diff --git a/src/grammar/verify.rs b/src/grammar/verify.rs
index a4641c40165ac..159a62f011072 100644
--- a/src/grammar/verify.rs
+++ b/src/grammar/verify.rs
@@ -178,7 +178,7 @@ fn parse_antlr_token(s: &str, tokens: &HashMap<String, Token>) -> TokenAndSpan {
     let toknum = m.name("toknum");
     let content = m.name("content");
 
-    let proto_tok = tokens.find_equiv(&toknum).expect(format!("didn't find token {} in the map",
+    let proto_tok = tokens.get(&toknum).expect(format!("didn't find token {} in the map",
                                                               toknum).as_slice());
 
     let nm = parse::token::intern(content);
diff --git a/src/libcollections/btree/map.rs b/src/libcollections/btree/map.rs
index 0b6d9e356b910..007e01ef9820c 100644
--- a/src/libcollections/btree/map.rs
+++ b/src/libcollections/btree/map.rs
@@ -21,6 +21,7 @@ use core::prelude::*;
 
 use self::StackOp::*;
 use super::node::*;
+use core::borrow::BorrowFrom;
 use std::hash::{Writer, Hash};
 use core::default::Default;
 use core::{iter, fmt, mem};
@@ -184,6 +185,9 @@ impl<K: Ord, V> BTreeMap<K, V> {
 
     /// Returns a reference to the value corresponding to the key.
     ///
+    /// The key may be any borrowed form of the map's key type, but the ordering
+    /// on the borrowed form *must* match the ordering on the key type.
+    ///
     /// # Example
     ///
     /// ```
@@ -195,7 +199,7 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// assert_eq!(map.get(&2), None);
     /// ```
     #[unstable = "matches collection reform specification, waiting for dust to settle"]
-    pub fn get(&self, key: &K) -> Option<&V> {
+    pub fn get<Sized? Q>(&self, key: &Q) -> Option<&V> where Q: BorrowFrom<K> + Ord {
         let mut cur_node = &self.root;
         loop {
             match cur_node.search(key) {
@@ -213,6 +217,9 @@ impl<K: Ord, V> BTreeMap<K, V> {
 
     /// Returns true if the map contains a value for the specified key.
     ///
+    /// The key may be any borrowed form of the map's key type, but the ordering
+    /// on the borrowed form *must* match the ordering on the key type.
+    ///
     /// # Example
     ///
     /// ```
@@ -224,7 +231,7 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// assert_eq!(map.contains_key(&2), false);
     /// ```
     #[unstable = "matches collection reform specification, waiting for dust to settle"]
-    pub fn contains_key(&self, key: &K) -> bool {
+    pub fn contains_key<Sized? Q>(&self, key: &Q) -> bool where Q: BorrowFrom<K> + Ord {
         self.get(key).is_some()
     }
 
@@ -236,6 +243,9 @@ impl<K: Ord, V> BTreeMap<K, V> {
 
     /// Returns a mutable reference to the value corresponding to the key.
     ///
+    /// The key may be any borrowed form of the map's key type, but the ordering
+    /// on the borrowed form *must* match the ordering on the key type.
+    ///
     /// # Example
     ///
     /// ```
@@ -251,7 +261,7 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// ```
     // See `get` for implementation notes, this is basically a copy-paste with mut's added
     #[unstable = "matches collection reform specification, waiting for dust to settle"]
-    pub fn get_mut(&mut self, key: &K) -> Option<&mut V> {
+    pub fn get_mut<Sized? Q>(&mut self, key: &Q) -> Option<&mut V> where Q: BorrowFrom<K> + Ord {
         // temp_node is a Borrowck hack for having a mutable value outlive a loop iteration
         let mut temp_node = &mut self.root;
         loop {
@@ -410,6 +420,9 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// Removes a key from the map, returning the value at the key if the key
     /// was previously in the map.
     ///
+    /// The key may be any borrowed form of the map's key type, but the ordering
+    /// on the borrowed form *must* match the ordering on the key type.
+    ///
     /// # Example
     ///
     /// ```
@@ -421,7 +434,7 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// assert_eq!(map.remove(&1), None);
     /// ```
     #[unstable = "matches collection reform specification, waiting for dust to settle"]
-    pub fn remove(&mut self, key: &K) -> Option<V> {
+    pub fn remove<Sized? Q>(&mut self, key: &Q) -> Option<V> where Q: BorrowFrom<K> + Ord {
         // See `swap` for a more thorough description of the stuff going on in here
         let mut stack = stack::PartialSearchStack::new(self);
         loop {
@@ -790,14 +803,18 @@ impl<K: Show, V: Show> Show for BTreeMap<K, V> {
     }
 }
 
-impl<K: Ord, V> Index<K, V> for BTreeMap<K, V> {
-    fn index(&self, key: &K) -> &V {
+impl<K: Ord, Sized? Q, V> Index<Q, V> for BTreeMap<K, V>
+    where Q: BorrowFrom<K> + Ord
+{
+    fn index(&self, key: &Q) -> &V {
         self.get(key).expect("no entry found for key")
     }
 }
 
-impl<K: Ord, V> IndexMut<K, V> for BTreeMap<K, V> {
-    fn index_mut(&mut self, key: &K) -> &mut V {
+impl<K: Ord, Sized? Q, V> IndexMut<Q, V> for BTreeMap<K, V>
+    where Q: BorrowFrom<K> + Ord
+{
+    fn index_mut(&mut self, key: &Q) -> &mut V {
         self.get_mut(key).expect("no entry found for key")
     }
 }
diff --git a/src/libcollections/btree/node.rs b/src/libcollections/btree/node.rs
index 6e9341231ad69..bdd7aa9c61172 100644
--- a/src/libcollections/btree/node.rs
+++ b/src/libcollections/btree/node.rs
@@ -19,6 +19,7 @@ use core::prelude::*;
 
 use core::{slice, mem, ptr};
 use core::iter::Zip;
+use core::borrow::BorrowFrom;
 
 use vec;
 use vec::Vec;
@@ -73,19 +74,19 @@ impl<K: Ord, V> Node<K, V> {
     /// Searches for the given key in the node. If it finds an exact match,
     /// `Found` will be yielded with the matching index. If it doesn't find an exact match,
     /// `GoDown` will be yielded with the index of the subtree the key must lie in.
-    pub fn search(&self, key: &K) -> SearchResult {
+    pub fn search<Sized? Q>(&self, key: &Q) -> SearchResult where Q: BorrowFrom<K> + Ord {
         // FIXME(Gankro): Tune when to search linear or binary based on B (and maybe K/V).
         // For the B configured as of this writing (B = 6), binary search was *significantly*
         // worse for uints.
         self.search_linear(key)
     }
 
-    fn search_linear(&self, key: &K) -> SearchResult {
+    fn search_linear<Sized? Q>(&self, key: &Q) -> SearchResult where Q: BorrowFrom<K> + Ord {
         for (i, k) in self.keys.iter().enumerate() {
-            match k.cmp(key) {
-                Less => {},
+            match key.cmp(BorrowFrom::borrow_from(k)) {
+                Greater => {},
                 Equal => return Found(i),
-                Greater => return GoDown(i),
+                Less => return GoDown(i),
             }
         }
         GoDown(self.len())
diff --git a/src/libcollections/btree/set.rs b/src/libcollections/btree/set.rs
index 56edf7719bb22..64ae4f6a50867 100644
--- a/src/libcollections/btree/set.rs
+++ b/src/libcollections/btree/set.rs
@@ -15,6 +15,7 @@ use core::prelude::*;
 
 use btree_map::{BTreeMap, Keys, MoveEntries};
 use std::hash::Hash;
+use core::borrow::BorrowFrom;
 use core::default::Default;
 use core::{iter, fmt};
 use core::iter::Peekable;
@@ -167,6 +168,10 @@ impl<T: Ord> BTreeSet<T> {
 
