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    // Copyright 2012-2015 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.

    //! A dynamically-sized view into a contiguous sequence, `[T]`.
    //!
    //! Slices are a view into a block of memory represented as a pointer and a
    //! length.
    //!
    //! ```
    //! // slicing a Vec
    //! let vec = vec![1, 2, 3];
    //! let int_slice = &vec[..];
    //! // coercing an array to a slice
    //! let str_slice: &[&str] = &["one", "two", "three"];
    //! ```
    //!
    //! Slices are either mutable or shared. The shared slice type is `&[T]`,
    //! while the mutable slice type is `&mut [T]`, where `T` represents the element
    //! type. For example, you can mutate the block of memory that a mutable slice
    //! points to:
    //!
    //! ```
    //! let x = &mut [1, 2, 3];
    //! x[1] = 7;
    //! assert_eq!(x, &[1, 7, 3]);
    //! ```
    //!
    //! Here are some of the things this module contains:
    //!
    //! ## Structs
    //!
    //! There are several structs that are useful for slices, such as `Iter`, which
    //! represents iteration over a slice.
    //!
    //! ## Trait Implementations
    //!
    //! There are several implementations of common traits for slices. Some examples
    //! include:
    //!
    //! * `Clone`
    //! * `Eq`, `Ord` - for slices whose element type are `Eq` or `Ord`.
    //! * `Hash` - for slices whose element type is `Hash`
    //!
    //! ## Iteration
    //!
    //! The slices implement `IntoIterator`. The iterator yields references to the
    //! slice elements.
    //!
    //! ```
    //! let numbers = &[0, 1, 2];
    //! for n in numbers {
    //!     println!("{} is a number!", n);
    //! }
    //! ```
    //!
    //! The mutable slice yields mutable references to the elements:
    //!
    //! ```
    //! let mut scores = [7, 8, 9];
    //! for score in &mut scores[..] {
    //!     *score += 1;
    //! }
    //! ```
    //!
    //! This iterator yields mutable references to the slice's elements, so while
    //! the element type of the slice is `i32`, the element type of the iterator is
    //! `&mut i32`.
    //!
    //! * `.iter()` and `.iter_mut()` are the explicit methods to return the default
    //!   iterators.
    //! * Further methods that return iterators are `.split()`, `.splitn()`,
    //!   `.chunks()`, `.windows()` and more.
    //!
    //! *[See also the slice primitive type](../primitive.slice.html).*
    #![stable(feature = "rust1", since = "1.0.0")]

    // Many of the usings in this module are only used in the test configuration.
    // It's cleaner to just turn off the unused_imports warning than to fix them.
    #![allow(unused_imports)]

    use alloc::boxed::Box;
    use core::clone::Clone;
    use core::cmp::Ordering::{self, Greater, Less};
    use core::cmp::{self, Ord, PartialEq};
    use core::iter::Iterator;
    use core::marker::Sized;
    use core::mem::size_of;
    use core::mem;
    use core::ops::FnMut;
    use core::option::Option::{self, Some, None};
    use core::ptr;
    use core::result::Result;
    use core::slice as core_slice;

    use borrow::{Borrow, BorrowMut, ToOwned};
    use vec::Vec;

    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::slice::{Chunks, Windows};
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::slice::{Iter, IterMut};
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::slice::{SplitMut, ChunksMut, Split};
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::slice::{SplitN, RSplitN, SplitNMut, RSplitNMut};
    #[unstable(feature = "slice_bytes", issue = "27740")]
    #[allow(deprecated)]
    pub use core::slice::bytes;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::slice::{from_raw_parts, from_raw_parts_mut};

    ////////////////////////////////////////////////////////////////////////////////
    // Basic slice extension methods
    ////////////////////////////////////////////////////////////////////////////////

    // HACK(japaric) needed for the implementation of `vec!` macro during testing
    // NB see the hack module in this file for more details
    #[cfg(test)]
    pub use self::hack::into_vec;

    // HACK(japaric) needed for the implementation of `Vec::clone` during testing
    // NB see the hack module in this file for more details
    #[cfg(test)]
    pub use self::hack::to_vec;

    // HACK(japaric): With cfg(test) `impl [T]` is not available, these three
    // functions are actually methods that are in `impl [T]` but not in
    // `core::slice::SliceExt` - we need to supply these functions for the
    // `test_permutations` test
    mod hack {
        use alloc::boxed::Box;
        use core::clone::Clone;
        #[cfg(test)]
        use core::iter::Iterator;
        use core::mem;
        #[cfg(test)]
        use core::option::Option::{Some, None};

