vec.rs

// 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 growable list type, written `Vec<T>` but pronounced 'vector.'
//!
//! Vectors have `O(1)` indexing, push (to the end) and pop (from the end).

use core::prelude::*;

use alloc::boxed::Box;
use alloc::heap::{EMPTY, allocate, reallocate, deallocate};
use core::cmp::max;
use core::default::Default;
use core::fmt;
use core::kinds::marker::{ContravariantLifetime, InvariantType};
use core::mem;
use core::num::{Int, UnsignedInt};
use core::ops;
use core::ptr;
use core::raw::Slice as RawSlice;
use core::uint;

use slice::{CloneSliceAllocPrelude};

/// An owned, growable vector.
///
/// # Examples
///
/// ```
/// let mut vec = Vec::new();
/// vec.push(1i);
/// vec.push(2i);
///
/// assert_eq!(vec.len(), 2);
/// assert_eq!(vec[0], 1);
///
/// assert_eq!(vec.pop(), Some(2));
/// assert_eq!(vec.len(), 1);
///
/// vec[0] = 7i;
/// assert_eq!(vec[0], 7);
///
/// vec.push_all([1, 2, 3]);
///
/// for x in vec.iter() {
///     println!("{}", x);
/// }
/// assert_eq!(vec, vec![7i, 1, 2, 3]);
/// ```
///
/// The `vec!` macro is provided to make initialization more convenient:
///
/// ```
/// let mut vec = vec![1i, 2i, 3i];
/// vec.push(4);
/// assert_eq!(vec, vec![1, 2, 3, 4]);
/// ```
///
/// Use a `Vec` as an efficient stack:
///
/// ```
/// let mut stack = Vec::new();
///
/// stack.push(1i);
/// stack.push(2i);
/// stack.push(3i);
///
/// loop {
///     let top = match stack.pop() {
///         None => break, // empty
///         Some(x) => x,
///     };
///     // Prints 3, 2, 1
///     println!("{}", top);
/// }
/// ```
///
/// # 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.
#[unsafe_no_drop_flag]
#[stable]
pub struct Vec<T> {
    ptr: *mut T,
    len: uint,
    cap: uint,
}

impl<T> Vec<T> {
    /// Constructs a new, empty `Vec`.
    ///
    /// The vector will not allocate until elements are pushed onto it.
    ///
    /// # Example
    ///
    /// ```
    /// let mut vec: Vec<int> = Vec::new();
    /// ```
    #[inline]
    #[stable]
    pub fn new() -> Vec<T> {
        // We want ptr to never be NULL so instead we set it to some arbitrary
        // non-null value which is fine since we never call deallocate on the ptr
        // if cap is 0. The reason for this is because the pointer of a slice
        // being NULL would break the null pointer optimization for enums.
        Vec { ptr: EMPTY as *mut T, len: 0, cap: 0 }
    }

    /// Constructs a new, empty `Vec` 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
    /// the main `Vec` docs above, 'Capacity and reallocation'.) To create
    /// a vector of a given length, use `Vec::from_elem` or `Vec::from_fn`.
    ///
    /// # Example
    ///
    /// ```
    /// let mut vec: Vec<int> = 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 range(0i, 10) {
    ///     vec.push(i);
    /// }
    ///
    /// // ...but this may make the vector reallocate
    /// vec.push(11);
    /// ```
    #[inline]
    #[stable]
    pub fn with_capacity(capacity: uint) -> Vec<T> {
        if mem::size_of::<T>() == 0 {
            Vec { ptr: EMPTY as *mut T, len: 0, cap: uint::MAX }
        } else if capacity == 0 {
            Vec::new()
        } else {
            let size = capacity.checked_mul(mem::size_of::<T>())
                               .expect("capacity overflow");
            let ptr = unsafe { allocate(size, mem::min_align_of::<T>()) };
            Vec { ptr: ptr as *mut T, len: 0, cap: capacity }
        }
    }

    /// Creates and initializes a `Vec`.
    ///
    /// Creates a `Vec` of size `length` and initializes the elements to the
    /// value returned by the closure `op`.
    ///
    /// # Example
    ///
    /// ```
    /// let vec = Vec::from_fn(3, |idx| idx * 2);
    /// assert_eq!(vec, vec![0, 2, 4]);
    /// ```
    #[inline]
    #[unstable = "the naming is uncertain as well as this migrating to unboxed \
                  closures in the future"]
    pub fn from_fn(length: uint, op: |uint| -> T) -> Vec<T> {
        unsafe {
            let mut xs = Vec::with_capacity(length);
            while xs.len < length {
                let len = xs.len;
                ptr::write(xs.as_mut_slice().unsafe_mut(len), op(len));
                xs.len += 1;
            }
            xs
        }
    }

    /// Creates a `Vec<T>` directly from the raw constituents.
    ///
    /// This is highly unsafe:
    ///
    /// - if `ptr` is null, then `length` and `capacity` should be 0
    /// - `ptr` must point to an allocation of size `capacity`
    /// - there must be `length` valid instances of type `T` at the
    ///   beginning of that allocation
    /// - `ptr` must be allocated by the default `Vec` allocator
    ///
    /// # Example
    ///
    /// ```
    /// use std::ptr;
    /// use std::mem;
    ///
    /// fn main() {
    ///     let mut v = vec![1i, 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 range(0, len as int) {
    ///             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, vec![4i, 5i, 6i]);
    ///     }
    /// }
    /// ```
    #[experimental]
    pub unsafe fn from_raw_parts(ptr: *mut T, length: uint,
                                 capacity: uint) -> Vec<T> {
        Vec { ptr: ptr, len: length, cap: capacity }
    }

    /// Consumes the `Vec`, partitioning it based on a predicate.
    ///
    /// Partitions the `Vec` into two `Vec`s `(A,B)`, where all elements of `A`
    /// satisfy `f` and all elements of `B` do not. The order of elements is
    /// preserved.
    ///
    /// # Example
    ///
    /// ```
    /// let vec = vec![1i, 2i, 3i, 4i];
    /// let (even, odd) = vec.partition(|&n| n % 2 == 0);
    /// assert_eq!(even, vec![2, 4]);
    /// assert_eq!(odd, vec![1, 3]);
    /// ```
    #[inline]
    #[experimental]
    pub fn partition(self, f: |&T| -> bool) -> (Vec<T>, Vec<T>) {
        let mut lefts  = Vec::new();
        let mut rights = Vec::new();

        for elt in self.into_iter() {
            if f(&elt) {
                lefts.push(elt);
            } else {
                rights.push(elt);
            }
        }

        (lefts, rights)
    }
}

impl<T: Clone> Vec<T> {
    /// Constructs a `Vec` with copies of a value.
    ///
    /// Creates a `Vec` with `length` copies of `value`.
    ///
    /// # Example
    /// ```
    /// let vec = Vec::from_elem(3, "hi");
    /// println!("{}", vec); // prints [hi, hi, hi]
    /// ```
    #[inline]
    #[unstable = "this functionality may become more generic over all collections"]
    pub fn from_elem(length: uint, value: T) -> Vec<T> {
        unsafe {
            let mut xs = Vec::with_capacity(length);
            while xs.len < length {
                let len = xs.len;
                ptr::write(xs.as_mut_slice().unsafe_mut(len),
                           value.clone());
                xs.len += 1;
            }
            xs
        }
    }

    /// 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.
    ///
    /// # Example
    ///
    /// ```
    /// let mut vec = vec![1i];
    /// vec.push_all([2i, 3, 4]);
    /// assert_eq!(vec, vec![1, 2, 3, 4]);
    /// ```
    #[inline]
    #[experimental]
    pub fn push_all(&mut self, other: &[T]) {
        self.reserve(other.len());

        for i in range(0, other.len()) {
            let len = self.len();

            // Unsafe code so this can be optimised to a memcpy (or something similarly
            // fast) when T is Copy. LLVM is easily confused, so any extra operations
            // during the loop can prevent this optimisation.
            unsafe {
                ptr::write(
                    self.as_mut_slice().unsafe_mut(len),
                    other.unsafe_get(i).clone());
                self.set_len(len + 1);
            }
        }
    }

    /// Grows the `Vec` in-place.
    ///
    /// Adds `n` copies of `value` to the `Vec`.
    ///
    /// # Example
    ///
    /// ```
    /// let mut vec = vec!["hello"];
    /// vec.grow(2, "world");
    /// assert_eq!(vec, vec!["hello", "world", "world"]);
    /// ```
    #[stable]
    pub fn grow(&mut self, n: uint, value: T) {
        self.reserve(n);
        let mut i: uint = 0u;

        while i < n {
            self.push(value.clone());
            i += 1u;
        }
    }

    /// Partitions a vector based on a predicate.
    ///
    /// Clones the elements of the vector, partitioning them into two `Vec`s
    /// `(a, b)`, where all elements of `a` satisfy `f` and all elements of `b`
    /// do not. The order of elements is preserved.
    ///
    /// # Example
    ///
    /// ```
    /// let vec = vec![1i, 2, 3, 4];
    /// let (even, odd) = vec.partitioned(|&n| n % 2 == 0);
    /// assert_eq!(even, vec![2i, 4]);
    /// assert_eq!(odd, vec![1i, 3]);
    /// ```
    #[experimental]
    pub fn partitioned(&self, f: |&T| -> bool) -> (Vec<T>, Vec<T>) {
        let mut lefts = Vec::new();
        let mut rights = Vec::new();

        for elt in self.iter() {
            if f(elt) {
                lefts.push(elt.clone());
            } else {
                rights.push(elt.clone());
            }
        }

