Merge crate `collections` into `alloc`

1 files changed, 2593 insertions, 0 deletions

diff --git a/src/liballoc/vec.rs b/src/liballoc/vec.rs
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+// Copyright 2014 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 contiguous growable array type with heap-allocated contents, written
+//! `Vec<T>`.
+//!
+//! Vectors have `O(1)` indexing, amortized `O(1)` push (to the end) and
+//! `O(1)` pop (from the end).
+//!
+//! # Examples
+//!
+//! You can explicitly create a [`Vec<T>`] with [`new`]:
+//!
+//! ```
+//! let v: Vec<i32> = Vec::new();
+//! ```
+//!
+//! ...or by using the [`vec!`] macro:
+//!
+//! ```
+//! let v: Vec<i32> = vec![];
+//!
+//! let v = vec![1, 2, 3, 4, 5];
+//!
+//! let v = vec![0; 10]; // ten zeroes
+//! ```
+//!
+//! You can [`push`] values onto the end of a vector (which will grow the vector
+//! as needed):
+//!
+//! ```
+//! let mut v = vec![1, 2];
+//!
+//! v.push(3);
+//! ```
+//!
+//! Popping values works in much the same way:
+//!
+//! ```
+//! let mut v = vec![1, 2];
+//!
+//! let two = v.pop();
+//! ```
+//!
+//! Vectors also support indexing (through the [`Index`] and [`IndexMut`] traits):
+//!
+//! ```
+//! let mut v = vec![1, 2, 3];
+//! let three = v[2];
+//! v[1] = v[1] + 5;
+//! ```
+//!
+//! [`Vec<T>`]: ../../std/vec/struct.Vec.html
+//! [`new`]: ../../std/vec/struct.Vec.html#method.new
+//! [`push`]: ../../std/vec/struct.Vec.html#method.push
+//! [`Index`]: ../../std/ops/trait.Index.html
+//! [`IndexMut`]: ../../std/ops/trait.IndexMut.html
+//! [`vec!`]: ../../std/macro.vec.html
+
+#![stable(feature = "rust1", since = "1.0.0")]
+
+use core::cmp::Ordering;
+use core::fmt;
+use core::hash::{self, Hash};
+use core::intrinsics::{arith_offset, assume};
+use core::iter::{FromIterator, FusedIterator, TrustedLen};
+use core::mem;
+#[cfg(not(test))]
+use core::num::Float;
+use core::ops::{InPlace, Index, IndexMut, Place, Placer};
+use core::ops;
+use core::ptr;
+use core::ptr::Shared;
+use core::slice;
+
+use borrow::ToOwned;
+use borrow::Cow;
+use boxed::Box;
+use raw_vec::RawVec;
+use super::range::RangeArgument;
+use Bound::{Excluded, Included, Unbounded};
+
+/// A contiguous growable array type, written `Vec<T>` but pronounced 'vector'.
+///
+/// # Examples
+///
+/// ```
+/// let mut vec = Vec::new();
+/// vec.push(1);
+/// vec.push(2);
+///
+/// assert_eq!(vec.len(), 2);
+/// assert_eq!(vec[0], 1);
+///
+/// assert_eq!(vec.pop(), Some(2));
+/// assert_eq!(vec.len(), 1);
+///
+/// vec[0] = 7;
+/// assert_eq!(vec[0], 7);
+///
+/// vec.extend([1, 2, 3].iter().cloned());
+///
+/// for x in &vec {
+///     println!("{}", x);
+/// }
+/// assert_eq!(vec, [7, 1, 2, 3]);
+/// ```
+///
+/// The [`vec!`] macro is provided to make initialization more convenient:
+///
+/// ```
+/// let mut vec = vec![1, 2, 3];
+/// vec.push(4);
+/// assert_eq!(vec, [1, 2, 3, 4]);
+/// ```
+///
+/// It can also initialize each element of a `Vec<T>` with a given value:
+///
+/// ```
+/// let vec = vec![0; 5];
+/// assert_eq!(vec, [0, 0, 0, 0, 0]);
+/// ```
+///
+/// Use a `Vec<T>` as an efficient stack:
+///
+/// ```
+/// let mut stack = Vec::new();
+///
+/// stack.push(1);
+/// stack.push(2);
+/// stack.push(3);
+///
+/// while let Some(top) = stack.pop() {
+///     // Prints 3, 2, 1
+///     println!("{}", top);
+/// }
+/// ```
+///
+/// # Indexing
+///
+/// The `Vec` type allows to access values by index, because it implements the
+/// [`Index`] trait. An example will be more explicit:
+///
+/// ```
+/// let v = vec![0, 2, 4, 6];
+/// println!("{}", v[1]); // it will display '2'
+/// ```
+///
+/// However be careful: if you try to access an index which isn't in the `Vec`,
+/// your software will panic! You cannot do this:
+///
+/// ```ignore
+/// let v = vec![0, 2, 4, 6];
+/// println!("{}", v[6]); // it will panic!
+/// ```
+///
+/// In conclusion: always check if the index you want to get really exists
+/// before doing it.
+///
+/// # Slicing
+///
+/// A `Vec` can be mutable. Slices, on the other hand, are read-only objects.
+/// To get a slice, use `&`. Example:
+///
+/// ```
+/// fn read_slice(slice: &[usize]) {
+///     // ...
+/// }
+///
+/// let v = vec![0, 1];
+/// read_slice(&v);
+///
+/// // ... and that's all!
+/// // you can also do it like this:
+/// let x : &[usize] = &v;
+/// ```
+///
+/// In Rust, it's more common to pass slices as arguments rather than vectors
+/// when you just want to provide a read access. The same goes for [`String`] and
+/// [`&str`].
+///
+/// # Capacity and reallocation
+///
+/// The capacity of a vector is the amount of space allocated for any future
+/// elements that will be added onto the vector. This is not to be confused with
+/// the *length* of a vector, which specifies the number of actual elements
+/// within the vector. If a vector's length exceeds its capacity, its capacity
+/// will automatically be increased, but its elements will have to be
+/// reallocated.
+///
+/// For example, a vector with capacity 10 and length 0 would be an empty vector
+/// with space for 10 more elements. Pushing 10 or fewer elements onto the
+/// vector will not change its capacity or cause reallocation to occur. However,
+/// if the vector's length is increased to 11, it will have to reallocate, which
+/// can be slow. For this reason, it is recommended to use [`Vec::with_capacity`]
+/// whenever possible to specify how big the vector is expected to get.
+///
+/// # Guarantees
+///
+/// Due to its incredibly fundamental nature, `Vec` makes a lot of guarantees
+/// about its design. This ensures that it's as low-overhead as possible in
+/// the general case, and can be correctly manipulated in primitive ways
+/// by unsafe code. Note that these guarantees refer to an unqualified `Vec<T>`.
+/// If additional type parameters are added (e.g. to support custom allocators),
+/// overriding their defaults may change the behavior.
+///
+/// Most fundamentally, `Vec` is and always will be a (pointer, capacity, length)
+/// triplet. No more, no less. The order of these fields is completely
+/// unspecified, and you should use the appropriate methods to modify these.
+/// The pointer will never be null, so this type is null-pointer-optimized.
+///
+/// However, the pointer may not actually point to allocated memory. In particular,
+/// if you construct a `Vec` with capacity 0 via [`Vec::new`], [`vec![]`][`vec!`],
+/// [`Vec::with_capacity(0)`][`Vec::with_capacity`], or by calling [`shrink_to_fit`]
+/// on an empty Vec, it will not allocate memory. Similarly, if you store zero-sized
+/// types inside a `Vec`, it will not allocate space for them. *Note that in this case
+/// the `Vec` may not report a [`capacity`] of 0*. `Vec` will allocate if and only
+/// if [`mem::size_of::<T>`]` * capacity() > 0`. In general, `Vec`'s allocation
+/// details are subtle enough that it is strongly recommended that you only
+/// free memory allocated by a `Vec` by creating a new `Vec` and dropping it.
+///
+/// If a `Vec` *has* allocated memory, then the memory it points to is on the heap
+/// (as defined by the allocator Rust is configured to use by default), and its
+/// pointer points to [`len`] initialized elements in order (what you would see
+/// if you coerced it to a slice), followed by [`capacity`]` - `[`len`]
+/// logically uninitialized elements.
+///
+/// `Vec` will never perform a "small optimization" where elements are actually
+/// stored on the stack for two reasons:
+///
+/// * It would make it more difficult for unsafe code to correctly manipulate
+///   a `Vec`. The contents of a `Vec` wouldn't have a stable address if it were
+///   only moved, and it would be more difficult to determine if a `Vec` had
+///   actually allocated memory.
+///
+/// * It would penalize the general case, incurring an additional branch
+///   on every access.
+///
+/// `Vec` will never automatically shrink itself, even if completely empty. This
+/// ensures no unnecessary allocations or deallocations occur. Emptying a `Vec`
+/// and then filling it back up to the same [`len`] should incur no calls to
+/// the allocator. If you wish to free up unused memory, use
+/// [`shrink_to_fit`][`shrink_to_fit`].
+///
+/// [`push`] and [`insert`] will never (re)allocate if the reported capacity is
+/// sufficient. [`push`] and [`insert`] *will* (re)allocate if
+/// [`len`]` == `[`capacity`]. That is, the reported capacity is completely
+/// accurate, and can be relied on. It can even be used to manually free the memory
+/// allocated by a `Vec` if desired. Bulk insertion methods *may* reallocate, even
+/// when not necessary.
+///
+/// `Vec` does not guarantee any particular growth strategy when reallocating
+/// when full, nor when [`reserve`] is called. The current strategy is basic
+/// and it may prove desirable to use a non-constant growth factor. Whatever
+/// strategy is used will of course guarantee `O(1)` amortized [`push`].
+///
+/// `vec![x; n]`, `vec![a, b, c, d]`, and
+/// [`Vec::with_capacity(n)`][`Vec::with_capacity`], will all produce a `Vec`
+/// with exactly the requested capacity. If [`len`]` == `[`capacity`],
+/// (as is the case for the [`vec!`] macro), then a `Vec<T>` can be converted to
+/// and from a [`Box<[T]>`][owned slice] without reallocating or moving the elements.