        #[cfg(test)]
        use string::ToString;
        use vec::Vec;

        pub fn into_vec<T>(mut b: Box<[T]>) -> Vec<T> {
            unsafe {
                let xs = Vec::from_raw_parts(b.as_mut_ptr(), b.len(), b.len());
                mem::forget(b);
                xs
            }
        }

        #[inline]
        pub fn to_vec<T>(s: &[T]) -> Vec<T>
            where T: Clone
        {
            let mut vector = Vec::with_capacity(s.len());
            vector.extend_from_slice(s);
            vector
        }
    }

    /// Allocating extension methods for slices.
    #[lang = "slice"]
    #[cfg(not(test))]
    impl<T> [T] {
        /// Returns the number of elements in the slice.
        ///
        /// # Example
        ///
        /// ```
        /// let a = [1, 2, 3];
        /// assert_eq!(a.len(), 3);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn len(&self) -> usize {
            core_slice::SliceExt::len(self)
        }

        /// Returns true if the slice has a length of 0
        ///
        /// # Example
        ///
        /// ```
        /// let a = [1, 2, 3];
        /// assert!(!a.is_empty());
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn is_empty(&self) -> bool {
            core_slice::SliceExt::is_empty(self)
        }

        /// Returns the first element of a slice, or `None` if it is empty.
        ///
        /// # Examples
        ///
        /// ```
        /// let v = [10, 40, 30];
        /// assert_eq!(Some(&10), v.first());
        ///
        /// let w: &[i32] = &[];
        /// assert_eq!(None, w.first());
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn first(&self) -> Option<&T> {
            core_slice::SliceExt::first(self)
        }

        /// Returns a mutable pointer to the first element of a slice, or `None` if it is empty
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn first_mut(&mut self) -> Option<&mut T> {
            core_slice::SliceExt::first_mut(self)
        }

        /// Returns the first and all the rest of the elements of a slice.
        #[stable(feature = "slice_splits", since = "1.5.0")]
        #[inline]
        pub fn split_first(&self) -> Option<(&T, &[T])> {
            core_slice::SliceExt::split_first(self)
        }

        /// Returns the first and all the rest of the elements of a slice.
        #[stable(feature = "slice_splits", since = "1.5.0")]
        #[inline]
        pub fn split_first_mut(&mut self) -> Option<(&mut T, &mut [T])> {
            core_slice::SliceExt::split_first_mut(self)
        }

        /// Returns the last and all the rest of the elements of a slice.
        #[stable(feature = "slice_splits", since = "1.5.0")]
        #[inline]
        pub fn split_last(&self) -> Option<(&T, &[T])> {
            core_slice::SliceExt::split_last(self)

        }

        /// Returns the last and all the rest of the elements of a slice.
        #[stable(feature = "slice_splits", since = "1.5.0")]
        #[inline]
        pub fn split_last_mut(&mut self) -> Option<(&mut T, &mut [T])> {
            core_slice::SliceExt::split_last_mut(self)
        }

        /// Returns the last element of a slice, or `None` if it is empty.
        ///
        /// # Examples
        ///
        /// ```
        /// let v = [10, 40, 30];
        /// assert_eq!(Some(&30), v.last());
        ///
        /// let w: &[i32] = &[];
        /// assert_eq!(None, w.last());
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn last(&self) -> Option<&T> {
            core_slice::SliceExt::last(self)
        }

        /// Returns a mutable pointer to the last item in the slice.
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn last_mut(&mut self) -> Option<&mut T> {
            core_slice::SliceExt::last_mut(self)
        }

        /// Returns the element of a slice at the given index, or `None` if the
        /// index is out of bounds.
        ///
        /// # Examples
        ///
        /// ```
        /// let v = [10, 40, 30];
        /// assert_eq!(Some(&40), v.get(1));
        /// assert_eq!(None, v.get(3));
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn get(&self, index: usize) -> Option<&T> {
            core_slice::SliceExt::get(self, index)
        }

        /// Returns a mutable reference to the element at the given index,
        /// or `None` if the index is out of bounds
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn get_mut(&mut self, index: usize) -> Option<&mut T> {
            core_slice::SliceExt::get_mut(self, index)
        }

        /// Returns a pointer to the element at the given index, without doing
        /// bounds checking.
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub unsafe fn get_unchecked(&self, index: usize) -> &T {
            core_slice::SliceExt::get_unchecked(self, index)
        }

        /// Returns an unsafe mutable pointer to the element in index
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub unsafe fn get_unchecked_mut(&mut self, index: usize) -> &mut T {
            core_slice::SliceExt::get_unchecked_mut(self, index)
        }