        (lefts, rights)
    }
}

#[unstable]
impl<T:Clone> Clone for Vec<T> {
    fn clone(&self) -> Vec<T> { self.as_slice().to_vec() }

    fn clone_from(&mut self, other: &Vec<T>) {
        // drop anything in self that will not be overwritten
        if self.len() > other.len() {
            self.truncate(other.len())
        }

        // reuse the contained values' allocations/resources.
        for (place, thing) in self.iter_mut().zip(other.iter()) {
            place.clone_from(thing)
        }

        // self.len <= other.len due to the truncate above, so the
        // slice here is always in-bounds.
        let slice = other[self.len()..];
        self.push_all(slice);
    }
}

#[experimental = "waiting on Index stability"]
impl<T> Index<uint,T> for Vec<T> {
    #[inline]
    fn index<'a>(&'a self, index: &uint) -> &'a T {
        &self.as_slice()[*index]
    }
}

impl<T> IndexMut<uint,T> for Vec<T> {
    #[inline]
    fn index_mut<'a>(&'a mut self, index: &uint) -> &'a mut T {
        &mut self.as_mut_slice()[*index]
    }
}

impl<T> ops::Slice<uint, [T]> for Vec<T> {
    #[inline]
    fn as_slice_<'a>(&'a self) -> &'a [T] {
        self.as_slice()
    }

    #[inline]
    fn slice_from_or_fail<'a>(&'a self, start: &uint) -> &'a [T] {
        self.as_slice().slice_from_or_fail(start)
    }

    #[inline]
    fn slice_to_or_fail<'a>(&'a self, end: &uint) -> &'a [T] {
        self.as_slice().slice_to_or_fail(end)
    }
    #[inline]
    fn slice_or_fail<'a>(&'a self, start: &uint, end: &uint) -> &'a [T] {
        self.as_slice().slice_or_fail(start, end)
    }
}

impl<T> ops::SliceMut<uint, [T]> for Vec<T> {
    #[inline]
    fn as_mut_slice_<'a>(&'a mut self) -> &'a mut [T] {
        self.as_mut_slice()
    }

    #[inline]
    fn slice_from_or_fail_mut<'a>(&'a mut self, start: &uint) -> &'a mut [T] {
        self.as_mut_slice().slice_from_or_fail_mut(start)
    }

    #[inline]
    fn slice_to_or_fail_mut<'a>(&'a mut self, end: &uint) -> &'a mut [T] {
        self.as_mut_slice().slice_to_or_fail_mut(end)
    }
    #[inline]
    fn slice_or_fail_mut<'a>(&'a mut self, start: &uint, end: &uint) -> &'a mut [T] {
        self.as_mut_slice().slice_or_fail_mut(start, end)
    }
}

#[experimental = "waiting on Deref stability"]
impl<T> ops::Deref<[T]> for Vec<T> {
    fn deref<'a>(&'a self) -> &'a [T] { self.as_slice() }
}

#[experimental = "waiting on DerefMut stability"]
impl<T> ops::DerefMut<[T]> for Vec<T> {
    fn deref_mut<'a>(&'a mut self) -> &'a mut [T] { self.as_mut_slice() }
}

#[experimental = "waiting on FromIterator stability"]
impl<T> FromIterator<T> for Vec<T> {
    #[inline]
    fn from_iter<I:Iterator<T>>(mut iterator: I) -> Vec<T> {
        let (lower, _) = iterator.size_hint();
        let mut vector = Vec::with_capacity(lower);
        for element in iterator {
            vector.push(element)
        }
        vector
    }
}

#[experimental = "waiting on Extend stability"]
impl<T> Extend<T> for Vec<T> {
    #[inline]
    fn extend<I: Iterator<T>>(&mut self, mut iterator: I) {
        let (lower, _) = iterator.size_hint();
        self.reserve(lower);
        for element in iterator {
            self.push(element)
        }
    }
}

#[unstable = "waiting on PartialEq stability"]
impl<T: PartialEq> PartialEq for Vec<T> {
    #[inline]
    fn eq(&self, other: &Vec<T>) -> bool {
        self.as_slice() == other.as_slice()
    }
}

#[unstable = "waiting on PartialOrd stability"]
impl<T: PartialOrd> PartialOrd for Vec<T> {
    #[inline]
    fn partial_cmp(&self, other: &Vec<T>) -> Option<Ordering> {
        self.as_slice().partial_cmp(other.as_slice())
    }
}

#[unstable = "waiting on Eq stability"]
impl<T: Eq> Eq for Vec<T> {}

#[experimental]
impl<T: PartialEq, V: AsSlice<T>> Equiv<V> for Vec<T> {
    #[inline]
    fn equiv(&self, other: &V) -> bool { self.as_slice() == other.as_slice() }
}

#[unstable = "waiting on Ord stability"]
impl<T: Ord> Ord for Vec<T> {
    #[inline]
    fn cmp(&self, other: &Vec<T>) -> Ordering {
        self.as_slice().cmp(other.as_slice())
    }
}

// FIXME: #13996: need a way to mark the return value as `noalias`
#[inline(never)]
unsafe fn alloc_or_realloc<T>(ptr: *mut T, old_size: uint, size: uint) -> *mut T {
    if old_size == 0 {
        allocate(size, mem::min_align_of::<T>()) as *mut T
    } else {
        reallocate(ptr as *mut u8, old_size, size, mem::min_align_of::<T>()) as *mut T
    }
}

#[inline]
unsafe fn dealloc<T>(ptr: *mut T, len: uint) {
    if mem::size_of::<T>() != 0 {
        deallocate(ptr as *mut u8,
                   len * mem::size_of::<T>(),
                   mem::min_align_of::<T>())
    }
}

impl<T> Vec<T> {
    /// Returns the number of elements the vector can hold without
    /// reallocating.
    ///
    /// # Example
    ///
    /// ```
    /// let vec: Vec<int> = Vec::with_capacity(10);
    /// assert_eq!(vec.capacity(), 10);
    /// ```
    #[inline]
    #[stable]
    pub fn capacity(&self) -> uint {
        self.cap
    }

    /// Deprecated: Renamed to `reserve`.
    #[deprecated = "Renamed to `reserve`"]
    pub fn reserve_additional(&mut self, extra: uint) {
        self.reserve(extra)
    }

    /// Reserves capacity for at least `additional` more elements to be inserted in the given
    /// `Vec`. The collection may reserve more space to avoid frequent reallocations.
    ///
    /// # Panics
    ///
    /// Panics if the new capacity overflows `uint`.
    ///
    /// # Example
    ///
    /// ```
    /// let mut vec: Vec<int> = vec![1];
    /// vec.reserve(10);
    /// assert!(vec.capacity() >= 11);
    /// ```
    #[unstable = "matches collection reform specification, waiting for dust to settle"]
    pub fn reserve(&mut self, additional: uint) {
        if self.cap - self.len < additional {
            match self.len.checked_add(additional) {
                None => panic!("Vec::reserve: `uint` overflow"),
                // if the checked_add
                Some(new_cap) => {
                    let amort_cap = new_cap.next_power_of_two();
                    // next_power_of_two will overflow to exactly 0 for really big capacities
                    if amort_cap == 0 {
                        self.grow_capacity(new_cap);
                    } else {
                        self.grow_capacity(amort_cap);
                    }
                }
            }
        }
    }

    /// Reserves the minimum capacity for exactly `additional` more elements to be inserted in the
    /// given `Vec`. 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 `uint`.
    ///
    /// # Example
    ///
    /// ```
    /// let mut vec: Vec<int> = vec![1];
    /// vec.reserve_exact(10);
    /// assert!(vec.capacity() >= 11);
    /// ```
    #[unstable = "matches collection reform specification, waiting for dust to settle"]
    pub fn reserve_exact(&mut self, additional: uint) {
        if self.cap - self.len < additional {
            match self.len.checked_add(additional) {
                None => panic!("Vec::reserve: `uint` overflow"),
                Some(new_cap) => self.grow_capacity(new_cap)
            }
        }
    }

    /// 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.
    ///
    /// # Example
    ///
    /// ```
    /// let mut vec: Vec<int> = Vec::with_capacity(10);
    /// vec.push_all([1, 2, 3]);
    /// assert_eq!(vec.capacity(), 10);
    /// vec.shrink_to_fit();
    /// assert!(vec.capacity() >= 3);
    /// ```
    #[stable]
    #[unstable = "matches collection reform specification, waiting for dust to settle"]
    pub fn shrink_to_fit(&mut self) {
        if mem::size_of::<T>() == 0 { return }

        if self.len == 0 {
            if self.cap != 0 {
                unsafe {
                    dealloc(self.ptr, self.cap)
                }
                self.cap = 0;
            }
        } else {
            unsafe {
                // Overflow check is unnecessary as the vector is already at
                // least this large.
                self.ptr = reallocate(self.ptr as *mut u8,
                                      self.cap * mem::size_of::<T>(),
                                      self.len * mem::size_of::<T>(),
                                      mem::min_align_of::<T>()) as *mut T;
                if self.ptr.is_null() { ::alloc::oom() }
            }
            self.cap = self.len;
        }
    }