+///
+/// `Vec` will not specifically overwrite any data that is removed from it,
+/// but also won't specifically preserve it. Its uninitialized memory is
+/// scratch space that it may use however it wants. It will generally just do
+/// whatever is most efficient or otherwise easy to implement. Do not rely on
+/// removed data to be erased for security purposes. Even if you drop a `Vec`, its
+/// buffer may simply be reused by another `Vec`. Even if you zero a `Vec`'s memory
+/// first, that may not actually happen because the optimizer does not consider
+/// this a side-effect that must be preserved. There is one case which we will
+/// not break, however: using `unsafe` code to write to the excess capacity,
+/// and then increasing the length to match, is always valid.
+///
+/// `Vec` does not currently guarantee the order in which elements are dropped
+/// (the order has changed in the past, and may change again).
+///
+/// [`vec!`]: ../../std/macro.vec.html
+/// [`Index`]: ../../std/ops/trait.Index.html
+/// [`String`]: ../../std/string/struct.String.html
+/// [`&str`]: ../../std/primitive.str.html
+/// [`Vec::with_capacity`]: ../../std/vec/struct.Vec.html#method.with_capacity
+/// [`Vec::new`]: ../../std/vec/struct.Vec.html#method.new
+/// [`shrink_to_fit`]: ../../std/vec/struct.Vec.html#method.shrink_to_fit
+/// [`capacity`]: ../../std/vec/struct.Vec.html#method.capacity
+/// [`mem::size_of::<T>`]: ../../std/mem/fn.size_of.html
+/// [`len`]: ../../std/vec/struct.Vec.html#method.len
+/// [`push`]: ../../std/vec/struct.Vec.html#method.push
+/// [`insert`]: ../../std/vec/struct.Vec.html#method.insert
+/// [`reserve`]: ../../std/vec/struct.Vec.html#method.reserve
+/// [owned slice]: ../../std/boxed/struct.Box.html
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct Vec<T> {
+    buf: RawVec<T>,
+    len: usize,
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Inherent methods
+////////////////////////////////////////////////////////////////////////////////
+
+impl<T> Vec<T> {
+    /// Constructs a new, empty `Vec<T>`.
+    ///
+    /// The vector will not allocate until elements are pushed onto it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #![allow(unused_mut)]
+    /// let mut vec: Vec<i32> = Vec::new();
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn new() -> Vec<T> {
+        Vec {
+            buf: RawVec::new(),
+            len: 0,
+        }
+    }
+
+    /// Constructs a new, empty `Vec<T>` with the specified capacity.
+    ///
+    /// The vector will be able to hold exactly `capacity` elements without
+    /// reallocating. If `capacity` is 0, the vector will not allocate.
+    ///
+    /// It is important to note that this function does not specify the *length*
+    /// of the returned vector, but only the *capacity*. For an explanation of
+    /// the difference between length and capacity, see *[Capacity and reallocation]*.
+    ///
+    /// [Capacity and reallocation]: #capacity-and-reallocation
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut vec = Vec::with_capacity(10);
+    ///
+    /// // The vector contains no items, even though it has capacity for more
+    /// assert_eq!(vec.len(), 0);
+    ///
+    /// // These are all done without reallocating...
+    /// for i in 0..10 {
+    ///     vec.push(i);
+    /// }
+    ///
+    /// // ...but this may make the vector reallocate
+    /// vec.push(11);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn with_capacity(capacity: usize) -> Vec<T> {
+        Vec {
+            buf: RawVec::with_capacity(capacity),
+            len: 0,
+        }
+    }
+
+    /// Creates a `Vec<T>` directly from the raw components of another vector.
+    ///
+    /// # Safety
+    ///
+    /// This is highly unsafe, due to the number of invariants that aren't
+    /// checked:
+    ///
+    /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
+    ///   (at least, it's highly likely to be incorrect if it wasn't).
+    /// * `length` needs to be less than or equal to `capacity`.
+    /// * `capacity` needs to be the capacity that the pointer was allocated with.
+    ///
+    /// Violating these may cause problems like corrupting the allocator's
+    /// internal datastructures. For example it is **not** safe
+    /// to build a `Vec<u8>` from a pointer to a C `char` array and a `size_t`.
+    ///
+    /// The ownership of `ptr` is effectively transferred to the
+    /// `Vec<T>` which may then deallocate, reallocate or change the
+    /// contents of memory pointed to by the pointer at will. Ensure
+    /// that nothing else uses the pointer after calling this
+    /// function.
+    ///
+    /// [`String`]: ../../std/string/struct.String.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::ptr;
+    /// use std::mem;
+    ///
+    /// fn main() {
+    ///     let mut v = vec![1, 2, 3];
+    ///
+    ///     // Pull out the various important pieces of information about `v`
+    ///     let p = v.as_mut_ptr();
+    ///     let len = v.len();
+    ///     let cap = v.capacity();
+    ///
+    ///     unsafe {
+    ///         // Cast `v` into the void: no destructor run, so we are in
+    ///         // complete control of the allocation to which `p` points.
+    ///         mem::forget(v);
+    ///
+    ///         // Overwrite memory with 4, 5, 6
+    ///         for i in 0..len as isize {
+    ///             ptr::write(p.offset(i), 4 + i);
+    ///         }
+    ///
+    ///         // Put everything back together into a Vec
+    ///         let rebuilt = Vec::from_raw_parts(p, len, cap);
+    ///         assert_eq!(rebuilt, [4, 5, 6]);
+    ///     }
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub unsafe fn from_raw_parts(ptr: *mut T, length: usize, capacity: usize) -> Vec<T> {
+        Vec {
+            buf: RawVec::from_raw_parts(ptr, capacity),
+            len: length,
+        }
+    }
+
+    /// Returns the number of elements the vector can hold without
+    /// reallocating.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let vec: Vec<i32> = Vec::with_capacity(10);
+    /// assert_eq!(vec.capacity(), 10);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn capacity(&self) -> usize {
+        self.buf.cap()
+    }
+
+    /// Reserves capacity for at least `additional` more elements to be inserted
+    /// in the given `Vec<T>`. The collection may reserve more space to avoid
+    /// frequent reallocations. After calling `reserve`, capacity will be
+    /// greater than or equal to `self.len() + additional`. Does nothing if
+    /// capacity is already sufficient.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the new capacity overflows `usize`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut vec = vec![1];
+    /// vec.reserve(10);
+    /// assert!(vec.capacity() >= 11);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn reserve(&mut self, additional: usize) {
+        self.buf.reserve(self.len, additional);
+    }
+
+    /// Reserves the minimum capacity for exactly `additional` more elements to
+    /// be inserted in the given `Vec<T>`. After calling `reserve_exact`,
+    /// capacity will be greater than or equal to `self.len() + additional`.
+    /// Does nothing if the capacity is already sufficient.
+    ///
+    /// Note that the allocator may give the collection more space than it
+    /// requests. Therefore capacity can not be relied upon to be precisely
+    /// minimal. Prefer `reserve` if future insertions are expected.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the new capacity overflows `usize`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut vec = vec![1];
+    /// vec.reserve_exact(10);
+    /// assert!(vec.capacity() >= 11);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn reserve_exact(&mut self, additional: usize) {
+        self.buf.reserve_exact(self.len, additional);
+    }
+
+    /// Shrinks the capacity of the vector as much as possible.
+    ///
+    /// It will drop down as close as possible to the length but the allocator
+    /// may still inform the vector that there is space for a few more elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut vec = Vec::with_capacity(10);
+    /// vec.extend([1, 2, 3].iter().cloned());
+    /// assert_eq!(vec.capacity(), 10);
+    /// vec.shrink_to_fit();
+    /// assert!(vec.capacity() >= 3);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn shrink_to_fit(&mut self) {
+        self.buf.shrink_to_fit(self.len);
+    }
+
+    /// Converts the vector into [`Box<[T]>`][owned slice].
+    ///
+    /// Note that this will drop any excess capacity. Calling this and
+    /// converting back to a vector with [`into_vec`] is equivalent to calling
+    /// [`shrink_to_fit`].
+    ///
+    /// [owned slice]: ../../std/boxed/struct.Box.html
+    /// [`into_vec`]: ../../std/primitive.slice.html#method.into_vec
+    /// [`shrink_to_fit`]: #method.shrink_to_fit
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let v = vec![1, 2, 3];
+    ///
+    /// let slice = v.into_boxed_slice();
+    /// ```
+    ///
+    /// Any excess capacity is removed:
+    ///
+    /// ```
+    /// let mut vec = Vec::with_capacity(10);
+    /// vec.extend([1, 2, 3].iter().cloned());
+    ///
+    /// assert_eq!(vec.capacity(), 10);
+    /// let slice = vec.into_boxed_slice();
+    /// assert_eq!(slice.into_vec().capacity(), 3);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn into_boxed_slice(mut self) -> Box<[T]> {
+        unsafe {
+            self.shrink_to_fit();
+            let buf = ptr::read(&self.buf);
+            mem::forget(self);
+            buf.into_box()
+        }
+    }
+
+    /// Shortens the vector, keeping the first `len` elements and dropping
+    /// the rest.
+    ///
+    /// If `len` is greater than the vector's current length, this has no
+    /// effect.
+    ///
+    /// The [`drain`] method can emulate `truncate`, but causes the excess
+    /// elements to be returned instead of dropped.
+    ///
+    /// Note that this method has no effect on the allocated capacity
+    /// of the vector.
+    ///
+    /// # Examples
+    ///
+    /// Truncating a five element vector to two elements:
+    ///
+    /// ```
+    /// let mut vec = vec![1, 2, 3, 4, 5];
+    /// vec.truncate(2);
+    /// assert_eq!(vec, [1, 2]);
+    /// ```
+    ///
+    /// No truncation occurs when `len` is greater than the vector's current
+    /// length:
+    ///
+    /// ```
+    /// let mut vec = vec![1, 2, 3];
+    /// vec.truncate(8);
+    /// assert_eq!(vec, [1, 2, 3]);
+    /// ```
+    ///
+    /// Truncating when `len == 0` is equivalent to calling the [`clear`]
+    /// method.