        /// Returns an raw pointer to the slice's buffer
        ///
        /// The caller must ensure that the slice outlives the pointer this
        /// function returns, or else it will end up pointing to garbage.
        ///
        /// Modifying the slice may cause its buffer to be reallocated, which
        /// would also make any pointers to it invalid.
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn as_ptr(&self) -> *const T {
            core_slice::SliceExt::as_ptr(self)
        }

        /// Returns an unsafe mutable pointer to the slice's buffer.
        ///
        /// The caller must ensure that the slice outlives the pointer this
        /// function returns, or else it will end up pointing to garbage.
        ///
        /// Modifying the slice may cause its buffer to be reallocated, which
        /// would also make any pointers to it invalid.
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn as_mut_ptr(&mut self) -> *mut T {
            core_slice::SliceExt::as_mut_ptr(self)
        }

        /// Swaps two elements in a slice.
        ///
        /// # Arguments
        ///
        /// * a - The index of the first element
        /// * b - The index of the second element
        ///
        /// # Panics
        ///
        /// Panics if `a` or `b` are out of bounds.
        ///
        /// # Example
        ///
        /// ```rust
        /// let mut v = ["a", "b", "c", "d"];
        /// v.swap(1, 3);
        /// assert!(v == ["a", "d", "c", "b"]);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn swap(&mut self, a: usize, b: usize) {
            core_slice::SliceExt::swap(self, a, b)
        }

        /// Reverse the order of elements in a slice, in place.
        ///
        /// # Example
        ///
        /// ```rust
        /// let mut v = [1, 2, 3];
        /// v.reverse();
        /// assert!(v == [3, 2, 1]);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn reverse(&mut self) {
            core_slice::SliceExt::reverse(self)
        }

        /// Returns an iterator over the slice.
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn iter(&self) -> Iter<T> {
            core_slice::SliceExt::iter(self)
        }

        /// Returns an iterator that allows modifying each value
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn iter_mut(&mut self) -> IterMut<T> {
            core_slice::SliceExt::iter_mut(self)
        }

        /// Returns an iterator over all contiguous windows of length
        /// `size`. The windows overlap. If the slice is shorter than
        /// `size`, the iterator returns no values.
        ///
        /// # Panics
        ///
        /// Panics if `size` is 0.
        ///
        /// # Example
        ///
        /// Print the adjacent pairs of a slice (i.e. `[1,2]`, `[2,3]`,
        /// `[3,4]`):
        ///
        /// ```rust
        /// let v = &[1, 2, 3, 4];
        /// for win in v.windows(2) {
        ///     println!("{:?}", win);
        /// }
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn windows(&self, size: usize) -> Windows<T> {
            core_slice::SliceExt::windows(self, size)
        }

        /// Returns an iterator over `size` elements of the slice at a
        /// time. The chunks do not overlap. If `size` does not divide the
        /// length of the slice, then the last chunk will not have length
        /// `size`.
        ///
        /// # Panics
        ///
        /// Panics if `size` is 0.
        ///
        /// # Example
        ///
        /// Print the slice two elements at a time (i.e. `[1,2]`,
        /// `[3,4]`, `[5]`):
        ///
        /// ```rust
        /// let v = &[1, 2, 3, 4, 5];
        /// for win in v.chunks(2) {
        ///     println!("{:?}", win);
        /// }
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn chunks(&self, size: usize) -> Chunks<T> {
            core_slice::SliceExt::chunks(self, size)
        }

        /// Returns an iterator over `chunk_size` elements of the slice at a time.
        /// The chunks are mutable and do not overlap. If `chunk_size` does
        /// not divide the length of the slice, then the last chunk will not
        /// have length `chunk_size`.
        ///
        /// # Panics
        ///
        /// Panics if `chunk_size` is 0.
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<T> {
            core_slice::SliceExt::chunks_mut(self, chunk_size)
        }

        /// Divides one slice into two at an index.
        ///
        /// The first will contain all indices from `[0, mid)` (excluding
        /// the index `mid` itself) and the second will contain all
        /// indices from `[mid, len)` (excluding the index `len` itself).
        ///
        /// # Panics
        ///
        /// Panics if `mid > len`.
        ///
        /// # Examples
        ///
        /// ```
        /// let v = [10, 40, 30, 20, 50];
        /// let (v1, v2) = v.split_at(2);
        /// assert_eq!([10, 40], v1);
        /// assert_eq!([30, 20, 50], v2);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn split_at(&self, mid: usize) -> (&[T], &[T]) {
            core_slice::SliceExt::split_at(self, mid)
        }