    /// Convert the vector into Box<[T]>.
    ///
    /// 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()`.
    #[experimental]
    pub fn into_boxed_slice(mut self) -> Box<[T]> {
        self.shrink_to_fit();
        unsafe {
            let xs: Box<[T]> = mem::transmute(self.as_mut_slice());
            mem::forget(self);
            xs
        }
    }

    /// Shorten a vector, dropping excess elements.
    ///
    /// If `len` is greater than the vector's current length, this has no
    /// effect.
    ///
    /// # Example
    ///
    /// ```
    /// let mut vec = vec![1i, 2, 3, 4];
    /// vec.truncate(2);
    /// assert_eq!(vec, vec![1, 2]);
    /// ```
    #[unstable = "matches collection reform specification; waiting on panic semantics"]
    pub fn truncate(&mut self, len: uint) {
        unsafe {
            // drop any extra elements
            while len < self.len {
                // decrement len before the read(), so a panic on Drop doesn't
                // re-drop the just-failed value.
                self.len -= 1;
                ptr::read(self.as_slice().unsafe_get(self.len));
            }
        }
    }

    /// Returns a mutable slice of the elements of `self`.
    ///
    /// # Example
    ///
    /// ```
    /// fn foo(slice: &mut [int]) {}
    ///
    /// let mut vec = vec![1i, 2];
    /// foo(vec.as_mut_slice());
    /// ```
    #[inline]
    #[stable]
    pub fn as_mut_slice<'a>(&'a mut self) -> &'a mut [T] {
        unsafe {
            mem::transmute(RawSlice {
                data: self.ptr as *const T,
                len: self.len,
            })
        }
    }

    /// 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.
    ///
    /// # Example
    ///
    /// ```
    /// let v = vec!["a".to_string(), "b".to_string()];
    /// for s in v.into_iter() {
    ///     // s has type String, not &String
    ///     println!("{}", s);
    /// }
    /// ```
    #[inline]
    #[unstable = "matches collection reform specification, waiting for dust to settle"]
    pub fn into_iter(self) -> MoveItems<T> {
        unsafe {
            let ptr = self.ptr;
            let cap = self.cap;
            let begin = self.ptr as *const T;
            let end = if mem::size_of::<T>() == 0 {
                (ptr as uint + self.len()) as *const T
            } else {
                ptr.offset(self.len() as int) as *const T
            };
            mem::forget(self);
            MoveItems { allocation: ptr, cap: cap, ptr: begin, end: end }
        }
    }

    /// 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.
    ///
    /// # Example
    ///
    /// ```
    /// let mut v = vec![1u, 2, 3, 4];
    /// unsafe {
    ///     v.set_len(1);
    /// }
    /// ```
    #[inline]
    #[stable]
    pub unsafe fn set_len(&mut self, len: uint) {
        self.len = len;
    }

    /// Removes an element from anywhere in the vector and return it, replacing
    /// it with the last element. This does not preserve ordering, but is O(1).
    ///
    /// Returns `None` if `index` is out of bounds.
    ///
    /// # Example
    /// ```
    /// let mut v = vec!["foo", "bar", "baz", "qux"];
    ///
    /// assert_eq!(v.swap_remove(1), Some("bar"));
    /// assert_eq!(v, vec!["foo", "qux", "baz"]);
    ///
    /// assert_eq!(v.swap_remove(0), Some("foo"));
    /// assert_eq!(v, vec!["baz", "qux"]);
    ///
    /// assert_eq!(v.swap_remove(2), None);
    /// ```
    #[inline]
    #[unstable = "the naming of this function may be altered"]
    pub fn swap_remove(&mut self, index: uint) -> Option<T> {
        let length = self.len();
        if length > 0 && index < length - 1 {
            self.as_mut_slice().swap(index, length - 1);
        } else if index >= length {
            return None
        }
        self.pop()
    }

    /// Inserts an element at position `index` within the vector, shifting all
    /// elements after position `i` one position to the right.
    ///
    /// # Panics
    ///
    /// Panics if `index` is not between `0` and the vector's length (both
    /// bounds inclusive).
    ///
    /// # Example
    ///
    /// ```
    /// let mut vec = vec![1i, 2, 3];
    /// vec.insert(1, 4);
    /// assert_eq!(vec, vec![1, 4, 2, 3]);
    /// vec.insert(4, 5);
    /// assert_eq!(vec, vec![1, 4, 2, 3, 5]);
    /// ```
    #[unstable = "panic semantics need settling"]
    pub fn insert(&mut self, index: uint, element: T) {
        let len = self.len();
        assert!(index <= len);
        // space for the new element
        self.reserve(1);

        unsafe { // infallible
            // The spot to put the new value
            {
                let p = self.as_mut_ptr().offset(index as int);
                // Shift everything over to make space. (Duplicating the
                // `index`th element into two consecutive places.)
                ptr::copy_memory(p.offset(1), &*p, len - index);
                // Write it in, overwriting the first copy of the `index`th
                // element.
                ptr::write(&mut *p, element);
            }
            self.set_len(len + 1);
        }
    }

    /// Removes and returns the element at position `index` within the vector,
    /// shifting all elements after position `index` one position to the left.
    /// Returns `None` if `i` is out of bounds.
    ///
    /// # Example
    ///
    /// ```
    /// let mut v = vec![1i, 2, 3];
    /// assert_eq!(v.remove(1), Some(2));
    /// assert_eq!(v, vec![1, 3]);
    ///
    /// assert_eq!(v.remove(4), None);
    /// // v is unchanged:
    /// assert_eq!(v, vec![1, 3]);
    /// ```
    #[unstable = "panic semantics need settling"]
    pub fn remove(&mut self, index: uint) -> Option<T> {
        let len = self.len();
        if index < len {
            unsafe { // infallible
                let ret;
                {
                    // the place we are taking from.
                    let ptr = self.as_mut_ptr().offset(index as int);
                    // copy it out, unsafely having a copy of the value on
                    // the stack and in the vector at the same time.
                    ret = Some(ptr::read(ptr as *const T));

                    // Shift everything down to fill in that spot.
                    ptr::copy_memory(ptr, &*ptr.offset(1), len - index - 1);
                }
                self.set_len(len - 1);
                ret
            }
        } else {
            None
        }
    }

    /// 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.
    ///
    /// # Example
    ///
    /// ```
    /// let mut vec = vec![1i, 2, 3, 4];
    /// vec.retain(|&x| x%2 == 0);
    /// assert_eq!(vec, vec![2, 4]);
    /// ```
    #[unstable = "the closure argument may become an unboxed closure"]
    pub fn retain(&mut self, f: |&T| -> bool) {
        let len = self.len();
        let mut del = 0u;
        {
            let v = self.as_mut_slice();

            for i in range(0u, len) {
                if !f(&v[i]) {
                    del += 1;
                } else if del > 0 {
                    v.swap(i-del, i);
                }
            }
        }
        if del > 0 {
            self.truncate(len - del);
        }
    }

    /// Expands a vector in place, initializing the new elements to the result of a function.
    ///
    /// The vector is grown by `n` elements. The i-th new element are initialized to the value
    /// returned by `f(i)` where `i` is in the range [0, n).
    ///
    /// # Example
    ///
    /// ```
    /// let mut vec = vec![0u, 1];
    /// vec.grow_fn(3, |i| i);
    /// assert_eq!(vec, vec![0, 1, 0, 1, 2]);
    /// ```
    #[unstable = "this function may be renamed or change to unboxed closures"]
    pub fn grow_fn(&mut self, n: uint, f: |uint| -> T) {
        self.reserve(n);
        for i in range(0u, n) {
            self.push(f(i));
        }
    }

    /// Appends an element to the back of a collection.
    ///
    /// # Panics
    ///
    /// Panics if the number of elements in the vector overflows a `uint`.
    ///
    /// # Example
    ///
    /// ```rust
    /// let mut vec = vec!(1i, 2);
    /// vec.push(3);
    /// assert_eq!(vec, vec!(1, 2, 3));
    /// ```
    #[inline]
    #[stable]
    pub fn push(&mut self, value: T) {
        if mem::size_of::<T>() == 0 {
            // zero-size types consume no memory, so we can't rely on the address space running out
            self.len = self.len.checked_add(1).expect("length overflow");
            unsafe { mem::forget(value); }
            return
        }
        if self.len == self.cap {
            let old_size = self.cap * mem::size_of::<T>();
            let size = max(old_size, 2 * mem::size_of::<T>()) * 2;
            if old_size > size { panic!("capacity overflow") }
            unsafe {
                self.ptr = alloc_or_realloc(self.ptr, old_size, size);
                if self.ptr.is_null() { ::alloc::oom() }
            }
            self.cap = max(self.cap, 2) * 2;
        }

        unsafe {
            let end = (self.ptr as *const T).offset(self.len as int) as *mut T;
            ptr::write(&mut *end, value);
            self.len += 1;
        }
    }