+    ///
+    /// ```
+    /// let mut vec = vec![1, 2, 3];
+    /// vec.truncate(0);
+    /// assert_eq!(vec, []);
+    /// ```
+    ///
+    /// [`clear`]: #method.clear
+    /// [`drain`]: #method.drain
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn truncate(&mut self, len: usize) {
+        unsafe {
+            // drop any extra elements
+            while len < self.len {
+                // decrement len before the drop_in_place(), so a panic on Drop
+                // doesn't re-drop the just-failed value.
+                self.len -= 1;
+                let len = self.len;
+                ptr::drop_in_place(self.get_unchecked_mut(len));
+            }
+        }
+    }
+
+    /// Extracts a slice containing the entire vector.
+    ///
+    /// Equivalent to `&s[..]`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::io::{self, Write};
+    /// let buffer = vec![1, 2, 3, 5, 8];
+    /// io::sink().write(buffer.as_slice()).unwrap();
+    /// ```
+    #[inline]
+    #[stable(feature = "vec_as_slice", since = "1.7.0")]
+    pub fn as_slice(&self) -> &[T] {
+        self
+    }
+
+    /// Extracts a mutable slice of the entire vector.
+    ///
+    /// Equivalent to `&mut s[..]`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::io::{self, Read};
+    /// let mut buffer = vec![0; 3];
+    /// io::repeat(0b101).read_exact(buffer.as_mut_slice()).unwrap();
+    /// ```
+    #[inline]
+    #[stable(feature = "vec_as_slice", since = "1.7.0")]
+    pub fn as_mut_slice(&mut self) -> &mut [T] {
+        self
+    }
+
+    /// Sets the length of a vector.
+    ///
+    /// This will explicitly set the size of the vector, without actually
+    /// modifying its buffers, so it is up to the caller to ensure that the
+    /// vector is actually the specified size.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::ptr;
+    ///
+    /// let mut vec = vec!['r', 'u', 's', 't'];
+    ///
+    /// unsafe {
+    ///     ptr::drop_in_place(&mut vec[3]);
+    ///     vec.set_len(3);
+    /// }
+    /// assert_eq!(vec, ['r', 'u', 's']);
+    /// ```
+    ///
+    /// In this example, there is a memory leak since the memory locations
+    /// owned by the inner vectors were not freed prior to the `set_len` call:
+    ///
+    /// ```
+    /// let mut vec = vec![vec![1, 0, 0],
+    ///                    vec![0, 1, 0],
+    ///                    vec![0, 0, 1]];
+    /// unsafe {
+    ///     vec.set_len(0);
+    /// }
+    /// ```
+    ///
+    /// In this example, the vector gets expanded from zero to four items
+    /// without any memory allocations occurring, resulting in vector
+    /// values of unallocated memory:
+    ///
+    /// ```
+    /// let mut vec: Vec<char> = Vec::new();
+    ///
+    /// unsafe {
+    ///     vec.set_len(4);
+    /// }
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub unsafe fn set_len(&mut self, len: usize) {
+        self.len = len;
+    }
+
+    /// Removes an element from the vector and returns it.
+    ///
+    /// The removed element is replaced by the last element of the vector.
+    ///
+    /// This does not preserve ordering, but is O(1).
+    ///
+    /// # Panics
+    ///
+    /// Panics if `index` is out of bounds.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = vec!["foo", "bar", "baz", "qux"];
+    ///
+    /// assert_eq!(v.swap_remove(1), "bar");
+    /// assert_eq!(v, ["foo", "qux", "baz"]);
+    ///
+    /// assert_eq!(v.swap_remove(0), "foo");
+    /// assert_eq!(v, ["baz", "qux"]);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn swap_remove(&mut self, index: usize) -> T {
+        let length = self.len();
+        self.swap(index, length - 1);
+        self.pop().unwrap()
+    }
+
+    /// Inserts an element at position `index` within the vector, shifting all
+    /// elements after it to the right.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `index` is out of bounds.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut vec = vec![1, 2, 3];
+    /// vec.insert(1, 4);
+    /// assert_eq!(vec, [1, 4, 2, 3]);
+    /// vec.insert(4, 5);
+    /// assert_eq!(vec, [1, 4, 2, 3, 5]);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn insert(&mut self, index: usize, element: T) {
+        let len = self.len();
+        assert!(index <= len);
+
+        // space for the new element
+        if len == self.buf.cap() {
+            self.buf.double();
+        }
+
+        unsafe {
+            // infallible
+            // The spot to put the new value
+            {
+                let p = self.as_mut_ptr().offset(index as isize);
+                // Shift everything over to make space. (Duplicating the
+                // `index`th element into two consecutive places.)
+                ptr::copy(p, p.offset(1), len - index);
+                // Write it in, overwriting the first copy of the `index`th
+                // element.
+                ptr::write(p, element);
+            }
+            self.set_len(len + 1);
+        }
+    }
+
+    /// Removes and returns the element at position `index` within the vector,
+    /// shifting all elements after it to the left.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `index` is out of bounds.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = vec![1, 2, 3];
+    /// assert_eq!(v.remove(1), 2);
+    /// assert_eq!(v, [1, 3]);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn remove(&mut self, index: usize) -> T {
+        let len = self.len();
+        assert!(index < len);
+        unsafe {
+            // infallible
+            let ret;
+            {
+                // the place we are taking from.
+                let ptr = self.as_mut_ptr().offset(index as isize);
+                // copy it out, unsafely having a copy of the value on
+                // the stack and in the vector at the same time.
+                ret = ptr::read(ptr);
+
+                // Shift everything down to fill in that spot.
+                ptr::copy(ptr.offset(1), ptr, len - index - 1);
+            }
+            self.set_len(len - 1);
+            ret
+        }
+    }
+
+    /// Retains only the elements specified by the predicate.
+    ///
+    /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
+    /// This method operates in place and preserves the order of the retained
+    /// elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut vec = vec![1, 2, 3, 4];
+    /// vec.retain(|&x| x%2 == 0);
+    /// assert_eq!(vec, [2, 4]);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn retain<F>(&mut self, mut f: F)
+        where F: FnMut(&T) -> bool
+    {
+        let len = self.len();
+        let mut del = 0;
+        {
+            let v = &mut **self;
+
+            for i in 0..len {
+                if !f(&v[i]) {
+                    del += 1;
+                } else if del > 0 {
+                    v.swap(i - del, i);
+                }
+            }
+        }
+        if del > 0 {
+            self.truncate(len - del);
+        }
+    }
+
+    /// Removes consecutive elements in the vector that resolve to the same key.
+    ///
+    /// If the vector is sorted, this removes all duplicates.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut vec = vec![10, 20, 21, 30, 20];
+    ///
+    /// vec.dedup_by_key(|i| *i / 10);
+    ///
+    /// assert_eq!(vec, [10, 20, 30, 20]);
+    /// ```
+    #[stable(feature = "dedup_by", since = "1.16.0")]
+    #[inline]
+    pub fn dedup_by_key<F, K>(&mut self, mut key: F) where F: FnMut(&mut T) -> K, K: PartialEq {
+        self.dedup_by(|a, b| key(a) == key(b))
+    }
+
+    /// Removes consecutive elements in the vector according to a predicate.
+    ///
+    /// The `same_bucket` function is passed references to two elements from the vector, and
+    /// returns `true` if the elements compare equal, or `false` if they do not. Only the first
+    /// of adjacent equal items is kept.
+    ///
+    /// If the vector is sorted, this removes all duplicates.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::ascii::AsciiExt;
+    ///
+    /// let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
+    ///
+    /// vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));
+    ///
+    /// assert_eq!(vec, ["foo", "bar", "baz", "bar"]);
+    /// ```
+    #[stable(feature = "dedup_by", since = "1.16.0")]
+    pub fn dedup_by<F>(&mut self, mut same_bucket: F) where F: FnMut(&mut T, &mut T) -> bool {
+        unsafe {
+            // Although we have a mutable reference to `self`, we cannot make
+            // *arbitrary* changes. The `same_bucket` calls could panic, so we
+            // must ensure that the vector is in a valid state at all time.
+            //
+            // The way that we handle this is by using swaps; we iterate
+            // over all the elements, swapping as we go so that at the end
+            // the elements we wish to keep are in the front, and those we
+            // wish to reject are at the back. We can then truncate the
+            // vector. This operation is still O(n).
+            //
+            // Example: We start in this state, where `r` represents "next
+            // read" and `w` represents "next_write`.
+            //
+            //           r
+            //     +---+---+---+---+---+---+
+            //     | 0 | 1 | 1 | 2 | 3 | 3 |
+            //     +---+---+---+---+---+---+
+            //           w
+            //
+            // Comparing self[r] against self[w-1], this is not a duplicate, so
+            // we swap self[r] and self[w] (no effect as r==w) and then increment both
+            // r and w, leaving us with:
+            //
+            //               r
+            //     +---+---+---+---+---+---+
+            //     | 0 | 1 | 1 | 2 | 3 | 3 |
+            //     +---+---+---+---+---+---+
+            //               w
+            //
+            // Comparing self[r] against self[w-1], this value is a duplicate,
+            // so we increment `r` but leave everything else unchanged:
+            //
+            //                   r
+            //     +---+---+---+---+---+---+
+            //     | 0 | 1 | 1 | 2 | 3 | 3 |
+            //     +---+---+---+---+---+---+
+            //               w
+            //
+            // Comparing self[r] against self[w-1], this is not a duplicate,
+            // so swap self[r] and self[w] and advance r and w:
+            //
+            //                       r
+            //     +---+---+---+---+---+---+
+            //     | 0 | 1 | 2 | 1 | 3 | 3 |
+            //     +---+---+---+---+---+---+
+            //                   w
+            //
+            // Not a duplicate, repeat:
+            //
+            //                           r
+            //     +---+---+---+---+---+---+
+            //     | 0 | 1 | 2 | 3 | 1 | 3 |
+            //     +---+---+---+---+---+---+
+            //                       w
+            //
+            // Duplicate, advance r. End of vec. Truncate to w.
+
+            let ln = self.len();
+            if ln <= 1 {
+                return;
+            }
+
+            // Avoid bounds checks by using raw pointers.