        /// Divides one `&mut` into two at an index.
        ///
        /// The first will contain all indices from `[0, mid)` (excluding
        /// the index `mid` itself) and the second will contain all
        /// indices from `[mid, len)` (excluding the index `len` itself).
        ///
        /// # Panics
        ///
        /// Panics if `mid > len`.
        ///
        /// # Example
        ///
        /// ```rust
        /// let mut v = [1, 2, 3, 4, 5, 6];
        ///
        /// // scoped to restrict the lifetime of the borrows
        /// {
        ///    let (left, right) = v.split_at_mut(0);
        ///    assert!(left == []);
        ///    assert!(right == [1, 2, 3, 4, 5, 6]);
        /// }
        ///
        /// {
        ///     let (left, right) = v.split_at_mut(2);
        ///     assert!(left == [1, 2]);
        ///     assert!(right == [3, 4, 5, 6]);
        /// }
        ///
        /// {
        ///     let (left, right) = v.split_at_mut(6);
        ///     assert!(left == [1, 2, 3, 4, 5, 6]);
        ///     assert!(right == []);
        /// }
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn split_at_mut(&mut self, mid: usize) -> (&mut [T], &mut [T]) {
            core_slice::SliceExt::split_at_mut(self, mid)
        }

        /// Returns an iterator over subslices separated by elements that match
        /// `pred`.  The matched element is not contained in the subslices.
        ///
        /// # Examples
        ///
        /// Print the slice split by numbers divisible by 3 (i.e. `[10, 40]`,
        /// `[20]`, `[50]`):
        ///
        /// ```
        /// let v = [10, 40, 30, 20, 60, 50];
        /// for group in v.split(|num| *num % 3 == 0) {
        ///     println!("{:?}", group);
        /// }
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn split<F>(&self, pred: F) -> Split<T, F>
            where F: FnMut(&T) -> bool
        {
            core_slice::SliceExt::split(self, pred)
        }

        /// Returns an iterator over mutable subslices separated by elements that
        /// match `pred`.  The matched element is not contained in the subslices.
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn split_mut<F>(&mut self, pred: F) -> SplitMut<T, F>
            where F: FnMut(&T) -> bool
        {
            core_slice::SliceExt::split_mut(self, pred)
        }

        /// Returns an iterator over subslices separated by elements that match
        /// `pred`, limited to returning at most `n` items.  The matched element is
        /// not contained in the subslices.
        ///
        /// The last element returned, if any, will contain the remainder of the
        /// slice.
        ///
        /// # Examples
        ///
        /// Print the slice split once by numbers divisible by 3 (i.e. `[10, 40]`,
        /// `[20, 60, 50]`):
        ///
        /// ```
        /// let v = [10, 40, 30, 20, 60, 50];
        /// for group in v.splitn(2, |num| *num % 3 == 0) {
        ///     println!("{:?}", group);
        /// }
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn splitn<F>(&self, n: usize, pred: F) -> SplitN<T, F>
            where F: FnMut(&T) -> bool
        {
            core_slice::SliceExt::splitn(self, n, pred)
        }

        /// Returns an iterator over subslices separated by elements that match
        /// `pred`, limited to returning at most `n` items.  The matched element is
        /// not contained in the subslices.
        ///
        /// The last element returned, if any, will contain the remainder of the
        /// slice.
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn splitn_mut<F>(&mut self, n: usize, pred: F) -> SplitNMut<T, F>
            where F: FnMut(&T) -> bool
        {
            core_slice::SliceExt::splitn_mut(self, n, pred)
        }

        /// Returns an iterator over subslices separated by elements that match
        /// `pred` limited to returning at most `n` items. This starts at the end of
        /// the slice and works backwards.  The matched element is not contained in
        /// the subslices.
        ///
        /// The last element returned, if any, will contain the remainder of the
        /// slice.
        ///
        /// # Examples
        ///
        /// Print the slice split once, starting from the end, by numbers divisible
        /// by 3 (i.e. `[50]`, `[10, 40, 30, 20]`):
        ///
        /// ```
        /// let v = [10, 40, 30, 20, 60, 50];
        /// for group in v.rsplitn(2, |num| *num % 3 == 0) {
        ///     println!("{:?}", group);
        /// }
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn rsplitn<F>(&self, n: usize, pred: F) -> RSplitN<T, F>
            where F: FnMut(&T) -> bool
        {
            core_slice::SliceExt::rsplitn(self, n, pred)
        }