    /// Removes the last element from a vector and returns it, or `None` if
    /// it is empty.
    ///
    /// # Example
    ///
    /// ```rust
    /// let mut vec = vec![1i, 2, 3];
    /// assert_eq!(vec.pop(), Some(3));
    /// assert_eq!(vec, vec![1, 2]);
    /// ```
    #[inline]
    #[stable]
    pub fn pop(&mut self) -> Option<T> {
        if self.len == 0 {
            None
        } else {
            unsafe {
                self.len -= 1;
                Some(ptr::read(self.as_slice().unsafe_get(self.len())))
            }
        }
    }

    /// Clears the vector, removing all values.
    ///
    /// # Example
    ///
    /// ```
    /// let mut v = vec![1i, 2, 3];
    /// v.clear();
    /// assert!(v.is_empty());
    /// ```
    #[inline]
    #[stable]
    pub fn clear(&mut self) {
        self.truncate(0)
    }

    /// Return the number of elements in the vector
    ///
    /// # Example
    ///
    /// ```
    /// let a = vec![1i, 2, 3];
    /// assert_eq!(a.len(), 3);
    /// ```
    #[inline]
    #[stable]
    pub fn len(&self) -> uint { self.len }

    /// Returns true if the vector contains no elements
    ///
    /// # Example
    ///
    /// ```
    /// let mut v = Vec::new();
    /// assert!(v.is_empty());
    /// v.push(1i);
    /// assert!(!v.is_empty());
    /// ```
    #[unstable = "matches collection reform specification, waiting for dust to settle"]
    pub fn is_empty(&self) -> bool { self.len() == 0 }

    /// Reserves capacity for exactly `capacity` elements in the given vector.
    ///
    /// If the capacity for `self` is already equal to or greater than the
    /// requested capacity, then no action is taken.
    fn grow_capacity(&mut self, capacity: uint) {
        if mem::size_of::<T>() == 0 { return }

        if capacity > self.cap {
            let size = capacity.checked_mul(mem::size_of::<T>())
                               .expect("capacity overflow");
            unsafe {
                self.ptr = alloc_or_realloc(self.ptr, self.cap * mem::size_of::<T>(), size);
                if self.ptr.is_null() { ::alloc::oom() }
            }
            self.cap = capacity;
        }
    }
}

impl<T: PartialEq> Vec<T> {
    /// Removes consecutive repeated elements in the vector.
    ///
    /// If the vector is sorted, this removes all duplicates.
    ///
    /// # Example
    ///
    /// ```
    /// let mut vec = vec![1i, 2, 2, 3, 2];
    /// vec.dedup();
    /// assert_eq!(vec, vec![1i, 2, 3, 2]);
    /// ```
    #[unstable = "this function may be renamed"]
    pub fn dedup(&mut self) {
        unsafe {
            // Although we have a mutable reference to `self`, we cannot make
            // *arbitrary* changes. The `PartialEq` comparisons 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 unsafe pointers.
            let p = self.as_mut_slice().as_mut_ptr();
            let mut r = 1;
            let mut w = 1;

            while r < ln {
                let p_r = p.offset(r as int);
                let p_wm1 = p.offset((w - 1) as int);
                if *p_r != *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);
        }
    }
}

impl<T> AsSlice<T> for Vec<T> {
    /// Returns a slice into `self`.
    ///
    /// # Example
    ///
    /// ```
    /// fn foo(slice: &[int]) {}
    ///
    /// let vec = vec![1i, 2];
    /// foo(vec.as_slice());
    /// ```
    #[inline]
    #[stable]
    fn as_slice<'a>(&'a self) -> &'a [T] {
        unsafe {
            mem::transmute(RawSlice {
                data: self.ptr as *const T,
                len: self.len
            })
        }
    }
}

impl<T: Clone, V: AsSlice<T>> Add<V, Vec<T>> for Vec<T> {
    #[inline]
    fn add(&self, rhs: &V) -> Vec<T> {
        let mut res = Vec::with_capacity(self.len() + rhs.as_slice().len());
        res.push_all(self.as_slice());
        res.push_all(rhs.as_slice());
        res
    }
}

#[unsafe_destructor]
impl<T> Drop for Vec<T> {
    fn drop(&mut self) {
        // This is (and should always remain) a no-op if the fields are
        // zeroed (when moving out, because of #[unsafe_no_drop_flag]).
        if self.cap != 0 {
            unsafe {
                for x in self.as_mut_slice().iter() {
                    ptr::read(x);
                }
                dealloc(self.ptr, self.cap)
            }
        }
    }
}

#[stable]
impl<T> Default for Vec<T> {
    fn default() -> Vec<T> {
        Vec::new()
    }
}

#[experimental = "waiting on Show stability"]
impl<T:fmt::Show> fmt::Show for Vec<T> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        self.as_slice().fmt(f)
    }
}

/// An iterator that moves out of a vector.
pub struct MoveItems<T> {
    allocation: *mut T, // the block of memory allocated for the vector
    cap: uint, // the capacity of the vector
    ptr: *const T,
    end: *const T
}

impl<T> MoveItems<T> {
    #[inline]
    /// Drops all items that have not yet been moved and returns the empty vector.
    pub fn unwrap(mut self) -> Vec<T> {
        unsafe {
            for _x in self { }
            let MoveItems { allocation, cap, ptr: _ptr, end: _end } = self;
            mem::forget(self);
            Vec { ptr: allocation, cap: cap, len: 0 }
        }
    }
}

impl<T> Iterator<T> for MoveItems<T> {
    #[inline]
    fn next<'a>(&'a mut self) -> Option<T> {
        unsafe {
            if self.ptr == 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 = mem::transmute(self.ptr as uint + 1);

                    // Use a non-null pointer value
                    Some(ptr::read(mem::transmute(1u)))
                } else {
                    let old = self.ptr;
                    self.ptr = self.ptr.offset(1);

                    Some(ptr::read(old))
                }
            }
        }
    }

    #[inline]
    fn size_hint(&self) -> (uint, Option<uint>) {
        let diff = (self.end as uint) - (self.ptr as uint);
        let size = mem::size_of::<T>();
        let exact = diff / (if size == 0 {1} else {size});
        (exact, Some(exact))
    }
}

impl<T> DoubleEndedIterator<T> for MoveItems<T> {
    #[inline]
    fn next_back<'a>(&'a 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 = mem::transmute(self.end as uint - 1);

                    // Use a non-null pointer value
                    Some(ptr::read(mem::transmute(1u)))
                } else {
                    self.end = self.end.offset(-1);

                    Some(ptr::read(mem::transmute(self.end)))
                }
            }
        }
    }
}

impl<T> ExactSize<T> for MoveItems<T> {}

#[unsafe_destructor]
impl<T> Drop for MoveItems<T> {
    fn drop(&mut self) {
        // destroy the remaining elements
        if self.cap != 0 {
            for _x in *self {}
            unsafe {
                dealloc(self.allocation, self.cap);
            }
        }
    }
}

/// Converts an iterator of pairs into a pair of vectors.
///
/// Returns a tuple containing two vectors where the i-th element of the first
/// vector contains the first element of the i-th tuple of the input iterator,
/// and the i-th element of the second vector contains the second element
/// of the i-th tuple of the input iterator.
#[unstable = "this functionality may become more generic over time"]
pub fn unzip<T, U, V: Iterator<(T, U)>>(mut iter: V) -> (Vec<T>, Vec<U>) {
    let (lo, _) = iter.size_hint();
    let mut ts = Vec::with_capacity(lo);
    let mut us = Vec::with_capacity(lo);
    for (t, u) in iter {
        ts.push(t);
        us.push(u);
    }
    (ts, us)
}

/// Wrapper type providing a `&Vec<T>` reference via `Deref`.
#[experimental]
pub struct DerefVec<'a, T> {
    x: Vec<T>,
    l: ContravariantLifetime<'a>
}

impl<'a, T> Deref<Vec<T>> for DerefVec<'a, T> {
    fn deref<'b>(&'b self) -> &'b Vec<T> {
        &self.x
    }
}

// Prevent the inner `Vec<T>` from attempting to deallocate memory.
#[unsafe_destructor]
impl<'a, T> Drop for DerefVec<'a, T> {
    fn drop(&mut self) {
        self.x.len = 0;
        self.x.cap = 0;
    }
}

/// Convert a slice to a wrapper type providing a `&Vec<T>` reference.
#[experimental]
pub fn as_vec<'a, T>(x: &'a [T]) -> DerefVec<'a, T> {
    unsafe {
        DerefVec {
            x: Vec::from_raw_parts(x.as_ptr() as *mut T, x.len(), x.len()),
            l: ContravariantLifetime::<'a>
        }
    }
}

/// Unsafe vector operations.
#[unstable]
pub mod raw {
    use super::Vec;
    use core::ptr;
    use core::slice::SlicePrelude;

    /// Constructs a vector from an unsafe pointer to a buffer.
    ///
    /// The elements of the buffer are copied into the vector without cloning,
    /// as if `ptr::read()` were called on them.
    #[inline]
    #[unstable]
    pub unsafe fn from_buf<T>(ptr: *const T, elts: uint) -> Vec<T> {
        let mut dst = Vec::with_capacity(elts);
        dst.set_len(elts);
        ptr::copy_nonoverlapping_memory(dst.as_mut_ptr(), ptr, elts);
        dst
    }
}

