std: Recreate a `collections` module

As with the previous commit with `librand`, this commit shuffles around some
`collections` code. The new state of the world is similar to that of librand:

* The libcollections crate now only depends on libcore and liballoc.
* The standard library has a new module, `std::collections`. All functionality
  of libcollections is reexported through this module.

I would like to stress that this change is purely cosmetic. There are very few
alterations to these primitives.

There are a number of notable points about the new organization:

* std::{str, slice, string, vec} all moved to libcollections. There is no reason
  that these primitives shouldn't be necessarily usable in a freestanding
  context that has allocation. These are all reexported in their usual places in
  the standard library.

* The `hashmap`, and transitively the `lru_cache`, modules no longer reside in
  `libcollections`, but rather in libstd. The reason for this is because the
  `HashMap::new` contructor requires access to the OSRng for initially seeding
  the hash map. Beyond this requirement, there is no reason that the hashmap
  could not move to libcollections.

  I do, however, have a plan to move the hash map to the collections module. The
  `HashMap::new` function could be altered to require that the `H` hasher
  parameter ascribe to the `Default` trait, allowing the entire `hashmap` module
  to live in libcollections. The key idea would be that the default hasher would
  be different in libstd. Something along the lines of:

      // src/libstd/collections/mod.rs

      pub type HashMap<K, V, H = RandomizedSipHasher> =
            core_collections::HashMap<K, V, H>;

  This is not possible today because you cannot invoke static methods through
  type aliases. If we modified the compiler, however, to allow invocation of
  static methods through type aliases, then this type definition would
  essentially be switching the default hasher from `SipHasher` in libcollections
  to a libstd-defined `RandomizedSipHasher` type. This type's `Default`
  implementation would randomly seed the `SipHasher` instance, and otherwise
  perform the same as `SipHasher`.

  This future state doesn't seem incredibly far off, but until that time comes,
  the hashmap module will live in libstd to not compromise on functionality.

* In preparation for the hashmap moving to libcollections, the `hash` module has
  moved from libstd to libcollections. A previously snapshotted commit enables a
  distinct `Writer` trait to live in the `hash` module which `Hash`
  implementations are now parameterized over.

  Due to using a custom trait, the `SipHasher` implementation has lost its
  specialized methods for writing integers. These can be re-added
  backwards-compatibly in the future via default methods if necessary, but the
  FNV hashing should satisfy much of the need for speedier hashing.

A list of breaking changes:

* HashMap::{get, get_mut} no longer fails with the key formatted into the error
  message with `{:?}`, instead, a generic message is printed. With backtraces,
  it should still be not-too-hard to track down errors.

* The HashMap, HashSet, and LruCache types are now available through
  std::collections instead of the collections crate.

* Manual implementations of hash should be parameterized over `hash::Writer`
  instead of just `Writer`.

[breaking-change]