+            let p = self.as_mut_ptr();
+            let mut r: usize = 1;
+            let mut w: usize = 1;
+
+            while r < ln {
+                let p_r = p.offset(r as isize);
+                let p_wm1 = p.offset((w - 1) as isize);
+                if !same_bucket(&mut *p_r, &mut *p_wm1) {
+                    if r != w {
+                        let p_w = p_wm1.offset(1);
+                        mem::swap(&mut *p_r, &mut *p_w);
+                    }
+                    w += 1;
+                }
+                r += 1;
+            }
+
+            self.truncate(w);
+        }
+    }
+
+    /// Appends an element to the back of a collection.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the number of elements in the vector overflows a `usize`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut vec = vec![1, 2];
+    /// vec.push(3);
+    /// assert_eq!(vec, [1, 2, 3]);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn push(&mut self, value: T) {
+        // This will panic or abort if we would allocate > isize::MAX bytes
+        // or if the length increment would overflow for zero-sized types.
+        if self.len == self.buf.cap() {
+            self.buf.double();
+        }
+        unsafe {
+            let end = self.as_mut_ptr().offset(self.len as isize);
+            ptr::write(end, value);
+            self.len += 1;
+        }
+    }
+
+    /// Returns a place for insertion at the back of the `Vec`.
+    ///
+    /// Using this method with placement syntax is equivalent to [`push`](#method.push),
+    /// but may be more efficient.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(collection_placement)]
+    /// #![feature(placement_in_syntax)]
+    ///
+    /// let mut vec = vec![1, 2];
+    /// vec.place_back() <- 3;
+    /// vec.place_back() <- 4;
+    /// assert_eq!(&vec, &[1, 2, 3, 4]);
+    /// ```
+    #[unstable(feature = "collection_placement",
+               reason = "placement protocol is subject to change",
+               issue = "30172")]
+    pub fn place_back(&mut self) -> PlaceBack<T> {
+        PlaceBack { vec: self }
+    }
+
+    /// Removes the last element from a vector and returns it, or [`None`] if it
+    /// is empty.
+    ///
+    /// [`None`]: ../../std/option/enum.Option.html#variant.None
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut vec = vec![1, 2, 3];
+    /// assert_eq!(vec.pop(), Some(3));
+    /// assert_eq!(vec, [1, 2]);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn pop(&mut self) -> Option<T> {
+        if self.len == 0 {
+            None
+        } else {
+            unsafe {
+                self.len -= 1;
+                Some(ptr::read(self.get_unchecked(self.len())))
+            }
+        }
+    }
+
+    /// Moves all the elements of `other` into `Self`, leaving `other` empty.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the number of elements in the vector overflows a `usize`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut vec = vec![1, 2, 3];
+    /// let mut vec2 = vec![4, 5, 6];
+    /// vec.append(&mut vec2);
+    /// assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
+    /// assert_eq!(vec2, []);
+    /// ```
+    #[inline]
+    #[stable(feature = "append", since = "1.4.0")]
+    pub fn append(&mut self, other: &mut Self) {
+        unsafe {
+            self.append_elements(other.as_slice() as _);
+            other.set_len(0);
+        }
+    }
+
+    /// Appends elements to `Self` from other buffer.
+    #[inline]
+    unsafe fn append_elements(&mut self, other: *const [T]) {
+        let count = (*other).len();
+        self.reserve(count);
+        let len = self.len();
+        ptr::copy_nonoverlapping(other as *const T, self.get_unchecked_mut(len), count);
+        self.len += count;
+    }
+
+    /// Creates a draining iterator that removes the specified range in the vector
+    /// and yields the removed items.
+    ///
+    /// Note 1: The element range is removed even if the iterator is only
+    /// partially consumed or not consumed at all.
+    ///
+    /// Note 2: It is unspecified how many elements are removed from the vector
+    /// if the `Drain` value is leaked.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the starting point is greater than the end point or if
+    /// the end point is greater than the length of the vector.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = vec![1, 2, 3];
+    /// let u: Vec<_> = v.drain(1..).collect();
+    /// assert_eq!(v, &[1]);
+    /// assert_eq!(u, &[2, 3]);
+    ///
+    /// // A full range clears the vector
+    /// v.drain(..);
+    /// assert_eq!(v, &[]);
+    /// ```
+    #[stable(feature = "drain", since = "1.6.0")]
+    pub fn drain<R>(&mut self, range: R) -> Drain<T>
+        where R: RangeArgument<usize>
+    {
+        // Memory safety
+        //
+        // When the Drain is first created, it shortens the length of
+        // the source vector to make sure no uninitalized or moved-from elements
+        // are accessible at all if the Drain's destructor never gets to run.
+        //
+        // Drain will ptr::read out the values to remove.
+        // When finished, remaining tail of the vec is copied back to cover
+        // the hole, and the vector length is restored to the new length.
+        //
+        let len = self.len();
+        let start = match range.start() {
+            Included(&n) => n,
+            Excluded(&n) => n + 1,
+            Unbounded    => 0,
+        };
+        let end = match range.end() {
+            Included(&n) => n + 1,
+            Excluded(&n) => n,
+            Unbounded    => len,
+        };
+        assert!(start <= end);
+        assert!(end <= len);
+
+        unsafe {
+            // set self.vec length's to start, to be safe in case Drain is leaked
+            self.set_len(start);
+            // Use the borrow in the IterMut to indicate borrowing behavior of the
+            // whole Drain iterator (like &mut T).
+            let range_slice = slice::from_raw_parts_mut(self.as_mut_ptr().offset(start as isize),
+                                                        end - start);
+            Drain {
+                tail_start: end,
+                tail_len: len - end,
+                iter: range_slice.iter(),
+                vec: Shared::new(self as *mut _),
+            }
+        }
+    }
+
+    /// Clears the vector, removing all values.
+    ///
+    /// Note that this method has no effect on the allocated capacity
+    /// of the vector.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = vec![1, 2, 3];
+    ///
+    /// v.clear();
+    ///
+    /// assert!(v.is_empty());
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn clear(&mut self) {
+        self.truncate(0)
+    }
+
+    /// Returns the number of elements in the vector, also referred to
+    /// as its 'length'.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let a = vec![1, 2, 3];
+    /// assert_eq!(a.len(), 3);
+    /// ```
+    #[inline]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn len(&self) -> usize {
+        self.len
+    }
+
+    /// Returns `true` if the vector contains no elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut v = Vec::new();
+    /// assert!(v.is_empty());
+    ///
+    /// v.push(1);
+    /// assert!(!v.is_empty());
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    /// Splits the collection into two at the given index.
+    ///
+    /// Returns a newly allocated `Self`. `self` contains elements `[0, at)`,
+    /// and the returned `Self` contains elements `[at, len)`.
+    ///
+    /// Note that the capacity of `self` does not change.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `at > len`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut vec = vec![1,2,3];
+    /// let vec2 = vec.split_off(1);
+    /// assert_eq!(vec, [1]);
+    /// assert_eq!(vec2, [2, 3]);
+    /// ```
+    #[inline]
+    #[stable(feature = "split_off", since = "1.4.0")]
+    pub fn split_off(&mut self, at: usize) -> Self {
+        assert!(at <= self.len(), "`at` out of bounds");
+
+        let other_len = self.len - at;
+        let mut other = Vec::with_capacity(other_len);
+
+        // Unsafely `set_len` and copy items to `other`.
+        unsafe {
+            self.set_len(at);
+            other.set_len(other_len);
+
+            ptr::copy_nonoverlapping(self.as_ptr().offset(at as isize),
+                                     other.as_mut_ptr(),
+                                     other.len());
+        }
+        other
+    }
+}
+
+impl<T: Clone> Vec<T> {
+    /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
+    ///
+    /// If `new_len` is greater than `len`, the `Vec` is extended by the
+    /// difference, with each additional slot filled with `value`.
+    /// If `new_len` is less than `len`, the `Vec` is simply truncated.
+    ///
+    /// This method requires `Clone` to clone the passed value. If you'd
+    /// rather create a value with `Default` instead, see [`resize_default`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut vec = vec!["hello"];
+    /// vec.resize(3, "world");
+    /// assert_eq!(vec, ["hello", "world", "world"]);
+    ///
+    /// let mut vec = vec![1, 2, 3, 4];
+    /// vec.resize(2, 0);
+    /// assert_eq!(vec, [1, 2]);
+    /// ```
+    ///
+    /// [`resize_default`]: #method.resize_default
+    #[stable(feature = "vec_resize", since = "1.5.0")]
+    pub fn resize(&mut self, new_len: usize, value: T) {
+        let len = self.len();
+
+        if new_len > len {
+            self.extend_with(new_len - len, ExtendElement(value))
+        } else {
+            self.truncate(new_len);
+        }
+    }
+
+    /// Clones and appends all elements in a slice to the `Vec`.
+    ///
+    /// Iterates over the slice `other`, clones each element, and then appends
+    /// it to this `Vec`. The `other` vector is traversed in-order.
+    ///
+    /// Note that this function is same as `extend` except that it is
+    /// specialized to work with slices instead. If and when Rust gets
+    /// specialization this function will likely be deprecated (but still
+    /// available).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut vec = vec![1];
+    /// vec.extend_from_slice(&[2, 3, 4]);
+    /// assert_eq!(vec, [1, 2, 3, 4]);
+    /// ```
+    #[stable(feature = "vec_extend_from_slice", since = "1.6.0")]
+    pub fn extend_from_slice(&mut self, other: &[T]) {
+        self.spec_extend(other.iter())
+    }
+}
+
+impl<T: Default> Vec<T> {
+    /// Resizes the `Vec` in-place so that `len` is equal to `new_len`.
+    ///
+    /// If `new_len` is greater than `len`, the `Vec` is extended by the
+    /// difference, with each additional slot filled with `Default::default()`.
+    /// If `new_len` is less than `len`, the `Vec` is simply truncated.
+    ///
+    /// This method uses `Default` to create new values on every push. If
+    /// you'd rather `Clone` a given value, use [`resize`].