/// An owned, partially type-converted vector of elements with non-zero size.
///
/// `T` and `U` must have the same, non-zero size. They must also have the same
/// alignment.
///
/// When the destructor of this struct runs, all `U`s from `start_u` (incl.) to
/// `end_u` (excl.) and all `T`s from `start_t` (incl.) to `end_t` (excl.) are
/// destructed. Additionally the underlying storage of `vec` will be freed.
struct PartialVecNonZeroSized<T,U> {
    vec: Vec<T>,

    start_u: *mut U,
    end_u: *mut U,
    start_t: *mut T,
    end_t: *mut T,
}

/// An owned, partially type-converted vector of zero-sized elements.
///
/// When the destructor of this struct runs, all `num_t` `T`s and `num_u` `U`s
/// are destructed.
struct PartialVecZeroSized<T,U> {
    num_t: uint,
    num_u: uint,
    marker_t: InvariantType<T>,
    marker_u: InvariantType<U>,
}

#[unsafe_destructor]
impl<T,U> Drop for PartialVecNonZeroSized<T,U> {
    fn drop(&mut self) {
        unsafe {
            // `vec` hasn't been modified until now. As it has a length
            // currently, this would run destructors of `T`s which might not be
            // there. So at first, set `vec`s length to `0`. This must be done
            // at first to remain memory-safe as the destructors of `U` or `T`
            // might cause unwinding where `vec`s destructor would be executed.
            self.vec.set_len(0);

            // We have instances of `U`s and `T`s in `vec`. Destruct them.
            while self.start_u != self.end_u {
                let _ = ptr::read(self.start_u as *const U); // Run a `U` destructor.
                self.start_u = self.start_u.offset(1);
            }
            while self.start_t != self.end_t {
                let _ = ptr::read(self.start_t as *const T); // Run a `T` destructor.
                self.start_t = self.start_t.offset(1);
            }
            // After this destructor ran, the destructor of `vec` will run,
            // deallocating the underlying memory.
        }
    }
}

#[unsafe_destructor]
impl<T,U> Drop for PartialVecZeroSized<T,U> {
    fn drop(&mut self) {
        unsafe {
            // Destruct the instances of `T` and `U` this struct owns.
            while self.num_t != 0 {
                let _: T = mem::uninitialized(); // Run a `T` destructor.
                self.num_t -= 1;
            }
            while self.num_u != 0 {
                let _: U = mem::uninitialized(); // Run a `U` destructor.
                self.num_u -= 1;
            }
        }
    }
}

impl<T> Vec<T> {
    /// Converts a `Vec<T>` to a `Vec<U>` where `T` and `U` have the same
    /// size and in case they are not zero-sized the same minimal alignment.
    ///
    /// # Panics
    ///
    /// Panics if `T` and `U` have differing sizes or are not zero-sized and
    /// have differing minimal alignments.
    ///
    /// # Example
    ///
    /// ```
    /// let v = vec![0u, 1, 2];
    /// let w = v.map_in_place(|i| i + 3);
    /// assert_eq!(w.as_slice(), [3, 4, 5].as_slice());
    ///
    /// #[deriving(PartialEq, Show)]
    /// struct Newtype(u8);
    /// let bytes = vec![0x11, 0x22];
    /// let newtyped_bytes = bytes.map_in_place(|x| Newtype(x));
    /// assert_eq!(newtyped_bytes.as_slice(), [Newtype(0x11), Newtype(0x22)].as_slice());
    /// ```
    pub fn map_in_place<U>(self, f: |T| -> U) -> Vec<U> {
        // FIXME: Assert statically that the types `T` and `U` have the same
        // size.
        assert!(mem::size_of::<T>() == mem::size_of::<U>());

        let mut vec = self;

        if mem::size_of::<T>() != 0 {
            // FIXME: Assert statically that the types `T` and `U` have the
            // same minimal alignment in case they are not zero-sized.

            // These asserts are necessary because the `min_align_of` of the
            // types are passed to the allocator by `Vec`.
            assert!(mem::min_align_of::<T>() == mem::min_align_of::<U>());

            // This `as int` cast is safe, because the size of the elements of the
            // vector is not 0, and:
            //
            // 1) If the size of the elements in the vector is 1, the `int` may
            //    overflow, but it has the correct bit pattern so that the
            //    `.offset()` function will work.
            //
            //    Example:
            //        Address space 0x0-0xF.
            //        `u8` array at: 0x1.
            //        Size of `u8` array: 0x8.
            //        Calculated `offset`: -0x8.
            //        After `array.offset(offset)`: 0x9.
            //        (0x1 + 0x8 = 0x1 - 0x8)
            //
            // 2) If the size of the elements in the vector is >1, the `uint` ->
            //    `int` conversion can't overflow.
            let offset = vec.len() as int;
            let start = vec.as_mut_ptr();

            let mut pv = PartialVecNonZeroSized {
                vec: vec,

                start_t: start,
                // This points inside the vector, as the vector has length
                // `offset`.
                end_t: unsafe { start.offset(offset) },
                start_u: start as *mut U,
                end_u: start as *mut U,
            };
            //  start_t
            //  start_u
            //  |
            // +-+-+-+-+-+-+
            // |T|T|T|...|T|
            // +-+-+-+-+-+-+
            //  |           |
            //  end_u       end_t

            while pv.end_u as *mut T != pv.end_t {
                unsafe {
                    //  start_u start_t
                    //  |       |
                    // +-+-+-+-+-+-+-+-+-+
                    // |U|...|U|T|T|...|T|
                    // +-+-+-+-+-+-+-+-+-+
                    //          |         |
                    //          end_u     end_t

                    let t = ptr::read(pv.start_t as *const T);
                    //  start_u start_t
                    //  |       |
                    // +-+-+-+-+-+-+-+-+-+
                    // |U|...|U|X|T|...|T|
                    // +-+-+-+-+-+-+-+-+-+
                    //          |         |
                    //          end_u     end_t
                    // We must not panic here, one cell is marked as `T`
                    // although it is not `T`.

                    pv.start_t = pv.start_t.offset(1);
                    //  start_u   start_t
                    //  |         |
                    // +-+-+-+-+-+-+-+-+-+
                    // |U|...|U|X|T|...|T|
                    // +-+-+-+-+-+-+-+-+-+
                    //          |         |
                    //          end_u     end_t
                    // We may panic again.

                    // The function given by the user might panic.
                    let u = f(t);

                    ptr::write(pv.end_u, u);
                    //  start_u   start_t
                    //  |         |
                    // +-+-+-+-+-+-+-+-+-+
                    // |U|...|U|U|T|...|T|
                    // +-+-+-+-+-+-+-+-+-+
                    //          |         |
                    //          end_u     end_t
                    // We should not panic here, because that would leak the `U`
                    // pointed to by `end_u`.

                    pv.end_u = pv.end_u.offset(1);
                    //  start_u   start_t
                    //  |         |
                    // +-+-+-+-+-+-+-+-+-+
                    // |U|...|U|U|T|...|T|
                    // +-+-+-+-+-+-+-+-+-+
                    //            |       |
                    //            end_u   end_t
                    // We may panic again.
                }
            }

            //  start_u     start_t
            //  |           |
            // +-+-+-+-+-+-+
            // |U|...|U|U|U|
            // +-+-+-+-+-+-+
            //              |
            //              end_t
            //              end_u
            // Extract `vec` and prevent the destructor of
            // `PartialVecNonZeroSized` from running. Note that none of the
            // function calls can panic, thus no resources can be leaked (as the
            // `vec` member of `PartialVec` is the only one which holds
            // allocations -- and it is returned from this function. None of
            // this can panic.
            unsafe {
                let vec_len = pv.vec.len();
                let vec_cap = pv.vec.capacity();
                let vec_ptr = pv.vec.as_mut_ptr() as *mut U;
                mem::forget(pv);
                Vec::from_raw_parts(vec_ptr, vec_len, vec_cap)
            }
        } else {
            // Put the `Vec` into the `PartialVecZeroSized` structure and
            // prevent the destructor of the `Vec` from running. Since the
            // `Vec` contained zero-sized objects, it did not allocate, so we
            // are not leaking memory here.
            let mut pv = PartialVecZeroSized::<T,U> {
                num_t: vec.len(),
                num_u: 0,
                marker_t: InvariantType,
                marker_u: InvariantType,
            };
            unsafe { mem::forget(vec); }

            while pv.num_t != 0 {
                unsafe {
                    // Create a `T` out of thin air and decrement `num_t`. This
                    // must not panic between these steps, as otherwise a
                    // destructor of `T` which doesn't exist runs.
                    let t = mem::uninitialized();
                    pv.num_t -= 1;

                    // The function given by the user might panic.
                    let u = f(t);

                    // Forget the `U` and increment `num_u`. This increment
                    // cannot overflow the `uint` as we only do this for a
                    // number of times that fits into a `uint` (and start with
                    // `0`). Again, we should not panic between these steps.
                    mem::forget(u);
                    pv.num_u += 1;
                }
            }
            // Create a `Vec` from our `PartialVecZeroSized` and make sure the
            // destructor of the latter will not run. None of this can panic.
            let mut result = Vec::new();
            unsafe { result.set_len(pv.num_u); }
            result
        }
    }
}