3 files changed, 2880 insertions, 0 deletions

diff --git a/src/libstd/collections/hashmap.rs b/src/libstd/collections/hashmap.rs
new file mode 100644
index 00000000000..bcf6d139c35
--- /dev/null
+++ b/src/libstd/collections/hashmap.rs
@@ -0,0 +1,2507 @@
+// 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.
+
+//! Unordered containers, implemented as hash-tables (`HashSet` and `HashMap` types)
+
+use clone::Clone;
+use cmp::{max, Eq, Equiv, PartialEq};
+use container::{Container, Mutable, Set, MutableSet, Map, MutableMap};
+use default::Default;
+use fmt::Show;
+use fmt;
+use hash::{Hash, Hasher, sip};
+use iter::{Iterator, FilterMap, Chain, Repeat, Zip, Extendable};
+use iter::{range, range_inclusive, FromIterator};
+use iter;
+use mem::replace;
+use num;
+use option::{Some, None, Option};
+use rand::Rng;
+use rand;
+use result::{Ok, Err};
+
+mod table {
+    use clone::Clone;
+    use cmp;
+    use hash::{Hash, Hasher};
+    use iter::range_step_inclusive;
+    use iter::{Iterator, range};
+    use kinds::marker;
+    use mem::{min_align_of, size_of};
+    use mem::{overwrite, transmute};
+    use num::{CheckedMul, is_power_of_two};
+    use ops::Drop;
+    use option::{Some, None, Option, Expect};
+    use ptr::RawPtr;
+    use ptr::set_memory;
+    use ptr;
+    use rt::heap::{allocate, deallocate};
+
+    static EMPTY_BUCKET: u64 = 0u64;
+
+    /// The raw hashtable, providing safe-ish access to the unzipped and highly
+    /// optimized arrays of hashes, keys, and values.
+    ///
+    /// This design uses less memory and is a lot faster than the naive
+    /// `Vec<Option<u64, K, V>>`, because we don't pay for the overhead of an
+    /// option on every element, and we get a generally more cache-aware design.
+    ///
+    /// Key invariants of this structure:
+    ///
+    ///   - if hashes[i] == EMPTY_BUCKET, then keys[i] and vals[i] have
+    ///     'undefined' contents. Don't read from them. This invariant is
+    ///     enforced outside this module with the `EmptyIndex`, `FullIndex`,
+    ///     and `SafeHash` types.
+    ///
+    ///   - An `EmptyIndex` is only constructed for a bucket at an index with
+    ///     a hash of EMPTY_BUCKET.
+    ///
+    ///   - A `FullIndex` is only constructed for a bucket at an index with a
+    ///     non-EMPTY_BUCKET hash.
+    ///
+    ///   - A `SafeHash` is only constructed for non-`EMPTY_BUCKET` hash. We get
+    ///     around hashes of zero by changing them to 0x8000_0000_0000_0000,
+    ///     which will likely map to the same bucket, while not being confused
+    ///     with "empty".
+    ///
+    ///   - All three "arrays represented by pointers" are the same length:
+    ///     `capacity`. This is set at creation and never changes. The arrays
+    ///     are unzipped to save space (we don't have to pay for the padding
+    ///     between odd sized elements, such as in a map from u64 to u8), and
+    ///     be more cache aware (scanning through 8 hashes brings in 2 cache
+    ///     lines, since they're all right beside each other).
+    ///
+    /// You can kind of think of this module/data structure as a safe wrapper
+    /// around just the "table" part of the hashtable. It enforces some
+    /// invariants at the type level and employs some performance trickery,
+    /// but in general is just a tricked out `Vec<Option<u64, K, V>>`.
+    ///
+    /// FIXME(cgaebel):
+    ///
+    /// Feb 11, 2014: This hashtable was just implemented, and, hard as I tried,
+    /// isn't yet totally safe. There's a "known exploit" that you can create
+    /// multiple FullIndexes for a bucket, `take` one, and then still `take`
+    /// the other causing undefined behavior. Currently, there's no story
+    /// for how to protect against this statically. Therefore, there are asserts
+    /// on `take`, `get`, `get_mut`, and `put` which check the bucket state.
+    /// With time, and when we're confident this works correctly, they should
+    /// be removed. Also, the bounds check in `peek` is especially painful,
+    /// as that's called in the innermost loops of the hashtable and has the
+    /// potential to be a major performance drain. Remove this too.
+    ///
+    /// Or, better than remove, only enable these checks for debug builds.
+    /// There's currently no "debug-only" asserts in rust, so if you're reading
+    /// this and going "what? of course there are debug-only asserts!", then
+    /// please make this use them!
+    #[unsafe_no_drop_flag]
+    pub struct RawTable<K, V> {
+        capacity: uint,
+        size:     uint,
+        hashes:   *mut u64,
+        keys:     *mut K,
+        vals:     *mut V,
+    }
+
+    /// Represents an index into a `RawTable` with no key or value in it.
+    pub struct EmptyIndex {
+        idx:    int,
+        nocopy: marker::NoCopy,
+    }
+
+    /// Represents an index into a `RawTable` with a key, value, and hash
+    /// in it.
+    pub struct FullIndex {
+        idx:    int,
+        hash:   SafeHash,
+        nocopy: marker::NoCopy,
+    }
+
+    impl FullIndex {
+        /// Since we get the hash for free whenever we check the bucket state,
+        /// this function is provided for fast access, letting us avoid
+        /// redundant trips back to the hashtable.
+        #[inline(always)]
+        pub fn hash(&self) -> SafeHash { self.hash }
+
+        /// Same comment as with `hash`.
+        #[inline(always)]
+        pub fn raw_index(&self) -> uint { self.idx as uint }
+    }
+
+    /// Represents the state of a bucket: it can either have a key/value
+    /// pair (be full) or not (be empty). You cannot `take` empty buckets,
+    /// and you cannot `put` into full buckets.
+    pub enum BucketState {
+        Empty(EmptyIndex),
+        Full(FullIndex),
+    }
+
+    /// A hash that is not zero, since we use a hash of zero to represent empty
+    /// buckets.
+    #[deriving(PartialEq)]
+    pub struct SafeHash {
+        hash: u64,
+    }
+
+    impl SafeHash {
+        /// Peek at the hash value, which is guaranteed to be non-zero.
+        #[inline(always)]
+        pub fn inspect(&self) -> u64 { self.hash }
+    }
+
+    /// We need to remove hashes of 0. That's reserved for empty buckets.
+    /// This function wraps up `hash_keyed` to be the only way outside this
+    /// module to generate a SafeHash.
+    pub fn make_hash<T: Hash<S>, S, H: Hasher<S>>(hasher: &H, t: &T) -> SafeHash {
+        match hasher.hash(t) {
+            // This constant is exceedingly likely to hash to the same
+            // bucket, but it won't be counted as empty!
+            EMPTY_BUCKET => SafeHash { hash: 0x8000_0000_0000_0000 },
+            h            => SafeHash { hash: h },
+        }
+    }
+
+    fn round_up_to_next(unrounded: uint, target_alignment: uint) -> uint {
+        assert!(is_power_of_two(target_alignment));
+        (unrounded + target_alignment - 1) & !(target_alignment - 1)
+    }
+
+    #[test]
+    fn test_rounding() {
+        assert_eq!(round_up_to_next(0, 4), 0);
+        assert_eq!(round_up_to_next(1, 4), 4);
+        assert_eq!(round_up_to_next(2, 4), 4);
+        assert_eq!(round_up_to_next(3, 4), 4);
+        assert_eq!(round_up_to_next(4, 4), 4);
+        assert_eq!(round_up_to_next(5, 4), 8);
+    }
+
+    // Returns a tuple of (minimum required malloc alignment, hash_offset,
+    // key_offset, val_offset, array_size), from the start of a mallocated array.
+    fn calculate_offsets(
+        hash_size: uint, hash_align: uint,
+        keys_size: uint, keys_align: uint,
+        vals_size: uint, vals_align: uint) -> (uint, uint, uint, uint, uint) {
+
+        let hash_offset   = 0;
+        let end_of_hashes = hash_offset + hash_size;
+
+        let keys_offset   = round_up_to_next(end_of_hashes, keys_align);
+        let end_of_keys   = keys_offset + keys_size;
+
+        let vals_offset   = round_up_to_next(end_of_keys, vals_align);
+        let end_of_vals   = vals_offset + vals_size;
+
+        let min_align = cmp::max(hash_align, cmp::max(keys_align, vals_align));
+
+        (min_align, hash_offset, keys_offset, vals_offset, end_of_vals)
+    }
+
+    #[test]
+    fn test_offset_calculation() {
+        assert_eq!(calculate_offsets(128, 8, 15, 1, 4, 4 ), (8, 0, 128, 144, 148));
+        assert_eq!(calculate_offsets(3,   1, 2,  1, 1, 1 ), (1, 0, 3,   5,   6));
+        assert_eq!(calculate_offsets(6,   2, 12, 4, 24, 8), (8, 0, 8,   24,  48));
+    }
+
+    impl<K, V> RawTable<K, V> {
+
+        /// Does not initialize the buckets. The caller should ensure they,
+        /// at the very least, set every hash to EMPTY_BUCKET.
+        unsafe fn new_uninitialized(capacity: uint) -> RawTable<K, V> {
+            let hashes_size = capacity.checked_mul(&size_of::<u64>())
+                                      .expect("capacity overflow");
+            let keys_size = capacity.checked_mul(&size_of::< K >())
+                                    .expect("capacity overflow");
+            let vals_size = capacity.checked_mul(&size_of::< V >())
+                                    .expect("capacity overflow");
+
+            // Allocating hashmaps is a little tricky. We need to allocate three
+            // arrays, but since we know their sizes and alignments up front,
+            // we just allocate a single array, and then have the subarrays
+            // point into it.
+            //
+            // This is great in theory, but in practice getting the alignment
+            // right is a little subtle. Therefore, calculating offsets has been
+            // factored out into a different function.
+            let (malloc_alignment, hash_offset, keys_offset, vals_offset, size) =
+                calculate_offsets(
+                    hashes_size, min_align_of::<u64>(),
+                    keys_size,   min_align_of::< K >(),
+                    vals_size,   min_align_of::< V >());
+
+            let buffer = allocate(size, malloc_alignment);
+
+            let hashes = buffer.offset(hash_offset as int) as *mut u64;
+            let keys   = buffer.offset(keys_offset as int) as *mut K;
+            let vals   = buffer.offset(vals_offset as int) as *mut V;
+
+            RawTable {
+                capacity: capacity,
+                size:     0,
+                hashes:   hashes,
+                keys:     keys,
+                vals:     vals,
+            }
+        }
+
+        /// Creates a new raw table from a given capacity. All buckets are
+        /// initially empty.
+        pub fn new(capacity: uint) -> RawTable<K, V> {
+            unsafe {
+                let ret = RawTable::new_uninitialized(capacity);
+                set_memory(ret.hashes, 0u8, capacity);
+                ret
+            }
+        }
+
+        /// Reads a bucket at a given index, returning an enum indicating whether
+        /// there's anything there or not. You need to match on this enum to get
+        /// the appropriate types to pass on to most of the other functions in
+        /// this module.
+        pub fn peek(&self, index: uint) -> BucketState {
+            debug_assert!(index < self.capacity);
+
+            let idx  = index as int;
+            let hash = unsafe { *self.hashes.offset(idx) };
+
+            let nocopy = marker::NoCopy;
+
+            match hash {
+                EMPTY_BUCKET =>
+                    Empty(EmptyIndex {
+                        idx:    idx,
+                        nocopy: nocopy
+                    }),
+                full_hash =>
+                    Full(FullIndex {
+                        idx:    idx,
+                        hash:   SafeHash { hash: full_hash },
+                        nocopy: nocopy,
+                    })
+            }
+        }
+
+        /// Gets references to the key and value at a given index.
+        pub fn read<'a>(&'a self, index: &FullIndex) -> (&'a K, &'a V) {
+            let idx = index.idx;
+
+            unsafe {
+                debug_assert!(*self.hashes.offset(idx) != EMPTY_BUCKET);
+                (&'a *self.keys.offset(idx),
+                 &'a *self.vals.offset(idx))
+            }
+        }
+
+        /// Gets references to the key and value at a given index, with the
+        /// value's reference being mutable.
+        pub fn read_mut<'a>(&'a mut self, index: &FullIndex) -> (&'a K, &'a mut V) {
+            let idx = index.idx;
+
+            unsafe {
+                debug_assert!(*self.hashes.offset(idx) != EMPTY_BUCKET);
+                (&'a     *self.keys.offset(idx),
+                 &'a mut *self.vals.offset(idx))
+            }
+        }
+
+        /// Read everything, mutably.
+        pub fn read_all_mut<'a>(&'a mut self, index: &FullIndex)
+            -> (&'a mut SafeHash, &'a mut K, &'a mut V) {
+            let idx = index.idx;
+
+            unsafe {
+                debug_assert!(*self.hashes.offset(idx) != EMPTY_BUCKET);
+                (transmute(self.hashes.offset(idx)),
+                 &'a mut *self.keys.offset(idx),
+                 &'a mut *self.vals.offset(idx))
+            }
+        }
+
+        /// Puts a key and value pair, along with the key's hash, into a given
+        /// index in the hashtable. Note how the `EmptyIndex` is 'moved' into this
+        /// function, because that slot will no longer be empty when we return!
+        /// A FullIndex is returned for later use, pointing to the newly-filled
+        /// slot in the hashtable.
+        ///
+        /// Use `make_hash` to construct a `SafeHash` to pass to this function.
+        pub fn put(&mut self, index: EmptyIndex, hash: SafeHash, k: K, v: V) -> FullIndex {
+            let idx = index.idx;
+
+            unsafe {
+                debug_assert_eq!(*self.hashes.offset(idx), EMPTY_BUCKET);