     /// Returns `true` if the set contains a value.
     ///
+    /// The value may be any borrowed form of the set's value type,
+    /// but the ordering on the borrowed form *must* match the
+    /// ordering on the value type.
+    ///
     /// # Example
     ///
     /// ```
@@ -177,7 +182,7 @@ impl<T: Ord> BTreeSet<T> {
     /// assert_eq!(set.contains(&4), false);
     /// ```
     #[unstable = "matches collection reform specification, waiting for dust to settle"]
-    pub fn contains(&self, value: &T) -> bool {
+    pub fn contains<Sized? Q>(&self, value: &Q) -> bool where Q: BorrowFrom<T> + Ord {
         self.map.contains_key(value)
     }
 
@@ -291,6 +296,10 @@ impl<T: Ord> BTreeSet<T> {
     /// Removes a value from the set. Returns `true` if the value was
     /// present in the set.
     ///
+    /// The value may be any borrowed form of the set's value type,
+    /// but the ordering on the borrowed form *must* match the
+    /// ordering on the value type.
+    ///
     /// # Example
     ///
     /// ```
@@ -303,7 +312,7 @@ impl<T: Ord> BTreeSet<T> {
     /// assert_eq!(set.remove(&2), false);
     /// ```
     #[unstable = "matches collection reform specification, waiting for dust to settle"]
-    pub fn remove(&mut self, value: &T) -> bool {
+    pub fn remove<Sized? Q>(&mut self, value: &Q) -> bool where Q: BorrowFrom<T> + Ord {
         self.map.remove(value).is_some()
     }
 }
diff --git a/src/libcollections/slice.rs b/src/libcollections/slice.rs
index 000c3e08c677b..132a07af6b67b 100644
--- a/src/libcollections/slice.rs
+++ b/src/libcollections/slice.rs
@@ -89,6 +89,7 @@
 
 use self::Direction::*;
 use alloc::boxed::Box;
+use core::borrow::{BorrowFrom, BorrowFromMut};
 use core::cmp;
 use core::kinds::Sized;
 use core::mem::size_of;
@@ -647,6 +648,16 @@ impl<T> SliceAllocPrelude<T> for [T] {
     }
 }
 
+#[unstable = "trait is unstable"]
+impl<T> BorrowFrom<Vec<T>> for [T] {
+    fn borrow_from(owned: &Vec<T>) -> &[T] { owned[] }
+}
+
+#[unstable = "trait is unstable"]
+impl<T> BorrowFromMut<Vec<T>> for [T] {
+    fn borrow_from_mut(owned: &mut Vec<T>) -> &mut [T] { owned[mut] }
+}
+
 /// Unsafe operations
 pub mod raw {
     pub use core::slice::raw::{buf_as_slice, mut_buf_as_slice};
diff --git a/src/libcollections/str.rs b/src/libcollections/str.rs
index ae8e92fc6cb9d..9ae009d8f6a59 100644
--- a/src/libcollections/str.rs
+++ b/src/libcollections/str.rs
@@ -54,7 +54,7 @@
 pub use self::MaybeOwned::*;
 use self::RecompositionState::*;
 use self::DecompositionType::*;
-
+use core::borrow::BorrowFrom;
 use core::default::Default;
 use core::fmt;
 use core::cmp;
@@ -604,6 +604,11 @@ impl<'a> fmt::Show for MaybeOwned<'a> {
     }
 }
 
+#[unstable = "trait is unstable"]
+impl BorrowFrom<String> for str {
+    fn borrow_from(owned: &String) -> &str { owned[] }
+}
+
 /// Unsafe string operations.
 pub mod raw {
     pub use core::str::raw::{from_utf8, c_str_to_static_slice, slice_bytes};
diff --git a/src/libcollections/tree/map.rs b/src/libcollections/tree/map.rs
index 50bfeafc43e29..119268c27eeac 100644
--- a/src/libcollections/tree/map.rs
+++ b/src/libcollections/tree/map.rs
@@ -11,6 +11,8 @@
 use core::prelude::*;
 
 use alloc::boxed::Box;
+
+use core::borrow::BorrowFrom;
 use core::default::Default;
 use core::fmt;
 use core::fmt::Show;
@@ -188,16 +190,16 @@ impl<K: Ord, V> Default for TreeMap<K,V> {
     fn default() -> TreeMap<K, V> { TreeMap::new() }
 }
 
-impl<K: Ord, V> Index<K, V> for TreeMap<K, V> {
+impl<K: Ord, Sized? Q, V> Index<Q, V> for TreeMap<K, V> where Q: BorrowFrom<K> + Ord {
     #[inline]
-    fn index<'a>(&'a self, i: &K) -> &'a V {
+    fn index<'a>(&'a self, i: &Q) -> &'a V {
         self.get(i).expect("no entry found for key")
     }
 }
 
-impl<K: Ord, V> IndexMut<K, V> for TreeMap<K, V> {
+impl<K: Ord, Sized? Q, V> IndexMut<Q, V> for TreeMap<K, V> where Q: BorrowFrom<K> + Ord {
     #[inline]
-    fn index_mut<'a>(&'a mut self, i: &K) -> &'a mut V {
+    fn index_mut<'a>(&'a mut self, i: &Q) -> &'a mut V {
         self.get_mut(i).expect("no entry found for key")
     }
 }
@@ -446,6 +448,9 @@ impl<K: Ord, V> TreeMap<K, V> {
 
     /// Returns a reference to the value corresponding to the key.
     ///
+    /// The key may be any borrowed form of the map's key type, but the ordering
+    /// on the borrowed form *must* match the ordering on the key type.
+    ///
     /// # Example
     ///
     /// ```
@@ -458,12 +463,17 @@ impl<K: Ord, V> TreeMap<K, V> {
     /// ```
     #[inline]
     #[unstable = "matches collection reform specification, waiting for dust to settle"]
-    pub fn get(&self, key: &K) -> Option<&V> {
-        tree_find_with(&self.root, |k2| key.cmp(k2))
+    pub fn get<Sized? Q>(&self, key: &Q) -> Option<&V>
+        where Q: BorrowFrom<K> + Ord
+    {
+        tree_find_with(&self.root, |k2| key.cmp(BorrowFrom::borrow_from(k2)))
     }
 
     /// Returns true if the map contains a value for the specified key.
     ///
+    /// The key may be any borrowed form of the map's key type, but the ordering
+    /// on the borrowed form *must* match the ordering on the key type.
+    ///
     /// # Example
     ///
     /// ```
@@ -476,7 +486,9 @@ impl<K: Ord, V> TreeMap<K, V> {
     /// ```
     #[inline]
     #[unstable = "matches collection reform specification, waiting for dust to settle"]
-    pub fn contains_key(&self, key: &K) -> bool {
+    pub fn contains_key<Sized? Q>(&self, key: &Q) -> bool
+        where Q: BorrowFrom<K> + Ord
+    {
         self.get(key).is_some()
     }
 