        /// Returns an iterator over subslices separated by elements that match
        /// `pred` limited to returning at most `n` items. This starts at the end of
        /// the slice and works backwards.  The matched element is not contained in
        /// the subslices.
        ///
        /// The last element returned, if any, will contain the remainder of the
        /// slice.
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn rsplitn_mut<F>(&mut self, n: usize, pred: F) -> RSplitNMut<T, F>
            where F: FnMut(&T) -> bool
        {
            core_slice::SliceExt::rsplitn_mut(self, n, pred)
        }

        /// Returns true if the slice contains an element with the given value.
        ///
        /// # Examples
        ///
        /// ```
        /// let v = [10, 40, 30];
        /// assert!(v.contains(&30));
        /// assert!(!v.contains(&50));
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn contains(&self, x: &T) -> bool
            where T: PartialEq
        {
            core_slice::SliceExt::contains(self, x)
        }

        /// Returns true if `needle` is a prefix of the slice.
        ///
        /// # Examples
        ///
        /// ```
        /// let v = [10, 40, 30];
        /// assert!(v.starts_with(&[10]));
        /// assert!(v.starts_with(&[10, 40]));
        /// assert!(!v.starts_with(&[50]));
        /// assert!(!v.starts_with(&[10, 50]));
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn starts_with(&self, needle: &[T]) -> bool
            where T: PartialEq
        {
            core_slice::SliceExt::starts_with(self, needle)
        }

        /// Returns true if `needle` is a suffix of the slice.
        ///
        /// # Examples
        ///
        /// ```
        /// let v = [10, 40, 30];
        /// assert!(v.ends_with(&[30]));
        /// assert!(v.ends_with(&[40, 30]));
        /// assert!(!v.ends_with(&[50]));
        /// assert!(!v.ends_with(&[50, 30]));
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn ends_with(&self, needle: &[T]) -> bool
            where T: PartialEq
        {
            core_slice::SliceExt::ends_with(self, needle)
        }

        /// Binary search a sorted slice for a given element.
        ///
        /// If the value is found then `Ok` is returned, containing the
        /// index of the matching element; if the value is not found then
        /// `Err` is returned, containing the index where a matching
        /// element could be inserted while maintaining sorted order.
        ///
        /// # Example
        ///
        /// Looks up a series of four elements. The first is found, with a
        /// uniquely determined position; the second and third are not
        /// found; the fourth could match any position in `[1,4]`.
        ///
        /// ```rust
        /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
        ///
        /// assert_eq!(s.binary_search(&13),  Ok(9));
        /// assert_eq!(s.binary_search(&4),   Err(7));
        /// assert_eq!(s.binary_search(&100), Err(13));
        /// let r = s.binary_search(&1);
        /// assert!(match r { Ok(1...4) => true, _ => false, });
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn binary_search(&self, x: &T) -> Result<usize, usize>
            where T: Ord
        {
            core_slice::SliceExt::binary_search(self, x)
        }

        /// Binary search a sorted slice with a comparator function.
        ///
        /// The comparator function should implement an order consistent
        /// with the sort order of the underlying slice, returning an
        /// order code that indicates whether its argument is `Less`,
        /// `Equal` or `Greater` the desired target.
        ///
        /// If a matching value is found then returns `Ok`, containing
        /// the index for the matched element; if no match is found then
        /// `Err` is returned, containing the index where a matching
        /// element could be inserted while maintaining sorted order.
        ///
        /// # Example
        ///
        /// Looks up a series of four elements. The first is found, with a
        /// uniquely determined position; the second and third are not
        /// found; the fourth could match any position in `[1,4]`.
        ///
        /// ```rust
        /// let s = [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
        ///
        /// let seek = 13;
        /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Ok(9));
        /// let seek = 4;
        /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(7));
        /// let seek = 100;
        /// assert_eq!(s.binary_search_by(|probe| probe.cmp(&seek)), Err(13));
        /// let seek = 1;
        /// let r = s.binary_search_by(|probe| probe.cmp(&seek));
        /// assert!(match r { Ok(1...4) => true, _ => false, });
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn binary_search_by<F>(&self, f: F) -> Result<usize, usize>
            where F: FnMut(&T) -> Ordering
        {
            core_slice::SliceExt::binary_search_by(self, f)
        }

        /// Sorts the slice, in place.
        ///
        /// This is equivalent to `self.sort_by(|a, b| a.cmp(b))`.
        ///
        /// This is a stable sort.
        ///
        /// # Examples
        ///
        /// ```rust
        /// let mut v = [-5, 4, 1, -3, 2];
        ///
        /// v.sort();
        /// assert!(v == [-5, -3, 1, 2, 4]);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn sort(&mut self)
            where T: Ord
        {
            self.sort_by(|a, b| a.cmp(b))
        }