+                *self.hashes.offset(idx) = hash.inspect();
+                overwrite(&mut *self.keys.offset(idx), k);
+                overwrite(&mut *self.vals.offset(idx), v);
+            }
+
+            self.size += 1;
+
+            FullIndex { idx: idx, hash: hash, nocopy: marker::NoCopy }
+        }
+
+        /// Removes a key and value from the hashtable.
+        ///
+        /// This works similarly to `put`, building an `EmptyIndex` out of the
+        /// taken FullIndex.
+        pub fn take(&mut self, index: FullIndex) -> (EmptyIndex, K, V) {
+            let idx  = index.idx;
+
+            unsafe {
+                debug_assert!(*self.hashes.offset(idx) != EMPTY_BUCKET);
+
+                *self.hashes.offset(idx) = EMPTY_BUCKET;
+
+                // Drop the mutable constraint.
+                let keys = self.keys as *K;
+                let vals = self.vals as *V;
+
+                let k = ptr::read(keys.offset(idx));
+                let v = ptr::read(vals.offset(idx));
+
+                self.size -= 1;
+
+                (EmptyIndex { idx: idx, nocopy: marker::NoCopy }, k, v)
+            }
+        }
+
+        /// The hashtable's capacity, similar to a vector's.
+        pub fn capacity(&self) -> uint {
+            self.capacity
+        }
+
+        /// The number of elements ever `put` in the hashtable, minus the number
+        /// of elements ever `take`n.
+        pub fn size(&self) -> uint {
+            self.size
+        }
+
+        pub fn iter<'a>(&'a self) -> Entries<'a, K, V> {
+            Entries { table: self, idx: 0, elems_seen: 0 }
+        }
+
+        pub fn mut_iter<'a>(&'a mut self) -> MutEntries<'a, K, V> {
+            MutEntries { table: self, idx: 0, elems_seen: 0 }
+        }
+
+        pub fn move_iter(self) -> MoveEntries<K, V> {
+            MoveEntries { table: self, idx: 0, elems_seen: 0 }
+        }
+    }
+
+    // `read_all_mut` casts a `*u64` to a `*SafeHash`. Since we statically
+    // ensure that a `FullIndex` points to an index with a non-zero hash,
+    // and a `SafeHash` is just a `u64` with a different name, this is
+    // safe.
+    //
+    // This test ensures that a `SafeHash` really IS the same size as a
+    // `u64`. If you need to change the size of `SafeHash` (and
+    // consequently made this test fail), `read_all_mut` needs to be
+    // modified to no longer assume this.
+    #[test]
+    fn can_alias_safehash_as_u64() {
+        assert_eq!(size_of::<SafeHash>(), size_of::<u64>())
+    }
+
+    pub struct Entries<'a, K, V> {
+        table: &'a RawTable<K, V>,
+        idx: uint,
+        elems_seen: uint,
+    }
+
+    pub struct MutEntries<'a, K, V> {
+        table: &'a mut RawTable<K, V>,
+        idx: uint,
+        elems_seen: uint,
+    }
+
+    pub struct MoveEntries<K, V> {
+        table: RawTable<K, V>,
+        idx: uint,
+        elems_seen: uint,
+    }
+
+    impl<'a, K, V> Iterator<(&'a K, &'a V)> for Entries<'a, K, V> {
+        fn next(&mut self) -> Option<(&'a K, &'a V)> {
+            while self.idx < self.table.capacity() {
+                let i = self.idx;
+                self.idx += 1;
+
+                match self.table.peek(i) {
+                    Empty(_)  => {},
+                    Full(idx) => {
+                        self.elems_seen += 1;
+                        return Some(self.table.read(&idx));
+                    }
+                }
+            }
+
+            None
+        }
+
+        fn size_hint(&self) -> (uint, Option<uint>) {
+            let size = self.table.size() - self.elems_seen;
+            (size, Some(size))
+        }
+    }
+
+    impl<'a, K, V> Iterator<(&'a K, &'a mut V)> for MutEntries<'a, K, V> {
+        fn next(&mut self) -> Option<(&'a K, &'a mut V)> {
+            while self.idx < self.table.capacity() {
+                let i = self.idx;
+                self.idx += 1;
+
+                match self.table.peek(i) {
+                    Empty(_)  => {},
+                    // the transmute here fixes:
+                    // error: lifetime of `self` is too short to guarantee its contents
+                    //        can be safely reborrowed
+                    Full(idx) => unsafe {
+                        self.elems_seen += 1;
+                        return Some(transmute(self.table.read_mut(&idx)));
+                    }
+                }
+            }
+
+            None
+        }
+
+        fn size_hint(&self) -> (uint, Option<uint>) {
+            let size = self.table.size() - self.elems_seen;
+            (size, Some(size))
+        }
+    }
+
+    impl<K, V> Iterator<(SafeHash, K, V)> for MoveEntries<K, V> {
+        fn next(&mut self) -> Option<(SafeHash, K, V)> {
+            while self.idx < self.table.capacity() {
+                let i = self.idx;
+                self.idx += 1;
+
+                match self.table.peek(i) {
+                    Empty(_) => {},
+                    Full(idx) => {
+                        let h = idx.hash();
+                        let (_, k, v) = self.table.take(idx);
+                        return Some((h, k, v));
+                    }
+                }
+            }
+
+            None
+        }
+
+        fn size_hint(&self) -> (uint, Option<uint>) {
+            let size = self.table.size();
+            (size, Some(size))
+        }
+    }
+
+    impl<K: Clone, V: Clone> Clone for RawTable<K, V> {
+        fn clone(&self) -> RawTable<K, V> {
+            unsafe {
+                let mut new_ht = RawTable::new_uninitialized(self.capacity());
+
+                for i in range(0, self.capacity()) {
+                    match self.peek(i) {
+                        Empty(_)  => {
+                            *new_ht.hashes.offset(i as int) = EMPTY_BUCKET;
+                        },
+                        Full(idx) => {
+                            let hash = idx.hash().inspect();
+                            let (k, v) = self.read(&idx);
+                            *new_ht.hashes.offset(i as int) = hash;
+                            overwrite(&mut *new_ht.keys.offset(i as int), (*k).clone());
+                            overwrite(&mut *new_ht.vals.offset(i as int), (*v).clone());
+                        }
+                    }
+                }
+
+                new_ht.size = self.size();
+
+                new_ht
+            }
+        }
+    }
+
+    #[unsafe_destructor]
+    impl<K, V> Drop for RawTable<K, V> {
+        fn drop(&mut self) {
+            // This is in reverse because we're likely to have partially taken
+            // some elements out with `.move_iter()` from the front.
+            for i in range_step_inclusive(self.capacity as int - 1, 0, -1) {
+                // Check if the size is 0, so we don't do a useless scan when
+                // dropping empty tables such as on resize.
+                if self.size == 0 { break }
+
+                match self.peek(i as uint) {
+                    Empty(_)  => {},
+                    Full(idx) => { self.take(idx); }
+                }
+            }
+
+            assert_eq!(self.size, 0);
+
+            if self.hashes.is_not_null() {
+                let hashes_size = self.capacity * size_of::<u64>();
+                let keys_size = self.capacity * size_of::<K>();
+                let vals_size = self.capacity * size_of::<V>();
+                let (align, _, _, _, size) = calculate_offsets(hashes_size, min_align_of::<u64>(),
+                                                               keys_size, min_align_of::<K>(),
+                                                               vals_size, min_align_of::<V>());
+
+                unsafe {
+                    deallocate(self.hashes as *mut u8, size, align);
+                    // Remember how everything was allocated out of one buffer
+                    // during initialization? We only need one call to free here.
+                }
+
+                self.hashes = RawPtr::null();
+            }
+        }
+    }
+}
+
+static INITIAL_LOG2_CAP: uint = 5;
+static INITIAL_CAPACITY: uint = 1 << INITIAL_LOG2_CAP; // 2^5
+
+/// The default behavior of HashMap implements a load factor of 90.9%.
+/// This behavior is characterized by the following conditions:
+///
+/// - if `size * 1.1 < cap < size * 4` then shouldn't resize
+/// - if `cap < minimum_capacity * 2` then shouldn't shrink
+#[deriving(Clone)]
+struct DefaultResizePolicy {
+    /// Doubled minimal capacity. The capacity must never drop below
+    /// the minimum capacity. (The check happens before the capacity
+    /// is potentially halved.)
+    minimum_capacity2: uint
+}
+
+impl DefaultResizePolicy {
+    fn new(new_capacity: uint) -> DefaultResizePolicy {
+        DefaultResizePolicy {
+            minimum_capacity2: new_capacity << 1
+        }
+    }
+
+    #[inline]
+    fn capacity_range(&self, new_size: uint) -> (uint, uint) {
+        ((new_size * 11) / 10, max(new_size << 3, self.minimum_capacity2))
+    }
+
+    #[inline]
+    fn reserve(&mut self, new_capacity: uint) {
+        self.minimum_capacity2 = new_capacity << 1;
+    }
+}
+
+// The main performance trick in this hashmap is called Robin Hood Hashing.
+// It gains its excellent performance from one key invariant:
+//
+//    If an insertion collides with an existing element, and that elements
+//    "probe distance" (how far away the element is from its ideal location)
+//    is higher than how far we've already probed, swap the elements.
+//
+// This massively lowers variance in probe distance, and allows us to get very
+// high load factors with good performance. The 90% load factor I use is rather
+// conservative.
+//
+// > Why a load factor of approximately 90%?
+//
+// In general, all the distances to initial buckets will converge on the mean.
+// At a load factor of α, the odds of finding the target bucket after k
+// probes is approximately 1-α^k. If we set this equal to 50% (since we converge
+// on the mean) and set k=8 (64-byte cache line / 8-byte hash), α=0.92. I round
+// this down to make the math easier on the CPU and avoid its FPU.
+// Since on average we start the probing in the middle of a cache line, this
+// strategy pulls in two cache lines of hashes on every lookup. I think that's
+// pretty good, but if you want to trade off some space, it could go down to one
+// cache line on average with an α of 0.84.
+//
+// > Wait, what? Where did you get 1-α^k from?
+//
+// On the first probe, your odds of a collision with an existing element is α.
+// The odds of doing this twice in a row is approximately α^2. For three times,
+// α^3, etc. Therefore, the odds of colliding k times is α^k. The odds of NOT
+// colliding after k tries is 1-α^k.
+//
+// Future Improvements (FIXME!)
+// ============================
+//
+// Allow the load factor to be changed dynamically and/or at initialization.
+//
+// Also, would it be possible for us to reuse storage when growing the
+// underlying table? This is exactly the use case for 'realloc', and may
+// be worth exploring.
+//
+// Future Optimizations (FIXME!)
+// =============================
+//
+// The paper cited below mentions an implementation which keeps track of the
+// distance-to-initial-bucket histogram. I'm suspicious of this approach because
+// it requires maintaining an internal map. If this map were replaced with a
+// hashmap, it would be faster, but now our data structure is self-referential
+// and blows up. Also, this allows very good first guesses, but array accesses
+// are no longer linear and in one direction, as we have now. There is also
+// memory and cache pressure that this map would entail that would be very
+// difficult to properly see in a microbenchmark.
+//
+// Another possible design choice that I made without any real reason is
+// parameterizing the raw table over keys and values. Technically, all we need
+// is the size and alignment of keys and values, and the code should be just as
+// efficient (well, we might need one for power-of-two size and one for not...).
+// This has the potential to reduce code bloat in rust executables, without
+// really losing anything except 4 words (key size, key alignment, val size,
+// val alignment) which can be passed in to every call of a `RawTable` function.
+// This would definitely be an avenue worth exploring if people start complaining
+// about the size of rust executables.
+//
+// There's also an "optimization" that has been omitted regarding how the
+// hashtable allocates. The vector type has set the expectation that a hashtable
+// which never has an element inserted should not allocate. I'm suspicious of
+// implementing this for hashtables, because supporting it has no performance
+// benefit over using an `Option<HashMap<K, V>>`, and is significantly more
+// complicated.
+
+/// A hash map implementation which uses linear probing with Robin
+/// Hood bucket stealing.
+///
+/// The hashes are all keyed by the task-local random number generator
+/// on creation by default, this means the ordering of the keys is
+/// randomized, but makes the tables more resistant to
+/// denial-of-service attacks (Hash DoS). This behaviour can be
+/// overridden with one of the constructors.
+///
+/// It is required that the keys implement the `PartialEq` and `Hash` traits, although
+/// this can frequently be achieved by using `#[deriving(PartialEq, Hash)]`.
+///
+/// Relevant papers/articles:
+///
+/// 1. Pedro Celis. ["Robin Hood Hashing"](https://cs.uwaterloo.ca/research/tr/1986/CS-86-14.pdf)
+/// 2. Emmanuel Goossaert. ["Robin Hood
+///    hashing"](http://codecapsule.com/2013/11/11/robin-hood-hashing/)
+/// 3. Emmanuel Goossaert. ["Robin Hood hashing: backward shift