@@ -488,6 +500,9 @@ impl<K: Ord, V> TreeMap<K, V> {
 
     /// Returns a mutable reference to the value corresponding to the key.
     ///
+    /// The key may be any borrowed form of the map's key type, but the ordering
+    /// on the borrowed form *must* match the ordering on the key type.
+    ///
     /// # Example
     ///
     /// ```
@@ -503,8 +518,10 @@ impl<K: Ord, V> TreeMap<K, V> {
     /// ```
     #[inline]
     #[unstable = "matches collection reform specification, waiting for dust to settle"]
-    pub fn get_mut(&mut self, key: &K) -> Option<&mut V> {
-        tree_find_with_mut(&mut self.root, |x| key.cmp(x))
+    pub fn get_mut<Sized? Q>(&mut self, key: &Q) -> Option<&mut V>
+        where Q: BorrowFrom<K> + Ord
+    {
+        tree_find_with_mut(&mut self.root, |x| key.cmp(BorrowFrom::borrow_from(x)))
     }
 
     /// Deprecated: Renamed to `insert`.
@@ -545,6 +562,9 @@ impl<K: Ord, V> TreeMap<K, V> {
     /// Removes a key from the map, returning the value at the key if the key
     /// was previously in the map.
     ///
+    /// The key may be any borrowed form of the map's key type, but the ordering
+    /// on the borrowed form *must* match the ordering on the key type.
+    ///
     /// # Example
     ///
     /// ```
@@ -556,7 +576,9 @@ impl<K: Ord, V> TreeMap<K, V> {
     /// assert_eq!(map.remove(&1), None);
     /// ```
     #[unstable = "matches collection reform specification, waiting for dust to settle"]
-    pub fn remove(&mut self, key: &K) -> Option<V> {
+    pub fn remove<Sized? Q>(&mut self, key: &Q) -> Option<V>
+        where Q: BorrowFrom<K> + Ord
+    {
         let ret = remove(&mut self.root, key);
         if ret.is_some() { self.length -= 1 }
         ret
@@ -589,6 +611,7 @@ impl<K, V> TreeMap<K, V> {
     /// assert_eq!((*ua.unwrap()).as_slice(), "Curl-Rust/0.1");
     /// ```
     #[inline]
+    #[experimental = "likely to be renamed, may be removed"]
     pub fn find_with(&self, f:|&K| -> Ordering) -> Option<&V> {
         tree_find_with(&self.root, f)
     }
@@ -613,6 +636,7 @@ impl<K, V> TreeMap<K, V> {
     /// assert_eq!(t.get(&"User-Agent"), Some(&new_ua));
     /// ```
     #[inline]
+    #[experimental = "likely to be renamed, may be removed"]
     pub fn find_with_mut<'a>(&'a mut self, f:|&K| -> Ordering) -> Option<&'a mut V> {
         tree_find_with_mut(&mut self.root, f)
     }
@@ -1168,10 +1192,11 @@ fn insert<K: Ord, V>(node: &mut Option<Box<TreeNode<K, V>>>,
     }
 }
 
-fn remove<K: Ord, V>(node: &mut Option<Box<TreeNode<K, V>>>,
-                          key: &K) -> Option<V> {
+fn remove<K, Sized? Q, V>(node: &mut Option<Box<TreeNode<K, V>>>, key: &Q) -> Option<V>
+    where K: Ord, Q: BorrowFrom<K> + Ord
+{
     fn heir_swap<K: Ord, V>(node: &mut Box<TreeNode<K, V>>,
-                                 child: &mut Option<Box<TreeNode<K, V>>>) {
+                            child: &mut Option<Box<TreeNode<K, V>>>) {
         // *could* be done without recursion, but it won't borrow check
         for x in child.iter_mut() {
             if x.right.is_some() {
@@ -1188,7 +1213,7 @@ fn remove<K: Ord, V>(node: &mut Option<Box<TreeNode<K, V>>>,
         return None; // bottom of tree
       }
       Some(ref mut save) => {
-        let (ret, rebalance) = match key.cmp(&save.key) {
+        let (ret, rebalance) = match key.cmp(BorrowFrom::borrow_from(&save.key)) {
           Less => (remove(&mut save.left, key), true),
           Greater => (remove(&mut save.right, key), true),
           Equal => {
@@ -1918,4 +1943,3 @@ mod bench {
         bench_iter(b, 100000);
     }
 }
-
diff --git a/src/libcollections/tree/mod.rs b/src/libcollections/tree/mod.rs
index ac8279c92feeb..20823a2affc7f 100644
--- a/src/libcollections/tree/mod.rs
+++ b/src/libcollections/tree/mod.rs
@@ -33,4 +33,4 @@
 //! ```
 
 pub mod map;
-pub mod set;
\ No newline at end of file
+pub mod set;
diff --git a/src/libcollections/tree/set.rs b/src/libcollections/tree/set.rs
index abfaeed7e7ed0..6988b929df689 100644
--- a/src/libcollections/tree/set.rs
+++ b/src/libcollections/tree/set.rs
@@ -10,6 +10,7 @@
 
 use core::prelude::*;
 
+use core::borrow::BorrowFrom;
 use core::default::Default;
 use core::fmt;
 use core::fmt::Show;
@@ -396,6 +397,10 @@ impl<T: Ord> TreeSet<T> {
 
     /// Returns `true` if the set contains a value.
     ///
+    /// The value may be any borrowed form of the set's value type,
+    /// but the ordering on the borrowed form *must* match the
+    /// ordering on the value type.
+    ///
     /// # Example
     ///
     /// ```
@@ -407,7 +412,9 @@ impl<T: Ord> TreeSet<T> {
     /// ```
     #[inline]
     #[unstable = "matches collection reform specification, waiting for dust to settle"]
-    pub fn contains(&self, value: &T) -> bool {
+    pub fn contains<Sized? Q>(&self, value: &Q) -> bool
+        where Q: Ord + BorrowFrom<T>
+    {
         self.map.contains_key(value)
     }
 
@@ -519,6 +526,10 @@ impl<T: Ord> TreeSet<T> {
     /// Removes a value from the set. Returns `true` if the value was
     /// present in the set.
     ///
+    /// The value may be any borrowed form of the set's value type,
+    /// but the ordering on the borrowed form *must* match the
+    /// ordering on the value type.
+    ///
     /// # Example
     ///
     /// ```
@@ -532,7 +543,11 @@ impl<T: Ord> TreeSet<T> {
     /// ```
     #[inline]
     #[unstable = "matches collection reform specification, waiting for dust to settle"]
-    pub fn remove(&mut self, value: &T) -> bool { self.map.remove(value).is_some() }
+    pub fn remove<Sized? Q>(&mut self, value: &Q) -> bool
+        where Q: Ord + BorrowFrom<T>
+    {
+        self.map.remove(value).is_some()
+    }
 }
 
 /// A lazy forward iterator over a set.
diff --git a/src/libcollections/trie/mod.rs b/src/libcollections/trie/mod.rs
index f0f8f00a6a0db..9dcb182cd2675 100644
--- a/src/libcollections/trie/mod.rs
+++ b/src/libcollections/trie/mod.rs
@@ -17,4 +17,4 @@
 //! `TrieMap` is ordered.
 