+    ///
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(vec_resize_default)]
+    ///
+    /// let mut vec = vec![1, 2, 3];
+    /// vec.resize_default(5);
+    /// assert_eq!(vec, [1, 2, 3, 0, 0]);
+    ///
+    /// let mut vec = vec![1, 2, 3, 4];
+    /// vec.resize_default(2);
+    /// assert_eq!(vec, [1, 2]);
+    /// ```
+    ///
+    /// [`resize`]: #method.resize
+    #[unstable(feature = "vec_resize_default", issue = "41758")]
+    pub fn resize_default(&mut self, new_len: usize) {
+        let len = self.len();
+
+        if new_len > len {
+            self.extend_with(new_len - len, ExtendDefault);
+        } else {
+            self.truncate(new_len);
+        }
+    }
+}
+
+// This code generalises `extend_with_{element,default}`.
+trait ExtendWith<T> {
+    fn next(&self) -> T;
+    fn last(self) -> T;
+}
+
+struct ExtendElement<T>(T);
+impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
+    fn next(&self) -> T { self.0.clone() }
+    fn last(self) -> T { self.0 }
+}
+
+struct ExtendDefault;
+impl<T: Default> ExtendWith<T> for ExtendDefault {
+    fn next(&self) -> T { Default::default() }
+    fn last(self) -> T { Default::default() }
+}
+impl<T> Vec<T> {
+    /// Extend the vector by `n` values, using the given generator.
+    fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, value: E) {
+        self.reserve(n);
+
+        unsafe {
+            let mut ptr = self.as_mut_ptr().offset(self.len() as isize);
+            // Use SetLenOnDrop to work around bug where compiler
+            // may not realize the store through `ptr` through self.set_len()
+            // don't alias.
+            let mut local_len = SetLenOnDrop::new(&mut self.len);
+
+            // Write all elements except the last one
+            for _ in 1..n {
+                ptr::write(ptr, value.next());
+                ptr = ptr.offset(1);
+                // Increment the length in every step in case next() panics
+                local_len.increment_len(1);
+            }
+
+            if n > 0 {
+                // We can write the last element directly without cloning needlessly
+                ptr::write(ptr, value.last());
+                local_len.increment_len(1);
+            }
+
+            // len set by scope guard
+        }
+    }
+}
+
+// Set the length of the vec when the `SetLenOnDrop` value goes out of scope.
+//
+// The idea is: The length field in SetLenOnDrop is a local variable
+// that the optimizer will see does not alias with any stores through the Vec's data
+// pointer. This is a workaround for alias analysis issue #32155
+struct SetLenOnDrop<'a> {
+    len: &'a mut usize,
+    local_len: usize,
+}
+
+impl<'a> SetLenOnDrop<'a> {
+    #[inline]
+    fn new(len: &'a mut usize) -> Self {
+        SetLenOnDrop { local_len: *len, len: len }
+    }
+
+    #[inline]
+    fn increment_len(&mut self, increment: usize) {
+        self.local_len += increment;
+    }
+}
+
+impl<'a> Drop for SetLenOnDrop<'a> {
+    #[inline]
+    fn drop(&mut self) {
+        *self.len = self.local_len;
+    }
+}
+
+impl<T: PartialEq> Vec<T> {
+    /// Removes consecutive repeated elements in the vector.
+    ///
+    /// If the vector is sorted, this removes all duplicates.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut vec = vec![1, 2, 2, 3, 2];
+    ///
+    /// vec.dedup();
+    ///
+    /// assert_eq!(vec, [1, 2, 3, 2]);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    pub fn dedup(&mut self) {
+        self.dedup_by(|a, b| a == b)
+    }
+
+    /// Removes the first instance of `item` from the vector if the item exists.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # #![feature(vec_remove_item)]
+    /// let mut vec = vec![1, 2, 3, 1];
+    ///
+    /// vec.remove_item(&1);
+    ///
+    /// assert_eq!(vec, vec![2, 3, 1]);
+    /// ```
+    #[unstable(feature = "vec_remove_item", reason = "recently added", issue = "40062")]
+    pub fn remove_item(&mut self, item: &T) -> Option<T> {
+        let pos = match self.iter().position(|x| *x == *item) {
+            Some(x) => x,
+            None => return None,
+        };
+        Some(self.remove(pos))
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Internal methods and functions
+////////////////////////////////////////////////////////////////////////////////
+
+#[doc(hidden)]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn from_elem<T: Clone>(elem: T, n: usize) -> Vec<T> {
+    <T as SpecFromElem>::from_elem(elem, n)
+}
+
+// Specialization trait used for Vec::from_elem
+trait SpecFromElem: Sized {
+    fn from_elem(elem: Self, n: usize) -> Vec<Self>;
+}
+
+impl<T: Clone> SpecFromElem for T {
+    default fn from_elem(elem: Self, n: usize) -> Vec<Self> {
+        let mut v = Vec::with_capacity(n);
+        v.extend_with(n, ExtendElement(elem));
+        v
+    }
+}
+
+impl SpecFromElem for u8 {
+    #[inline]
+    fn from_elem(elem: u8, n: usize) -> Vec<u8> {
+        if elem == 0 {
+            return Vec {
+                buf: RawVec::with_capacity_zeroed(n),
+                len: n,
+            }
+        }
+        unsafe {
+            let mut v = Vec::with_capacity(n);
+            ptr::write_bytes(v.as_mut_ptr(), elem, n);
+            v.set_len(n);
+            v
+        }
+    }
+}
+
+macro_rules! impl_spec_from_elem {
+    ($t: ty, $is_zero: expr) => {
+        impl SpecFromElem for $t {
+            #[inline]
+            fn from_elem(elem: $t, n: usize) -> Vec<$t> {
+                if $is_zero(elem) {
+                    return Vec {
+                        buf: RawVec::with_capacity_zeroed(n),
+                        len: n,
+                    }
+                }
+                let mut v = Vec::with_capacity(n);
+                v.extend_with(n, ExtendElement(elem));
+                v
+            }
+        }
+    };
+}
+
+impl_spec_from_elem!(i8, |x| x == 0);
+impl_spec_from_elem!(i16, |x| x == 0);
+impl_spec_from_elem!(i32, |x| x == 0);
+impl_spec_from_elem!(i64, |x| x == 0);
+impl_spec_from_elem!(i128, |x| x == 0);
+impl_spec_from_elem!(isize, |x| x == 0);
+
+impl_spec_from_elem!(u16, |x| x == 0);
+impl_spec_from_elem!(u32, |x| x == 0);
+impl_spec_from_elem!(u64, |x| x == 0);
+impl_spec_from_elem!(u128, |x| x == 0);
+impl_spec_from_elem!(usize, |x| x == 0);
+
+impl_spec_from_elem!(f32, |x: f32| x == 0. && x.is_sign_positive());
+impl_spec_from_elem!(f64, |x: f64| x == 0. && x.is_sign_positive());
+
+////////////////////////////////////////////////////////////////////////////////
+// Common trait implementations for Vec
+////////////////////////////////////////////////////////////////////////////////
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Clone> Clone for Vec<T> {
+    #[cfg(not(test))]
+    fn clone(&self) -> Vec<T> {
+        <[T]>::to_vec(&**self)
+    }
+
+    // HACK(japaric): with cfg(test) the inherent `[T]::to_vec` method, which is
+    // required for this method definition, is not available. Instead use the
+    // `slice::to_vec`  function which is only available with cfg(test)
+    // NB see the slice::hack module in slice.rs for more information
+    #[cfg(test)]
+    fn clone(&self) -> Vec<T> {
+        ::slice::to_vec(&**self)
+    }
+
+    fn clone_from(&mut self, other: &Vec<T>) {
+        other.as_slice().clone_into(self);
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Hash> Hash for Vec<T> {
+    #[inline]
+    fn hash<H: hash::Hasher>(&self, state: &mut H) {
+        Hash::hash(&**self, state)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> Index<usize> for Vec<T> {
+    type Output = T;
+
+    #[inline]
+    fn index(&self, index: usize) -> &T {
+        // NB built-in indexing via `&[T]`
+        &(**self)[index]
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> IndexMut<usize> for Vec<T> {
+    #[inline]
+    fn index_mut(&mut self, index: usize) -> &mut T {
+        // NB built-in indexing via `&mut [T]`
+        &mut (**self)[index]
+    }
+}
+
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> ops::Index<ops::Range<usize>> for Vec<T> {
+    type Output = [T];
+
+    #[inline]
+    fn index(&self, index: ops::Range<usize>) -> &[T] {
+        Index::index(&**self, index)
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> ops::Index<ops::RangeTo<usize>> for Vec<T> {
+    type Output = [T];
+
+    #[inline]
+    fn index(&self, index: ops::RangeTo<usize>) -> &[T] {
+        Index::index(&**self, index)
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> ops::Index<ops::RangeFrom<usize>> for Vec<T> {
+    type Output = [T];
+
+    #[inline]
+    fn index(&self, index: ops::RangeFrom<usize>) -> &[T] {
+        Index::index(&**self, index)
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> ops::Index<ops::RangeFull> for Vec<T> {
+    type Output = [T];
+
+    #[inline]
+    fn index(&self, _index: ops::RangeFull) -> &[T] {
+        self
+    }
+}
+#[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
+impl<T> ops::Index<ops::RangeInclusive<usize>> for Vec<T> {
+    type Output = [T];
+
+    #[inline]
+    fn index(&self, index: ops::RangeInclusive<usize>) -> &[T] {
+        Index::index(&**self, index)
+    }
+}
+#[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
+impl<T> ops::Index<ops::RangeToInclusive<usize>> for Vec<T> {
+    type Output = [T];
+
+    #[inline]
+    fn index(&self, index: ops::RangeToInclusive<usize>) -> &[T] {
+        Index::index(&**self, index)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> ops::IndexMut<ops::Range<usize>> for Vec<T> {
+    #[inline]
+    fn index_mut(&mut self, index: ops::Range<usize>) -> &mut [T] {
+        IndexMut::index_mut(&mut **self, index)
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> ops::IndexMut<ops::RangeTo<usize>> for Vec<T> {
+    #[inline]