#[cfg(test)]
mod tests {
    extern crate test;

    use std::prelude::*;
    use std::mem::size_of;
    use test::Bencher;
    use super::{as_vec, unzip, raw, Vec};

    struct DropCounter<'a> {
        count: &'a mut int
    }

    #[unsafe_destructor]
    impl<'a> Drop for DropCounter<'a> {
        fn drop(&mut self) {
            *self.count += 1;
        }
    }

    #[test]
    fn test_as_vec() {
        let xs = [1u8, 2u8, 3u8];
        assert_eq!(as_vec(xs).as_slice(), xs.as_slice());
    }

    #[test]
    fn test_as_vec_dtor() {
        let (mut count_x, mut count_y) = (0, 0);
        {
            let xs = &[DropCounter { count: &mut count_x }, DropCounter { count: &mut count_y }];
            assert_eq!(as_vec(xs).len(), 2);
        }
        assert_eq!(count_x, 1);
        assert_eq!(count_y, 1);
    }

    #[test]
    fn test_small_vec_struct() {
        assert!(size_of::<Vec<u8>>() == size_of::<uint>() * 3);
    }

    #[test]
    fn test_double_drop() {
        struct TwoVec<T> {
            x: Vec<T>,
            y: Vec<T>
        }

        let (mut count_x, mut count_y) = (0, 0);
        {
            let mut tv = TwoVec {
                x: Vec::new(),
                y: Vec::new()
            };
            tv.x.push(DropCounter {count: &mut count_x});
            tv.y.push(DropCounter {count: &mut count_y});

            // If Vec had a drop flag, here is where it would be zeroed.
            // Instead, it should rely on its internal state to prevent
            // doing anything significant when dropped multiple times.
            drop(tv.x);

            // Here tv goes out of scope, tv.y should be dropped, but not tv.x.
        }

        assert_eq!(count_x, 1);
        assert_eq!(count_y, 1);
    }

    #[test]
    fn test_reserve() {
        let mut v = Vec::new();
        assert_eq!(v.capacity(), 0);

        v.reserve(2);
        assert!(v.capacity() >= 2);

        for i in range(0i, 16) {
            v.push(i);
        }

        assert!(v.capacity() >= 16);
        v.reserve(16);
        assert!(v.capacity() >= 32);

        v.push(16);

        v.reserve(16);
        assert!(v.capacity() >= 33)
    }

    #[test]
    fn test_extend() {
        let mut v = Vec::new();
        let mut w = Vec::new();

        v.extend(range(0i, 3));
        for i in range(0i, 3) { w.push(i) }

        assert_eq!(v, w);

        v.extend(range(3i, 10));
        for i in range(3i, 10) { w.push(i) }

        assert_eq!(v, w);
    }

    #[test]
    fn test_slice_from_mut() {
        let mut values = vec![1u8,2,3,4,5];
        {
            let slice = values.slice_from_mut(2);
            assert!(slice == [3, 4, 5]);
            for p in slice.iter_mut() {
                *p += 2;
            }
        }

        assert!(values.as_slice() == [1, 2, 5, 6, 7]);
    }

    #[test]
    fn test_slice_to_mut() {
        let mut values = vec![1u8,2,3,4,5];
        {
            let slice = values.slice_to_mut(2);
            assert!(slice == [1, 2]);
            for p in slice.iter_mut() {
                *p += 1;
            }
        }

        assert!(values.as_slice() == [2, 3, 3, 4, 5]);
    }

    #[test]
    fn test_split_at_mut() {
        let mut values = vec![1u8,2,3,4,5];
        {
            let (left, right) = values.split_at_mut(2);
            {
                let left: &[_] = left;
                assert!(left[0..left.len()] == [1, 2][]);
            }
            for p in left.iter_mut() {
                *p += 1;
            }

            {
                let right: &[_] = right;
                assert!(right[0..right.len()] == [3, 4, 5][]);
            }
            for p in right.iter_mut() {
                *p += 2;
            }
        }

        assert!(values == vec![2u8, 3, 5, 6, 7]);
    }

    #[test]
    fn test_clone() {
        let v: Vec<int> = vec!();
        let w = vec!(1i, 2, 3);

        assert_eq!(v, v.clone());

        let z = w.clone();
        assert_eq!(w, z);
        // they should be disjoint in memory.
        assert!(w.as_ptr() != z.as_ptr())
    }

    #[test]
    fn test_clone_from() {
        let mut v = vec!();
        let three = vec!(box 1i, box 2, box 3);
        let two = vec!(box 4i, box 5);
        // zero, long
        v.clone_from(&three);
        assert_eq!(v, three);

        // equal
        v.clone_from(&three);
        assert_eq!(v, three);

        // long, short
        v.clone_from(&two);
        assert_eq!(v, two);

        // short, long
        v.clone_from(&three);
        assert_eq!(v, three)
    }

    #[test]
    fn test_grow_fn() {
        let mut v = vec![0u, 1];
        v.grow_fn(3, |i| i);
        assert!(v == vec![0u, 1, 0, 1, 2]);
    }

    #[test]
    fn test_retain() {
        let mut vec = vec![1u, 2, 3, 4];
        vec.retain(|&x| x % 2 == 0);
        assert!(vec == vec![2u, 4]);
    }

    #[test]
    fn zero_sized_values() {
        let mut v = Vec::new();
        assert_eq!(v.len(), 0);
        v.push(());
        assert_eq!(v.len(), 1);
        v.push(());
        assert_eq!(v.len(), 2);
        assert_eq!(v.pop(), Some(()));
        assert_eq!(v.pop(), Some(()));
        assert_eq!(v.pop(), None);

        assert_eq!(v.iter().count(), 0);
        v.push(());
        assert_eq!(v.iter().count(), 1);
        v.push(());
        assert_eq!(v.iter().count(), 2);

        for &() in v.iter() {}

        assert_eq!(v.iter_mut().count(), 2);
        v.push(());
        assert_eq!(v.iter_mut().count(), 3);
        v.push(());
        assert_eq!(v.iter_mut().count(), 4);

        for &() in v.iter_mut() {}
        unsafe { v.set_len(0); }
        assert_eq!(v.iter_mut().count(), 0);
    }

    #[test]
    fn test_partition() {
        assert_eq!(vec![].partition(|x: &int| *x < 3), (vec![], vec![]));
        assert_eq!(vec![1i, 2, 3].partition(|x: &int| *x < 4), (vec![1, 2, 3], vec![]));
        assert_eq!(vec![1i, 2, 3].partition(|x: &int| *x < 2), (vec![1], vec![2, 3]));
        assert_eq!(vec![1i, 2, 3].partition(|x: &int| *x < 0), (vec![], vec![1, 2, 3]));
    }

    #[test]
    fn test_partitioned() {
        assert_eq!(vec![].partitioned(|x: &int| *x < 3), (vec![], vec![]))
        assert_eq!(vec![1i, 2, 3].partitioned(|x: &int| *x < 4), (vec![1, 2, 3], vec![]));
        assert_eq!(vec![1i, 2, 3].partitioned(|x: &int| *x < 2), (vec![1], vec![2, 3]));
        assert_eq!(vec![1i, 2, 3].partitioned(|x: &int| *x < 0), (vec![], vec![1, 2, 3]));
    }

    #[test]
    fn test_zip_unzip() {
        let z1 = vec![(1i, 4i), (2, 5), (3, 6)];

        let (left, right) = unzip(z1.iter().map(|&x| x));

        let (left, right) = (left.as_slice(), right.as_slice());
        assert_eq!((1, 4), (left[0], right[0]));
        assert_eq!((2, 5), (left[1], right[1]));
        assert_eq!((3, 6), (left[2], right[2]));
    }

    #[test]
    fn test_unsafe_ptrs() {
        unsafe {
            // Test on-stack copy-from-buf.
            let a = [1i, 2, 3];
            let ptr = a.as_ptr();
            let b = raw::from_buf(ptr, 3u);
            assert_eq!(b, vec![1, 2, 3]);

            // Test on-heap copy-from-buf.
            let c = vec![1i, 2, 3, 4, 5];
            let ptr = c.as_ptr();
            let d = raw::from_buf(ptr, 5u);
            assert_eq!(d, vec![1, 2, 3, 4, 5]);
        }
    }

    #[test]
    fn test_vec_truncate_drop() {
        static mut drops: uint = 0;
        struct Elem(int);
        impl Drop for Elem {
            fn drop(&mut self) {
                unsafe { drops += 1; }
            }
        }

        let mut v = vec![Elem(1), Elem(2), Elem(3), Elem(4), Elem(5)];
        assert_eq!(unsafe { drops }, 0);
        v.truncate(3);
        assert_eq!(unsafe { drops }, 2);
        v.truncate(0);
        assert_eq!(unsafe { drops }, 5);
    }

    #[test]
    #[should_fail]
    fn test_vec_truncate_fail() {
        struct BadElem(int);
        impl Drop for BadElem {
            fn drop(&mut self) {
                let BadElem(ref mut x) = *self;
                if *x == 0xbadbeef {
                    panic!("BadElem panic: 0xbadbeef")
                }
            }
        }

        let mut v = vec![BadElem(1), BadElem(2), BadElem(0xbadbeef), BadElem(4)];
        v.truncate(0);
    }

