let zipper: Vec<_> = (0..).zip("foo".chars()).collect();
+    ///
+    /// assert_eq!((0, 'f'), enumerate[0]);
+    /// assert_eq!((0, 'f'), zipper[0]);
+    ///
+    /// assert_eq!((1, 'o'), enumerate[1]);
+    /// assert_eq!((1, 'o'), zipper[1]);
+    ///
+    /// assert_eq!((2, 'o'), enumerate[2]);
+    /// assert_eq!((2, 'o'), zipper[2]);
+    /// ```
+    ///
+    /// [`enumerate()`]: trait.Iterator.html#method.enumerate
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn zip<U>(self, other: U) -> Zip<Self, U::IntoIter> where
+        Self: Sized, U: IntoIterator
+    {
+        Zip{a: self, b: other.into_iter()}
+    }
+
+    /// Takes a closure and creates an iterator which calls that closure on each
+    /// element.
+    ///
+    /// `map()` transforms one iterator into another, by means of its argument:
+    /// something that implements `FnMut`. It produces a new iterator which
+    /// calls this closure on each element of the original iterator.
+    ///
+    /// If you are good at thinking in types, you can think of `map()` like this:
+    /// If you have an iterator that gives you elements of some type `A`, and
+    /// you want an iterator of some other type `B`, you can use `map()`,
+    /// passing a closure that takes an `A` and returns a `B`.
+    ///
+    /// `map()` is conceptually similar to a [`for`] loop. However, as `map()` is
+    /// lazy, it is best used when you're already working with other iterators.
+    /// If you're doing some sort of looping for a side effect, it's considered
+    /// more idiomatic to use [`for`] than `map()`.
+    ///
+    /// [`for`]: ../../book/loops.html#for
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// let mut iter = a.into_iter().map(|x| 2 * x);
+    ///
+    /// assert_eq!(iter.next(), Some(2));
+    /// assert_eq!(iter.next(), Some(4));
+    /// assert_eq!(iter.next(), Some(6));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    ///
+    /// If you're doing some sort of side effect, prefer [`for`] to `map()`:
+    ///
+    /// ```
+    /// # #![allow(unused_must_use)]
+    /// // don't do this:
+    /// (0..5).map(|x| println!("{}", x));
+    ///
+    /// // it won't even execute, as it is lazy. Rust will warn you about this.
+    ///
+    /// // Instead, use for:
+    /// for x in 0..5 {
+    ///     println!("{}", x);
+    /// }
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn map<B, F>(self, f: F) -> Map<Self, F> where
+        Self: Sized, F: FnMut(Self::Item) -> B,
+    {
+        Map{iter: self, f: f}
+    }
+
+    /// Creates an iterator which uses a closure to determine if an element
+    /// should be yielded.
+    ///
+    /// The closure must return `true` or `false`. `filter()` creates an
+    /// iterator which calls this closure on each element. If the closure
+    /// returns `true`, then the element is returned. If the closure returns
+    /// `false`, it will try again, and call the closure on the next element,
+    /// seeing if it passes the test.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [0i32, 1, 2];
+    ///
+    /// let mut iter = a.into_iter().filter(|x| x.is_positive());
+    ///
+    /// assert_eq!(iter.next(), Some(&1));
+    /// assert_eq!(iter.next(), Some(&2));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    ///
+    /// Because the closure passed to `filter()` takes a reference, and many
+    /// iterators iterate over references, this leads to a possibly confusing
+    /// situation, where the type of the closure is a double reference:
+    ///
+    /// ```
+    /// let a = [0, 1, 2];
+    ///
+    /// let mut iter = a.into_iter().filter(|x| **x > 1); // need two *s!
+    ///
+    /// assert_eq!(iter.next(), Some(&2));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    ///
+    /// It's common to instead use destructuring on the argument to strip away
+    /// one:
+    ///
+    /// ```
+    /// let a = [0, 1, 2];
+    ///
+    /// let mut iter = a.into_iter().filter(|&x| *x > 1); // both & and *
+    ///
+    /// assert_eq!(iter.next(), Some(&2));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    ///
+    /// or both:
+    ///
+    /// ```
+    /// let a = [0, 1, 2];
+    ///
+    /// let mut iter = a.into_iter().filter(|&&x| x > 1); // two &s
+    ///
+    /// assert_eq!(iter.next(), Some(&2));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    ///
+    /// of these layers.
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn filter<P>(self, predicate: P) -> Filter<Self, P> where
+        Self: Sized, P: FnMut(&Self::Item) -> bool,
+    {
+        Filter{iter: self, predicate: predicate}
+    }
+
+    /// Creates an iterator that both filters and maps.
+    ///
+    /// The closure must return an [`Option<T>`]. `filter_map()` creates an
+    /// iterator which calls this closure on each element. If the closure
+    /// returns `Some(element)`, then that element is returned. If the
+    /// closure returns `None`, it will try again, and call the closure on the
+    /// next element, seeing if it will return `Some`.
+    ///
+    /// [`Option<T>`]: ../../std/option/enum.Option.html
+    ///
+    /// Why `filter_map()` and not just [`filter()`].[`map()`]? The key is in this
+    /// part:
+    ///
+    /// [`filter()`]: #method.filter
+    /// [`map()`]: #method.map
+    ///
+    /// > If the closure returns `Some(element)`, then that element is returned.
+    ///
+    /// In other words, it removes the [`Option<T>`] layer automatically. If your
+    /// mapping is already returning an [`Option<T>`] and you want to skip over
+    /// `None`s, then `filter_map()` is much, much nicer to use.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = ["1", "2", "lol"];
+    ///
+    /// let mut iter = a.iter().filter_map(|s| s.parse().ok());
+    ///
+    /// assert_eq!(iter.next(), Some(1));
+    /// assert_eq!(iter.next(), Some(2));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    ///
+    /// Here's the same example, but with [`filter()`] and [`map()`]:
+    ///
+    /// ```
+    /// let a = ["1", "2", "lol"];
+    ///
+    /// let mut iter = a.iter()
+    ///                 .map(|s| s.parse().ok())
+    ///                 .filter(|s| s.is_some());
+    ///
+    /// assert_eq!(iter.next(), Some(Some(1)));
+    /// assert_eq!(iter.next(), Some(Some(2)));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    ///
+    /// There's an extra layer of `Some` in there.
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> where
+        Self: Sized, F: FnMut(Self::Item) -> Option<B>,
+    {
+        FilterMap { iter: self, f: f }
+    }
+
+    /// Creates an iterator which gives the current iteration count as well as
+    /// the next value.