+///    deletion"](http://codecapsule.com/2013/11/17/robin-hood-hashing-backward-shift-deletion/)
+///
+/// # Example
+///
+/// ```rust
+/// use collections::HashMap;
+///
+/// // type inference lets us omit an explicit type signature (which
+/// // would be `HashMap<&str, &str>` in this example).
+/// let mut book_reviews = HashMap::new();
+///
+/// // review some books.
+/// book_reviews.insert("Adventures of Huckleberry Finn",    "My favorite book.");
+/// book_reviews.insert("Grimms' Fairy Tales",               "Masterpiece.");
+/// book_reviews.insert("Pride and Prejudice",               "Very enjoyable.");
+/// book_reviews.insert("The Adventures of Sherlock Holmes", "Eye lyked it alot.");
+///
+/// // check for a specific one.
+/// if !book_reviews.contains_key(&("Les Misérables")) {
+///     println!("We've got {} reviews, but Les Misérables ain't one.",
+///              book_reviews.len());
+/// }
+///
+/// // oops, this review has a lot of spelling mistakes, let's delete it.
+/// book_reviews.remove(&("The Adventures of Sherlock Holmes"));
+///
+/// // look up the values associated with some keys.
+/// let to_find = ["Pride and Prejudice", "Alice's Adventure in Wonderland"];
+/// for book in to_find.iter() {
+///     match book_reviews.find(book) {
+///         Some(review) => println!("{}: {}", *book, *review),
+///         None => println!("{} is unreviewed.", *book)
+///     }
+/// }
+///
+/// // iterate over everything.
+/// for (book, review) in book_reviews.iter() {
+///     println!("{}: \"{}\"", *book, *review);
+/// }
+/// ```
+#[deriving(Clone)]
+pub struct HashMap<K, V, H = sip::SipHasher> {
+    // All hashes are keyed on these values, to prevent hash collision attacks.
+    hasher: H,
+
+    table: table::RawTable<K, V>,
+
+    // We keep this at the end since it might as well have tail padding.
+    resize_policy: DefaultResizePolicy,
+}
+
+impl<K: Eq + Hash<S>, V, S, H: Hasher<S>> HashMap<K, V, H> {
+    // Probe the `idx`th bucket for a given hash, returning the index of the
+    // target bucket.
+    //
+    // This exploits the power-of-two size of the hashtable. As long as this
+    // is always true, we can use a bitmask of cap-1 to do modular arithmetic.
+    //
+    // Prefer using this with increasing values of `idx` rather than repeatedly
+    // calling `probe_next`. This reduces data-dependencies between loops, which
+    // can help the optimizer, and certainly won't hurt it. `probe_next` is
+    // simply for convenience, and is no more efficient than `probe`.
+    fn probe(&self, hash: &table::SafeHash, idx: uint) -> uint {
+        let hash_mask = self.table.capacity() - 1;
+
+        // So I heard a rumor that unsigned overflow is safe in rust..
+        ((hash.inspect() as uint) + idx) & hash_mask
+    }
+
+    // Generate the next probe in a sequence. Prefer using 'probe' by itself,
+    // but this can sometimes be useful.
+    fn probe_next(&self, probe: uint) -> uint {
+        let hash_mask = self.table.capacity() - 1;
+        (probe + 1) & hash_mask
+    }
+
+    fn make_hash<X: Hash<S>>(&self, x: &X) -> table::SafeHash {
+        table::make_hash(&self.hasher, x)
+    }
+
+    /// Get the distance of the bucket at the given index that it lies
+    /// from its 'ideal' location.
+    ///
+    /// In the cited blog posts above, this is called the "distance to
+    /// initial bucket", or DIB.
+    fn bucket_distance(&self, index_of_elem: &table::FullIndex) -> uint {
+        // where the hash of the element that happens to reside at
+        // `index_of_elem` tried to place itself first.
+        let first_probe_index = self.probe(&index_of_elem.hash(), 0);
+
+        let raw_index = index_of_elem.raw_index();
+
+        if first_probe_index <= raw_index {
+             // probe just went forward
+            raw_index - first_probe_index
+        } else {
+            // probe wrapped around the hashtable
+            raw_index + (self.table.capacity() - first_probe_index)
+        }
+    }
+
+    /// Search for a pre-hashed key.
+    fn search_hashed_generic(&self, hash: &table::SafeHash, is_match: |&K| -> bool)
+        -> Option<table::FullIndex> {
+        for num_probes in range(0u, self.table.size()) {
+            let probe = self.probe(hash, num_probes);
+
+            let idx = match self.table.peek(probe) {
+                table::Empty(_)  => return None, // hit an empty bucket
+                table::Full(idx) => idx
+            };
+
+            // We can finish the search early if we hit any bucket
+            // with a lower distance to initial bucket than we've probed.
+            if self.bucket_distance(&idx) < num_probes { return None }
+
+            // If the hash doesn't match, it can't be this one..
+            if *hash != idx.hash() { continue }
+
+            let (k, _) = self.table.read(&idx);
+
+            // If the key doesn't match, it can't be this one..
+            if !is_match(k) { continue }
+
+            return Some(idx);
+        }
+
+        return None
+    }
+
+    fn search_hashed(&self, hash: &table::SafeHash, k: &K) -> Option<table::FullIndex> {
+        self.search_hashed_generic(hash, |k_| *k == *k_)
+    }
+
+    fn search_equiv<Q: Hash<S> + Equiv<K>>(&self, q: &Q) -> Option<table::FullIndex> {
+        self.search_hashed_generic(&self.make_hash(q), |k| q.equiv(k))
+    }
+
+    /// Search for a key, yielding the index if it's found in the hashtable.
+    /// If you already have the hash for the key lying around, use
+    /// search_hashed.
+    fn search(&self, k: &K) -> Option<table::FullIndex> {
+        self.search_hashed(&self.make_hash(k), k)
+    }
+
+    fn pop_internal(&mut self, starting_index: table::FullIndex) -> Option<V> {
+        let starting_probe = starting_index.raw_index();
+
+        let ending_probe = {
+            let mut probe = self.probe_next(starting_probe);
+            for _ in range(0u, self.table.size()) {
+                match self.table.peek(probe) {
+                    table::Empty(_) => {}, // empty bucket. this is the end of our shifting.
+                    table::Full(idx) => {
+                        // Bucket that isn't us, which has a non-zero probe distance.
+                        // This isn't the ending index, so keep searching.
+                        if self.bucket_distance(&idx) != 0 {
+                            probe = self.probe_next(probe);
+                            continue;
+                        }
+
+                        // if we do have a bucket_distance of zero, we're at the end
+                        // of what we need to shift.
+                    }
+                }
+                break;
+            }
+
+            probe
+        };
+
+        let (_, _, retval) = self.table.take(starting_index);
+
+        let mut      probe = starting_probe;
+        let mut next_probe = self.probe_next(probe);
+
+        // backwards-shift all the elements after our newly-deleted one.
+        while next_probe != ending_probe {
+            match self.table.peek(next_probe) {
+                table::Empty(_) => {
+                    // nothing to shift in. just empty it out.
+                    match self.table.peek(probe) {
+                        table::Empty(_) => {},
+                        table::Full(idx) => { self.table.take(idx); }
+                    }
+                },
+                table::Full(next_idx) => {
+                    // something to shift. move it over!
+                    let next_hash = next_idx.hash();
+                    let (_, next_key, next_val) = self.table.take(next_idx);
+                    match self.table.peek(probe) {
+                        table::Empty(idx) => {
+                            self.table.put(idx, next_hash, next_key, next_val);
+                        },
+                        table::Full(idx) => {
+                            let (emptyidx, _, _) = self.table.take(idx);
+                            self.table.put(emptyidx, next_hash, next_key, next_val);
+                        }
+                    }
+                }
+            }
+
+            probe = next_probe;
+            next_probe = self.probe_next(next_probe);
+        }
+
+        // Done the backwards shift, but there's still an element left!
+        // Empty it out.
+        match self.table.peek(probe) {
+            table::Empty(_) => {},
+            table::Full(idx) => { self.table.take(idx); }
+        }
+
+        // Now we're done all our shifting. Return the value we grabbed
+        // earlier.
+        return Some(retval);
+    }
+
+    /// Like `pop`, but can operate on any type that is equivalent to a key.
+    #[experimental]
+    pub fn pop_equiv<Q:Hash<S> + Equiv<K>>(&mut self, k: &Q) -> Option<V> {
+        if self.table.size() == 0 {
+            return None
+        }
+
+        let potential_new_size = self.table.size() - 1;
+        self.make_some_room(potential_new_size);
+
+        let starting_index = match self.search_equiv(k) {
+            Some(idx) => idx,
+            None      => return None,
+        };
+
+        self.pop_internal(starting_index)
+    }
+}
+
+impl<K: Eq + Hash<S>, V, S, H: Hasher<S>> Container for HashMap<K, V, H> {
+    /// Return the number of elements in the map
+    fn len(&self) -> uint { self.table.size() }
+}
+
+impl<K: Eq + Hash<S>, V, S, H: Hasher<S>> Mutable for HashMap<K, V, H> {
+    /// Clear the map, removing all key-value pairs. Keeps the allocated memory
+    /// for reuse.
+    fn clear(&mut self) {
+        // Prevent reallocations from happening from now on. Makes it possible
+        // for the map to be reused but has a downside: reserves permanently.
+        self.resize_policy.reserve(self.table.size());
+
+        for i in range(0, self.table.capacity()) {
+            match self.table.peek(i) {
+                table::Empty(_)  => {},
+                table::Full(idx) => { self.table.take(idx); }
+            }
+        }
+    }
+}
+
+impl<K: Eq + Hash<S>, V, S, H: Hasher<S>> Map<K, V> for HashMap<K, V, H> {
+    fn find<'a>(&'a self, k: &K) -> Option<&'a V> {
+        self.search(k).map(|idx| {
+            let (_, v) = self.table.read(&idx);
+            v
+        })
+    }
+
+    fn contains_key(&self, k: &K) -> bool {
+        self.search(k).is_some()
+    }
+}
+
+impl<K: Eq + Hash<S>, V, S, H: Hasher<S>> MutableMap<K, V> for HashMap<K, V, H> {
+    fn find_mut<'a>(&'a mut self, k: &K) -> Option<&'a mut V> {
+        match self.search(k) {
+            None => None,
+            Some(idx) => {
+                let (_, v) = self.table.read_mut(&idx);
+                Some(v)
+            }
+        }
+    }
+
+    fn swap(&mut self, k: K, v: V) -> Option<V> {
+        let hash = self.make_hash(&k);
+        let potential_new_size = self.table.size() + 1;
+        self.make_some_room(potential_new_size);
+
+        for dib in range_inclusive(0u, self.table.size()) {
+            let probe = self.probe(&hash, dib);
+
+            let idx = match self.table.peek(probe) {
+                table::Empty(idx) => {
+                    // Found a hole!
+                    self.table.put(idx, hash, k, v);
+                    return None;
+                },
+                table::Full(idx) => idx
+            };
+
+            if idx.hash() == hash {
+                let (bucket_k, bucket_v) = self.table.read_mut(&idx);
+                if k == *bucket_k {
+                    // Found an existing value.
+                    return Some(replace(bucket_v, v));
+                }
+            }
+
+            let probe_dib = self.bucket_distance(&idx);
+
+            if probe_dib < dib {
+                // Found a luckier bucket. This implies that the key does not
+                // already exist in the hashtable. Just do a robin hood
+                // insertion, then.
+                self.robin_hood(idx, probe_dib, hash, k, v);
+                return None;
+            }
+        }
+
+        // We really shouldn't be here.
+        fail!("Internal HashMap error: Out of space.");
+    }
+
+    fn pop(&mut self, k: &K) -> Option<V> {
+        if self.table.size() == 0 {
+            return None
+        }
+
+        let potential_new_size = self.table.size() - 1;
+        self.make_some_room(potential_new_size);
+
+        let starting_index = match self.search(k) {
+            Some(idx) => idx,
+            None      => return None,
+        };
+
+        self.pop_internal(starting_index)
+    }
+
+}
+
+impl<K: Hash + Eq, V> HashMap<K, V, sip::SipHasher> {
+    /// Create an empty HashMap.
+    pub fn new() -> HashMap<K, V, sip::SipHasher> {
+        HashMap::with_capacity(INITIAL_CAPACITY)
+    }
+
+    /// Creates an empty hash map with the given initial capacity.
+    pub fn with_capacity(capacity: uint) -> HashMap<K, V, sip::SipHasher> {
+        let mut r = rand::task_rng();
+        let r0 = r.gen();
+        let r1 = r.gen();
+        let hasher = sip::SipHasher::new_with_keys(r0, r1);
+        HashMap::with_capacity_and_hasher(capacity, hasher)
+    }
+}
+
+impl<K: Eq + Hash<S>, V, S, H: Hasher<S>> HashMap<K, V, H> {
+    /// Creates an empty hashmap which will use the given hasher to hash keys.
+    ///
+    /// The creates map has the default initial capacity.
+    pub fn with_hasher(hasher: H) -> HashMap<K, V, H> {
+        HashMap::with_capacity_and_hasher(INITIAL_CAPACITY, hasher)
+    }
+
+    /// Create an empty HashMap with space for at least `capacity`
+    /// elements, using `hasher` to hash the keys.
+    ///
+    /// Warning: `hasher` is normally randomly generated, and
+    /// is designed to allow HashMaps to be resistant to attacks that
+    /// cause many collisions and very poor performance. Setting it