+    fn index_mut(&mut self, index: ops::RangeTo<usize>) -> &mut [T] {
+        IndexMut::index_mut(&mut **self, index)
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> ops::IndexMut<ops::RangeFrom<usize>> for Vec<T> {
+    #[inline]
+    fn index_mut(&mut self, index: ops::RangeFrom<usize>) -> &mut [T] {
+        IndexMut::index_mut(&mut **self, index)
+    }
+}
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> ops::IndexMut<ops::RangeFull> for Vec<T> {
+    #[inline]
+    fn index_mut(&mut self, _index: ops::RangeFull) -> &mut [T] {
+        self
+    }
+}
+#[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
+impl<T> ops::IndexMut<ops::RangeInclusive<usize>> for Vec<T> {
+    #[inline]
+    fn index_mut(&mut self, index: ops::RangeInclusive<usize>) -> &mut [T] {
+        IndexMut::index_mut(&mut **self, index)
+    }
+}
+#[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
+impl<T> ops::IndexMut<ops::RangeToInclusive<usize>> for Vec<T> {
+    #[inline]
+    fn index_mut(&mut self, index: ops::RangeToInclusive<usize>) -> &mut [T] {
+        IndexMut::index_mut(&mut **self, index)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> ops::Deref for Vec<T> {
+    type Target = [T];
+
+    fn deref(&self) -> &[T] {
+        unsafe {
+            let p = self.buf.ptr();
+            assume(!p.is_null());
+            slice::from_raw_parts(p, self.len)
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> ops::DerefMut for Vec<T> {
+    fn deref_mut(&mut self) -> &mut [T] {
+        unsafe {
+            let ptr = self.buf.ptr();
+            assume(!ptr.is_null());
+            slice::from_raw_parts_mut(ptr, self.len)
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> FromIterator<T> for Vec<T> {
+    #[inline]
+    fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Vec<T> {
+        <Self as SpecExtend<T, I::IntoIter>>::from_iter(iter.into_iter())
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> IntoIterator for Vec<T> {
+    type Item = T;
+    type IntoIter = IntoIter<T>;
+
+    /// Creates a consuming iterator, that is, one that moves each value out of
+    /// the vector (from start to end). The vector cannot be used after calling
+    /// this.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let v = vec!["a".to_string(), "b".to_string()];
+    /// for s in v.into_iter() {
+    ///     // s has type String, not &String
+    ///     println!("{}", s);
+    /// }
+    /// ```
+    #[inline]
+    fn into_iter(mut self) -> IntoIter<T> {
+        unsafe {
+            let begin = self.as_mut_ptr();
+            assume(!begin.is_null());
+            let end = if mem::size_of::<T>() == 0 {
+                arith_offset(begin as *const i8, self.len() as isize) as *const T
+            } else {
+                begin.offset(self.len() as isize) as *const T
+            };
+            let cap = self.buf.cap();
+            mem::forget(self);
+            IntoIter {
+                buf: Shared::new(begin),
+                cap: cap,
+                ptr: begin,
+                end: end,
+            }
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> IntoIterator for &'a Vec<T> {
+    type Item = &'a T;
+    type IntoIter = slice::Iter<'a, T>;
+
+    fn into_iter(self) -> slice::Iter<'a, T> {
+        self.iter()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> IntoIterator for &'a mut Vec<T> {
+    type Item = &'a mut T;
+    type IntoIter = slice::IterMut<'a, T>;
+
+    fn into_iter(mut self) -> slice::IterMut<'a, T> {
+        self.iter_mut()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> Extend<T> for Vec<T> {
+    #[inline]
+    fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
+        <Self as SpecExtend<T, I::IntoIter>>::spec_extend(self, iter.into_iter())
+    }
+}
+
+// Specialization trait used for Vec::from_iter and Vec::extend
+trait SpecExtend<T, I> {
+    fn from_iter(iter: I) -> Self;
+    fn spec_extend(&mut self, iter: I);
+}
+
+impl<T, I> SpecExtend<T, I> for Vec<T>
+    where I: Iterator<Item=T>,
+{
+    default fn from_iter(mut iterator: I) -> Self {
+        // Unroll the first iteration, as the vector is going to be
+        // expanded on this iteration in every case when the iterable is not
+        // empty, but the loop in extend_desugared() is not going to see the
+        // vector being full in the few subsequent loop iterations.
+        // So we get better branch prediction.
+        let mut vector = match iterator.next() {
+            None => return Vec::new(),
+            Some(element) => {
+                let (lower, _) = iterator.size_hint();
+                let mut vector = Vec::with_capacity(lower.saturating_add(1));
+                unsafe {
+                    ptr::write(vector.get_unchecked_mut(0), element);
+                    vector.set_len(1);
+                }
+                vector
+            }
+        };
+        <Vec<T> as SpecExtend<T, I>>::spec_extend(&mut vector, iterator);
+        vector
+    }
+
+    default fn spec_extend(&mut self, iter: I) {
+        self.extend_desugared(iter)
+    }
+}
+
+impl<T, I> SpecExtend<T, I> for Vec<T>
+    where I: TrustedLen<Item=T>,
+{
+    default fn from_iter(iterator: I) -> Self {
+        let mut vector = Vec::new();
+        vector.spec_extend(iterator);
+        vector
+    }
+
+    default fn spec_extend(&mut self, iterator: I) {
+        // This is the case for a TrustedLen iterator.
+        let (low, high) = iterator.size_hint();
+        if let Some(high_value) = high {
+            debug_assert_eq!(low, high_value,
+                             "TrustedLen iterator's size hint is not exact: {:?}",
+                             (low, high));
+        }
+        if let Some(additional) = high {
+            self.reserve(additional);
+            unsafe {
+                let mut ptr = self.as_mut_ptr().offset(self.len() as isize);
+                let mut local_len = SetLenOnDrop::new(&mut self.len);
+                for element in iterator {
+                    ptr::write(ptr, element);
+                    ptr = ptr.offset(1);
+                    // NB can't overflow since we would have had to alloc the address space
+                    local_len.increment_len(1);
+                }
+            }
+        } else {
+            self.extend_desugared(iterator)
+        }
+    }
+}
+
+impl<T> SpecExtend<T, IntoIter<T>> for Vec<T> {
+    fn from_iter(iterator: IntoIter<T>) -> Self {
+        // A common case is passing a vector into a function which immediately
+        // re-collects into a vector. We can short circuit this if the IntoIter
+        // has not been advanced at all.
+        if iterator.buf.as_ptr() as *const _ == iterator.ptr {
+            unsafe {
+                let vec = Vec::from_raw_parts(iterator.buf.as_ptr(),
+                                              iterator.len(),
+                                              iterator.cap);
+                mem::forget(iterator);
+                vec
+            }
+        } else {
+            let mut vector = Vec::new();
+            vector.spec_extend(iterator);
+            vector
+        }
+    }
+
+    fn spec_extend(&mut self, mut iterator: IntoIter<T>) {
+        unsafe {
+            self.append_elements(iterator.as_slice() as _);
+        }
+        iterator.ptr = iterator.end;
+    }
+}
+
+impl<'a, T: 'a, I> SpecExtend<&'a T, I> for Vec<T>
+    where I: Iterator<Item=&'a T>,
+          T: Clone,
+{
+    default fn from_iter(iterator: I) -> Self {
+        SpecExtend::from_iter(iterator.cloned())
+    }
+
+    default fn spec_extend(&mut self, iterator: I) {
+        self.spec_extend(iterator.cloned())
+    }
+}
+
+impl<'a, T: 'a> SpecExtend<&'a T, slice::Iter<'a, T>> for Vec<T>
+    where T: Copy,
+{
+    fn spec_extend(&mut self, iterator: slice::Iter<'a, T>) {
+        let slice = iterator.as_slice();
+        self.reserve(slice.len());
+        unsafe {
+            let len = self.len();
+            self.set_len(len + slice.len());
+            self.get_unchecked_mut(len..).copy_from_slice(slice);
+        }
+    }
+}
+
+impl<T> Vec<T> {
+    fn extend_desugared<I: Iterator<Item = T>>(&mut self, mut iterator: I) {
+        // This is the case for a general iterator.
+        //
+        // This function should be the moral equivalent of:
+        //
+        //      for item in iterator {
+        //          self.push(item);
+        //      }
+        while let Some(element) = iterator.next() {
+            let len = self.len();
+            if len == self.capacity() {
+                let (lower, _) = iterator.size_hint();
+                self.reserve(lower.saturating_add(1));
+            }
+            unsafe {
+                ptr::write(self.get_unchecked_mut(len), element);
+                // NB can't overflow since we would have had to alloc the address space
+                self.set_len(len + 1);
+            }
+        }
+    }
+
+    /// Creates a splicing iterator that replaces the specified range in the vector
+    /// with the given `replace_with` iterator and yields the removed items.
+    /// `replace_with` does not need to be the same length as `range`.
+    ///
+    /// Note 1: The element range is removed even if the iterator is not
+    /// consumed until the end.
+    ///
+    /// Note 2: It is unspecified how many elements are removed from the vector,
+    /// if the `Splice` value is leaked.
+    ///
+    /// Note 3: The input iterator `replace_with` is only consumed
+    /// when the `Splice` value is dropped.
+    ///
+    /// Note 4: This is optimal if:
+    ///
+    /// * The tail (elements in the vector after `range`) is empty,
+    /// * or `replace_with` yields fewer elements than `range`’s length
+    /// * or the lower bound of its `size_hint()` is exact.