+    ///
+    /// The iterator returned yields pairs `(i, val)`, where `i` is the
+    /// current index of iteration and `val` is the value returned by the
+    /// iterator.
+    ///
+    /// `enumerate()` keeps its count as a [`usize`]. If you want to count by a
+    /// different sized integer, the [`zip()`] function provides similar
+    /// functionality.
+    ///
+    /// [`usize`]: ../../std/primitive.usize.html
+    /// [`zip()`]: #method.zip
+    ///
+    /// # Overflow Behavior
+    ///
+    /// The method does no guarding against overflows, so enumerating more than
+    /// [`usize::MAX`] elements either produces the wrong result or panics. If
+    /// debug assertions are enabled, a panic is guaranteed.
+    ///
+    /// [`usize::MAX`]: ../../std/usize/constant.MAX.html
+    ///
+    /// # Panics
+    ///
+    /// The returned iterator might panic if the to-be-returned index would
+    /// overflow a `usize`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let a = ['a', 'b', 'c'];
+    ///
+    /// let mut iter = a.iter().enumerate();
+    ///
+    /// assert_eq!(iter.next(), Some((0, &'a')));
+    /// assert_eq!(iter.next(), Some((1, &'b')));
+    /// assert_eq!(iter.next(), Some((2, &'c')));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn enumerate(self) -> Enumerate<Self> where Self: Sized {
+        Enumerate { iter: self, count: 0 }
+    }
+
+    /// Creates an iterator which can use `peek` to look at the next element of
+    /// the iterator without consuming it.
+    ///
+    /// Adds a [`peek()`] method to an iterator. See its documentation for
+    /// more information.
+    ///
+    /// Note that the underlying iterator is still advanced when `peek` is
+    /// called for the first time: In order to retrieve the next element,
+    /// `next` is called on the underlying iterator, hence any side effects of
+    /// the `next` method will occur.
+    ///
+    /// [`peek()`]: struct.Peekable.html#method.peek
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let xs = [1, 2, 3];
+    ///
+    /// let mut iter = xs.iter().peekable();
+    ///
+    /// // peek() lets us see into the future
+    /// assert_eq!(iter.peek(), Some(&&1));
+    /// assert_eq!(iter.next(), Some(&1));
+    ///
+    /// assert_eq!(iter.next(), Some(&2));
+    ///
+    /// // we can peek() multiple times, the iterator won't advance
+    /// assert_eq!(iter.peek(), Some(&&3));
+    /// assert_eq!(iter.peek(), Some(&&3));
+    ///
+    /// assert_eq!(iter.next(), Some(&3));
+    ///
+    /// // after the iterator is finished, so is peek()
+    /// assert_eq!(iter.peek(), None);
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn peekable(self) -> Peekable<Self> where Self: Sized {
+        Peekable{iter: self, peeked: None}
+    }
+
+    /// Creates an iterator that [`skip()`]s elements based on a predicate.
+    ///
+    /// [`skip()`]: #method.skip
+    ///
+    /// `skip_while()` takes a closure as an argument. It will call this
+    /// closure on each element of the iterator, and ignore elements
+    /// until it returns `false`.
+    ///
+    /// After `false` is returned, `skip_while()`'s job is over, and the
+    /// rest of the elements are yielded.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [-1i32, 0, 1];
+    ///
+    /// let mut iter = a.into_iter().skip_while(|x| x.is_negative());
+    ///
+    /// assert_eq!(iter.next(), Some(&0));
+    /// assert_eq!(iter.next(), Some(&1));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    ///
+    /// Because the closure passed to `skip_while()` takes a reference, and many
+    /// iterators iterate over references, this leads to a possibly confusing
+    /// situation, where the type of the closure is a double reference:
+    ///
+    /// ```
+    /// let a = [-1, 0, 1];
+    ///
+    /// let mut iter = a.into_iter().skip_while(|x| **x < 0); // need two *s!
+    ///
+    /// assert_eq!(iter.next(), Some(&0));
+    /// assert_eq!(iter.next(), Some(&1));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    ///
+    /// Stopping after an initial `false`:
+    ///
+    /// ```
+    /// let a = [-1, 0, 1, -2];
+    ///
+    /// let mut iter = a.into_iter().skip_while(|x| **x < 0);
+    ///
+    /// assert_eq!(iter.next(), Some(&0));
+    /// assert_eq!(iter.next(), Some(&1));
+    ///
+    /// // while this would have been false, since we already got a false,
+    /// // skip_while() isn't used any more
+    /// assert_eq!(iter.next(), Some(&-2));
+    ///
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> where
+        Self: Sized, P: FnMut(&Self::Item) -> bool,
+    {
+        SkipWhile{iter: self, flag: false, predicate: predicate}
+    }
+
+    /// Creates an iterator that yields elements based on a predicate.
+    ///
+    /// `take_while()` takes a closure as an argument. It will call this
+    /// closure on each element of the iterator, and yield elements
+    /// while it returns `true`.
+    ///
+    /// After `false` is returned, `take_while()`'s job is over, and the
+    /// rest of the elements are ignored.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [-1i32, 0, 1];
+    ///
+    /// let mut iter = a.into_iter().take_while(|x| x.is_negative());
+    ///
+    /// assert_eq!(iter.next(), Some(&-1));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    ///
+    /// Because the closure passed to `take_while()` takes a reference, and many
+    /// iterators iterate over references, this leads to a possibly confusing
+    /// situation, where the type of the closure is a double reference:
+    ///
+    /// ```
+    /// let a = [-1, 0, 1];
+    ///
+    /// let mut iter = a.into_iter().take_while(|x| **x < 0); // need two *s!
+    ///
+    /// assert_eq!(iter.next(), Some(&-1));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    ///
+    /// Stopping after an initial `false`:
+    ///
+    /// ```
+    /// let a = [-1, 0, 1, -2];
+    ///
+    /// let mut iter = a.into_iter().take_while(|x| **x < 0);
+    ///
+    /// assert_eq!(iter.next(), Some(&-1));
+    ///
+    /// // We have more elements that are less than zero, but since we already
+    /// // got a false, take_while() isn't used any more
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    ///
+    /// Because `take_while()` needs to look at the value in order to see if it
+    /// should be included or not, consuming iterators will see that it is
+    /// removed:
+    ///
+    /// ```
+    /// let a = [1, 2, 3, 4];
+    /// let mut iter = a.into_iter();
+    ///
+    /// let result: Vec<i32> = iter.by_ref()
+    ///                            .take_while(|n| **n != 3)
+    ///                            .cloned()
+    ///                            .collect();
+    ///
+    /// assert_eq!(result, &[1, 2]);
+    ///
+    /// let result: Vec<i32> = iter.cloned().collect();
+    ///
+    /// assert_eq!(result, &[4]);
+    /// ```
+    ///
+    /// The `3` is no longer there, because it was consumed in order to see if
+    /// the iteration should stop, but wasn't placed back into the iterator or
+    /// some similar thing.