        /// Sorts the slice, in place, using `key` to extract a key by which to
        /// order the sort by.
        ///
        /// This sort is `O(n log n)` worst-case and stable, but allocates
        /// approximately `2 * n`, where `n` is the length of `self`.
        ///
        /// This is a stable sort.
        ///
        /// # Examples
        ///
        /// ```rust
        /// let mut v = [-5i32, 4, 1, -3, 2];
        ///
        /// v.sort_by_key(|k| k.abs());
        /// assert!(v == [1, 2, -3, 4, -5]);
        /// ```
        #[stable(feature = "slice_sort_by_key", since = "1.7.0")]
        #[inline]
        pub fn sort_by_key<B, F>(&mut self, mut f: F)
            where F: FnMut(&T) -> B, B: Ord
        {
            self.sort_by(|a, b| f(a).cmp(&f(b)))
        }

        /// Sorts the slice, in place, using `compare` to compare
        /// elements.
        ///
        /// This sort is `O(n log n)` worst-case and stable, but allocates
        /// approximately `2 * n`, where `n` is the length of `self`.
        ///
        /// # Examples
        ///
        /// ```rust
        /// let mut v = [5, 4, 1, 3, 2];
        /// v.sort_by(|a, b| a.cmp(b));
        /// assert!(v == [1, 2, 3, 4, 5]);
        ///
        /// // reverse sorting
        /// v.sort_by(|a, b| b.cmp(a));
        /// assert!(v == [5, 4, 3, 2, 1]);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn sort_by<F>(&mut self, compare: F)
            where F: FnMut(&T, &T) -> Ordering
        {
            merge_sort(self, compare)
        }

        /// Copies the elements from `src` into `self`.
        ///
        /// The length of this slice must be the same as the slice passed in.
        ///
        /// # Panics
        ///
        /// This function will panic if the two slices have different lengths.
        ///
        /// # Example
        ///
        /// ```rust
        /// let mut dst = [0, 0, 0];
        /// let src = [1, 2, 3];
        ///
        /// dst.clone_from_slice(&src);
        /// assert!(dst == [1, 2, 3]);
        /// ```
        #[stable(feature = "clone_from_slice", since = "1.7.0")]
        pub fn clone_from_slice(&mut self, src: &[T]) where T: Clone {
            core_slice::SliceExt::clone_from_slice(self, src)
        }

        /// Copies `self` into a new `Vec`.
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn to_vec(&self) -> Vec<T>
            where T: Clone
        {
            // NB see hack module in this file
            hack::to_vec(self)
        }

        /// Converts `self` into a vector without clones or allocation.
        #[stable(feature = "rust1", since = "1.0.0")]
        #[inline]
        pub fn into_vec(self: Box<Self>) -> Vec<T> {
            // NB see hack module in this file
            hack::into_vec(self)
        }
    }

    ////////////////////////////////////////////////////////////////////////////////
    // Extension traits for slices over specific kinds of data
    ////////////////////////////////////////////////////////////////////////////////
    #[unstable(feature = "slice_concat_ext",
               reason = "trait should not have to exist",
               issue = "27747")]
    /// An extension trait for concatenating slices
    pub trait SliceConcatExt<T: ?Sized> {
        #[unstable(feature = "slice_concat_ext",
                   reason = "trait should not have to exist",
                   issue = "27747")]
        /// The resulting type after concatenation
        type Output;

        /// Flattens a slice of `T` into a single value `Self::Output`.
        ///
        /// # Examples
        ///
        /// ```
        /// assert_eq!(["hello", "world"].concat(), "helloworld");
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        fn concat(&self) -> Self::Output;

        /// Flattens a slice of `T` into a single value `Self::Output`, placing a
        /// given separator between each.
        ///
        /// # Examples
        ///
        /// ```
        /// assert_eq!(["hello", "world"].join(" "), "hello world");
        /// ```
        #[stable(feature = "rename_connect_to_join", since = "1.3.0")]
        fn join(&self, sep: &T) -> Self::Output;

        #[stable(feature = "rust1", since = "1.0.0")]
        #[rustc_deprecated(since = "1.3.0", reason = "renamed to join")]
        fn connect(&self, sep: &T) -> Self::Output;
    }