+    /// manually using this function can expose a DoS attack vector.
+    pub fn with_capacity_and_hasher(capacity: uint, hasher: H) -> HashMap<K, V, H> {
+        let cap = num::next_power_of_two(max(INITIAL_CAPACITY, capacity));
+        HashMap {
+            hasher:        hasher,
+            resize_policy: DefaultResizePolicy::new(cap),
+            table:         table::RawTable::new(cap),
+        }
+    }
+
+    /// The hashtable will never try to shrink below this size. You can use
+    /// this function to reduce reallocations if your hashtable frequently
+    /// grows and shrinks by large amounts.
+    ///
+    /// This function has no effect on the operational semantics of the
+    /// hashtable, only on performance.
+    pub fn reserve(&mut self, new_minimum_capacity: uint) {
+        let cap = num::next_power_of_two(
+            max(INITIAL_CAPACITY, new_minimum_capacity));
+
+        self.resize_policy.reserve(cap);
+
+        if self.table.capacity() < cap {
+            self.resize(cap);
+        }
+    }
+
+    /// Resizes the internal vectors to a new capacity. It's your responsibility to:
+    ///   1) Make sure the new capacity is enough for all the elements, accounting
+    ///      for the load factor.
+    ///   2) Ensure new_capacity is a power of two.
+    fn resize(&mut self, new_capacity: uint) {
+        assert!(self.table.size() <= new_capacity);
+        assert!(num::is_power_of_two(new_capacity));
+
+        let old_table = replace(&mut self.table, table::RawTable::new(new_capacity));
+        let old_size  = old_table.size();
+
+        for (h, k, v) in old_table.move_iter() {
+            self.insert_hashed_nocheck(h, k, v);
+        }
+
+        assert_eq!(self.table.size(), old_size);
+    }
+
+    /// Performs any necessary resize operations, such that there's space for
+    /// new_size elements.
+    fn make_some_room(&mut self, new_size: uint) {
+        let (grow_at, shrink_at) = self.resize_policy.capacity_range(new_size);
+        let cap = self.table.capacity();
+
+        // An invalid value shouldn't make us run out of space.
+        debug_assert!(grow_at >= new_size);
+
+        if cap <= grow_at {
+            let new_capacity = cap << 1;
+            self.resize(new_capacity);
+        } else if shrink_at <= cap {
+            let new_capacity = cap >> 1;
+            self.resize(new_capacity);
+        }
+    }
+
+    /// Perform robin hood bucket stealing at the given 'index'. You must
+    /// also pass that probe's "distance to initial bucket" so we don't have
+    /// to recalculate it, as well as the total number of probes already done
+    /// so we have some sort of upper bound on the number of probes to do.
+    ///
+    /// 'hash', 'k', and 'v' are the elements to robin hood into the hashtable.
+    fn robin_hood(&mut self, mut index: table::FullIndex, mut dib_param: uint,
+                  mut hash: table::SafeHash, mut k: K, mut v: V) {
+        'outer: loop {
+            let (old_hash, old_key, old_val) = {
+                let (old_hash_ref, old_key_ref, old_val_ref) =
+                        self.table.read_all_mut(&index);
+
+                let old_hash = replace(old_hash_ref, hash);
+                let old_key  = replace(old_key_ref,  k);
+                let old_val  = replace(old_val_ref,  v);
+
+                (old_hash, old_key, old_val)
+            };
+
+            let mut probe = self.probe_next(index.raw_index());
+
+            for dib in range(dib_param + 1, self.table.size()) {
+                let full_index = match self.table.peek(probe) {
+                    table::Empty(idx) => {
+                        // Finally. A hole!
+                        self.table.put(idx, old_hash, old_key, old_val);
+                        return;
+                    },
+                    table::Full(idx) => idx
+                };
+
+                let probe_dib = self.bucket_distance(&full_index);
+
+                // Robin hood! Steal the spot.
+                if probe_dib < dib {
+                    index = full_index;
+                    dib_param = probe_dib;
+                    hash = old_hash;
+                    k = old_key;
+                    v = old_val;
+                    continue 'outer;
+                }
+
+                probe = self.probe_next(probe);
+            }
+
+            fail!("HashMap fatal error: 100% load factor?");
+        }
+    }
+
+    /// Insert a pre-hashed key-value pair, without first checking
+    /// that there's enough room in the buckets. Returns a reference to the
+    /// newly insert value.
+    ///
+    /// If the key already exists, the hashtable will be returned untouched
+    /// and a reference to the existing element will be returned.
+    fn insert_hashed_nocheck<'a>(
+        &'a mut self, hash: table::SafeHash, k: K, v: V) -> &'a mut V {
+
+        for dib in range_inclusive(0u, self.table.size()) {
+            let probe = self.probe(&hash, dib);
+
+            let idx = match self.table.peek(probe) {
+                table::Empty(idx) => {
+                    // Found a hole!
+                    let fullidx  = self.table.put(idx, hash, k, v);
+                    let (_, val) = self.table.read_mut(&fullidx);
+                    return val;
+                },
+                table::Full(idx) => idx
+            };
+
+            if idx.hash() == hash {
+                let (bucket_k, bucket_v) = self.table.read_mut(&idx);
+                // FIXME #12147 the conditional return confuses
+                // borrowck if we return bucket_v directly
+                let bv: *mut V = bucket_v;
+                if k == *bucket_k {
+                    // Key already exists. Get its reference.
+                    return unsafe {&mut *bv};
+                }
+            }
+
+            let probe_dib = self.bucket_distance(&idx);
+
+            if  probe_dib < dib {
+                // Found a luckier bucket than me. Better steal his spot.
+                self.robin_hood(idx, probe_dib, hash, k, v);
+
+                // Now that it's stolen, just read the value's pointer
+                // right out of the table!
+                match self.table.peek(probe) {
+                    table::Empty(_)  => fail!("Just stole a spot, but now that spot's empty."),
+                    table::Full(idx) => {
+                        let (_, v) = self.table.read_mut(&idx);
+                        return v;
+                    }
+                }
+            }
+        }
+
+        // We really shouldn't be here.
+        fail!("Internal HashMap error: Out of space.");
+    }
+
+    /// Inserts an element which has already been hashed, returning a reference
+    /// to that element inside the hashtable. This is more efficient that using
+    /// `insert`, since the key will not be rehashed.
+    fn insert_hashed<'a>(&'a mut self, hash: table::SafeHash, k: K, v: V) -> &'a mut V {
+        let potential_new_size = self.table.size() + 1;
+        self.make_some_room(potential_new_size);
+        self.insert_hashed_nocheck(hash, k, v)
+    }
+
+    /// Return the value corresponding to the key in the map, or insert
+    /// and return the value if it doesn't exist.
+    pub fn find_or_insert<'a>(&'a mut self, k: K, v: V) -> &'a mut V {
+        self.find_with_or_insert_with(k, v, |_k, _v, _a| (), |_k, a| a)
+    }
+
+    /// Return the value corresponding to the key in the map, or create,
+    /// insert, and return a new value if it doesn't exist.
+    pub fn find_or_insert_with<'a>(&'a mut self, k: K, f: |&K| -> V)
+                               -> &'a mut V {
+        self.find_with_or_insert_with(k, (), |_k, _v, _a| (), |k, _a| f(k))
+    }
+
+    /// Insert a key-value pair into the map if the key is not already present.
+    /// Otherwise, modify the existing value for the key.
+    /// Returns the new or modified value for the key.
+    pub fn insert_or_update_with<'a>(
+                                 &'a mut self,
+                                 k: K,
+                                 v: V,
+                                 f: |&K, &mut V|)
+                                 -> &'a mut V {
+        self.find_with_or_insert_with(k, v, |k, v, _a| f(k, v), |_k, a| a)
+    }
+
+    /// Modify and return the value corresponding to the key in the map, or
+    /// insert and return a new value if it doesn't exist.
+    ///
+    /// This method allows for all insertion behaviours of a hashmap;
+    /// see methods like `insert`, `find_or_insert` and
+    /// `insert_or_update_with` for less general and more friendly
+    /// variations of this.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// use collections::HashMap;
+    ///
+    /// // map some strings to vectors of strings
+    /// let mut map = HashMap::new();
+    /// map.insert("a key", vec!["value"]);
+    /// map.insert("z key", vec!["value"]);
+    ///
+    /// let new = vec!["a key", "b key", "z key"];
+    ///
+    /// for k in new.move_iter() {
+    ///     map.find_with_or_insert_with(
+    ///         k, "new value",
+    ///         // if the key does exist either prepend or append this
+    ///         // new value based on the first letter of the key.
+    ///         |key, already, new| {
+    ///             if key.as_slice().starts_with("z") {
+    ///                 already.unshift(new);
+    ///             } else {
+    ///                 already.push(new);
+    ///             }
+    ///         },
+    ///         // if the key doesn't exist in the map yet, add it in
+    ///         // the obvious way.
+    ///         |_k, v| vec![v]);
+    /// }
+    ///
+    /// assert_eq!(map.len(), 3);
+    /// assert_eq!(map.get(&"a key"), &vec!["value", "new value"]);
+    /// assert_eq!(map.get(&"b key"), &vec!["new value"]);
+    /// assert_eq!(map.get(&"z key"), &vec!["new value", "value"]);
+    /// ```
+    pub fn find_with_or_insert_with<'a, A>(&'a mut self,
+                                           k: K,
+                                           a: A,
+                                           found: |&K, &mut V, A|,
+                                           not_found: |&K, A| -> V)
+                                          -> &'a mut V {
+        let hash = self.make_hash(&k);
+        match self.search_hashed(&hash, &k) {
+            None => {
+                let v = not_found(&k, a);
+                self.insert_hashed(hash, k, v)
+            },
+            Some(idx) => {
+                let (_, v_ref) = self.table.read_mut(&idx);
+                found(&k, v_ref, a);
+                v_ref
+            }
+        }
+    }
+
+    /// Retrieves a value for the given key, failing if the key is not present.
+    pub fn get<'a>(&'a self, k: &K) -> &'a V {
+        match self.find(k) {
+            Some(v) => v,
+            None => fail!("no entry found for key")
+        }
+    }
+
+    /// Retrieves a (mutable) value for the given key, failing if the key is not present.
+    pub fn get_mut<'a>(&'a mut self, k: &K) -> &'a mut V {
+        match self.find_mut(k) {
+            Some(v) => v,
+            None => fail!("no entry found for key")
+        }
+    }
+
+    /// Return true if the map contains a value for the specified key,
+    /// using equivalence.
+    pub fn contains_key_equiv<Q: Hash<S> + Equiv<K>>(&self, key: &Q) -> bool {
+        self.search_equiv(key).is_some()
+    }
+
+    /// Return the value corresponding to the key in the map, using
+    /// equivalence.
+    pub fn find_equiv<'a, Q: Hash<S> + Equiv<K>>(&'a self, k: &Q) -> Option<&'a V> {
+        match self.search_equiv(k) {
+            None      => None,
+            Some(idx) => {
+                let (_, v_ref) = self.table.read(&idx);
+                Some(v_ref)
+            }
+        }
+    }
+
+    /// An iterator visiting all keys in arbitrary order.
+    /// Iterator element type is &'a K.
+    pub fn keys<'a>(&'a self) -> Keys<'a, K, V> {
+        self.iter().map(|(k, _v)| k)
+    }
+
+    /// An iterator visiting all values in arbitrary order.
+    /// Iterator element type is &'a V.
+    pub fn values<'a>(&'a self) -> Values<'a, K, V> {
+        self.iter().map(|(_k, v)| v)
+    }
+
+    /// An iterator visiting all key-value pairs in arbitrary order.
+    /// Iterator element type is (&'a K, &'a V).
+    pub fn iter<'a>(&'a self) -> Entries<'a, K, V> {
+        self.table.iter()
+    }
+
+    /// An iterator visiting all key-value pairs in arbitrary order,
+    /// with mutable references to the values.
+    /// Iterator element type is (&'a K, &'a mut V).
+    pub fn mut_iter<'a>(&'a mut self) -> MutEntries<'a, K, V> {
+        self.table.mut_iter()
+    }
+
+    /// Creates a consuming iterator, that is, one that moves each key-value
+    /// pair out of the map in arbitrary order. The map cannot be used after
+    /// calling this.
+    pub fn move_iter(self) -> MoveEntries<K, V> {
+        self.table.move_iter().map(|(_, k, v)| (k, v))
+    }
+}
+
+impl<K: Eq + Hash<S>, V: Clone, S, H: Hasher<S>> HashMap<K, V, H> {
+    /// Like `find`, but returns a copy of the value.
+    pub fn find_copy(&self, k: &K) -> Option<V> {
+        self.find(k).map(|v| (*v).clone())
+    }
+
+    /// Like `get`, but returns a copy of the value.
+    pub fn get_copy(&self, k: &K) -> V {
+        (*self.get(k)).clone()
+    }
+}
+
+impl<K: Eq + Hash<S>, V: PartialEq, S, H: Hasher<S>> PartialEq for HashMap<K, V, H> {
+    fn eq(&self, other: &HashMap<K, V, H>) -> bool {
+        if self.len() != other.len() { return false; }
+
+        self.iter()
+          .all(|(key, value)| {
+            match other.find(key) {
+                None    => false,
+                Some(v) => *value == *v
+            }
+        })
+    }
+}
+