+    ///
+    /// Otherwise, a temporary vector is allocated and the tail is moved twice.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the starting point is greater than the end point or if
+    /// the end point is greater than the length of the vector.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(splice)]
+    /// let mut v = vec![1, 2, 3];
+    /// let new = [7, 8];
+    /// let u: Vec<_> = v.splice(..2, new.iter().cloned()).collect();
+    /// assert_eq!(v, &[7, 8, 3]);
+    /// assert_eq!(u, &[1, 2]);
+    /// ```
+    #[inline]
+    #[unstable(feature = "splice", reason = "recently added", issue = "32310")]
+    pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<I::IntoIter>
+        where R: RangeArgument<usize>, I: IntoIterator<Item=T>
+    {
+        Splice {
+            drain: self.drain(range),
+            replace_with: replace_with.into_iter(),
+        }
+    }
+
+}
+
+#[stable(feature = "extend_ref", since = "1.2.0")]
+impl<'a, T: 'a + Copy> Extend<&'a T> for Vec<T> {
+    fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
+        self.spec_extend(iter.into_iter())
+    }
+}
+
+macro_rules! __impl_slice_eq1 {
+    ($Lhs: ty, $Rhs: ty) => {
+        __impl_slice_eq1! { $Lhs, $Rhs, Sized }
+    };
+    ($Lhs: ty, $Rhs: ty, $Bound: ident) => {
+        #[stable(feature = "rust1", since = "1.0.0")]
+        impl<'a, 'b, A: $Bound, B> PartialEq<$Rhs> for $Lhs where A: PartialEq<B> {
+            #[inline]
+            fn eq(&self, other: &$Rhs) -> bool { self[..] == other[..] }
+            #[inline]
+            fn ne(&self, other: &$Rhs) -> bool { self[..] != other[..] }
+        }
+    }
+}
+
+__impl_slice_eq1! { Vec<A>, Vec<B> }
+__impl_slice_eq1! { Vec<A>, &'b [B] }
+__impl_slice_eq1! { Vec<A>, &'b mut [B] }
+__impl_slice_eq1! { Cow<'a, [A]>, &'b [B], Clone }
+__impl_slice_eq1! { Cow<'a, [A]>, &'b mut [B], Clone }
+__impl_slice_eq1! { Cow<'a, [A]>, Vec<B>, Clone }
+
+macro_rules! array_impls {
+    ($($N: expr)+) => {
+        $(
+            // NOTE: some less important impls are omitted to reduce code bloat
+            __impl_slice_eq1! { Vec<A>, [B; $N] }
+            __impl_slice_eq1! { Vec<A>, &'b [B; $N] }
+            // __impl_slice_eq1! { Vec<A>, &'b mut [B; $N] }
+            // __impl_slice_eq1! { Cow<'a, [A]>, [B; $N], Clone }
+            // __impl_slice_eq1! { Cow<'a, [A]>, &'b [B; $N], Clone }
+            // __impl_slice_eq1! { Cow<'a, [A]>, &'b mut [B; $N], Clone }
+        )+
+    }
+}
+
+array_impls! {
+     0  1  2  3  4  5  6  7  8  9
+    10 11 12 13 14 15 16 17 18 19
+    20 21 22 23 24 25 26 27 28 29
+    30 31 32
+}
+
+/// Implements comparison of vectors, lexicographically.
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: PartialOrd> PartialOrd for Vec<T> {
+    #[inline]
+    fn partial_cmp(&self, other: &Vec<T>) -> Option<Ordering> {
+        PartialOrd::partial_cmp(&**self, &**other)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Eq> Eq for Vec<T> {}
+
+/// Implements ordering of vectors, lexicographically.
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Ord> Ord for Vec<T> {
+    #[inline]
+    fn cmp(&self, other: &Vec<T>) -> Ordering {
+        Ord::cmp(&**self, &**other)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<#[may_dangle] T> Drop for Vec<T> {
+    fn drop(&mut self) {
+        unsafe {
+            // use drop for [T]
+            ptr::drop_in_place(&mut self[..]);
+        }
+        // RawVec handles deallocation
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> Default for Vec<T> {
+    /// Creates an empty `Vec<T>`.
+    fn default() -> Vec<T> {
+        Vec::new()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: fmt::Debug> fmt::Debug for Vec<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> AsRef<Vec<T>> for Vec<T> {
+    fn as_ref(&self) -> &Vec<T> {
+        self
+    }
+}
+
+#[stable(feature = "vec_as_mut", since = "1.5.0")]
+impl<T> AsMut<Vec<T>> for Vec<T> {
+    fn as_mut(&mut self) -> &mut Vec<T> {
+        self
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> AsRef<[T]> for Vec<T> {
+    fn as_ref(&self) -> &[T] {
+        self
+    }
+}
+
+#[stable(feature = "vec_as_mut", since = "1.5.0")]
+impl<T> AsMut<[T]> for Vec<T> {
+    fn as_mut(&mut self) -> &mut [T] {
+        self
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T: Clone> From<&'a [T]> for Vec<T> {
+    #[cfg(not(test))]
+    fn from(s: &'a [T]) -> Vec<T> {
+        s.to_vec()
+    }
+    #[cfg(test)]
+    fn from(s: &'a [T]) -> Vec<T> {
+        ::slice::to_vec(s)
+    }
+}
+
+#[stable(feature = "vec_from_mut", since = "1.19.0")]
+impl<'a, T: Clone> From<&'a mut [T]> for Vec<T> {
+    #[cfg(not(test))]
+    fn from(s: &'a mut [T]) -> Vec<T> {
+        s.to_vec()
+    }
+    #[cfg(test)]
+    fn from(s: &'a mut [T]) -> Vec<T> {
+        ::slice::to_vec(s)
+    }
+}
+
+#[stable(feature = "vec_from_cow_slice", since = "1.14.0")]
+impl<'a, T> From<Cow<'a, [T]>> for Vec<T> where [T]: ToOwned<Owned=Vec<T>> {
+    fn from(s: Cow<'a, [T]>) -> Vec<T> {
+        s.into_owned()
+    }
+}
+
+// note: test pulls in libstd, which causes errors here
+#[cfg(not(test))]
+#[stable(feature = "vec_from_box", since = "1.18.0")]
+impl<T> From<Box<[T]>> for Vec<T> {
+    fn from(s: Box<[T]>) -> Vec<T> {
+        s.into_vec()
+    }
+}
+
+#[stable(feature = "box_from_vec", since = "1.18.0")]
+impl<T> Into<Box<[T]>> for Vec<T> {
+    fn into(self) -> Box<[T]> {
+        self.into_boxed_slice()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a> From<&'a str> for Vec<u8> {
+    fn from(s: &'a str) -> Vec<u8> {
+        From::from(s.as_bytes())
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Clone-on-write
+////////////////////////////////////////////////////////////////////////////////
+
+#[stable(feature = "cow_from_vec", since = "1.8.0")]
+impl<'a, T: Clone> From<&'a [T]> for Cow<'a, [T]> {
+    fn from(s: &'a [T]) -> Cow<'a, [T]> {
+        Cow::Borrowed(s)
+    }
+}
+
+#[stable(feature = "cow_from_vec", since = "1.8.0")]
+impl<'a, T: Clone> From<Vec<T>> for Cow<'a, [T]> {
+    fn from(v: Vec<T>) -> Cow<'a, [T]> {
+        Cow::Owned(v)
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> FromIterator<T> for Cow<'a, [T]> where T: Clone {
+    fn from_iter<I: IntoIterator<Item = T>>(it: I) -> Cow<'a, [T]> {
+        Cow::Owned(FromIterator::from_iter(it))
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Iterators
+////////////////////////////////////////////////////////////////////////////////
+
+/// An iterator that moves out of a vector.
+///
+/// This `struct` is created by the `into_iter` method on [`Vec`][`Vec`] (provided
+/// by the [`IntoIterator`] trait).
+///
+/// [`Vec`]: struct.Vec.html
+/// [`IntoIterator`]: ../../std/iter/trait.IntoIterator.html
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct IntoIter<T> {
+    buf: Shared<T>,
+    cap: usize,
+    ptr: *const T,
+    end: *const T,
+}
+
+#[stable(feature = "vec_intoiter_debug", since = "1.13.0")]
+impl<T: fmt::Debug> fmt::Debug for IntoIter<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_tuple("IntoIter")
+            .field(&self.as_slice())
+            .finish()
+    }
+}
+
+impl<T> IntoIter<T> {
+    /// Returns the remaining items of this iterator as a slice.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let vec = vec!['a', 'b', 'c'];
+    /// let mut into_iter = vec.into_iter();
+    /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
+    /// let _ = into_iter.next().unwrap();
+    /// assert_eq!(into_iter.as_slice(), &['b', 'c']);
+    /// ```
+    #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
+    pub fn as_slice(&self) -> &[T] {
+        unsafe {
+            slice::from_raw_parts(self.ptr, self.len())
+        }
+    }
+
+    /// Returns the remaining items of this iterator as a mutable slice.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let vec = vec!['a', 'b', 'c'];
+    /// let mut into_iter = vec.into_iter();
+    /// assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
+    /// into_iter.as_mut_slice()[2] = 'z';
+    /// assert_eq!(into_iter.next().unwrap(), 'a');
+    /// assert_eq!(into_iter.next().unwrap(), 'b');
+    /// assert_eq!(into_iter.next().unwrap(), 'z');
+    /// ```
+    #[stable(feature = "vec_into_iter_as_slice", since = "1.15.0")]
+    pub fn as_mut_slice(&mut self) -> &mut [T] {
+        unsafe {
+            slice::from_raw_parts_mut(self.ptr as *mut T, self.len())
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<T: Send> Send for IntoIter<T> {}
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<T: Sync> Sync for IntoIter<T> {}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> Iterator for IntoIter<T> {
+    type Item = T;
+
+    #[inline]
+    fn next(&mut self) -> Option<T> {
+        unsafe {
+            if self.ptr as *const _ == self.end {
+                None
+            } else {
+                if mem::size_of::<T>() == 0 {
+                    // purposefully don't use 'ptr.offset' because for
+                    // vectors with 0-size elements this would return the
+                    // same pointer.