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> where
+        Self: Sized, P: FnMut(&Self::Item) -> bool,
+    {
+        TakeWhile{iter: self, flag: false, predicate: predicate}
+    }
+
+    /// Creates an iterator that skips the first `n` elements.
+    ///
+    /// After they have been consumed, the rest of the elements are yielded.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// let mut iter = a.iter().skip(2);
+    ///
+    /// assert_eq!(iter.next(), Some(&3));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn skip(self, n: usize) -> Skip<Self> where Self: Sized {
+        Skip{iter: self, n: n}
+    }
+
+    /// Creates an iterator that yields its first `n` elements.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// let mut iter = a.iter().take(2);
+    ///
+    /// assert_eq!(iter.next(), Some(&1));
+    /// assert_eq!(iter.next(), Some(&2));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    ///
+    /// `take()` is often used with an infinite iterator, to make it finite:
+    ///
+    /// ```
+    /// let mut iter = (0..).take(3);
+    ///
+    /// assert_eq!(iter.next(), Some(0));
+    /// assert_eq!(iter.next(), Some(1));
+    /// assert_eq!(iter.next(), Some(2));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn take(self, n: usize) -> Take<Self> where Self: Sized, {
+        Take{iter: self, n: n}
+    }
+
+    /// An iterator adaptor similar to [`fold()`] that holds internal state and
+    /// produces a new iterator.
+    ///
+    /// [`fold()`]: #method.fold
+    ///
+    /// `scan()` takes two arguments: an initial value which seeds the internal
+    /// state, and a closure with two arguments, the first being a mutable
+    /// reference to the internal state and the second an iterator element.
+    /// The closure can assign to the internal state to share state between
+    /// iterations.
+    ///
+    /// On iteration, the closure will be applied to each element of the
+    /// iterator and the return value from the closure, an [`Option`], is
+    /// yielded by the iterator.
+    ///
+    /// [`Option`]: ../../std/option/enum.Option.html
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// let mut iter = a.iter().scan(1, |state, &x| {
+    ///     // each iteration, we'll multiply the state by the element
+    ///     *state = *state * x;
+    ///
+    ///     // the value passed on to the next iteration
+    ///     Some(*state)
+    /// });
+    ///
+    /// assert_eq!(iter.next(), Some(1));
+    /// assert_eq!(iter.next(), Some(2));
+    /// assert_eq!(iter.next(), Some(6));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F>
+        where Self: Sized, F: FnMut(&mut St, Self::Item) -> Option<B>,
+    {
+        Scan{iter: self, f: f, state: initial_state}
+    }
+
+    /// Creates an iterator that works like map, but flattens nested structure.
+    ///
+    /// The [`map()`] adapter is very useful, but only when the closure
+    /// argument produces values. If it produces an iterator instead, there's
+    /// an extra layer of indirection. `flat_map()` will remove this extra layer
+    /// on its own.
+    ///
+    /// [`map()`]: #method.map
+    ///
+    /// Another way of thinking about `flat_map()`: [`map()`]'s closure returns
+    /// one item for each element, and `flat_map()`'s closure returns an
+    /// iterator for each element.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let words = ["alpha", "beta", "gamma"];
+    ///
+    /// // chars() returns an iterator
+    /// let merged: String = words.iter()
+    ///                           .flat_map(|s| s.chars())
+    ///                           .collect();
+    /// assert_eq!(merged, "alphabetagamma");
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F>
+        where Self: Sized, U: IntoIterator, F: FnMut(Self::Item) -> U,
+    {
+        FlatMap{iter: self, f: f, frontiter: None, backiter: None }
+    }
+
+    /// Creates an iterator which ends after the first `None`.
+    ///
+    /// After an iterator returns `None`, future calls may or may not yield
+    /// `Some(T)` again. `fuse()` adapts an iterator, ensuring that after a
+    /// `None` is given, it will always return `None` forever.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// // an iterator which alternates between Some and None
+    /// struct Alternate {
+    ///     state: i32,
+    /// }
+    ///
+    /// impl Iterator for Alternate {
+    ///     type Item = i32;
+    ///
+    ///     fn next(&mut self) -> Option<i32> {
+    ///         let val = self.state;
+    ///         self.state = self.state + 1;
+    ///
+    ///         // if it's even, Some(i32), else None
+    ///         if val % 2 == 0 {
+    ///             Some(val)
+    ///         } else {
+    ///             None
+    ///         }
+    ///     }
+    /// }
+    ///
+    /// let mut iter = Alternate { state: 0 };
+    ///
+    /// // we can see our iterator going back and forth
+    /// assert_eq!(iter.next(), Some(0));
+    /// assert_eq!(iter.next(), None);
+    /// assert_eq!(iter.next(), Some(2));
+    /// assert_eq!(iter.next(), None);
+    ///
+    /// // however, once we fuse it...
+    /// let mut iter = iter.fuse();
+    ///
+    /// assert_eq!(iter.next(), Some(4));
+    /// assert_eq!(iter.next(), None);
+    ///
+    /// // it will always return None after the first time.
+    /// assert_eq!(iter.next(), None);
+    /// assert_eq!(iter.next(), None);
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn fuse(self) -> Fuse<Self> where Self: Sized {
+        Fuse{iter: self, done: false}
+    }
+
+    /// Do something with each element of an iterator, passing the value on.
+    ///
+    /// When using iterators, you'll often chain several of them together.
+    /// While working on such code, you might want to check out what's
+    /// happening at various parts in the pipeline. To do that, insert
+    /// a call to `inspect()`.
+    ///
+    /// It's much more common for `inspect()` to be used as a debugging tool
+    /// than to exist in your final code, but never say never.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 4, 2, 3];
+    ///
+    /// // this iterator sequence is complex.