+impl<K: Eq + Hash<S> + Show, V: Show, S, H: Hasher<S>> Show for HashMap<K, V, H> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        try!(write!(f, r"\{"));
+
+        for (i, (k, v)) in self.iter().enumerate() {
+            if i != 0 { try!(write!(f, ", ")); }
+            try!(write!(f, "{}: {}", *k, *v));
+        }
+
+        write!(f, r"\}")
+    }
+}
+
+impl<K: Eq + Hash<S>, V, S, H: Hasher<S> + Default> Default for HashMap<K, V, H> {
+    fn default() -> HashMap<K, V, H> {
+        HashMap::with_hasher(Default::default())
+    }
+}
+
+/// HashMap iterator
+pub type Entries<'a, K, V> = table::Entries<'a, K, V>;
+
+/// HashMap mutable values iterator
+pub type MutEntries<'a, K, V> = table::MutEntries<'a, K, V>;
+
+/// HashMap move iterator
+pub type MoveEntries<K, V> =
+    iter::Map<'static, (table::SafeHash, K, V), (K, V), table::MoveEntries<K, V>>;
+
+/// HashMap keys iterator
+pub type Keys<'a, K, V> =
+    iter::Map<'static, (&'a K, &'a V), &'a K, Entries<'a, K, V>>;
+
+/// HashMap values iterator
+pub type Values<'a, K, V> =
+    iter::Map<'static, (&'a K, &'a V), &'a V, Entries<'a, K, V>>;
+
+impl<K: Eq + Hash<S>, V, S, H: Hasher<S> + Default> FromIterator<(K, V)> for HashMap<K, V, H> {
+    fn from_iter<T: Iterator<(K, V)>>(iter: T) -> HashMap<K, V, H> {
+        let (lower, _) = iter.size_hint();
+        let mut map = HashMap::with_capacity_and_hasher(lower, Default::default());
+        map.extend(iter);
+        map
+    }
+}
+
+impl<K: Eq + Hash<S>, V, S, H: Hasher<S> + Default> Extendable<(K, V)> for HashMap<K, V, H> {
+    fn extend<T: Iterator<(K, V)>>(&mut self, mut iter: T) {
+        for (k, v) in iter {
+            self.insert(k, v);
+        }
+    }
+}
+
+/// HashSet iterator
+pub type SetItems<'a, K> =
+    iter::Map<'static, (&'a K, &'a ()), &'a K, Entries<'a, K, ()>>;
+
+/// HashSet move iterator
+pub type SetMoveItems<K> =
+    iter::Map<'static, (K, ()), K, MoveEntries<K, ()>>;
+
+/// An implementation of a hash set using the underlying representation of a
+/// HashMap where the value is (). As with the `HashMap` type, a `HashSet`
+/// requires that the elements implement the `PartialEq` and `Hash` traits.
+#[deriving(Clone)]
+pub struct HashSet<T, H = sip::SipHasher> {
+    map: HashMap<T, (), H>
+}
+
+impl<T: Eq + Hash<S>, S, H: Hasher<S>> PartialEq for HashSet<T, H> {
+    fn eq(&self, other: &HashSet<T, H>) -> bool {
+        if self.len() != other.len() { return false; }
+
+        self.iter().all(|key| other.contains(key))
+    }
+}
+
+impl<T: Eq + Hash<S>, S, H: Hasher<S>> Container for HashSet<T, H> {
+    fn len(&self) -> uint { self.map.len() }
+}
+
+impl<T: Eq + Hash<S>, S, H: Hasher<S>> Mutable for HashSet<T, H> {
+    fn clear(&mut self) { self.map.clear() }
+}
+
+impl<T: Eq + Hash<S>, S, H: Hasher<S>> Set<T> for HashSet<T, H> {
+    fn contains(&self, value: &T) -> bool { self.map.contains_key(value) }
+
+    fn is_disjoint(&self, other: &HashSet<T, H>) -> bool {
+        self.iter().all(|v| !other.contains(v))
+    }
+
+    fn is_subset(&self, other: &HashSet<T, H>) -> bool {
+        self.iter().all(|v| other.contains(v))
+    }
+}
+
+impl<T: Eq + Hash<S>, S, H: Hasher<S>> MutableSet<T> for HashSet<T, H> {
+    fn insert(&mut self, value: T) -> bool { self.map.insert(value, ()) }
+
+    fn remove(&mut self, value: &T) -> bool { self.map.remove(value) }
+}
+
+impl<T: Hash + Eq> HashSet<T, sip::SipHasher> {
+    /// Create an empty HashSet
+    pub fn new() -> HashSet<T, sip::SipHasher> {
+        HashSet::with_capacity(INITIAL_CAPACITY)
+    }
+
+    /// Create an empty HashSet with space for at least `n` elements in
+    /// the hash table.
+    pub fn with_capacity(capacity: uint) -> HashSet<T, sip::SipHasher> {
+        HashSet { map: HashMap::with_capacity(capacity) }
+    }
+}
+
+impl<T: Eq + Hash<S>, S, H: Hasher<S>> HashSet<T, H> {
+    /// Creates a new empty hash set which will use the given hasher to hash
+    /// keys.
+    ///
+    /// The hash set is also created with the default initial capacity.
+    pub fn with_hasher(hasher: H) -> HashSet<T, H> {
+        HashSet::with_capacity_and_hasher(INITIAL_CAPACITY, hasher)
+    }
+
+    /// Create an empty HashSet with space for at least `capacity`
+    /// elements in the hash table, using `hasher` to hash the keys.
+    ///
+    /// Warning: `hasher` is normally randomly generated, and
+    /// is designed to allow `HashSet`s to be resistant to attacks that
+    /// cause many collisions and very poor performance. Setting it
+    /// manually using this function can expose a DoS attack vector.
+    pub fn with_capacity_and_hasher(capacity: uint, hasher: H) -> HashSet<T, H> {
+        HashSet { map: HashMap::with_capacity_and_hasher(capacity, hasher) }
+    }
+
+    /// Reserve space for at least `n` elements in the hash table.
+    pub fn reserve(&mut self, n: uint) {
+        self.map.reserve(n)
+    }
+
+    /// Returns true if the hash set contains a value equivalent to the
+    /// given query value.
+    pub fn contains_equiv<Q: Hash<S> + Equiv<T>>(&self, value: &Q) -> bool {
+      self.map.contains_key_equiv(value)
+    }
+
+    /// An iterator visiting all elements in arbitrary order.
+    /// Iterator element type is &'a T.
+    pub fn iter<'a>(&'a self) -> SetItems<'a, T> {
+        self.map.keys()
+    }
+
+    /// Creates a consuming iterator, that is, one that moves each value out
+    /// of the set in arbitrary order. The set cannot be used after calling
+    /// this.
+    pub fn move_iter(self) -> SetMoveItems<T> {
+        self.map.move_iter().map(|(k, _)| k)
+    }
+
+    /// Visit the values representing the difference
+    pub fn difference<'a>(&'a self, other: &'a HashSet<T, H>) -> SetAlgebraItems<'a, T, H> {
+        Repeat::new(other).zip(self.iter())
+            .filter_map(|(other, elt)| {
+                if !other.contains(elt) { Some(elt) } else { None }
+            })
+    }
+
+    /// Visit the values representing the symmetric difference
+    pub fn symmetric_difference<'a>(&'a self, other: &'a HashSet<T, H>)
+        -> Chain<SetAlgebraItems<'a, T, H>, SetAlgebraItems<'a, T, H>> {
+        self.difference(other).chain(other.difference(self))
+    }
+
+    /// Visit the values representing the intersection
+    pub fn intersection<'a>(&'a self, other: &'a HashSet<T, H>)
+        -> SetAlgebraItems<'a, T, H> {
+        Repeat::new(other).zip(self.iter())
+            .filter_map(|(other, elt)| {
+                if other.contains(elt) { Some(elt) } else { None }
+            })
+    }
+
+    /// Visit the values representing the union
+    pub fn union<'a>(&'a self, other: &'a HashSet<T, H>)
+        -> Chain<SetItems<'a, T>, SetAlgebraItems<'a, T, H>> {
+        self.iter().chain(other.difference(self))
+    }
+}
+
+impl<T: Eq + Hash<S> + fmt::Show, S, H: Hasher<S>> fmt::Show for HashSet<T, H> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        try!(write!(f, r"\{"));
+
+        for (i, x) in self.iter().enumerate() {
+            if i != 0 { try!(write!(f, ", ")); }
+            try!(write!(f, "{}", *x));
+        }
+
+        write!(f, r"\}")
+    }
+}
+
+impl<T: Eq + Hash<S>, S, H: Hasher<S> + Default> FromIterator<T> for HashSet<T, H> {
+    fn from_iter<I: Iterator<T>>(iter: I) -> HashSet<T, H> {
+        let (lower, _) = iter.size_hint();
+        let mut set = HashSet::with_capacity_and_hasher(lower, Default::default());
+        set.extend(iter);
+        set
+    }
+}
+
+impl<T: Eq + Hash<S>, S, H: Hasher<S> + Default> Extendable<T> for HashSet<T, H> {
+    fn extend<I: Iterator<T>>(&mut self, mut iter: I) {
+        for k in iter {
+            self.insert(k);
+        }
+    }
+}
+
+impl<T: TotalEq + Hash<S>, S, H: Hasher<S> + Default> Default for HashSet<T, H> {
+    fn default() -> HashSet<T, H> {
+        HashSet::with_hasher(Default::default())
+    }
+}
+
+// `Repeat` is used to feed the filter closure an explicit capture
+// of a reference to the other set
+/// Set operations iterator
+pub type SetAlgebraItems<'a, T, H> =
+    FilterMap<'static, (&'a HashSet<T, H>, &'a T), &'a T,
+              Zip<Repeat<&'a HashSet<T, H>>, SetItems<'a, T>>>;
+
+#[cfg(test)]
+mod test_map {
+    use super::HashMap;
+    use std::cmp::Equiv;
+    use std::hash::Hash;
+    use std::iter::{Iterator,range_inclusive,range_step_inclusive};
+    use std::cell::RefCell;
+
+    struct KindaIntLike(int);
+
+    impl Equiv<int> for KindaIntLike {
+        fn equiv(&self, other: &int) -> bool {
+            let KindaIntLike(this) = *self;
+            this == *other
+        }
+    }
+    impl<S: Writer> Hash<S> for KindaIntLike {
+        fn hash(&self, state: &mut S) {
+            let KindaIntLike(this) = *self;
+            this.hash(state)
+        }
+    }
+
+    #[test]
+    fn test_create_capacity_zero() {
+        let mut m = HashMap::with_capacity(0);
+
+        assert!(m.insert(1, 1));
+
+        assert!(m.contains_key(&1));
+        assert!(!m.contains_key(&0));
+    }
+
+    #[test]
+    fn test_insert() {
+        let mut m = HashMap::new();
+        assert_eq!(m.len(), 0);
+        assert!(m.insert(1, 2));
+        assert_eq!(m.len(), 1);
+        assert!(m.insert(2, 4));
+        assert_eq!(m.len(), 2);
+        assert_eq!(*m.find(&1).unwrap(), 2);
+        assert_eq!(*m.find(&2).unwrap(), 4);
+    }
+
+    local_data_key!(drop_vector: RefCell<Vec<int>>)
+
+    #[deriving(Hash, PartialEq, Eq)]
+    struct Dropable {
+        k: uint
+    }
+
+
+    impl Dropable {
+        fn new(k: uint) -> Dropable {
+            let v = drop_vector.get().unwrap();
+            v.borrow_mut().as_mut_slice()[k] += 1;
+
+            Dropable { k: k }
+        }
+    }
+
+    impl Drop for Dropable {
+        fn drop(&mut self) {
+            let v = drop_vector.get().unwrap();
+            v.borrow_mut().as_mut_slice()[self.k] -= 1;
+        }
+    }
+
+    #[test]
+    fn test_drops() {
+        drop_vector.replace(Some(RefCell::new(Vec::from_elem(200, 0))));
+
+        {
+            let mut m = HashMap::new();
+
+            let v = drop_vector.get().unwrap();
+            for i in range(0u, 200) {
+                assert_eq!(v.borrow().as_slice()[i], 0);
+            }
+            drop(v);
+
+            for i in range(0u, 100) {
+                let d1 = Dropable::new(i);
+                let d2 = Dropable::new(i+100);
+                m.insert(d1, d2);
+            }
+
+            let v = drop_vector.get().unwrap();
+            for i in range(0u, 200) {
+                assert_eq!(v.borrow().as_slice()[i], 1);
+            }
+            drop(v);
+
+            for i in range(0u, 50) {
+                let k = Dropable::new(i);
+                let v = m.pop(&k);
+
+                assert!(v.is_some());
+
+                let v = drop_vector.get().unwrap();
+                assert_eq!(v.borrow().as_slice()[i], 1);
+                assert_eq!(v.borrow().as_slice()[i+100], 1);
+            }
+
+            let v = drop_vector.get().unwrap();
+            for i in range(0u, 50) {
+                assert_eq!(v.borrow().as_slice()[i], 0);
+                assert_eq!(v.borrow().as_slice()[i+100], 0);
+            }
+
+            for i in range(50u, 100) {
+                assert_eq!(v.borrow().as_slice()[i], 1);
+                assert_eq!(v.borrow().as_slice()[i+100], 1);
+            }
+        }
+
+        let v = drop_vector.get().unwrap();
+        for i in range(0u, 200) {
+            assert_eq!(v.borrow().as_slice()[i], 0);
+        }
+    }
+
+    #[test]
+    fn test_empty_pop() {
+        let mut m: HashMap<int, bool> = HashMap::new();
+        assert_eq!(m.pop(&0), None);
+    }
+
+    #[test]
+    fn test_lots_of_insertions() {
+        let mut m = HashMap::new();
+
+        // Try this a few times to make sure we never screw up the hashmap's
+        // internal state.
+        for _ in range(0, 10) {
+            assert!(m.is_empty());
+
+            for i in range_inclusive(1, 1000) {
+                assert!(m.insert(i, i));
+
+                for j in range_inclusive(1, i) {
+                    let r = m.find(&j);
+                    assert_eq!(r, Some(&j));
+                }
+
+                for j in range_inclusive(i+1, 1000) {
+                    let r = m.find(&j);
+                    assert_eq!(r, None);
+                }
+            }
+
+            for i in range_inclusive(1001, 2000) {
+                assert!(!m.contains_key(&i));
+            }
+
+            // remove forwards
+            for i in range_inclusive(1, 1000) {
+                assert!(m.remove(&i));
+
+                for j in range_inclusive(1, i) {
+                    assert!(!m.contains_key(&j));
+                }
+
+                for j in range_inclusive(i+1, 1000) {
+                    assert!(m.contains_key(&j));
+                }
+            }
+
+            for i in range_inclusive(1, 1000) {
+                assert!(!m.contains_key(&i));
+            }
+
+            for i in range_inclusive(1, 1000) {
+                assert!(m.insert(i, i));
+            }
+
+            // remove backwards
+            for i in range_step_inclusive(1000, 1, -1) {
+                assert!(m.remove(&i));
+
+                for j in range_inclusive(i, 1000) {
+                    assert!(!m.contains_key(&j));
+                }
+
+                for j in range_inclusive(1, i-1) {
+                    assert!(m.contains_key(&j));
+                }
+            }
+        }
+    }
+
+    #[test]
+    fn test_find_mut() {
+        let mut m = HashMap::new();
+        assert!(m.insert(1, 12));
+        assert!(m.insert(2, 8));
+        assert!(m.insert(5, 14));
+        let new = 100;
+        match m.find_mut(&5) {
+            None => fail!(), Some(x) => *x = new