 pub mod map;
-pub mod set;
\ No newline at end of file
+pub mod set;
diff --git a/src/libcore/borrow.rs b/src/libcore/borrow.rs
new file mode 100644
index 0000000000000..34cf55334aef3
--- /dev/null
+++ b/src/libcore/borrow.rs
@@ -0,0 +1,126 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! A module for working with borrowed data.
+//!
+//! # The `BorrowFrom` traits
+//!
+//! In general, there may be several ways to "borrow" a piece of data.  The
+//! typical ways of borrowing a type `T` are `&T` (a shared borrow) and `&mut T`
+//! (a mutable borrow). But types like `Vec<T>` provide additional kinds of
+//! borrows: the borrowed slices `&[T]` and `&mut [T]`.
+//!
+//! When writing generic code, it is often desirable to abstract over all ways
+//! of borrowing data from a given type. That is the role of the `BorrowFrom`
+//! trait: if `T: BorrowFrom<U>`, then `&T` can be borrowed from `&U`.  A given
+//! type can be borrowed as multiple different types. In particular, `Vec<T>:
+//! BorrowFrom<Vec<T>>` and `[T]: BorrowFrom<Vec<T>>`.
+//!
+//! # The `ToOwned` trait
+//!
+//! Some types make it possible to go from borrowed to owned, usually by
+//! implementing the `Clone` trait. But `Clone` works only for going from `&T`
+//! to `T`. The `ToOwned` trait generalizes `Clone` to construct owned data
+//! from any borrow of a given type.
+//!
+//! # The `Cow` (clone-on-write) type
+//!
+//! The type `Cow` is a smart pointer providing clone-on-write functionality: it
+//! can enclose and provide immutable access to borrowed data, and clone the
+//! data lazily when mutation or ownership is required. The type is designed to
+//! work with general borrowed data via the `BorrowFrom` trait.
+//!
+//! `Cow` implements both `Deref` and `DerefMut`, which means that you can call
+//! methods directly on the data it encloses. The first time a mutable reference
+//! is required, the data will be cloned (via `to_owned`) if it is not
+//! already owned.
+
+#![unstable = "recently added as part of collections reform"]
+
+use clone::Clone;
+use kinds::Sized;
+use ops::Deref;
+
+/// A trait for borrowing data.
+pub trait BorrowFrom<Sized? Owned> for Sized? {
+    /// Immutably borrow from an owned value.
+    fn borrow_from(owned: &Owned) -> &Self;
+}
+
+/// A trait for mutably borrowing data.
+pub trait BorrowFromMut<Sized? Owned> for Sized? : BorrowFrom<Owned> {
+    /// Mutably borrow from an owned value.
+    fn borrow_from_mut(owned: &mut Owned) -> &mut Self;
+}
+
+impl<Sized? T> BorrowFrom<T> for T {
+    fn borrow_from(owned: &T) -> &T { owned }
+}
+
+impl<Sized? T> BorrowFromMut<T> for T {
+    fn borrow_from_mut(owned: &mut T) -> &mut T { owned }
+}
+
+impl BorrowFrom<&'static str> for str {
+    fn borrow_from<'a>(owned: &'a &'static str) -> &'a str { &**owned }
+}
+
+/// A generalization of Clone to borrowed data.
+pub trait ToOwned<Owned> for Sized?: BorrowFrom<Owned> {
+    /// Create owned data from borrowed data, usually by copying.
+    fn to_owned(&self) -> Owned;
+}
+
+impl<T> ToOwned<T> for T where T: Clone {
+    fn to_owned(&self) -> T { self.clone() }
+}
+
+/// A clone-on-write smart pointer.
+pub enum Cow<'a, T, B: 'a> where B: ToOwned<T> {
+    /// Borrowed data.
+    Borrowed(&'a B),
+
+    /// Owned data.
+    Owned(T)
+}
+
+impl<'a, T, B> Cow<'a, T, B> where B: ToOwned<T> {
+    /// Acquire a mutable reference to the owned form of the data.
+    ///
+    /// Copies the data if it is not already owned.
+    pub fn to_mut(&mut self) -> &mut T {
+        match *self {
+            Borrowed(borrowed) => {
+                *self = Owned(borrowed.to_owned());
+                self.to_mut()
+            }
+            Owned(ref mut owned) => owned
+        }
+    }
+
+    /// Extract the owned data.
+    ///
+    /// Copies the data if it is not already owned.
+    pub fn into_owned(self) -> T {
+        match self {
+            Borrowed(borrowed) => borrowed.to_owned(),
+            Owned(owned) => owned
+        }
+    }
+}
+
+impl<'a, T, B> Deref<B> for Cow<'a, T, B> where B: ToOwned<T>  {
+    fn deref(&self) -> &B {
+        match *self {
+            Borrowed(borrowed) => borrowed,
+            Owned(ref owned) => BorrowFrom::borrow_from(owned)
+        }
+    }
+}
diff --git a/src/libcore/lib.rs b/src/libcore/lib.rs
index 9689f7cdd7114..5e3c74477d15c 100644
--- a/src/libcore/lib.rs
+++ b/src/libcore/lib.rs
@@ -108,6 +108,7 @@ pub mod default;
 pub mod any;
 pub mod atomic;
 pub mod bool;
+pub mod borrow;
 pub mod cell;
 pub mod char;
 pub mod panicking;
diff --git a/src/libcore/ops.rs b/src/libcore/ops.rs
index 3a2e178d2ea0a..b4bf5351e597b 100644
--- a/src/libcore/ops.rs
+++ b/src/libcore/ops.rs
@@ -638,7 +638,7 @@ shr_impl!(uint u8 u16 u32 u64 int i8 i16 i32 i64)
  * ```
  */
 #[lang="index"]
-pub trait Index<Index, Sized? Result> for Sized? {
+pub trait Index<Sized? Index, Sized? Result> for Sized? {
     /// The method for the indexing (`Foo[Bar]`) operation
     fn index<'a>(&'a self, index: &Index) -> &'a Result;
 }
@@ -669,7 +669,7 @@ pub trait Index<Index, Sized? Result> for Sized? {
  * ```
  */
 #[lang="index_mut"]
-pub trait IndexMut<Index, Result> for Sized? {
+pub trait IndexMut<Sized? Index, Result> for Sized? {
     /// The method for the indexing (`Foo[Bar]`) operation
     fn index_mut<'a>(&'a mut self, index: &Index) -> &'a mut Result;
 }
diff --git a/src/libregex/re.rs b/src/libregex/re.rs
index dbdb271874474..e1e2abcb1b7c5 100644
--- a/src/libregex/re.rs
+++ b/src/libregex/re.rs
@@ -726,7 +726,7 @@ impl<'t> Captures<'t> {
         match self.named {
             None => "",
             Some(ref h) => {
-                match h.find_equiv(name) {
+                match h.get(name) {
                     None => "",
                     Some(i) => self.at(*i),
                 }
diff --git a/src/librustc/lint/context.rs b/src/librustc/lint/context.rs
index 85cc413a1b801..aa6a021a210ef 100644
--- a/src/librustc/lint/context.rs
+++ b/src/librustc/lint/context.rs
@@ -165,7 +165,7 @@ impl LintStore {
     }
 