+    /// let sum = a.iter()
+    ///             .cloned()
+    ///             .filter(|&x| x % 2 == 0)
+    ///             .fold(0, |sum, i| sum + i);
+    ///
+    /// println!("{}", sum);
+    ///
+    /// // let's add some inspect() calls to investigate what's happening
+    /// let sum = a.iter()
+    ///             .cloned()
+    ///             .inspect(|x| println!("about to filter: {}", x))
+    ///             .filter(|&x| x % 2 == 0)
+    ///             .inspect(|x| println!("made it through filter: {}", x))
+    ///             .fold(0, |sum, i| sum + i);
+    ///
+    /// println!("{}", sum);
+    /// ```
+    ///
+    /// This will print:
+    ///
+    /// ```text
+    /// about to filter: 1
+    /// about to filter: 4
+    /// made it through filter: 4
+    /// about to filter: 2
+    /// made it through filter: 2
+    /// about to filter: 3
+    /// 6
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn inspect<F>(self, f: F) -> Inspect<Self, F> where
+        Self: Sized, F: FnMut(&Self::Item),
+    {
+        Inspect{iter: self, f: f}
+    }
+
+    /// Borrows an iterator, rather than consuming it.
+    ///
+    /// This is useful to allow applying iterator adaptors while still
+    /// retaining ownership of the original iterator.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// let iter = a.into_iter();
+    ///
+    /// let sum: i32 = iter.take(5)
+    ///                    .fold(0, |acc, &i| acc + i );
+    ///
+    /// assert_eq!(sum, 6);
+    ///
+    /// // if we try to use iter again, it won't work. The following line
+    /// // gives "error: use of moved value: `iter`
+    /// // assert_eq!(iter.next(), None);
+    ///
+    /// // let's try that again
+    /// let a = [1, 2, 3];
+    ///
+    /// let mut iter = a.into_iter();
+    ///
+    /// // instead, we add in a .by_ref()
+    /// let sum: i32 = iter.by_ref()
+    ///                    .take(2)
+    ///                    .fold(0, |acc, &i| acc + i );
+    ///
+    /// assert_eq!(sum, 3);
+    ///
+    /// // now this is just fine:
+    /// assert_eq!(iter.next(), Some(&3));
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn by_ref(&mut self) -> &mut Self where Self: Sized { self }
+
+    /// Transforms an iterator into a collection.
+    ///
+    /// `collect()` can take anything iterable, and turn it into a relevant
+    /// collection. This is one of the more powerful methods in the standard
+    /// library, used in a variety of contexts.
+    ///
+    /// The most basic pattern in which `collect()` is used is to turn one
+    /// collection into another. You take a collection, call `iter()` on it,
+    /// do a bunch of transformations, and then `collect()` at the end.
+    ///
+    /// One of the keys to `collect()`'s power is that many things you might
+    /// not think of as 'collections' actually are. For example, a [`String`]
+    /// is a collection of [`char`]s. And a collection of [`Result<T, E>`] can
+    /// be thought of as single `Result<Collection<T>, E>`. See the examples
+    /// below for more.
+    ///
+    /// [`String`]: ../../std/string/struct.String.html
+    /// [`Result<T, E>`]: ../../std/result/enum.Result.html
+    /// [`char`]: ../../std/primitive.char.html
+    ///
+    /// Because `collect()` is so general, it can cause problems with type
+    /// inference. As such, `collect()` is one of the few times you'll see
+    /// the syntax affectionately known as the 'turbofish': `::<>`. This
+    /// helps the inference algorithm understand specifically which collection
+    /// you're trying to collect into.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// let doubled: Vec<i32> = a.iter()
+    ///                          .map(|&x| x * 2)
+    ///                          .collect();
+    ///
+    /// assert_eq!(vec![2, 4, 6], doubled);
+    /// ```
+    ///
+    /// Note that we needed the `: Vec<i32>` on the left-hand side. This is because
+    /// we could collect into, for example, a [`VecDeque<T>`] instead:
+    ///
+    /// [`VecDeque<T>`]: ../../std/collections/struct.VecDeque.html
+    ///
+    /// ```
+    /// use std::collections::VecDeque;
+    ///
+    /// let a = [1, 2, 3];
+    ///
+    /// let doubled: VecDeque<i32> = a.iter()
+    ///                               .map(|&x| x * 2)
+    ///                               .collect();
+    ///
+    /// assert_eq!(2, doubled[0]);
+    /// assert_eq!(4, doubled[1]);
+    /// assert_eq!(6, doubled[2]);
+    /// ```
+    ///
+    /// Using the 'turbofish' instead of annotating `doubled`:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// let doubled = a.iter()
+    ///                .map(|&x| x * 2)
+    ///                .collect::<Vec<i32>>();
+    ///
+    /// assert_eq!(vec![2, 4, 6], doubled);
+    /// ```
+    ///
+    /// Because `collect()` cares about what you're collecting into, you can
+    /// still use a partial type hint, `_`, with the turbofish:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// let doubled = a.iter()
+    ///                .map(|&x| x * 2)
+    ///                .collect::<Vec<_>>();
+    ///
+    /// assert_eq!(vec![2, 4, 6], doubled);
+    /// ```
+    ///
+    /// Using `collect()` to make a [`String`]:
+    ///
+    /// ```
+    /// let chars = ['g', 'd', 'k', 'k', 'n'];
+    ///
+    /// let hello: String = chars.iter()
+    ///                          .map(|&x| x as u8)
+    ///                          .map(|x| (x + 1) as char)
+    ///                          .collect();
+    ///
+    /// assert_eq!("hello", hello);
+    /// ```
+    ///
+    /// If you have a list of [`Result<T, E>`]s, you can use `collect()` to
+    /// see if any of them failed:
+    ///
+    /// ```
+    /// let results = [Ok(1), Err("nope"), Ok(3), Err("bad")];
+    ///
+    /// let result: Result<Vec<_>, &str> = results.iter().cloned().collect();
+    ///
+    /// // gives us the first error
+    /// assert_eq!(Err("nope"), result);
+    ///
+    /// let results = [Ok(1), Ok(3)];
+    ///
+    /// let result: Result<Vec<_>, &str> = results.iter().cloned().collect();
+    ///
+    /// // gives us the list of answers
+    /// assert_eq!(Ok(vec![1, 3]), result);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn collect<B: FromIterator<Self::Item>>(self) -> B where Self: Sized {
+        FromIterator::from_iter(self)
+    }
+
+    /// Consumes an iterator, creating two collections from it.
+    ///
+    /// The predicate passed to `partition()` can return `true`, or `false`.