    #[test]
    fn test_index() {
        let vec = vec!(1i, 2, 3);
        assert!(vec[1] == 2);
    }

    #[test]
    #[should_fail]
    fn test_index_out_of_bounds() {
        let vec = vec!(1i, 2, 3);
        let _ = vec[3];
    }

    #[test]
    #[should_fail]
    fn test_slice_out_of_bounds_1() {
        let x: Vec<int> = vec![1, 2, 3, 4, 5];
        x[-1..];
    }

    #[test]
    #[should_fail]
    fn test_slice_out_of_bounds_2() {
        let x: Vec<int> = vec![1, 2, 3, 4, 5];
        x[..6];
    }

    #[test]
    #[should_fail]
    fn test_slice_out_of_bounds_3() {
        let x: Vec<int> = vec![1, 2, 3, 4, 5];
        x[-1..4];
    }

    #[test]
    #[should_fail]
    fn test_slice_out_of_bounds_4() {
        let x: Vec<int> = vec![1, 2, 3, 4, 5];
        x[1..6];
    }

    #[test]
    #[should_fail]
    fn test_slice_out_of_bounds_5() {
        let x: Vec<int> = vec![1, 2, 3, 4, 5];
        x[3..2];
    }

    #[test]
    fn test_swap_remove_empty() {
        let mut vec: Vec<uint> = vec!();
        assert_eq!(vec.swap_remove(0), None);
    }

    #[test]
    fn test_move_iter_unwrap() {
        let mut vec: Vec<uint> = Vec::with_capacity(7);
        vec.push(1);
        vec.push(2);
        let ptr = vec.as_ptr();
        vec = vec.into_iter().unwrap();
        assert_eq!(vec.as_ptr(), ptr);
        assert_eq!(vec.capacity(), 7);
        assert_eq!(vec.len(), 0);
    }

    #[test]
    #[should_fail]
    fn test_map_in_place_incompatible_types_fail() {
        let v = vec![0u, 1, 2];
        v.map_in_place(|_| ());
    }

    #[test]
    fn test_map_in_place() {
        let v = vec![0u, 1, 2];
        assert_eq!(v.map_in_place(|i: uint| i as int - 1).as_slice(), [-1i, 0, 1].as_slice());
    }

    #[test]
    fn test_map_in_place_zero_sized() {
        let v = vec![(), ()];
        #[deriving(PartialEq, Show)]
        struct ZeroSized;
        assert_eq!(v.map_in_place(|_| ZeroSized).as_slice(), [ZeroSized, ZeroSized].as_slice());
    }

    #[test]
    fn test_move_items() {
        let vec = vec![1, 2, 3];
        let mut vec2 : Vec<i32> = vec![];
        for i in vec.into_iter() {
            vec2.push(i);
        }
        assert!(vec2 == vec![1, 2, 3]);
    }

    #[test]
    fn test_move_items_reverse() {
        let vec = vec![1, 2, 3];
        let mut vec2 : Vec<i32> = vec![];
        for i in vec.into_iter().rev() {
            vec2.push(i);
        }
        assert!(vec2 == vec![3, 2, 1]);
    }

    #[test]
    fn test_move_items_zero_sized() {
        let vec = vec![(), (), ()];
        let mut vec2 : Vec<()> = vec![];
        for i in vec.into_iter() {
            vec2.push(i);
        }
        assert!(vec2 == vec![(), (), ()]);
    }

    #[test]
    fn test_into_boxed_slice() {
        let xs = vec![1u, 2, 3];
        let ys = xs.into_boxed_slice();
        assert_eq!(ys.as_slice(), [1u, 2, 3].as_slice());
    }

    #[bench]
    fn bench_new(b: &mut Bencher) {
        b.iter(|| {
            let v: Vec<uint> = Vec::new();
            assert_eq!(v.len(), 0);
            assert_eq!(v.capacity(), 0);
        })
    }

    fn do_bench_with_capacity(b: &mut Bencher, src_len: uint) {
        b.bytes = src_len as u64;

        b.iter(|| {
            let v: Vec<uint> = Vec::with_capacity(src_len);
            assert_eq!(v.len(), 0);
            assert_eq!(v.capacity(), src_len);
        })
    }

    #[bench]
    fn bench_with_capacity_0000(b: &mut Bencher) {
        do_bench_with_capacity(b, 0)
    }

    #[bench]
    fn bench_with_capacity_0010(b: &mut Bencher) {
        do_bench_with_capacity(b, 10)
    }

    #[bench]
    fn bench_with_capacity_0100(b: &mut Bencher) {
        do_bench_with_capacity(b, 100)
    }

    #[bench]
    fn bench_with_capacity_1000(b: &mut Bencher) {
        do_bench_with_capacity(b, 1000)
    }

    fn do_bench_from_fn(b: &mut Bencher, src_len: uint) {
        b.bytes = src_len as u64;

        b.iter(|| {
            let dst = Vec::from_fn(src_len, |i| i);
            assert_eq!(dst.len(), src_len);
            assert!(dst.iter().enumerate().all(|(i, x)| i == *x));
        })
    }

    #[bench]
    fn bench_from_fn_0000(b: &mut Bencher) {
        do_bench_from_fn(b, 0)
    }

    #[bench]
    fn bench_from_fn_0010(b: &mut Bencher) {
        do_bench_from_fn(b, 10)
    }

    #[bench]
    fn bench_from_fn_0100(b: &mut Bencher) {
        do_bench_from_fn(b, 100)
    }

    #[bench]
    fn bench_from_fn_1000(b: &mut Bencher) {
        do_bench_from_fn(b, 1000)
    }

    fn do_bench_from_elem(b: &mut Bencher, src_len: uint) {
        b.bytes = src_len as u64;

        b.iter(|| {
            let dst: Vec<uint> = Vec::from_elem(src_len, 5);
            assert_eq!(dst.len(), src_len);
            assert!(dst.iter().all(|x| *x == 5));
        })
    }

    #[bench]
    fn bench_from_elem_0000(b: &mut Bencher) {
        do_bench_from_elem(b, 0)
    }

    #[bench]
    fn bench_from_elem_0010(b: &mut Bencher) {
        do_bench_from_elem(b, 10)
    }

    #[bench]
    fn bench_from_elem_0100(b: &mut Bencher) {
        do_bench_from_elem(b, 100)
    }

    #[bench]
    fn bench_from_elem_1000(b: &mut Bencher) {
        do_bench_from_elem(b, 1000)
    }

    fn do_bench_from_slice(b: &mut Bencher, src_len: uint) {
        let src: Vec<uint> = FromIterator::from_iter(range(0, src_len));

        b.bytes = src_len as u64;

        b.iter(|| {
            let dst = src.clone().as_slice().to_vec();
            assert_eq!(dst.len(), src_len);
            assert!(dst.iter().enumerate().all(|(i, x)| i == *x));
        });
    }

    #[bench]
    fn bench_from_slice_0000(b: &mut Bencher) {
        do_bench_from_slice(b, 0)
    }

    #[bench]
    fn bench_from_slice_0010(b: &mut Bencher) {
        do_bench_from_slice(b, 10)
    }

    #[bench]
    fn bench_from_slice_0100(b: &mut Bencher) {
        do_bench_from_slice(b, 100)
    }

    #[bench]
    fn bench_from_slice_1000(b: &mut Bencher) {
        do_bench_from_slice(b, 1000)
    }

    fn do_bench_from_iter(b: &mut Bencher, src_len: uint) {
        let src: Vec<uint> = FromIterator::from_iter(range(0, src_len));

        b.bytes = src_len as u64;

        b.iter(|| {
            let dst: Vec<uint> = FromIterator::from_iter(src.clone().into_iter());
            assert_eq!(dst.len(), src_len);
            assert!(dst.iter().enumerate().all(|(i, x)| i == *x));
        });
    }

    #[bench]
    fn bench_from_iter_0000(b: &mut Bencher) {
        do_bench_from_iter(b, 0)
    }

    #[bench]
    fn bench_from_iter_0010(b: &mut Bencher) {
        do_bench_from_iter(b, 10)
    }

    #[bench]
    fn bench_from_iter_0100(b: &mut Bencher) {
        do_bench_from_iter(b, 100)
    }

    #[bench]
    fn bench_from_iter_1000(b: &mut Bencher) {
        do_bench_from_iter(b, 1000)
    }

    fn do_bench_extend(b: &mut Bencher, dst_len: uint, src_len: uint) {
        let dst: Vec<uint> = FromIterator::from_iter(range(0, dst_len));
        let src: Vec<uint> = FromIterator::from_iter(range(dst_len, dst_len + src_len));

        b.bytes = src_len as u64;

        b.iter(|| {
            let mut dst = dst.clone();
            dst.extend(src.clone().into_iter());
            assert_eq!(dst.len(), dst_len + src_len);
            assert!(dst.iter().enumerate().all(|(i, x)| i == *x));
        });
    }

    #[bench]
    fn bench_extend_0000_0000(b: &mut Bencher) {
        do_bench_extend(b, 0, 0)
    }

    #[bench]
    fn bench_extend_0000_0010(b: &mut Bencher) {
        do_bench_extend(b, 0, 10)
    }