     fn register_renamed(&mut self, old_name: &str, new_name: &str) {
-        let target = match self.by_name.find_equiv(new_name) {
+        let target = match self.by_name.get(new_name) {
             Some(&Id(lint_id)) => lint_id.clone(),
             _ => panic!("invalid lint renaming of {} to {}", old_name, new_name)
         };
@@ -259,7 +259,7 @@ impl LintStore {
     fn find_lint(&self, lint_name: &str, sess: &Session, span: Option<Span>)
                  -> Option<LintId>
     {
-        match self.by_name.find_equiv(lint_name) {
+        match self.by_name.get(lint_name) {
             Some(&Id(lint_id)) => Some(lint_id),
             Some(&Renamed(ref new_name, lint_id)) => {
                 let warning = format!("lint {} has been renamed to {}",
@@ -282,7 +282,7 @@ impl LintStore {
                     match self.lint_groups.iter().map(|(&x, pair)| (x, pair.ref0().clone()))
                                                  .collect::<FnvHashMap<&'static str,
                                                                        Vec<LintId>>>()
-                                                 .find_equiv(lint_name.as_slice()) {
+                                                 .get(lint_name.as_slice()) {
                         Some(v) => {
                             v.iter()
                              .map(|lint_id: &LintId|
@@ -489,7 +489,7 @@ impl<'a, 'tcx> Context<'a, 'tcx> {
                     match self.lints.find_lint(lint_name.get(), &self.tcx.sess, Some(span)) {
                         Some(lint_id) => vec![(lint_id, level, span)],
                         None => {
-                            match self.lints.lint_groups.find_equiv(lint_name.get()) {
+                            match self.lints.lint_groups.get(lint_name.get()) {
                                 Some(&(ref v, _)) => v.iter()
                                                       .map(|lint_id: &LintId|
                                                            (*lint_id, level, span))
diff --git a/src/librustc/metadata/creader.rs b/src/librustc/metadata/creader.rs
index dbf0e4054085c..1cfe565fd7dee 100644
--- a/src/librustc/metadata/creader.rs
+++ b/src/librustc/metadata/creader.rs
@@ -321,7 +321,7 @@ fn existing_match(e: &Env, name: &str,
         // `source` stores paths which are normalized which may be different
         // from the strings on the command line.
         let source = e.sess.cstore.get_used_crate_source(cnum).unwrap();
-        match e.sess.opts.externs.find_equiv(name) {
+        match e.sess.opts.externs.get(name) {
             Some(locs) => {
                 let found = locs.iter().any(|l| {
                     let l = fs::realpath(&Path::new(l.as_slice())).ok();
diff --git a/src/librustc/metadata/decoder.rs b/src/librustc/metadata/decoder.rs
index 2af1f12a2cd82..e0110a81c179f 100644
--- a/src/librustc/metadata/decoder.rs
+++ b/src/librustc/metadata/decoder.rs
@@ -298,7 +298,7 @@ fn item_path(item_doc: rbml::Doc) -> Vec<ast_map::PathElem> {
 fn item_name(intr: &IdentInterner, item: rbml::Doc) -> ast::Name {
     let name = reader::get_doc(item, tag_paths_data_name);
     let string = name.as_str_slice();
-    match intr.find_equiv(string) {
+    match intr.find(string) {
         None => token::intern(string),
         Some(val) => val,
     }
@@ -1449,4 +1449,3 @@ pub fn is_associated_type(cdata: Cmd, id: ast::NodeId) -> bool {
         Some(item) => item_sort(item) == 't',
     }
 }
-
diff --git a/src/librustc/metadata/filesearch.rs b/src/librustc/metadata/filesearch.rs
index aeed829f8055b..f7d666e48150d 100644
--- a/src/librustc/metadata/filesearch.rs
+++ b/src/librustc/metadata/filesearch.rs
@@ -54,7 +54,7 @@ impl<'a> FileSearch<'a> {
         debug!("filesearch: searching lib path");
         let tlib_path = make_target_lib_path(self.sysroot,
                                     self.triple);
-        if !visited_dirs.contains_equiv(tlib_path.as_vec()) {
+        if !visited_dirs.contains(tlib_path.as_vec()) {
             match f(&tlib_path) {
                 FileMatches => found = true,
                 FileDoesntMatch => ()
@@ -69,9 +69,9 @@ impl<'a> FileSearch<'a> {
                 let tlib_path = make_rustpkg_lib_path(
                     self.sysroot, path, self.triple);
                 debug!("is {} in visited_dirs? {}", tlib_path.display(),
-                        visited_dirs.contains_equiv(&tlib_path.as_vec().to_vec()));
+                        visited_dirs.contains(&tlib_path.as_vec().to_vec()));
 
-                if !visited_dirs.contains_equiv(tlib_path.as_vec()) {
+                if !visited_dirs.contains(tlib_path.as_vec()) {
                     visited_dirs.insert(tlib_path.as_vec().to_vec());
                     // Don't keep searching the RUST_PATH if one match turns up --
                     // if we did, we'd get a "multiple matching crates" error
diff --git a/src/librustc/metadata/loader.rs b/src/librustc/metadata/loader.rs
index c3d92a19a2056..30bef248b4738 100644
--- a/src/librustc/metadata/loader.rs
+++ b/src/librustc/metadata/loader.rs
@@ -596,7 +596,7 @@ impl<'a> Context<'a> {
     }
 
     fn find_commandline_library(&mut self) -> Option<Library> {
-        let locs = match self.sess.opts.externs.find_equiv(self.crate_name) {
+        let locs = match self.sess.opts.externs.get(self.crate_name) {
             Some(s) => s,
             None => return None,
         };
diff --git a/src/librustc/middle/lang_items.rs b/src/librustc/middle/lang_items.rs
index 4fe770a1e0fb3..ffc8a83e42eda 100644
--- a/src/librustc/middle/lang_items.rs
+++ b/src/librustc/middle/lang_items.rs
@@ -132,7 +132,7 @@ impl<'a, 'v> Visitor<'v> for LanguageItemCollector<'a> {
     fn visit_item(&mut self, item: &ast::Item) {
         match extract(item.attrs.as_slice()) {
             Some(value) => {
-                let item_index = self.item_refs.find_equiv(&value).map(|x| *x);
+                let item_index = self.item_refs.get(value.get()).map(|x| *x);
 
                 match item_index {
                     Some(item_index) => {
diff --git a/src/librustc/middle/trans/base.rs b/src/librustc/middle/trans/base.rs
index b267d1d7f3e1e..cc51be31760a3 100644
--- a/src/librustc/middle/trans/base.rs
+++ b/src/librustc/middle/trans/base.rs
@@ -216,7 +216,7 @@ pub fn get_extern_fn(ccx: &CrateContext,
                      ty: Type,
                      output: ty::t)
                      -> ValueRef {
-    match externs.find_equiv(name) {
+    match externs.get(name) {
         Some(n) => return *n,
         None => {}
     }
@@ -226,7 +226,7 @@ pub fn get_extern_fn(ccx: &CrateContext,
 }
 
 fn get_extern_rust_fn(ccx: &CrateContext, fn_ty: ty::t, name: &str, did: ast::DefId) -> ValueRef {
-    match ccx.externs().borrow().find_equiv(name) {
+    match ccx.externs().borrow().get(name) {
         Some(n) => return *n,
         None => ()
     }
@@ -2983,7 +2983,7 @@ fn internalize_symbols(cx: &SharedCrateContext, reachable: &HashSet<String>) {
 
                 let name = CString::new(llvm::LLVMGetValueName(val), false);
                 if !declared.contains(&name) &&
-                   !reachable.contains_equiv(name.as_str().unwrap()) {
+                   !reachable.contains(name.as_str().unwrap()) {
                     llvm::SetLinkage(val, llvm::InternalLinkage);
                 }
             }
diff --git a/src/librustc/middle/trans/debuginfo.rs b/src/librustc/middle/trans/debuginfo.rs
index eaff757679aa0..de8e80b02757b 100644
--- a/src/librustc/middle/trans/debuginfo.rs
+++ b/src/librustc/middle/trans/debuginfo.rs
@@ -1677,7 +1677,7 @@ fn declare_local(bcx: Block,
 }
 
 fn file_metadata(cx: &CrateContext, full_path: &str) -> DIFile {
-    match debug_context(cx).created_files.borrow().find_equiv(full_path) {
+    match debug_context(cx).created_files.borrow().get(full_path) {
         Some(file_metadata) => return *file_metadata,
         None => ()
     }
diff --git a/src/librustc/middle/trans/type_.rs b/src/librustc/middle/trans/type_.rs
index d6a2d0c86a111..69861290b8d0d 100644
--- a/src/librustc/middle/trans/type_.rs
+++ b/src/librustc/middle/trans/type_.rs
@@ -336,7 +336,7 @@ impl TypeNames {
     }
 