+    /// `partition()` returns a pair, all of the elements for which it returned
+    /// `true`, and all of the elements for which it returned `false`.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// let (even, odd): (Vec<i32>, Vec<i32>) = a.into_iter()
+    ///                                          .partition(|&n| n % 2 == 0);
+    ///
+    /// assert_eq!(even, vec![2]);
+    /// assert_eq!(odd, vec![1, 3]);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn partition<B, F>(self, mut f: F) -> (B, B) where
+        Self: Sized,
+        B: Default + Extend<Self::Item>,
+        F: FnMut(&Self::Item) -> bool
+    {
+        let mut left: B = Default::default();
+        let mut right: B = Default::default();
+
+        for x in self {
+            if f(&x) {
+                left.extend(Some(x))
+            } else {
+                right.extend(Some(x))
+            }
+        }
+
+        (left, right)
+    }
+
+    /// An iterator adaptor that applies a function, producing a single, final value.
+    ///
+    /// `fold()` takes two arguments: an initial value, and a closure with two
+    /// arguments: an 'accumulator', and an element. The closure returns the value that
+    /// the accumulator should have for the next iteration.
+    ///
+    /// The initial value is the value the accumulator will have on the first
+    /// call.
+    ///
+    /// After applying this closure to every element of the iterator, `fold()`
+    /// returns the accumulator.
+    ///
+    /// This operation is sometimes called 'reduce' or 'inject'.
+    ///
+    /// Folding is useful whenever you have a collection of something, and want
+    /// to produce a single value from it.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// // the sum of all of the elements of a
+    /// let sum = a.iter()
+    ///            .fold(0, |acc, &x| acc + x);
+    ///
+    /// assert_eq!(sum, 6);
+    /// ```
+    ///
+    /// Let's walk through each step of the iteration here:
+    ///
+    /// | element | acc | x | result |
+    /// |---------|-----|---|--------|
+    /// |         | 0   |   |        |
+    /// | 1       | 0   | 1 | 1      |
+    /// | 2       | 1   | 2 | 3      |
+    /// | 3       | 3   | 3 | 6      |
+    ///
+    /// And so, our final result, `6`.
+    ///
+    /// It's common for people who haven't used iterators a lot to
+    /// use a `for` loop with a list of things to build up a result. Those
+    /// can be turned into `fold()`s:
+    ///
+    /// ```
+    /// let numbers = [1, 2, 3, 4, 5];
+    ///
+    /// let mut result = 0;
+    ///
+    /// // for loop:
+    /// for i in &numbers {
+    ///     result = result + i;
+    /// }
+    ///
+    /// // fold:
+    /// let result2 = numbers.iter().fold(0, |acc, &x| acc + x);
+    ///
+    /// // they're the same
+    /// assert_eq!(result, result2);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn fold<B, F>(self, init: B, mut f: F) -> B where
+        Self: Sized, F: FnMut(B, Self::Item) -> B,
+    {
+        let mut accum = init;
+        for x in self {
+            accum = f(accum, x);
+        }
+        accum
+    }
+
+    /// Tests if every element of the iterator matches a predicate.
+    ///
+    /// `all()` takes a closure that returns `true` or `false`. It applies
+    /// this closure to each element of the iterator, and if they all return
+    /// `true`, then so does `all()`. If any of them return `false`, it
+    /// returns `false`.
+    ///
+    /// `all()` is short-circuiting; in other words, it will stop processing
+    /// as soon as it finds a `false`, given that no matter what else happens,
+    /// the result will also be `false`.
+    ///
+    /// An empty iterator returns `true`.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// assert!(a.iter().all(|&x| x > 0));
+    ///
+    /// assert!(!a.iter().all(|&x| x > 2));
+    /// ```
+    ///
+    /// Stopping at the first `false`:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// let mut iter = a.iter();
+    ///
+    /// assert!(!iter.all(|&x| x != 2));
+    ///
+    /// // we can still use `iter`, as there are more elements.
+    /// assert_eq!(iter.next(), Some(&3));
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn all<F>(&mut self, mut f: F) -> bool where
+        Self: Sized, F: FnMut(Self::Item) -> bool
+    {
+        for x in self {
+            if !f(x) {
+                return false;
+            }
+        }
+        true
+    }
+
+    /// Tests if any element of the iterator matches a predicate.
+    ///
+    /// `any()` takes a closure that returns `true` or `false`. It applies
+    /// this closure to each element of the iterator, and if any of them return
+    /// `true`, then so does `any()`. If they all return `false`, it
+    /// returns `false`.
+    ///
+    /// `any()` is short-circuiting; in other words, it will stop processing
+    /// as soon as it finds a `true`, given that no matter what else happens,
+    /// the result will also be `true`.
+    ///
+    /// An empty iterator returns `false`.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// assert!(a.iter().any(|&x| x > 0));
+    ///
+    /// assert!(!a.iter().any(|&x| x > 5));
+    /// ```
+    ///
+    /// Stopping at the first `true`:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// let mut iter = a.iter();
+    ///
+    /// assert!(iter.any(|&x| x != 2));
+    ///
+    /// // we can still use `iter`, as there are more elements.
+    /// assert_eq!(iter.next(), Some(&2));
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn any<F>(&mut self, mut f: F) -> bool where
+        Self: Sized,
+        F: FnMut(Self::Item) -> bool
+    {
+        for x in self {
+            if f(x) {
+                return true;
+            }
+        }
+        false
+    }
+
+    /// Searches for an element of an iterator that satisfies a predicate.
+    ///
+    /// `find()` takes a closure that returns `true` or `false`. It applies
+    /// this closure to each element of the iterator, and if any of them return
+    /// `true`, then `find()` returns `Some(element)`. If they all return
+    /// `false`, it returns `None`.
+    ///
+    /// `find()` is short-circuiting; in other words, it will stop processing
+    /// as soon as the closure returns `true`.
+    ///
+    /// Because `find()` takes a reference, and many iterators iterate over
+    /// references, this leads to a possibly confusing situation where the
+    /// argument is a double reference. You can see this effect in the
+    /// examples below, with `&&x`.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// assert_eq!(a.iter().find(|&&x| x == 2), Some(&2));
+    ///
+    /// assert_eq!(a.iter().find(|&&x| x == 5), None);
+    /// ```
+    ///
+    /// Stopping at the first `true`:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// let mut iter = a.iter();
+    ///
+    /// assert_eq!(iter.find(|&&x| x == 2), Some(&2));
+    ///
+    /// // we can still use `iter`, as there are more elements.