    #[unstable(feature = "slice_concat_ext",
               reason = "trait should not have to exist",
               issue = "27747")]
    impl<T: Clone, V: Borrow<[T]>> SliceConcatExt<T> for [V] {
        type Output = Vec<T>;

        fn concat(&self) -> Vec<T> {
            let size = self.iter().fold(0, |acc, v| acc + v.borrow().len());
            let mut result = Vec::with_capacity(size);
            for v in self {
                result.extend_from_slice(v.borrow())
            }
            result
        }

        fn join(&self, sep: &T) -> Vec<T> {
            let size = self.iter().fold(0, |acc, v| acc + v.borrow().len());
            let mut result = Vec::with_capacity(size + self.len());
            let mut first = true;
            for v in self {
                if first {
                    first = false
                } else {
                    result.push(sep.clone())
                }
                result.extend_from_slice(v.borrow())
            }
            result
        }

        fn connect(&self, sep: &T) -> Vec<T> {
            self.join(sep)
        }
    }

    ////////////////////////////////////////////////////////////////////////////////
    // Standard trait implementations for slices
    ////////////////////////////////////////////////////////////////////////////////

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T> Borrow<[T]> for Vec<T> {
        fn borrow(&self) -> &[T] {
            &self[..]
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T> BorrowMut<[T]> for Vec<T> {
        fn borrow_mut(&mut self) -> &mut [T] {
            &mut self[..]
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: Clone> ToOwned for [T] {
        type Owned = Vec<T>;
        #[cfg(not(test))]
        fn to_owned(&self) -> Vec<T> {
            self.to_vec()
        }

        // HACK(japaric): with cfg(test) the inherent `[T]::to_vec`, which is required for this method
        // definition, is not available. Since we don't require this method for testing purposes, I'll
        // just stub it
        // NB see the slice::hack module in slice.rs for more information
        #[cfg(test)]
        fn to_owned(&self) -> Vec<T> {
            panic!("not available with cfg(test)")
        }
    }

    ////////////////////////////////////////////////////////////////////////////////
    // Sorting
    ////////////////////////////////////////////////////////////////////////////////

    fn insertion_sort<T, F>(v: &mut [T], mut compare: F)
        where F: FnMut(&T, &T) -> Ordering
    {
        let len = v.len() as isize;
        let buf_v = v.as_mut_ptr();

        // 1 <= i < len;
        for i in 1..len {
            // j satisfies: 0 <= j <= i;
            let mut j = i;
            unsafe {
                // `i` is in bounds.
                let read_ptr = buf_v.offset(i) as *const T;

                // find where to insert, we need to do strict <,
                // rather than <=, to maintain stability.

                // 0 <= j - 1 < len, so .offset(j - 1) is in bounds.
                while j > 0 && compare(&*read_ptr, &*buf_v.offset(j - 1)) == Less {
                    j -= 1;
                }

                // shift everything to the right, to make space to
                // insert this value.

                // j + 1 could be `len` (for the last `i`), but in
                // that case, `i == j` so we don't copy. The
                // `.offset(j)` is always in bounds.

                if i != j {
                    let tmp = ptr::read(read_ptr);
                    ptr::copy(&*buf_v.offset(j), buf_v.offset(j + 1), (i - j) as usize);
                    ptr::copy_nonoverlapping(&tmp, buf_v.offset(j), 1);
                    mem::forget(tmp);
                }
            }
        }
    }

    fn merge_sort<T, F>(v: &mut [T], mut compare: F)
        where F: FnMut(&T, &T) -> Ordering
    {
        // warning: this wildly uses unsafe.
        const BASE_INSERTION: usize = 32;
        const LARGE_INSERTION: usize = 16;

        // FIXME #12092: smaller insertion runs seems to make sorting
        // vectors of large elements a little faster on some platforms,
        // but hasn't been tested/tuned extensively
        let insertion = if size_of::<T>() <= 16 {
            BASE_INSERTION
        } else {
            LARGE_INSERTION
        };

        let len = v.len();

        // short vectors get sorted in-place via insertion sort to avoid allocations
        if len <= insertion {
            insertion_sort(v, compare);
            return;
        }

        // allocate some memory to use as scratch memory, we keep the
        // length 0 so we can keep shallow copies of the contents of `v`
        // without risking the dtors running on an object twice if
        // `compare` panics.
        let mut working_space = Vec::with_capacity(2 * len);
        // these both are buffers of length `len`.
        let mut buf_dat = working_space.as_mut_ptr();
        let mut buf_tmp = unsafe { buf_dat.offset(len as isize) };

        // length `len`.
        let buf_v = v.as_ptr();

        // step 1. sort short runs with insertion sort. This takes the
        // values from `v` and sorts them into `buf_dat`, leaving that
        // with sorted runs of length INSERTION.