     pub fn find_type(&self, s: &str) -> Option<Type> {
-        self.named_types.borrow().find_equiv(s).map(|x| Type::from_ref(*x))
+        self.named_types.borrow().get(s).map(|x| Type::from_ref(*x))
     }
 
     pub fn type_to_string(&self, ty: Type) -> String {
diff --git a/src/librustdoc/html/render.rs b/src/librustdoc/html/render.rs
index 1dd651481693f..8e9ac7095dae1 100644
--- a/src/librustdoc/html/render.rs
+++ b/src/librustdoc/html/render.rs
@@ -2122,7 +2122,7 @@ impl<'a> fmt::Show for Sidebar<'a> {
 
         fn block(w: &mut fmt::Formatter, short: &str, longty: &str,
                  cur: &clean::Item, cx: &Context) -> fmt::Result {
-            let items = match cx.sidebar.find_equiv(short) {
+            let items = match cx.sidebar.get(short) {
                 Some(items) => items.as_slice(),
                 None => return Ok(())
             };
diff --git a/src/libserialize/json.rs b/src/libserialize/json.rs
index 80238f6df415d..03e0452a4158d 100644
--- a/src/libserialize/json.rs
+++ b/src/libserialize/json.rs
@@ -901,7 +901,7 @@ impl Json {
     /// Otherwise, returns None.
     pub fn find<'a>(&'a self, key: &str) -> Option<&'a Json>{
         match self {
-            &Object(ref map) => map.find_with(|s| key.cmp(s.as_slice())),
+            &Object(ref map) => map.get(key),
             _ => None
         }
     }
@@ -926,7 +926,7 @@ impl Json {
     pub fn search<'a>(&'a self, key: &str) -> Option<&'a Json> {
         match self {
             &Object(ref map) => {
-                match map.find_with(|s| key.cmp(s.as_slice())) {
+                match map.get(key) {
                     Some(json_value) => Some(json_value),
                     None => {
                         for (_, v) in map.iter() {
diff --git a/src/libstd/collections/hash/map.rs b/src/libstd/collections/hash/map.rs
index 0471d5e902c21..69375e8d4f84e 100644
--- a/src/libstd/collections/hash/map.rs
+++ b/src/libstd/collections/hash/map.rs
@@ -14,6 +14,7 @@ pub use self::Entry::*;
 use self::SearchResult::*;
 use self::VacantEntryState::*;
 
+use borrow::BorrowFrom;
 use clone::Clone;
 use cmp::{max, Eq, Equiv, PartialEq};
 use default::Default;
@@ -142,7 +143,7 @@ impl DefaultResizePolicy {
 // about the size of rust executables.
 //
 // Annotate exceedingly likely branches in `table::make_hash`
-// and `search_hashed_generic` to reduce instruction cache pressure
+// and `search_hashed` to reduce instruction cache pressure
 // and mispredictions once it becomes possible (blocked on issue #11092).
 //
 // Shrinking the table could simply reallocate in place after moving buckets
@@ -286,10 +287,10 @@ pub struct HashMap<K, V, H = RandomSipHasher> {
 }
 
 /// Search for a pre-hashed key.
-fn search_hashed_generic<K, V, M: Deref<RawTable<K, V>>>(table: M,
-                                                         hash: &SafeHash,
-                                                         is_match: |&K| -> bool)
-                                                         -> SearchResult<K, V, M> {
+fn search_hashed<K, V, M: Deref<RawTable<K, V>>>(table: M,
+                                                 hash: &SafeHash,
+                                                 is_match: |&K| -> bool)
+                                                 -> SearchResult<K, V, M> {
     let size = table.size();
     let mut probe = Bucket::new(table, hash);
     let ib = probe.index();
@@ -325,11 +326,6 @@ fn search_hashed_generic<K, V, M: Deref<RawTable<K, V>>>(table: M,
     TableRef(probe.into_table())
 }
 
-fn search_hashed<K: Eq, V, M: Deref<RawTable<K, V>>>(table: M, hash: &SafeHash, k: &K)
-                                                     -> SearchResult<K, V, M> {
-    search_hashed_generic(table, hash, |k_| *k == *k_)
-}
-
 fn pop_internal<K, V>(starting_bucket: FullBucketMut<K, V>) -> (K, V) {
     let (empty, retkey, retval) = starting_bucket.take();
     let mut gap = match empty.gap_peek() {
@@ -432,26 +428,32 @@ impl<K: Eq + Hash<S>, V, S, H: Hasher<S>> HashMap<K, V, H> {
     fn search_equiv<'a, Sized? Q: Hash<S> + Equiv<K>>(&'a self, q: &Q)
                     -> Option<FullBucketImm<'a, K, V>> {
         let hash = self.make_hash(q);
-        search_hashed_generic(&self.table, &hash, |k| q.equiv(k)).into_option()
+        search_hashed(&self.table, &hash, |k| q.equiv(k)).into_option()
     }
 
     fn search_equiv_mut<'a, Sized? Q: Hash<S> + Equiv<K>>(&'a mut self, q: &Q)
                     -> Option<FullBucketMut<'a, K, V>> {
         let hash = self.make_hash(q);
-        search_hashed_generic(&mut self.table, &hash, |k| q.equiv(k)).into_option()
+        search_hashed(&mut self.table, &hash, |k| q.equiv(k)).into_option()
     }
 
     /// 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<'a>(&'a self, k: &K) -> Option<FullBucketImm<'a, K, V>> {
-        let hash = self.make_hash(k);
-        search_hashed(&self.table, &hash, k).into_option()
+    fn search<'a, Sized? Q>(&'a self, q: &Q) -> Option<FullBucketImm<'a, K, V>>
+        where Q: BorrowFrom<K> + Eq + Hash<S>
+    {
+        let hash = self.make_hash(q);
+        search_hashed(&self.table, &hash, |k| q.eq(BorrowFrom::borrow_from(k)))
+            .into_option()
     }
 
-    fn search_mut<'a>(&'a mut self, k: &K) -> Option<FullBucketMut<'a, K, V>> {
-        let hash = self.make_hash(k);
-        search_hashed(&mut self.table, &hash, k).into_option()
+    fn search_mut<'a, Sized? Q>(&'a mut self, q: &Q) -> Option<FullBucketMut<'a, K, V>>
+        where Q: BorrowFrom<K> + Eq + Hash<S>
+    {
+        let hash = self.make_hash(q);
+        search_hashed(&mut self.table, &hash, |k| q.eq(BorrowFrom::borrow_from(k)))
+            .into_option()
     }
 
     // The caller should ensure that invariants by Robin Hood Hashing hold.
@@ -748,18 +750,14 @@ impl<K: Eq + Hash<S>, V, S, H: Hasher<S>> HashMap<K, V, H> {
         }
     }
 
-    /// Return true if the map contains a value for the specified key,
-    /// using equivalence.
-    ///
-    /// See [pop_equiv](#method.pop_equiv) for an extended example.
+    /// Deprecated: use `contains_key` and `BorrowFrom` instead.
+    #[deprecated = "use contains_key and BorrowFrom instead"]
     pub fn contains_key_equiv<Sized? 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.
-    ///
-    /// See [pop_equiv](#method.pop_equiv) for an extended example.
+    /// Deprecated: use `get` and `BorrowFrom` instead.
+    #[deprecated = "use get and BorrowFrom instead"]
     pub fn find_equiv<'a, Sized? Q: Hash<S> + Equiv<K>>(&'a self, k: &Q) -> Option<&'a V> {
         match self.search_equiv(k) {
             None      => None,
@@ -770,52 +768,8 @@ impl<K: Eq + Hash<S>, V, S, H: Hasher<S>> HashMap<K, V, H> {
         }
     }
 