+                    self.ptr = arith_offset(self.ptr as *const i8, 1) as *mut T;
+
+                    // Use a non-null pointer value
+                    // (self.ptr might be null because of wrapping)
+                    Some(ptr::read(1 as *mut T))
+                } else {
+                    let old = self.ptr;
+                    self.ptr = self.ptr.offset(1);
+
+                    Some(ptr::read(old))
+                }
+            }
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let exact = match self.ptr.offset_to(self.end) {
+            Some(x) => x as usize,
+            None => (self.end as usize).wrapping_sub(self.ptr as usize),
+        };
+        (exact, Some(exact))
+    }
+
+    #[inline]
+    fn count(self) -> usize {
+        self.len()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> DoubleEndedIterator for IntoIter<T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<T> {
+        unsafe {
+            if self.end == self.ptr {
+                None
+            } else {
+                if mem::size_of::<T>() == 0 {
+                    // See above for why 'ptr.offset' isn't used
+                    self.end = arith_offset(self.end as *const i8, -1) as *mut T;
+
+                    // Use a non-null pointer value
+                    // (self.end might be null because of wrapping)
+                    Some(ptr::read(1 as *mut T))
+                } else {
+                    self.end = self.end.offset(-1);
+
+                    Some(ptr::read(self.end))
+                }
+            }
+        }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> ExactSizeIterator for IntoIter<T> {
+    fn is_empty(&self) -> bool {
+        self.ptr == self.end
+    }
+}
+
+#[unstable(feature = "fused", issue = "35602")]
+impl<T> FusedIterator for IntoIter<T> {}
+
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<T> TrustedLen for IntoIter<T> {}
+
+#[stable(feature = "vec_into_iter_clone", since = "1.8.0")]
+impl<T: Clone> Clone for IntoIter<T> {
+    fn clone(&self) -> IntoIter<T> {
+        self.as_slice().to_owned().into_iter()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+unsafe impl<#[may_dangle] T> Drop for IntoIter<T> {
+    fn drop(&mut self) {
+        // destroy the remaining elements
+        for _x in self.by_ref() {}
+
+        // RawVec handles deallocation
+        let _ = unsafe { RawVec::from_raw_parts(self.buf.as_ptr(), self.cap) };
+    }
+}
+
+/// A draining iterator for `Vec<T>`.
+///
+/// This `struct` is created by the [`drain`] method on [`Vec`].
+///
+/// [`drain`]: struct.Vec.html#method.drain
+/// [`Vec`]: struct.Vec.html
+#[stable(feature = "drain", since = "1.6.0")]
+pub struct Drain<'a, T: 'a> {
+    /// Index of tail to preserve
+    tail_start: usize,
+    /// Length of tail
+    tail_len: usize,
+    /// Current remaining range to remove
+    iter: slice::Iter<'a, T>,
+    vec: Shared<Vec<T>>,
+}
+
+#[stable(feature = "collection_debug", since = "1.17.0")]
+impl<'a, T: 'a + fmt::Debug> fmt::Debug for Drain<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_tuple("Drain")
+         .field(&self.iter.as_slice())
+         .finish()
+    }
+}
+
+#[stable(feature = "drain", since = "1.6.0")]
+unsafe impl<'a, T: Sync> Sync for Drain<'a, T> {}
+#[stable(feature = "drain", since = "1.6.0")]
+unsafe impl<'a, T: Send> Send for Drain<'a, T> {}
+
+#[stable(feature = "drain", since = "1.6.0")]
+impl<'a, T> Iterator for Drain<'a, T> {
+    type Item = T;
+
+    #[inline]
+    fn next(&mut self) -> Option<T> {
+        self.iter.next().map(|elt| unsafe { ptr::read(elt as *const _) })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+#[stable(feature = "drain", since = "1.6.0")]
+impl<'a, T> DoubleEndedIterator for Drain<'a, T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<T> {
+        self.iter.next_back().map(|elt| unsafe { ptr::read(elt as *const _) })
+    }
+}
+
+#[stable(feature = "drain", since = "1.6.0")]
+impl<'a, T> Drop for Drain<'a, T> {
+    fn drop(&mut self) {
+        // exhaust self first
+        while let Some(_) = self.next() {}
+
+        if self.tail_len > 0 {
+            unsafe {
+                let source_vec = self.vec.as_mut();
+                // memmove back untouched tail, update to new length
+                let start = source_vec.len();
+                let tail = self.tail_start;
+                let src = source_vec.as_ptr().offset(tail as isize);
+                let dst = source_vec.as_mut_ptr().offset(start as isize);
+                ptr::copy(src, dst, self.tail_len);
+                source_vec.set_len(start + self.tail_len);
+            }
+        }
+    }
+}
+
+
+#[stable(feature = "drain", since = "1.6.0")]
+impl<'a, T> ExactSizeIterator for Drain<'a, T> {
+    fn is_empty(&self) -> bool {
+        self.iter.is_empty()
+    }
+}
+
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, T> FusedIterator for Drain<'a, T> {}
+
+/// A place for insertion at the back of a `Vec`.
+///
+/// See [`Vec::place_back`](struct.Vec.html#method.place_back) for details.
+#[must_use = "places do nothing unless written to with `<-` syntax"]
+#[unstable(feature = "collection_placement",
+           reason = "struct name and placement protocol are subject to change",
+           issue = "30172")]
+#[derive(Debug)]
+pub struct PlaceBack<'a, T: 'a> {
+    vec: &'a mut Vec<T>,
+}
+
+#[unstable(feature = "collection_placement",
+           reason = "placement protocol is subject to change",
+           issue = "30172")]
+impl<'a, T> Placer<T> for PlaceBack<'a, T> {
+    type Place = PlaceBack<'a, T>;
+
+    fn make_place(self) -> Self {
+        // This will panic or abort if we would allocate > isize::MAX bytes
+        // or if the length increment would overflow for zero-sized types.
+        if self.vec.len == self.vec.buf.cap() {
+            self.vec.buf.double();
+        }
+        self
+    }
+}
+
+#[unstable(feature = "collection_placement",
+           reason = "placement protocol is subject to change",
+           issue = "30172")]
+impl<'a, T> Place<T> for PlaceBack<'a, T> {
+    fn pointer(&mut self) -> *mut T {
+        unsafe { self.vec.as_mut_ptr().offset(self.vec.len as isize) }
+    }
+}
+
+#[unstable(feature = "collection_placement",
+           reason = "placement protocol is subject to change",
+           issue = "30172")]
+impl<'a, T> InPlace<T> for PlaceBack<'a, T> {
+    type Owner = &'a mut T;
+
+    unsafe fn finalize(mut self) -> &'a mut T {
+        let ptr = self.pointer();
+        self.vec.len += 1;
+        &mut *ptr
+    }
+}
+
+
+/// A splicing iterator for `Vec`.
+///
+/// This struct is created by the [`splice()`] method on [`Vec`]. See its
+/// documentation for more.
+///
+/// [`splice()`]: struct.Vec.html#method.splice
+/// [`Vec`]: struct.Vec.html
+#[derive(Debug)]
+#[unstable(feature = "splice", reason = "recently added", issue = "32310")]
+pub struct Splice<'a, I: Iterator + 'a> {
+    drain: Drain<'a, I::Item>,
+    replace_with: I,
+}
+
+#[unstable(feature = "splice", reason = "recently added", issue = "32310")]
+impl<'a, I: Iterator> Iterator for Splice<'a, I> {
+    type Item = I::Item;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.drain.next()
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.drain.size_hint()
+    }
+}
+
+#[unstable(feature = "splice", reason = "recently added", issue = "32310")]
+impl<'a, I: Iterator> DoubleEndedIterator for Splice<'a, I> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.drain.next_back()
+    }
+}
+
+#[unstable(feature = "splice", reason = "recently added", issue = "32310")]
+impl<'a, I: Iterator> ExactSizeIterator for Splice<'a, I> {}
+
+
+#[unstable(feature = "splice", reason = "recently added", issue = "32310")]
+impl<'a, I: Iterator> Drop for Splice<'a, I> {
+    fn drop(&mut self) {
+        // exhaust drain first
+        while let Some(_) = self.drain.next() {}
+
+
+        unsafe {
+            if self.drain.tail_len == 0 {
+                self.drain.vec.as_mut().extend(self.replace_with.by_ref());
+                return
+            }
+
+            // First fill the range left by drain().
+            if !self.drain.fill(&mut self.replace_with) {
+                return
+            }
+
+            // There may be more elements. Use the lower bound as an estimate.
+            // FIXME: Is the upper bound a better guess? Or something else?
+            let (lower_bound, _upper_bound) = self.replace_with.size_hint();
+            if lower_bound > 0  {
+                self.drain.move_tail(lower_bound);
+                if !self.drain.fill(&mut self.replace_with) {
+                    return
+                }
+            }
+
+            // Collect any remaining elements.
+            // This is a zero-length vector which does not allocate if `lower_bound` was exact.
+            let mut collected = self.replace_with.by_ref().collect::<Vec<I::Item>>().into_iter();
+            // Now we have an exact count.
+            if collected.len() > 0 {
+                self.drain.move_tail(collected.len());
+                let filled = self.drain.fill(&mut collected);
+                debug_assert!(filled);
+                debug_assert_eq!(collected.len(), 0);
+            }
+        }
+        // Let `Drain::drop` move the tail back if necessary and restore `vec.len`.
+    }
+}
+
+/// Private helper methods for `Splice::drop`
+impl<'a, T> Drain<'a, T> {
+    /// The range from `self.vec.len` to `self.tail_start` contains elements
+    /// that have been moved out.
+    /// Fill that range as much as possible with new elements from the `replace_with` iterator.
+    /// Return whether we filled the entire range. (`replace_with.next()` didn’t return `None`.)
+    unsafe fn fill<I: Iterator<Item=T>>(&mut self, replace_with: &mut I) -> bool {
+        let vec = self.vec.as_mut();
+        let range_start = vec.len;
+        let range_end = self.tail_start;
+        let range_slice = slice::from_raw_parts_mut(
+            vec.as_mut_ptr().offset(range_start as isize),
+            range_end - range_start);
+
+        for place in range_slice {
+            if let Some(new_item) = replace_with.next() {
+                ptr::write(place, new_item);
+                vec.len += 1;
+            } else {
+                return false
+            }
+        }
+        true
+    }
+
+    /// Make room for inserting more elements before the tail.
+    unsafe fn move_tail(&mut self, extra_capacity: usize) {
+        let vec = self.vec.as_mut();
+        let used_capacity = self.tail_start + self.tail_len;
+        vec.buf.reserve(used_capacity, extra_capacity);
+
+        let new_tail_start = self.tail_start + extra_capacity;
+        let src = vec.as_ptr().offset(self.tail_start as isize);
+        let dst = vec.as_mut_ptr().offset(new_tail_start as isize);
+        ptr::copy(src, dst, self.tail_len);
+        self.tail_start = new_tail_start;
+    }
+}