        // We could hardcode the sorting comparisons here, and we could
        // manipulate/step the pointers themselves, rather than repeatedly
        // .offset-ing.
        for start in (0..len).step_by(insertion) {
            // start <= i < len;
            for i in start..cmp::min(start + insertion, len) {
                // j satisfies: start <= j <= i;
                let mut j = i as isize;
                unsafe {
                    // `i` is in bounds.
                    let read_ptr = buf_v.offset(i as isize);

                    // find where to insert, we need to do strict <,
                    // rather than <=, to maintain stability.

                    // start <= j - 1 < len, so .offset(j - 1) is in
                    // bounds.
                    while j > start as isize && compare(&*read_ptr, &*buf_dat.offset(j - 1)) == Less {
                        j -= 1;
                    }

                    // shift everything to the right, to make space to
                    // insert this value.

                    // j + 1 could be `len` (for the last `i`), but in
                    // that case, `i == j` so we don't copy. The
                    // `.offset(j)` is always in bounds.
                    ptr::copy(&*buf_dat.offset(j), buf_dat.offset(j + 1), i - j as usize);
                    ptr::copy_nonoverlapping(read_ptr, buf_dat.offset(j), 1);
                }
            }
        }

        // step 2. merge the sorted runs.
        let mut width = insertion;
        while width < len {
            // merge the sorted runs of length `width` in `buf_dat` two at
            // a time, placing the result in `buf_tmp`.

            // 0 <= start <= len.
            for start in (0..len).step_by(2 * width) {
                // manipulate pointers directly for speed (rather than
                // using a `for` loop with `range` and `.offset` inside
                // that loop).
                unsafe {
                    // the end of the first run & start of the
                    // second. Offset of `len` is defined, since this is
                    // precisely one byte past the end of the object.
                    let right_start = buf_dat.offset(cmp::min(start + width, len) as isize);
                    // end of the second. Similar reasoning to the above re safety.
                    let right_end_idx = cmp::min(start + 2 * width, len);
                    let right_end = buf_dat.offset(right_end_idx as isize);

                    // the pointers to the elements under consideration
                    // from the two runs.

                    // both of these are in bounds.
                    let mut left = buf_dat.offset(start as isize);
                    let mut right = right_start;

                    // where we're putting the results, it is a run of
                    // length `2*width`, so we step it once for each step
                    // of either `left` or `right`.  `buf_tmp` has length
                    // `len`, so these are in bounds.
                    let mut out = buf_tmp.offset(start as isize);
                    let out_end = buf_tmp.offset(right_end_idx as isize);

                    // If left[last] <= right[0], they are already in order:
                    // fast-forward the left side (the right side is handled
                    // in the loop).
                    // If `right` is not empty then left is not empty, and
                    // the offsets are in bounds.
                    if right != right_end && compare(&*right.offset(-1), &*right) != Greater {
                        let elems = (right_start as usize - left as usize) / mem::size_of::<T>();
                        ptr::copy_nonoverlapping(&*left, out, elems);
                        out = out.offset(elems as isize);
                        left = right_start;
                    }

                    while out < out_end {
                        // Either the left or the right run are exhausted,
                        // so just copy the remainder from the other run
                        // and move on; this gives a huge speed-up (order
                        // of 25%) for mostly sorted vectors (the best
                        // case).
                        if left == right_start {
                            // the number remaining in this run.
                            let elems = (right_end as usize - right as usize) / mem::size_of::<T>();
                            ptr::copy_nonoverlapping(&*right, out, elems);
                            break;
                        } else if right == right_end {
                            let elems = (right_start as usize - left as usize) / mem::size_of::<T>();
                            ptr::copy_nonoverlapping(&*left, out, elems);
                            break;
                        }

                        // check which side is smaller, and that's the
                        // next element for the new run.

                        // `left < right_start` and `right < right_end`,
                        // so these are valid.
                        let to_copy = if compare(&*left, &*right) == Greater {
                            step(&mut right)
                        } else {
                            step(&mut left)
                        };
                        ptr::copy_nonoverlapping(&*to_copy, out, 1);
                        step(&mut out);
                    }
                }
            }

            mem::swap(&mut buf_dat, &mut buf_tmp);

            width *= 2;
        }

        // write the result to `v` in one go, so that there are never two copies
        // of the same object in `v`.
        unsafe {
            ptr::copy_nonoverlapping(&*buf_dat, v.as_mut_ptr(), len);
        }

        // increment the pointer, returning the old pointer.
        #[inline(always)]
        unsafe fn step<T>(ptr: &mut *mut T) -> *mut T {
            let old = *ptr;
            *ptr = ptr.offset(1);
            old
        }
    }

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