-    /// Remove an equivalent key from the map, returning the value at the
-    /// key if the key was previously in the map.
-    ///
-    /// # Example
-    ///
-    /// This is a slightly silly example where we define the number's
-    /// parity as the equivalence class. It is important that the
-    /// values hash the same, which is why we implement `Hash`.
-    ///
-    /// ```
-    /// use std::collections::HashMap;
-    /// use std::hash::Hash;
-    /// use std::hash::sip::SipState;
-    ///
-    /// #[deriving(Eq, PartialEq)]
-    /// struct EvenOrOdd {
-    ///     num: uint
-    /// };
-    ///
-    /// impl Hash for EvenOrOdd {
-    ///     fn hash(&self, state: &mut SipState) {
-    ///         let parity = self.num % 2;
-    ///         parity.hash(state);
-    ///     }
-    /// }
-    ///
-    /// impl Equiv<EvenOrOdd> for EvenOrOdd {
-    ///     fn equiv(&self, other: &EvenOrOdd) -> bool {
-    ///         self.num % 2 == other.num % 2
-    ///     }
-    /// }
-    ///
-    /// let mut map = HashMap::new();
-    /// map.insert(EvenOrOdd { num: 3 }, "foo");
-    ///
-    /// assert!(map.contains_key_equiv(&EvenOrOdd { num: 1 }));
-    /// assert!(!map.contains_key_equiv(&EvenOrOdd { num: 4 }));
-    ///
-    /// assert_eq!(map.find_equiv(&EvenOrOdd { num: 5 }), Some(&"foo"));
-    /// assert_eq!(map.find_equiv(&EvenOrOdd { num: 2 }), None);
-    ///
-    /// assert_eq!(map.pop_equiv(&EvenOrOdd { num: 1 }), Some("foo"));
-    /// assert_eq!(map.pop_equiv(&EvenOrOdd { num: 2 }), None);
-    ///
-    /// ```
-    #[experimental]
+    /// Deprecated: use `remove` and `BorrowFrom` instead.
+    #[deprecated = "use remove and BorrowFrom instead"]
     pub fn pop_equiv<Sized? Q:Hash<S> + Equiv<K>>(&mut self, k: &Q) -> Option<V> {
         if self.table.size() == 0 {
             return None
@@ -1036,6 +990,10 @@ impl<K: Eq + Hash<S>, V, S, H: Hasher<S>> HashMap<K, V, H> {
 
     /// Returns a reference to the value corresponding to the key.
     ///
+    /// The key may be any borrowed form of the map's key type, but
+    /// `Hash` and `Eq` on the borrowed form *must* match those for
+    /// the key type.
+    ///
     /// # Example
     ///
     /// ```
@@ -1047,7 +1005,9 @@ impl<K: Eq + Hash<S>, V, S, H: Hasher<S>> HashMap<K, V, H> {
     /// assert_eq!(map.get(&2), None);
     /// ```
     #[unstable = "matches collection reform specification, waiting for dust to settle"]
-    pub fn get(&self, k: &K) -> Option<&V> {
+    pub fn get<Sized? Q>(&self, k: &Q) -> Option<&V>
+        where Q: Hash<S> + Eq + BorrowFrom<K>
+    {
         self.search(k).map(|bucket| {
             let (_, v) = bucket.into_refs();
             v
@@ -1056,6 +1016,10 @@ impl<K: Eq + Hash<S>, V, S, H: Hasher<S>> HashMap<K, V, H> {
 
     /// Returns true if the map contains a value for the specified key.
     ///
+    /// The key may be any borrowed form of the map's key type, but
+    /// `Hash` and `Eq` on the borrowed form *must* match those for
+    /// the key type.
+    ///
     /// # Example
     ///
     /// ```
@@ -1067,7 +1031,9 @@ impl<K: Eq + Hash<S>, V, S, H: Hasher<S>> HashMap<K, V, H> {
     /// assert_eq!(map.contains_key(&2), false);
     /// ```
     #[unstable = "matches collection reform specification, waiting for dust to settle"]
-    pub fn contains_key(&self, k: &K) -> bool {
+    pub fn contains_key<Sized? Q>(&self, k: &Q) -> bool
+        where Q: Hash<S> + Eq + BorrowFrom<K>
+    {
         self.search(k).is_some()
     }
 
@@ -1079,6 +1045,10 @@ impl<K: Eq + Hash<S>, V, S, H: Hasher<S>> HashMap<K, V, H> {
 
     /// Returns a mutable reference to the value corresponding to the key.
     ///
+    /// The key may be any borrowed form of the map's key type, but
+    /// `Hash` and `Eq` on the borrowed form *must* match those for
+    /// the key type.
+    ///
     /// # Example
     ///
     /// ```
@@ -1093,7 +1063,9 @@ impl<K: Eq + Hash<S>, V, S, H: Hasher<S>> HashMap<K, V, H> {
     /// assert_eq!(map[1], "b");
     /// ```
     #[unstable = "matches collection reform specification, waiting for dust to settle"]
-    pub fn get_mut(&mut self, k: &K) -> Option<&mut V> {
+    pub fn get_mut<Sized? Q>(&mut self, k: &Q) -> Option<&mut V>
+        where Q: Hash<S> + Eq + BorrowFrom<K>
+    {
         match self.search_mut(k) {
             Some(bucket) => {
                 let (_, v) = bucket.into_mut_refs();
@@ -1147,6 +1119,10 @@ impl<K: Eq + Hash<S>, V, S, H: Hasher<S>> HashMap<K, V, H> {
     /// Removes a key from the map, returning the value at the key if the key
     /// was previously in the map.
     ///
+    /// The key may be any borrowed form of the map's key type, but
+    /// `Hash` and `Eq` on the borrowed form *must* match those for
+    /// the key type.
+    ///
     /// # Example
     ///
     /// ```
@@ -1158,7 +1134,9 @@ impl<K: Eq + Hash<S>, V, S, H: Hasher<S>> HashMap<K, V, H> {
     /// assert_eq!(map.remove(&1), None);
     /// ```
     #[unstable = "matches collection reform specification, waiting for dust to settle"]
-    pub fn remove(&mut self, k: &K) -> Option<V> {
+    pub fn remove<Sized? Q>(&mut self, k: &Q) -> Option<V>
+        where Q: Hash<S> + Eq + BorrowFrom<K>
+    {
         if self.table.size() == 0 {
             return None
         }
@@ -1271,16 +1249,20 @@ impl<K: Eq + Hash<S>, V, S, H: Hasher<S> + Default> Default for HashMap<K, V, H>
     }
 }
 
-impl<K: Eq + Hash<S>, V, S, H: Hasher<S>> Index<K, V> for HashMap<K, V, H> {
+impl<K: Hash<S> + Eq, Sized? Q, V, S, H: Hasher<S>> Index<Q, V> for HashMap<K, V, H>
+    where Q: BorrowFrom<K> + Hash<S> + Eq
+{
     #[inline]
-    fn index<'a>(&'a self, index: &K) -> &'a V {
+    fn index<'a>(&'a self, index: &Q) -> &'a V {
         self.get(index).expect("no entry found for key")
     }
 }
 