    #[bench]
    fn bench_extend_0000_0100(b: &mut Bencher) {
        do_bench_extend(b, 0, 100)
    }

    #[bench]
    fn bench_extend_0000_1000(b: &mut Bencher) {
        do_bench_extend(b, 0, 1000)
    }

    #[bench]
    fn bench_extend_0010_0010(b: &mut Bencher) {
        do_bench_extend(b, 10, 10)
    }

    #[bench]
    fn bench_extend_0100_0100(b: &mut Bencher) {
        do_bench_extend(b, 100, 100)
    }

    #[bench]
    fn bench_extend_1000_1000(b: &mut Bencher) {
        do_bench_extend(b, 1000, 1000)
    }

    fn do_bench_push_all(b: &mut Bencher, dst_len: uint, src_len: uint) {
        let dst: Vec<uint> = FromIterator::from_iter(range(0, dst_len));
        let src: Vec<uint> = FromIterator::from_iter(range(dst_len, dst_len + src_len));

        b.bytes = src_len as u64;

        b.iter(|| {
            let mut dst = dst.clone();
            dst.push_all(src.as_slice());
            assert_eq!(dst.len(), dst_len + src_len);
            assert!(dst.iter().enumerate().all(|(i, x)| i == *x));
        });
    }

    #[bench]
    fn bench_push_all_0000_0000(b: &mut Bencher) {
        do_bench_push_all(b, 0, 0)
    }

    #[bench]
    fn bench_push_all_0000_0010(b: &mut Bencher) {
        do_bench_push_all(b, 0, 10)
    }

    #[bench]
    fn bench_push_all_0000_0100(b: &mut Bencher) {
        do_bench_push_all(b, 0, 100)
    }

    #[bench]
    fn bench_push_all_0000_1000(b: &mut Bencher) {
        do_bench_push_all(b, 0, 1000)
    }

    #[bench]
    fn bench_push_all_0010_0010(b: &mut Bencher) {
        do_bench_push_all(b, 10, 10)
    }

    #[bench]
    fn bench_push_all_0100_0100(b: &mut Bencher) {
        do_bench_push_all(b, 100, 100)
    }

    #[bench]
    fn bench_push_all_1000_1000(b: &mut Bencher) {
        do_bench_push_all(b, 1000, 1000)
    }

    fn do_bench_push_all_move(b: &mut Bencher, dst_len: uint, src_len: uint) {
        let dst: Vec<uint> = FromIterator::from_iter(range(0u, dst_len));
        let src: Vec<uint> = FromIterator::from_iter(range(dst_len, dst_len + src_len));

        b.bytes = src_len as u64;

        b.iter(|| {
            let mut dst = dst.clone();
            dst.extend(src.clone().into_iter());
            assert_eq!(dst.len(), dst_len + src_len);
            assert!(dst.iter().enumerate().all(|(i, x)| i == *x));
        });
    }

    #[bench]
    fn bench_push_all_move_0000_0000(b: &mut Bencher) {
        do_bench_push_all_move(b, 0, 0)
    }

    #[bench]
    fn bench_push_all_move_0000_0010(b: &mut Bencher) {
        do_bench_push_all_move(b, 0, 10)
    }

    #[bench]
    fn bench_push_all_move_0000_0100(b: &mut Bencher) {
        do_bench_push_all_move(b, 0, 100)
    }

    #[bench]
    fn bench_push_all_move_0000_1000(b: &mut Bencher) {
        do_bench_push_all_move(b, 0, 1000)
    }

    #[bench]
    fn bench_push_all_move_0010_0010(b: &mut Bencher) {
        do_bench_push_all_move(b, 10, 10)
    }

    #[bench]
    fn bench_push_all_move_0100_0100(b: &mut Bencher) {
        do_bench_push_all_move(b, 100, 100)
    }

    #[bench]
    fn bench_push_all_move_1000_1000(b: &mut Bencher) {
        do_bench_push_all_move(b, 1000, 1000)
    }

    fn do_bench_clone(b: &mut Bencher, src_len: uint) {
        let src: Vec<uint> = FromIterator::from_iter(range(0, src_len));

        b.bytes = src_len as u64;

        b.iter(|| {
            let dst = src.clone();
            assert_eq!(dst.len(), src_len);
            assert!(dst.iter().enumerate().all(|(i, x)| i == *x));
        });
    }

    #[bench]
    fn bench_clone_0000(b: &mut Bencher) {
        do_bench_clone(b, 0)
    }

    #[bench]
    fn bench_clone_0010(b: &mut Bencher) {
        do_bench_clone(b, 10)
    }

    #[bench]
    fn bench_clone_0100(b: &mut Bencher) {
        do_bench_clone(b, 100)
    }

    #[bench]
    fn bench_clone_1000(b: &mut Bencher) {
        do_bench_clone(b, 1000)
    }

    fn do_bench_clone_from(b: &mut Bencher, times: uint, dst_len: uint, src_len: uint) {
        let dst: Vec<uint> = FromIterator::from_iter(range(0, src_len));
        let src: Vec<uint> = FromIterator::from_iter(range(dst_len, dst_len + src_len));

        b.bytes = (times * src_len) as u64;

        b.iter(|| {
            let mut dst = dst.clone();

            for _ in range(0, times) {
                dst.clone_from(&src);

                assert_eq!(dst.len(), src_len);
                assert!(dst.iter().enumerate().all(|(i, x)| dst_len + i == *x));
            }
        });
    }

    #[bench]
    fn bench_clone_from_01_0000_0000(b: &mut Bencher) {
        do_bench_clone_from(b, 1, 0, 0)
    }

    #[bench]
    fn bench_clone_from_01_0000_0010(b: &mut Bencher) {
        do_bench_clone_from(b, 1, 0, 10)
    }

    #[bench]
    fn bench_clone_from_01_0000_0100(b: &mut Bencher) {
        do_bench_clone_from(b, 1, 0, 100)
    }

    #[bench]
    fn bench_clone_from_01_0000_1000(b: &mut Bencher) {
        do_bench_clone_from(b, 1, 0, 1000)
    }

    #[bench]
    fn bench_clone_from_01_0010_0010(b: &mut Bencher) {
        do_bench_clone_from(b, 1, 10, 10)
    }

    #[bench]
    fn bench_clone_from_01_0100_0100(b: &mut Bencher) {
        do_bench_clone_from(b, 1, 100, 100)
    }

    #[bench]
    fn bench_clone_from_01_1000_1000(b: &mut Bencher) {
        do_bench_clone_from(b, 1, 1000, 1000)
    }

    #[bench]
    fn bench_clone_from_01_0010_0100(b: &mut Bencher) {
        do_bench_clone_from(b, 1, 10, 100)
    }

    #[bench]
    fn bench_clone_from_01_0100_1000(b: &mut Bencher) {
        do_bench_clone_from(b, 1, 100, 1000)
    }

    #[bench]
    fn bench_clone_from_01_0010_0000(b: &mut Bencher) {
        do_bench_clone_from(b, 1, 10, 0)
    }

    #[bench]
    fn bench_clone_from_01_0100_0010(b: &mut Bencher) {
        do_bench_clone_from(b, 1, 100, 10)
    }

    #[bench]
    fn bench_clone_from_01_1000_0100(b: &mut Bencher) {
        do_bench_clone_from(b, 1, 1000, 100)
    }

    #[bench]
    fn bench_clone_from_10_0000_0000(b: &mut Bencher) {
        do_bench_clone_from(b, 10, 0, 0)
    }

    #[bench]
    fn bench_clone_from_10_0000_0010(b: &mut Bencher) {
        do_bench_clone_from(b, 10, 0, 10)
    }

    #[bench]
    fn bench_clone_from_10_0000_0100(b: &mut Bencher) {
        do_bench_clone_from(b, 10, 0, 100)
    }

    #[bench]
    fn bench_clone_from_10_0000_1000(b: &mut Bencher) {
        do_bench_clone_from(b, 10, 0, 1000)
    }

    #[bench]
    fn bench_clone_from_10_0010_0010(b: &mut Bencher) {
        do_bench_clone_from(b, 10, 10, 10)
    }

    #[bench]
    fn bench_clone_from_10_0100_0100(b: &mut Bencher) {
        do_bench_clone_from(b, 10, 100, 100)
    }

    #[bench]
    fn bench_clone_from_10_1000_1000(b: &mut Bencher) {
        do_bench_clone_from(b, 10, 1000, 1000)
    }

    #[bench]
    fn bench_clone_from_10_0010_0100(b: &mut Bencher) {
        do_bench_clone_from(b, 10, 10, 100)
    }

    #[bench]
    fn bench_clone_from_10_0100_1000(b: &mut Bencher) {
        do_bench_clone_from(b, 10, 100, 1000)
    }

    #[bench]
    fn bench_clone_from_10_0010_0000(b: &mut Bencher) {
        do_bench_clone_from(b, 10, 10, 0)
    }

    #[bench]
    fn bench_clone_from_10_0100_0010(b: &mut Bencher) {
        do_bench_clone_from(b, 10, 100, 10)
    }

    #[bench]
    fn bench_clone_from_10_1000_0100(b: &mut Bencher) {
        do_bench_clone_from(b, 10, 1000, 100)
    }
}