+    /// assert_eq!(iter.next(), Some(&3));
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn find<P>(&mut self, mut predicate: P) -> Option<Self::Item> where
+        Self: Sized,
+        P: FnMut(&Self::Item) -> bool,
+    {
+        for x in self {
+            if predicate(&x) { return Some(x) }
+        }
+        None
+    }
+
+    /// Searches for an element in an iterator, returning its index.
+    ///
+    /// `position()` takes a closure that returns `true` or `false`. It applies
+    /// this closure to each element of the iterator, and if one of them
+    /// returns `true`, then `position()` returns `Some(index)`. If all of
+    /// them return `false`, it returns `None`.
+    ///
+    /// `position()` is short-circuiting; in other words, it will stop
+    /// processing as soon as it finds a `true`.
+    ///
+    /// # Overflow Behavior
+    ///
+    /// The method does no guarding against overflows, so if there are more
+    /// than `usize::MAX` non-matching elements, it either produces the wrong
+    /// result or panics. If debug assertions are enabled, a panic is
+    /// guaranteed.
+    ///
+    /// # Panics
+    ///
+    /// This function might panic if the iterator has more than `usize::MAX`
+    /// non-matching elements.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// assert_eq!(a.iter().position(|&x| x == 2), Some(1));
+    ///
+    /// assert_eq!(a.iter().position(|&x| x == 5), None);
+    /// ```
+    ///
+    /// Stopping at the first `true`:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// let mut iter = a.iter();
+    ///
+    /// assert_eq!(iter.position(|&x| x == 2), Some(1));
+    ///
+    /// // we can still use `iter`, as there are more elements.
+    /// assert_eq!(iter.next(), Some(&3));
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn position<P>(&mut self, mut predicate: P) -> Option<usize> where
+        Self: Sized,
+        P: FnMut(Self::Item) -> bool,
+    {
+        // `enumerate` might overflow.
+        for (i, x) in self.enumerate() {
+            if predicate(x) {
+                return Some(i);
+            }
+        }
+        None
+    }
+
+    /// Searches for an element in an iterator from the right, returning its
+    /// index.
+    ///
+    /// `rposition()` takes a closure that returns `true` or `false`. It applies
+    /// this closure to each element of the iterator, starting from the end,
+    /// and if one of them returns `true`, then `rposition()` returns
+    /// `Some(index)`. If all of them return `false`, it returns `None`.
+    ///
+    /// `rposition()` is short-circuiting; in other words, it will stop
+    /// processing as soon as it finds a `true`.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// assert_eq!(a.iter().rposition(|&x| x == 3), Some(2));
+    ///
+    /// assert_eq!(a.iter().rposition(|&x| x == 5), None);
+    /// ```
+    ///
+    /// Stopping at the first `true`:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// let mut iter = a.iter();
+    ///
+    /// assert_eq!(iter.rposition(|&x| x == 2), Some(1));
+    ///
+    /// // we can still use `iter`, as there are more elements.
+    /// assert_eq!(iter.next(), Some(&1));
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn rposition<P>(&mut self, mut predicate: P) -> Option<usize> where
+        P: FnMut(Self::Item) -> bool,
+        Self: Sized + ExactSizeIterator + DoubleEndedIterator
+    {
+        let mut i = self.len();
+
+        while let Some(v) = self.next_back() {
+            if predicate(v) {
+                return Some(i - 1);
+            }
+            // No need for an overflow check here, because `ExactSizeIterator`
+            // implies that the number of elements fits into a `usize`.
+            i -= 1;
+        }
+        None
+    }
+
+    /// Returns the maximum element of an iterator.
+    ///
+    /// If the two elements are equally maximum, the latest element is
+    /// returned.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// assert_eq!(a.iter().max(), Some(&3));
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn max(self) -> Option<Self::Item> where Self: Sized, Self::Item: Ord
+    {
+        select_fold1(self,
+                     |_| (),
+                     // switch to y even if it is only equal, to preserve
+                     // stability.
+                     |_, x, _, y| *x <= *y)
+            .map(|(_, x)| x)
+    }
+
+    /// Returns the minimum element of an iterator.
+    ///
+    /// If the two elements are equally minimum, the first element is
+    /// returned.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// assert_eq!(a.iter().min(), Some(&1));
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn min(self) -> Option<Self::Item> where Self: Sized, Self::Item: Ord
+    {
+        select_fold1(self,
+                     |_| (),
+                     // only switch to y if it is strictly smaller, to
+                     // preserve stability.
+                     |_, x, _, y| *x > *y)
+            .map(|(_, x)| x)
+    }
+
+    /// Returns the element that gives the maximum value from the
+    /// specified function.
+    ///
+    /// Returns the rightmost element if the comparison determines two elements
+    /// to be equally maximum.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let a = [-3_i32, 0, 1, 5, -10];
+    /// assert_eq!(*a.iter().max_by_key(|x| x.abs()).unwrap(), -10);
+    /// ```
+    #[inline]
+    #[stable(feature = "iter_cmp_by_key", since = "1.6.0")]
+    fn max_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item>
+        where Self: Sized, F: FnMut(&Self::Item) -> B,
+    {
+        select_fold1(self,
+                     f,
+                     // switch to y even if it is only equal, to preserve
+                     // stability.
+                     |x_p, _, y_p, _| x_p <= y_p)
+            .map(|(_, x)| x)
+    }
+
+    /// Returns the element that gives the minimum value from the
+    /// specified function.
+    ///
+    /// Returns the latest element if the comparison determines two elements
+    /// to be equally minimum.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let a = [-3_i32, 0, 1, 5, -10];
+    /// assert_eq!(*a.iter().min_by_key(|x| x.abs()).unwrap(), 0);
+    /// ```
+    #[stable(feature = "iter_cmp_by_key", since = "1.6.0")]
+    fn min_by_key<B: Ord, F>(self, f: F) -> Option<Self::Item>
+        where Self: Sized, F: FnMut(&Self::Item) -> B,
+    {
+        select_fold1(self,
+                     f,
+                     // only switch to y if it is strictly smaller, to
+                     // preserve stability.
+                     |x_p, _, y_p, _| x_p > y_p)
+            .map(|(_, x)| x)
+    }
+
+    /// Reverses an iterator's direction.
+    ///
+    /// Usually, iterators iterate from left to right. After using `rev()`,
+    /// an iterator will instead iterate from right to left.