+        }
+        assert_eq!(m.find(&5), Some(&new));
+    }
+
+    #[test]
+    fn test_insert_overwrite() {
+        let mut m = HashMap::new();
+        assert!(m.insert(1, 2));
+        assert_eq!(*m.find(&1).unwrap(), 2);
+        assert!(!m.insert(1, 3));
+        assert_eq!(*m.find(&1).unwrap(), 3);
+    }
+
+    #[test]
+    fn test_insert_conflicts() {
+        let mut m = HashMap::with_capacity(4);
+        assert!(m.insert(1, 2));
+        assert!(m.insert(5, 3));
+        assert!(m.insert(9, 4));
+        assert_eq!(*m.find(&9).unwrap(), 4);
+        assert_eq!(*m.find(&5).unwrap(), 3);
+        assert_eq!(*m.find(&1).unwrap(), 2);
+    }
+
+    #[test]
+    fn test_conflict_remove() {
+        let mut m = HashMap::with_capacity(4);
+        assert!(m.insert(1, 2));
+        assert_eq!(*m.find(&1).unwrap(), 2);
+        assert!(m.insert(5, 3));
+        assert_eq!(*m.find(&1).unwrap(), 2);
+        assert_eq!(*m.find(&5).unwrap(), 3);
+        assert!(m.insert(9, 4));
+        assert_eq!(*m.find(&1).unwrap(), 2);
+        assert_eq!(*m.find(&5).unwrap(), 3);
+        assert_eq!(*m.find(&9).unwrap(), 4);
+        assert!(m.remove(&1));
+        assert_eq!(*m.find(&9).unwrap(), 4);
+        assert_eq!(*m.find(&5).unwrap(), 3);
+    }
+
+    #[test]
+    fn test_is_empty() {
+        let mut m = HashMap::with_capacity(4);
+        assert!(m.insert(1, 2));
+        assert!(!m.is_empty());
+        assert!(m.remove(&1));
+        assert!(m.is_empty());
+    }
+
+    #[test]
+    fn test_pop() {
+        let mut m = HashMap::new();
+        m.insert(1, 2);
+        assert_eq!(m.pop(&1), Some(2));
+        assert_eq!(m.pop(&1), None);
+    }
+
+    #[test]
+    #[allow(experimental)]
+    fn test_pop_equiv() {
+        let mut m = HashMap::new();
+        m.insert(1, 2);
+        assert_eq!(m.pop_equiv(&KindaIntLike(1)), Some(2));
+        assert_eq!(m.pop_equiv(&KindaIntLike(1)), None);
+    }
+
+    #[test]
+    fn test_swap() {
+        let mut m = HashMap::new();
+        assert_eq!(m.swap(1, 2), None);
+        assert_eq!(m.swap(1, 3), Some(2));
+        assert_eq!(m.swap(1, 4), Some(3));
+    }
+
+    #[test]
+    fn test_move_iter() {
+        let hm = {
+            let mut hm = HashMap::new();
+
+            hm.insert('a', 1);
+            hm.insert('b', 2);
+
+            hm
+        };
+
+        let v = hm.move_iter().collect::<Vec<(char, int)>>();
+        assert!([('a', 1), ('b', 2)] == v.as_slice() || [('b', 2), ('a', 1)] == v.as_slice());
+    }
+
+    #[test]
+    fn test_iterate() {
+        let mut m = HashMap::with_capacity(4);
+        for i in range(0u, 32) {
+            assert!(m.insert(i, i*2));
+        }
+        assert_eq!(m.len(), 32);
+
+        let mut observed: u32 = 0;
+
+        for (k, v) in m.iter() {
+            assert_eq!(*v, *k * 2);
+            observed |= 1 << *k;
+        }
+        assert_eq!(observed, 0xFFFF_FFFF);
+    }
+
+    #[test]
+    fn test_keys() {
+        let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
+        let map = vec.move_iter().collect::<HashMap<int, char>>();
+        let keys = map.keys().map(|&k| k).collect::<Vec<int>>();
+        assert_eq!(keys.len(), 3);
+        assert!(keys.contains(&1));
+        assert!(keys.contains(&2));
+        assert!(keys.contains(&3));
+    }
+
+    #[test]
+    fn test_values() {
+        let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
+        let map = vec.move_iter().collect::<HashMap<int, char>>();
+        let values = map.values().map(|&v| v).collect::<Vec<char>>();
+        assert_eq!(values.len(), 3);
+        assert!(values.contains(&'a'));
+        assert!(values.contains(&'b'));
+        assert!(values.contains(&'c'));
+    }
+
+    #[test]
+    fn test_find() {
+        let mut m = HashMap::new();
+        assert!(m.find(&1).is_none());
+        m.insert(1, 2);
+        match m.find(&1) {
+            None => fail!(),
+            Some(v) => assert_eq!(*v, 2)
+        }
+    }
+
+    #[test]
+    fn test_eq() {
+        let mut m1 = HashMap::new();
+        m1.insert(1, 2);
+        m1.insert(2, 3);
+        m1.insert(3, 4);
+
+        let mut m2 = HashMap::new();
+        m2.insert(1, 2);
+        m2.insert(2, 3);
+
+        assert!(m1 != m2);
+
+        m2.insert(3, 4);
+
+        assert_eq!(m1, m2);
+    }
+
+    #[test]
+    fn test_show() {
+        let mut map: HashMap<int, int> = HashMap::new();
+        let empty: HashMap<int, int> = HashMap::new();
+
+        map.insert(1, 2);
+        map.insert(3, 4);
+
+        let map_str = format!("{}", map);
+
+        assert!(map_str == "{1: 2, 3: 4}".to_string() || map_str == "{3: 4, 1: 2}".to_string());
+        assert_eq!(format!("{}", empty), "{}".to_string());
+    }
+
+    #[test]
+    fn test_expand() {
+        let mut m = HashMap::new();
+
+        assert_eq!(m.len(), 0);
+        assert!(m.is_empty());
+
+        let mut i = 0u;
+        let old_cap = m.table.capacity();
+        while old_cap == m.table.capacity() {
+            m.insert(i, i);
+            i += 1;
+        }
+
+        assert_eq!(m.len(), i);
+        assert!(!m.is_empty());
+    }
+
+    #[test]
+    fn test_resize_policy() {
+        let mut m = HashMap::new();
+
+        assert_eq!(m.len(), 0);
+        assert!(m.is_empty());
+
+        let initial_cap = m.table.capacity();
+        m.reserve(initial_cap * 2);
+        let cap = m.table.capacity();
+
+        assert_eq!(cap, initial_cap * 2);
+
+        let mut i = 0u;
+        for _ in range(0, cap * 3 / 4) {
+            m.insert(i, i);
+            i += 1;
+        }
+
+        assert_eq!(m.len(), i);
+        assert_eq!(m.table.capacity(), cap);
+
+        for _ in range(0, cap / 4) {
+            m.insert(i, i);
+            i += 1;
+        }
+
+        let new_cap = m.table.capacity();
+        assert_eq!(new_cap, cap * 2);
+
+        for _ in range(0, cap / 2) {
+            i -= 1;
+            m.remove(&i);
+            assert_eq!(m.table.capacity(), new_cap);
+        }
+
+        for _ in range(0, cap / 2 - 1) {
+            i -= 1;
+            m.remove(&i);
+        }
+
+        assert_eq!(m.table.capacity(), cap);
+        assert_eq!(m.len(), i);
+        assert!(!m.is_empty());
+    }
+
+    #[test]
+    fn test_find_equiv() {
+        let mut m = HashMap::new();
+
+        let (foo, bar, baz) = (1,2,3);
+        m.insert("foo".to_string(), foo);
+        m.insert("bar".to_string(), bar);
+        m.insert("baz".to_string(), baz);
+
+
+        assert_eq!(m.find_equiv(&("foo")), Some(&foo));
+        assert_eq!(m.find_equiv(&("bar")), Some(&bar));
+        assert_eq!(m.find_equiv(&("baz")), Some(&baz));
+
+        assert_eq!(m.find_equiv(&("qux")), None);
+    }
+
+    #[test]
+    fn test_from_iter() {
+        let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
+
+        let map: HashMap<int, int> = xs.iter().map(|&x| x).collect();
+
+        for &(k, v) in xs.iter() {
+            assert_eq!(map.find(&k), Some(&v));
+        }
+    }
+
+    #[test]
+    fn test_size_hint() {
+        let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
+
+        let map: HashMap<int, int> = xs.iter().map(|&x| x).collect();
+
+        let mut iter = map.iter();
+
+        for _ in iter.by_ref().take(3) {}
+
+        assert_eq!(iter.size_hint(), (3, Some(3)));
+    }
+
+    #[test]
+    fn test_mut_size_hint() {
+        let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
+
+        let mut map: HashMap<int, int> = xs.iter().map(|&x| x).collect();
+
+        let mut iter = map.mut_iter();
+
+        for _ in iter.by_ref().take(3) {}
+
+        assert_eq!(iter.size_hint(), (3, Some(3)));
+    }
+}
+
+#[cfg(test)]
+mod test_set {
+    use super::HashSet;
+    use std::container::Container;
+    use std::slice::ImmutableEqVector;
+
+    #[test]
+    fn test_disjoint() {
+        let mut xs = HashSet::new();
+        let mut ys = HashSet::new();
+        assert!(xs.is_disjoint(&ys));
+        assert!(ys.is_disjoint(&xs));
+        assert!(xs.insert(5));
+        assert!(ys.insert(11));
+        assert!(xs.is_disjoint(&ys));
+        assert!(ys.is_disjoint(&xs));
+        assert!(xs.insert(7));
+        assert!(xs.insert(19));
+        assert!(xs.insert(4));
+        assert!(ys.insert(2));
+        assert!(ys.insert(-11));
+        assert!(xs.is_disjoint(&ys));
+        assert!(ys.is_disjoint(&xs));
+        assert!(ys.insert(7));
+        assert!(!xs.is_disjoint(&ys));
+        assert!(!ys.is_disjoint(&xs));
+    }
+
+    #[test]
+    fn test_subset_and_superset() {
+        let mut a = HashSet::new();
+        assert!(a.insert(0));
+        assert!(a.insert(5));
+        assert!(a.insert(11));
+        assert!(a.insert(7));
+
+        let mut b = HashSet::new();
+        assert!(b.insert(0));
+        assert!(b.insert(7));
+        assert!(b.insert(19));
+        assert!(b.insert(250));
+        assert!(b.insert(11));
+        assert!(b.insert(200));
+
+        assert!(!a.is_subset(&b));
+        assert!(!a.is_superset(&b));
+        assert!(!b.is_subset(&a));
+        assert!(!b.is_superset(&a));
+
+        assert!(b.insert(5));
+
+        assert!(a.is_subset(&b));
+        assert!(!a.is_superset(&b));
+        assert!(!b.is_subset(&a));
+        assert!(b.is_superset(&a));
+    }
+
+    #[test]
+    fn test_iterate() {
+        let mut a = HashSet::new();
+        for i in range(0u, 32) {
+            assert!(a.insert(i));
+        }
+        let mut observed: u32 = 0;
+        for k in a.iter() {
+            observed |= 1 << *k;
+        }
+        assert_eq!(observed, 0xFFFF_FFFF);
+    }
+
+    #[test]
+    fn test_intersection() {
+        let mut a = HashSet::new();
+        let mut b = HashSet::new();
+
+        assert!(a.insert(11));
+        assert!(a.insert(1));
+        assert!(a.insert(3));
+        assert!(a.insert(77));
+        assert!(a.insert(103));
+        assert!(a.insert(5));
+        assert!(a.insert(-5));
+
+        assert!(b.insert(2));
+        assert!(b.insert(11));
+        assert!(b.insert(77));
+        assert!(b.insert(-9));
+        assert!(b.insert(-42));
+        assert!(b.insert(5));
+        assert!(b.insert(3));
+
+        let mut i = 0;
+        let expected = [3, 5, 11, 77];
+        for x in a.intersection(&b) {
+            assert!(expected.contains(x));
+            i += 1
+        }
+        assert_eq!(i, expected.len());
+    }
+
+    #[test]
+    fn test_difference() {
+        let mut a = HashSet::new();
+        let mut b = HashSet::new();
+
+        assert!(a.insert(1));
+        assert!(a.insert(3));
+        assert!(a.insert(5));
+        assert!(a.insert(9));
+        assert!(a.insert(11));
+
+        assert!(b.insert(3));
+        assert!(b.insert(9));
+
+        let mut i = 0;
+        let expected = [1, 5, 11];
+        for x in a.difference(&b) {
+            assert!(expected.contains(x));
+            i += 1
+        }
+        assert_eq!(i, expected.len());
+    }
+
+    #[test]
+    fn test_symmetric_difference() {
+        let mut a = HashSet::new();
+        let mut b = HashSet::new();
+
+        assert!(a.insert(1));
+        assert!(a.insert(3));
+        assert!(a.insert(5));
+        assert!(a.insert(9));
+        assert!(a.insert(11));
+
+        assert!(b.insert(-2));
+        assert!(b.insert(3));
+        assert!(b.insert(9));
+        assert!(b.insert(14));
+        assert!(b.insert(22));
+
+        let mut i = 0;
+        let expected = [-2, 1, 5, 11, 14, 22];
+        for x in a.symmetric_difference(&b) {
+            assert!(expected.contains(x));
+            i += 1
+        }
+        assert_eq!(i, expected.len());
+    }
+
+    #[test]
+    fn test_union() {
+        let mut a = HashSet::new();
+        let mut b = HashSet::new();
+
+        assert!(a.insert(1));
+        assert!(a.insert(3));
+        assert!(a.insert(5));
+        assert!(a.insert(9));
+        assert!(a.insert(11));
+        assert!(a.insert(16));
+        assert!(a.insert(19));
+        assert!(a.insert(24));
+
+        assert!(b.insert(-2));
+        assert!(b.insert(1));
+        assert!(b.insert(5));
+        assert!(b.insert(9));
+        assert!(b.insert(13));
+        assert!(b.insert(19));
+
+        let mut i = 0;
+        let expected = [-2, 1, 3, 5, 9, 11, 13, 16, 19, 24];
+        for x in a.union(&b) {
+            assert!(expected.contains(x));
+            i += 1
+        }
+        assert_eq!(i, expected.len());
+    }
+
+    #[test]
+    fn test_from_iter() {
+        let xs = [1, 2, 3, 4, 5, 6, 7, 8, 9];
+
+        let set: HashSet<int> = xs.iter().map(|&x| x).collect();
+
+        for x in xs.iter() {
+            assert!(set.contains(x));
+        }
+    }
+
+    #[test]
+    fn test_move_iter() {
+        let hs = {
+            let mut hs = HashSet::new();
+
+            hs.insert('a');
+            hs.insert('b');
+
+            hs
+        };
+
+        let v = hs.move_iter().collect::<Vec<char>>();
+        assert!(['a', 'b'] == v.as_slice() || ['b', 'a'] == v.as_slice());
+    }
+
+    #[test]
+    fn test_eq() {
+        // These constants once happened to expose a bug in insert().
+        // I'm keeping them around to prevent a regression.
+        let mut s1 = HashSet::new();
+
+        s1.insert(1);
+        s1.insert(2);
+        s1.insert(3);
+
+        let mut s2 = HashSet::new();
+
+        s2.insert(1);
+        s2.insert(2);
+
+        assert!(s1 != s2);
+
+        s2.insert(3);
+
+        assert_eq!(s1, s2);
+    }
+
+    #[test]
+    fn test_show() {
+        let mut set: HashSet<int> = HashSet::new();
+        let empty: HashSet<int> = HashSet::new();
+
+        set.insert(1);
+        set.insert(2);
+
+        let set_str = format!("{}", set);
+
+        assert!(set_str == "{1, 2}".to_string() || set_str == "{2, 1}".to_string());