+    ///
+    /// This is only possible if the iterator has an end, so `rev()` only
+    /// works on [`DoubleEndedIterator`]s.
+    ///
+    /// [`DoubleEndedIterator`]: trait.DoubleEndedIterator.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// let mut iter = a.iter().rev();
+    ///
+    /// assert_eq!(iter.next(), Some(&3));
+    /// assert_eq!(iter.next(), Some(&2));
+    /// assert_eq!(iter.next(), Some(&1));
+    ///
+    /// assert_eq!(iter.next(), None);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn rev(self) -> Rev<Self> where Self: Sized + DoubleEndedIterator {
+        Rev{iter: self}
+    }
+
+    /// Converts an iterator of pairs into a pair of containers.
+    ///
+    /// `unzip()` consumes an entire iterator of pairs, producing two
+    /// collections: one from the left elements of the pairs, and one
+    /// from the right elements.
+    ///
+    /// This function is, in some sense, the opposite of [`zip()`].
+    ///
+    /// [`zip()`]: #method.zip
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [(1, 2), (3, 4)];
+    ///
+    /// let (left, right): (Vec<_>, Vec<_>) = a.iter().cloned().unzip();
+    ///
+    /// assert_eq!(left, [1, 3]);
+    /// assert_eq!(right, [2, 4]);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB) where
+        FromA: Default + Extend<A>,
+        FromB: Default + Extend<B>,
+        Self: Sized + Iterator<Item=(A, B)>,
+    {
+        struct SizeHint<A>(usize, Option<usize>, marker::PhantomData<A>);
+        impl<A> Iterator for SizeHint<A> {
+            type Item = A;
+
+            fn next(&mut self) -> Option<A> { None }
+            fn size_hint(&self) -> (usize, Option<usize>) {
+                (self.0, self.1)
+            }
+        }
+
+        let (lo, hi) = self.size_hint();
+        let mut ts: FromA = Default::default();
+        let mut us: FromB = Default::default();
+
+        ts.extend(SizeHint(lo, hi, marker::PhantomData));
+        us.extend(SizeHint(lo, hi, marker::PhantomData));
+
+        for (t, u) in self {
+            ts.extend(Some(t));
+            us.extend(Some(u));
+        }
+
+        (ts, us)
+    }
+
+    /// Creates an iterator which `clone()`s all of its elements.
+    ///
+    /// This is useful when you have an iterator over `&T`, but you need an
+    /// iterator over `T`.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// let v_cloned: Vec<_> = a.iter().cloned().collect();
+    ///
+    /// // cloned is the same as .map(|&x| x), for integers
+    /// let v_map: Vec<_> = a.iter().map(|&x| x).collect();
+    ///
+    /// assert_eq!(v_cloned, vec![1, 2, 3]);
+    /// assert_eq!(v_map, vec![1, 2, 3]);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    fn cloned<'a, T: 'a>(self) -> Cloned<Self>
+        where Self: Sized + Iterator<Item=&'a T>, T: Clone
+    {
+        Cloned { it: self }
+    }
+
+    /// Repeats an iterator endlessly.
+    ///
+    /// Instead of stopping at `None`, the iterator will instead start again,
+    /// from the beginning. After iterating again, it will start at the
+    /// beginning again. And again. And again. Forever.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let a = [1, 2, 3];
+    ///
+    /// let mut it = a.iter().cycle();
+    ///
+    /// assert_eq!(it.next(), Some(&1));
+    /// assert_eq!(it.next(), Some(&2));
+    /// assert_eq!(it.next(), Some(&3));
+    /// assert_eq!(it.next(), Some(&1));
+    /// assert_eq!(it.next(), Some(&2));
+    /// assert_eq!(it.next(), Some(&3));
+    /// assert_eq!(it.next(), Some(&1));
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    fn cycle(self) -> Cycle<Self> where Self: Sized + Clone {
+        Cycle{orig: self.clone(), iter: self}
+    }
+
+    /// Sums the elements of an iterator.
+    ///
+    /// Takes each element, adds them together, and returns the result.
+    ///
+    /// An empty iterator returns the zero value of the type.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// #![feature(iter_arith)]
+    ///
+    /// let a = [1, 2, 3];
+    /// let sum: i32 = a.iter().sum();
+    ///
+    /// assert_eq!(sum, 6);
+    /// ```
+    #[unstable(feature = "iter_arith", reason = "bounds recently changed",
+               issue = "27739")]
+    fn sum<S>(self) -> S where
+        S: Add<Self::Item, Output=S> + Zero,
+        Self: Sized,
+    {
+        self.fold(Zero::zero(), |s, e| s + e)
+    }
+
+    /// Iterates over the entire iterator, multiplying all the elements
+    ///
+    /// An empty iterator returns the one value of the type.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(iter_arith)]
+    ///
+    /// fn factorial(n: u32) -> u32 {
+    ///     (1..).take_while(|&i| i <= n).product()
+    /// }
+    /// assert_eq!(factorial(0), 1);
+    /// assert_eq!(factorial(1), 1);
+    /// assert_eq!(factorial(5), 120);
+    /// ```
+    #[unstable(feature="iter_arith", reason = "bounds recently changed",
+               issue = "27739")]
+    fn product<P>(self) -> P where
+        P: Mul<Self::Item, Output=P> + One,
+        Self: Sized,
+    {
+        self.fold(One::one(), |p, e| p * e)
+    }
+
+    /// Lexicographically compares the elements of this `Iterator` with those
+    /// of another.
+    #[stable(feature = "iter_order", since = "1.5.0")]
+    fn cmp<I>(mut self, other: I) -> Ordering where
+        I: IntoIterator<Item = Self::Item>,
+        Self::Item: Ord,
+        Self: Sized,
+    {
+        let mut other = other.into_iter();
+
+        loop {
+            match (self.next(), other.next()) {
+                (None, None) => return Ordering::Equal,
+                (None, _   ) => return Ordering::Less,
+                (_   , None) => return Ordering::Greater,
+                (Some(x), Some(y)) => match x.cmp(&y) {
+                    Ordering::Equal => (),
+                    non_eq => return non_eq,
+                },
+            }
+        }
+    }
+
+    /// Lexicographically compares the elements of this `Iterator` with those
+    /// of another.
+    #[stable(feature = "iter_order", since = "1.5.0")]
+    fn partial_cmp<I>(mut self, other: I) -> Option<Ordering> where
+        I: IntoIterator,
+        Self::Item: PartialOrd<I::Item>,
+        Self: Sized,
+    {
+        let mut other = other.into_iter();
+
+        loop {
+            match (self.next(), other.next()) {
+                (None, None) => return Some(Ordering::Equal),
+                (None, _   ) => return Some(Ordering::Less),
+                (_   , None) => return Some(Ordering::Greater),
+                (Some(x), Some(y)) => match x.partial_cmp(&y) {
+                    Some(Ordering::Equal) => (),
+                    non_eq => return non_eq,
+                },
+            }
+        }
+    }
+
+    /// Determines if the elements of this `Iterator` are equal to those of
+    /// another.
+    #[stable(feature = "iter_order", since = "1.5.0")]
+    fn eq<I>(mut self, other: I) -> bool where
+        I: IntoIterator,
+        Self::Item: PartialEq<I::Item>,
+        Self: Sized,
+    {
+        let mut other = other.into_iter();
+
+        loop {
+            match (self.next(), other.next()) {
+                (None, None) => return true,
+                (None, _) | (_, None) => return false,
+                (Some(x), Some(y)) => if x != y { return false },
+            }
+        }
+    }
+
+    /// Determines if the elements of this `Iterator` are unequal to those of
+    /// another.
+    #[stable(feature = "iter_order", since = "1.5.0")]
+    fn ne<I>(mut self, other: I) -> bool where
+        I: IntoIterator,
+        Self::Item: PartialEq<I::Item>,
+        Self: Sized,
+    {
+        let mut other = other.into_iter();
+
+        loop {
+            match (self.next(), other.next()) {
+                (None, None) => return false,
+                (None, _) | (_, None) => return true,
+                (Some(x), Some(y)) => if x.ne(&y) { return true },
+            }
+        }
+    }
+
+    /// Determines if the elements of this `Iterator` are lexicographically
+    /// less than those of another.
+    #[stable(feature = "iter_order", since = "1.5.0")]
+    fn lt<I>(mut self, other: I) -> bool where
+        I: IntoIterator,
+        Self::Item: PartialOrd<I::Item>,
+        Self: Sized,
+    {
+        let mut other = other.into_iter();
+
+        loop {
+            match (self.next(), other.next()) {
+                (None, None) => return false,
+                (None, _   ) => return true,
+                (_   , None) => return false,
+                (Some(x), Some(y)) => {
+                    match x.partial_cmp(&y) {
+                        Some(Ordering::Less) => return true,
+                        Some(Ordering::Equal) => {}
+                        Some(Ordering::Greater) => return false,
+                        None => return false,
+                    }
+                },
+            }
+        }
+    }
+
+    /// Determines if the elements of this `Iterator` are lexicographically
+    /// less or equal to those of another.
+    #[stable(feature = "iter_order", since = "1.5.0")]
+    fn le<I>(mut self, other: I) -> bool where
+        I: IntoIterator,
+        Self::Item: PartialOrd<I::Item>,
+        Self: Sized,
+    {
+        let mut other = other.into_iter();
+
+        loop {
+            match (self.next(), other.next()) {
+                (None, None) => return true,
+                (None, _   ) => return true,
+                (_   , None) => return false,
+                (Some(x), Some(y)) => {
+                    match x.partial_cmp(&y) {
+                        Some(Ordering::Less) => return true,
+                        Some(Ordering::Equal) => {}
+                        Some(Ordering::Greater) => return false,
+                        None => return false,
+                    }
+                },
+            }
+        }
+    }
+
+    /// Determines if the elements of this `Iterator` are lexicographically
+    /// greater than those of another.
+    #[stable(feature = "iter_order", since = "1.5.0")]
+    fn gt<I>(mut self, other: I) -> bool where
+        I: IntoIterator,
+        Self::Item: PartialOrd<I::Item>,
+        Self: Sized,
+    {
+        let mut other = other.into_iter();
+
+        loop {
+            match (self.next(), other.next()) {
+                (None, None) => return false,
+                (None, _   ) => return false,
+                (_   , None) => return true,
+                (Some(x), Some(y)) => {
+                    match x.partial_cmp(&y) {
+                        Some(Ordering::Less) => return false,
+                        Some(Ordering::Equal) => {}
+                        Some(Ordering::Greater) => return true,
+                        None => return false,
+                    }
+                }
+            }
+        }
+    }
+
+    /// Determines if the elements of this `Iterator` are lexicographically
+    /// greater than or equal to those of another.
+    #[stable(feature = "iter_order", since = "1.5.0")]
+    fn ge<I>(mut self, other: I) -> bool where
+        I: IntoIterator,
+        Self::Item: PartialOrd<I::Item>,
+        Self: Sized,
+    {
+        let mut other = other.into_iter();
+
+        loop {
+            match (self.next(), other.next()) {
+                (None, None) => return true,
+                (None, _   ) => return false,
+                (_   , None) => return true,
+                (Some(x), Some(y)) => {
+                    match x.partial_cmp(&y) {
+                        Some(Ordering::Less) => return false,
+                        Some(Ordering::Equal) => {}
+                        Some(Ordering::Greater) => return true,
+                        None => return false,
+                    }
+                },
+            }
+        }
+    }
+}
+
+/// Select an element from an iterator based on the given projection
+/// and "comparison" function.
+///
+/// This is an idiosyncratic helper to try to factor out the
+/// commonalities of {max,min}{,_by}. In particular, this avoids
+/// having to implement optimizations several times.
+#[inline]
+fn select_fold1<I,B, FProj, FCmp>(mut it: I,
+                                  mut f_proj: FProj,
+                                  mut f_cmp: FCmp) -> Option<(B, I::Item)>
+    where I: Iterator,
+          FProj: FnMut(&I::Item) -> B,
+          FCmp: FnMut(&B, &I::Item, &B, &I::Item) -> bool
+{
+    // start with the first element as our selection. This avoids
+    // having to use `Option`s inside the loop, translating to a
+    // sizeable performance gain (6x in one case).
+    it.next().map(|mut sel| {
+        let mut sel_p = f_proj(&sel);
+
+        for x in it {
+            let x_p = f_proj(&x);
+            if f_cmp(&sel_p,  &sel, &x_p, &x) {
+                sel = x;
+                sel_p = x_p;
+            }
+        }
+        (sel_p, sel)
+    })
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, I: Iterator + ?Sized> Iterator for &'a mut I {
+    type Item = I::Item;
+    fn next(&mut self) -> Option<I::Item> { (**self).next() }
+    fn size_hint(&self) -> (usize, Option<usize>) { (**self).size_hint() }
+}