+        assert_eq!(format!("{}", empty), "{}".to_string());
+    }
+}
+
+#[cfg(test)]
+mod bench {
+    extern crate test;
+    use self::test::Bencher;
+    use std::iter::{range_inclusive};
+
+    #[bench]
+    fn new_drop(b : &mut Bencher) {
+        use super::HashMap;
+
+        b.iter(|| {
+            let m : HashMap<int, int> = HashMap::new();
+            assert_eq!(m.len(), 0);
+        })
+    }
+
+    #[bench]
+    fn new_insert_drop(b : &mut Bencher) {
+        use super::HashMap;
+
+        b.iter(|| {
+            let mut m = HashMap::new();
+            m.insert(0, 0);
+            assert_eq!(m.len(), 1);
+        })
+    }
+
+    #[bench]
+    fn insert(b: &mut Bencher) {
+        use super::HashMap;
+
+        let mut m = HashMap::new();
+
+        for i in range_inclusive(1, 1000) {
+            m.insert(i, i);
+        }
+
+        let mut k = 1001;
+
+        b.iter(|| {
+            m.insert(k, k);
+            k += 1;
+        });
+    }
+
+    #[bench]
+    fn find_existing(b: &mut Bencher) {
+        use super::HashMap;
+
+        let mut m = HashMap::new();
+
+        for i in range_inclusive(1, 1000) {
+            m.insert(i, i);
+        }
+
+        b.iter(|| {
+            for i in range_inclusive(1, 1000) {
+                m.contains_key(&i);
+            }
+        });
+    }
+
+    #[bench]
+    fn find_nonexisting(b: &mut Bencher) {
+        use super::HashMap;
+
+        let mut m = HashMap::new();
+
+        for i in range_inclusive(1, 1000) {
+            m.insert(i, i);
+        }
+
+        b.iter(|| {
+            for i in range_inclusive(1001, 2000) {
+                m.contains_key(&i);
+            }
+        });
+    }
+
+    #[bench]
+    fn hashmap_as_queue(b: &mut Bencher) {
+        use super::HashMap;
+
+        let mut m = HashMap::new();
+
+        for i in range_inclusive(1, 1000) {
+            m.insert(i, i);
+        }
+
+        let mut k = 1;
+
+        b.iter(|| {
+            m.pop(&k);
+            m.insert(k + 1000, k + 1000);
+            k += 1;
+        });
+    }
+
+    #[bench]
+    fn find_pop_insert(b: &mut Bencher) {
+        use super::HashMap;
+
+        let mut m = HashMap::new();
+
+        for i in range_inclusive(1, 1000) {
+            m.insert(i, i);
+        }
+
+        let mut k = 1;
+
+        b.iter(|| {
+            m.find(&(k + 400));
+            m.find(&(k + 2000));
+            m.pop(&k);
+            m.insert(k + 1000, k + 1000);
+            k += 1;
+        })
+    }
+}
diff --git a/src/libstd/collections/lru_cache.rs b/src/libstd/collections/lru_cache.rs
new file mode 100644
index 00000000000..09511316a67
--- /dev/null
+++ b/src/libstd/collections/lru_cache.rs
@@ -0,0 +1,348 @@
+// Copyright 2013 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 cache that holds a limited number of key-value pairs. When the
+//! capacity of the cache is exceeded, the least-recently-used
+//! (where "used" means a look-up or putting the pair into the cache)
+//! pair is automatically removed.
+//!
+//! # Example
+//!
+//! ```rust
+//! use collections::LruCache;
+//!
+//! let mut cache: LruCache<int, int> = LruCache::new(2);
+//! cache.put(1, 10);
+//! cache.put(2, 20);
+//! cache.put(3, 30);
+//! assert!(cache.get(&1).is_none());
+//! assert_eq!(*cache.get(&2).unwrap(), 20);
+//! assert_eq!(*cache.get(&3).unwrap(), 30);
+//!
+//! cache.put(2, 22);
+//! assert_eq!(*cache.get(&2).unwrap(), 22);
+//!
+//! cache.put(6, 60);
+//! assert!(cache.get(&3).is_none());
+//!
+//! cache.change_capacity(1);
+//! assert!(cache.get(&2).is_none());
+//! ```
+
+use cmp::{Eq, TotalEq};
+use collections::HashMap;
+use container::{Container, Mutable, MutableMap};
+use fmt;
+use hash::Hash;
+use iter::{range, Iterator};
+use mem;
+use ops::Drop;
+use option::{Some, None, Option};
+use owned::Box;
+use ptr;
+use result::{Ok, Err};
+
+struct KeyRef<K> { k: *K }
+
+struct LruEntry<K, V> {
+    next: *mut LruEntry<K, V>,
+    prev: *mut LruEntry<K, V>,
+    key: K,
+    value: V,
+}
+
+/// An LRU Cache.
+pub struct LruCache<K, V> {
+    map: HashMap<KeyRef<K>, Box<LruEntry<K, V>>>,
+    max_size: uint,
+    head: *mut LruEntry<K, V>,
+}
+
+impl<S, K: Hash<S>> Hash<S> for KeyRef<K> {
+    fn hash(&self, state: &mut S) {
+        unsafe { (*self.k).hash(state) }
+    }
+}
+
+impl<K: PartialEq> PartialEq for KeyRef<K> {
+    fn eq(&self, other: &KeyRef<K>) -> bool {
+        unsafe{ (*self.k).eq(&*other.k) }
+    }
+}
+
+impl<K: Eq> Eq for KeyRef<K> {}
+
+impl<K, V> LruEntry<K, V> {
+    fn new(k: K, v: V) -> LruEntry<K, V> {
+        LruEntry {
+            key: k,
+            value: v,
+            next: ptr::mut_null(),
+            prev: ptr::mut_null(),
+        }
+    }
+}
+
+impl<K: Hash + Eq, V> LruCache<K, V> {
+    /// Create an LRU Cache that holds at most `capacity` items.
+    pub fn new(capacity: uint) -> LruCache<K, V> {
+        let cache = LruCache {
+            map: HashMap::new(),
+            max_size: capacity,
+            head: unsafe{ mem::transmute(box mem::uninitialized::<LruEntry<K, V>>()) },
+        };
+        unsafe {
+            (*cache.head).next = cache.head;
+            (*cache.head).prev = cache.head;
+        }
+        return cache;
+    }
+
+    /// Put a key-value pair into cache.
+    pub fn put(&mut self, k: K, v: V) {
+        let (node_ptr, node_opt) = match self.map.find_mut(&KeyRef{k: &k}) {
+            Some(node) => {
+                node.value = v;
+                let node_ptr: *mut LruEntry<K, V> = &mut **node;
+                (node_ptr, None)
+            }
+            None => {
+                let mut node = box LruEntry::new(k, v);
+                let node_ptr: *mut LruEntry<K, V> = &mut *node;
+                (node_ptr, Some(node))
+            }
+        };
+        match node_opt {
+            None => {
+                // Existing node, just update LRU position
+                self.detach(node_ptr);
+                self.attach(node_ptr);
+            }
+            Some(node) => {
+                let keyref = unsafe { &(*node_ptr).key };
+                self.map.swap(KeyRef{k: keyref}, node);
+                self.attach(node_ptr);
+                if self.len() > self.capacity() {
+                    self.remove_lru();
+                }
+            }
+        }
+    }
+
+    /// Return a value corresponding to the key in the cache.
+    pub fn get<'a>(&'a mut self, k: &K) -> Option<&'a V> {
+        let (value, node_ptr_opt) = match self.map.find_mut(&KeyRef{k: k}) {
+            None => (None, None),
+            Some(node) => {
+                let node_ptr: *mut LruEntry<K, V> = &mut **node;
+                (Some(unsafe { &(*node_ptr).value }), Some(node_ptr))
+            }
+        };
+        match node_ptr_opt {
+            None => (),
+            Some(node_ptr) => {
+                self.detach(node_ptr);
+                self.attach(node_ptr);
+            }
+        }
+        return value;
+    }
+
+    /// Remove and return a value corresponding to the key from the cache.
+    pub fn pop(&mut self, k: &K) -> Option<V> {
+        match self.map.pop(&KeyRef{k: k}) {
+            None => None,
+            Some(lru_entry) => Some(lru_entry.value)
+        }
+    }
+
+    /// Return the maximum number of key-value pairs the cache can hold.
+    pub fn capacity(&self) -> uint {
+        self.max_size
+    }
+
+    /// Change the number of key-value pairs the cache can hold. Remove
+    /// least-recently-used key-value pairs if necessary.
+    pub fn change_capacity(&mut self, capacity: uint) {
+        for _ in range(capacity, self.len()) {
+            self.remove_lru();
+        }
+        self.max_size = capacity;
+    }
+
+    #[inline]
+    fn remove_lru(&mut self) {
+        if self.len() > 0 {
+            let lru = unsafe { (*self.head).prev };
+            self.detach(lru);
+            self.map.pop(&KeyRef{k: unsafe { &(*lru).key }});
+        }
+    }
+
+    #[inline]
+    fn detach(&mut self, node: *mut LruEntry<K, V>) {
+        unsafe {
+            (*(*node).prev).next = (*node).next;
+            (*(*node).next).prev = (*node).prev;
+        }
+    }
+
+    #[inline]
+    fn attach(&mut self, node: *mut LruEntry<K, V>) {
+        unsafe {
+            (*node).next = (*self.head).next;
+            (*node).prev = self.head;
+            (*self.head).next = node;
+            (*(*node).next).prev = node;
+        }
+    }
+}
+
+impl<A: fmt::Show + Hash + Eq, B: fmt::Show> fmt::Show for LruCache<A, B> {
+    /// Return a string that lists the key-value pairs from most-recently
+    /// used to least-recently used.
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        try!(write!(f, r"\{"));
+        let mut cur = self.head;
+        for i in range(0, self.len()) {
+            if i > 0 { try!(write!(f, ", ")) }
+            unsafe {
+                cur = (*cur).next;
+                try!(write!(f, "{}", (*cur).key));
+            }
+            try!(write!(f, ": "));
+            unsafe {
+                try!(write!(f, "{}", (*cur).value));
+            }
+        }
+        write!(f, r"\}")
+    }
+}
+
+impl<K: Hash + Eq, V> Container for LruCache<K, V> {
+    /// Return the number of key-value pairs in the cache.
+    fn len(&self) -> uint {
+        self.map.len()
+    }
+}
+
+impl<K: Hash + Eq, V> Mutable for LruCache<K, V> {
+    /// Clear the cache of all key-value pairs.
+    fn clear(&mut self) {
+        self.map.clear();
+    }
+}
+
+#[unsafe_destructor]
+impl<K, V> Drop for LruCache<K, V> {
+    fn drop(&mut self) {
+        unsafe {
+            let node: Box<LruEntry<K, V>> = mem::transmute(self.head);
+            // Prevent compiler from trying to drop the un-initialized field in the sigil node.
+            let box LruEntry { key: k, value: v, .. } = node;
+            mem::forget(k);
+            mem::forget(v);
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::LruCache;
+
+    fn assert_opt_eq<V: PartialEq>(opt: Option<&V>, v: V) {
+        assert!(opt.is_some());
+        assert!(opt.unwrap() == &v);
+    }
+
+    #[test]
+    fn test_put_and_get() {
+        let mut cache: LruCache<int, int> = LruCache::new(2);
+        cache.put(1, 10);
+        cache.put(2, 20);
+        assert_opt_eq(cache.get(&1), 10);
+        assert_opt_eq(cache.get(&2), 20);
+        assert_eq!(cache.len(), 2);
+    }
+
+    #[test]
+    fn test_put_update() {
+        let mut cache: LruCache<String, Vec<u8>> = LruCache::new(1);
+        cache.put("1".to_string(), vec![10, 10]);
+        cache.put("1".to_string(), vec![10, 19]);
+        assert_opt_eq(cache.get(&"1".to_string()), vec![10, 19]);
+        assert_eq!(cache.len(), 1);
+    }
+
+    #[test]
+    fn test_expire_lru() {
+        let mut cache: LruCache<String, String> = LruCache::new(2);
+        cache.put("foo1".to_string(), "bar1".to_string());
+        cache.put("foo2".to_string(), "bar2".to_string());
+        cache.put("foo3".to_string(), "bar3".to_string());
+        assert!(cache.get(&"foo1".to_string()).is_none());
+        cache.put("foo2".to_string(), "bar2update".to_string());
+        cache.put("foo4".to_string(), "bar4".to_string());
+        assert!(cache.get(&"foo3".to_string()).is_none());
+    }
+
+    #[test]
+    fn test_pop() {
+        let mut cache: LruCache<int, int> = LruCache::new(2);
+        cache.put(1, 10);
+        cache.put(2, 20);
+        assert_eq!(cache.len(), 2);
+        let opt1 = cache.pop(&1);
+        assert!(opt1.is_some());
+        assert_eq!(opt1.unwrap(), 10);
+        assert!(cache.get(&1).is_none());
+        assert_eq!(cache.len(), 1);
+    }
+
+    #[test]
+    fn test_change_capacity() {
+        let mut cache: LruCache<int, int> = LruCache::new(2);
+        assert_eq!(cache.capacity(), 2);
+        cache.put(1, 10);
+        cache.put(2, 20);
+        cache.change_capacity(1);
+        assert!(cache.get(&1).is_none());
+        assert_eq!(cache.capacity(), 1);
+    }
+
+    #[test]
+    fn test_to_str() {
+        let mut cache: LruCache<int, int> = LruCache::new(3);
+        cache.put(1, 10);
+        cache.put(2, 20);
+        cache.put(3, 30);
+        assert_eq!(cache.to_str(), "{3: 30, 2: 20, 1: 10}".to_string());
+        cache.put(2, 22);
+        assert_eq!(cache.to_str(), "{2: 22, 3: 30, 1: 10}".to_string());
+        cache.put(6, 60);
+        assert_eq!(cache.to_str(), "{6: 60, 2: 22, 3: 30}".to_string());
+        cache.get(&3);
+        assert_eq!(cache.to_str(), "{3: 30, 6: 60, 2: 22}".to_string());
+        cache.change_capacity(2);
+        assert_eq!(cache.to_str(), "{3: 30, 6: 60}".to_string());
+    }
+
+    #[test]
+    fn test_clear() {
+        let mut cache: LruCache<int, int> = LruCache::new(2);
+        cache.put(1, 10);
+        cache.put(2, 20);
+        cache.clear();
+        assert!(cache.get(&1).is_none());
+        assert!(cache.get(&2).is_none());
+        assert_eq!(cache.to_str(), "{}".to_string());
+    }
+}
diff --git a/src/libstd/collections/mod.rs b/src/libstd/collections/mod.rs
new file mode 100644
index 00000000000..16a6a35d9d5
--- /dev/null
+++ b/src/libstd/collections/mod.rs
@@ -0,0 +1,25 @@
+// Copyright 2013-2014 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.
+
+/*!
+ * Collection types.
+ */
+
+pub use core_collections::{Bitv, BitvSet, BTree, Deque, DList, EnumSet};
+pub use core_collections::{PriorityQueue, RingBuf, SmallIntMap};
+pub use core_collections::{TreeMap, TreeSet, TrieMap, TrieSet};
+pub use core_collections::{bitv, btree, deque, dlist, enum_set};
+pub use core_collections::{priority_queue, ringbuf, smallintmap, treemap, trie};
+
+pub use self::hashmap::{HashMap, HashSet};
+pub use self::lru_cache::LruCache;
+
+pub mod hashmap;
+pub mod lru_cache;