-impl<K: Eq + Hash<S>, V, S, H: Hasher<S>> IndexMut<K, V> for HashMap<K, V, H> {
+impl<K: Hash<S> + Eq, Sized? Q, V, S, H: Hasher<S>> IndexMut<Q, V> for HashMap<K, V, H>
+    where Q: BorrowFrom<K> + Hash<S> + Eq
+{
     #[inline]
-    fn index_mut<'a>(&'a mut self, index: &K) -> &'a mut V {
+    fn index_mut<'a>(&'a mut self, index: &Q) -> &'a mut V {
         match self.get_mut(index) {
             Some(v) => v,
             None => panic!("no entry found for key")
@@ -1962,11 +1944,11 @@ mod test_map {
         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.get("foo"), Some(&foo));
+        assert_eq!(m.get("bar"), Some(&bar));
+        assert_eq!(m.get("baz"), Some(&baz));
 
-        assert_eq!(m.find_equiv("qux"), None);
+        assert_eq!(m.get("qux"), None);
     }
 
     #[test]
diff --git a/src/libstd/collections/hash/set.rs b/src/libstd/collections/hash/set.rs
index 4326fae16fc91..2fbcb464358b3 100644
--- a/src/libstd/collections/hash/set.rs
+++ b/src/libstd/collections/hash/set.rs
@@ -10,6 +10,7 @@
 //
 // ignore-lexer-test FIXME #15883
 
+use borrow::BorrowFrom;
 use cmp::{Eq, Equiv, PartialEq};
 use core::kinds::Sized;
 use default::Default;
@@ -184,47 +185,9 @@ impl<T: Eq + Hash<S>, S, H: Hasher<S>> HashSet<T, H> {
         self.map.reserve(n)
     }
 
-    /// Returns true if the hash set contains a value equivalent to the
-    /// given query value.
-    ///
-    /// # Example
-    ///
-    /// This is a slightly silly example where we define the number's
-    /// parity as the equivalance class. It is important that the
-    /// values hash the same, which is why we implement `Hash`.
-    ///
-    /// ```
-    /// use std::collections::HashSet;
-    /// use std::hash::Hash;
-    /// use std::hash::sip::SipState;
-    ///
-    /// #[deriving(Eq, PartialEq)]
-    /// struct EvenOrOdd {
-    ///     num: uint
-    /// };
-    ///
-    /// impl Hash for EvenOrOdd {
-    ///     fn hash(&self, state: &mut SipState) {
-    ///         let parity = self.num % 2;
-    ///         parity.hash(state);
-    ///     }
-    /// }
-    ///
-    /// impl Equiv<EvenOrOdd> for EvenOrOdd {
-    ///     fn equiv(&self, other: &EvenOrOdd) -> bool {
-    ///         self.num % 2 == other.num % 2
-    ///     }
-    /// }
-    ///
-    /// let mut set = HashSet::new();
-    /// set.insert(EvenOrOdd { num: 3u });
-    ///
-    /// assert!(set.contains_equiv(&EvenOrOdd { num: 3u }));
-    /// assert!(set.contains_equiv(&EvenOrOdd { num: 5u }));
-    /// assert!(!set.contains_equiv(&EvenOrOdd { num: 4u }));
-    /// assert!(!set.contains_equiv(&EvenOrOdd { num: 2u }));
-    ///
-    /// ```
+    /// Deprecated: use `contains` and `BorrowFrom`.
+    #[deprecated = "use contains and BorrowFrom"]
+    #[allow(deprecated)]
     pub fn contains_equiv<Sized? Q: Hash<S> + Equiv<T>>(&self, value: &Q) -> bool {
       self.map.contains_key_equiv(value)
     }
@@ -427,6 +390,10 @@ impl<T: Eq + Hash<S>, S, H: Hasher<S>> HashSet<T, H> {
 
     /// Returns `true` if the set contains a value.
     ///
+    /// The value may be any borrowed form of the set's value type, but
+    /// `Hash` and `Eq` on the borrowed form *must* match those for
+    /// the value type.
+    ///
     /// # Example
     ///
     /// ```
@@ -437,7 +404,11 @@ impl<T: Eq + Hash<S>, S, H: Hasher<S>> HashSet<T, H> {
     /// assert_eq!(set.contains(&4), false);
     /// ```
     #[unstable = "matches collection reform specification, waiting for dust to settle"]
-    pub fn contains(&self, value: &T) -> bool { self.map.contains_key(value) }
+    pub fn contains<Sized? Q>(&self, value: &Q) -> bool
+        where Q: BorrowFrom<T> + Hash<S> + Eq
+    {
+        self.map.contains_key(value)
+    }
 
     /// Returns `true` if the set has no elements in common with `other`.
     /// This is equivalent to checking for an empty intersection.
@@ -527,6 +498,10 @@ impl<T: Eq + Hash<S>, S, H: Hasher<S>> HashSet<T, H> {
     /// Removes a value from the set. Returns `true` if the value was
     /// present in the set.
     ///
+    /// The value may be any borrowed form of the set's value type, but
+    /// `Hash` and `Eq` on the borrowed form *must* match those for
+    /// the value type.
+    ///
     /// # Example
     ///
     /// ```
@@ -539,7 +514,11 @@ impl<T: Eq + Hash<S>, S, H: Hasher<S>> HashSet<T, H> {
     /// assert_eq!(set.remove(&2), false);
     /// ```
     #[unstable = "matches collection reform specification, waiting for dust to settle"]
-    pub fn remove(&mut self, value: &T) -> bool { self.map.remove(value).is_some() }
+    pub fn remove<Sized? Q>(&mut self, value: &Q) -> bool
+        where Q: BorrowFrom<T> + Hash<S> + Eq
+    {
+        self.map.remove(value).is_some()
+    }
 }
 
 impl<T: Eq + Hash<S>, S, H: Hasher<S>> PartialEq for HashSet<T, H> {
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index 612613134d448..7f2a4c7e36569 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -141,6 +141,7 @@ extern crate rustrt;
 
 pub use core::any;
 pub use core::bool;
+pub use core::borrow;
 pub use core::cell;
 pub use core::clone;
 #[cfg(not(test))] pub use core::cmp;
diff --git a/src/libstd/time/duration.rs b/src/libstd/time/duration.rs
index 83340c9faac22..39ca3128ccb2b 100644
--- a/src/libstd/time/duration.rs
+++ b/src/libstd/time/duration.rs
@@ -554,11 +554,4 @@ mod tests {
         assert_eq!(format!("{:30}", Duration::days(1) + Duration::milliseconds(2345)),
                    "P1DT2.345S".to_string());
     }
-
-    #[test]
-    fn span() {
-        use io::timer::sleep;
-        let dur = Duration::span(|| sleep(Duration::milliseconds(5)));
-        assert!(dur > Duration::milliseconds(1));
-    }
 }
diff --git a/src/libsyntax/diagnostics/registry.rs b/src/libsyntax/diagnostics/registry.rs
index 71d82a41f3868..4caef247aebc2 100644
--- a/src/libsyntax/diagnostics/registry.rs
+++ b/src/libsyntax/diagnostics/registry.rs
@@ -20,6 +20,6 @@ impl Registry {
     }
 
     pub fn find_description(&self, code: &str) -> Option<&'static str> {
-        self.descriptions.find_equiv(code).map(|desc| *desc)
+        self.descriptions.get(code).map(|desc| *desc)
     }
 }
diff --git a/src/libsyntax/ext/format.rs b/src/libsyntax/ext/format.rs
index 9a9724de8fb70..f1b92b4d6bc1d 100644
--- a/src/libsyntax/ext/format.rs
+++ b/src/libsyntax/ext/format.rs
@@ -144,7 +144,7 @@ fn parse_args(ecx: &mut ExtCtxt, sp: Span, allow_method: bool,
             let name = interned_name.get();
             p.expect(&token::Eq);
             let e = p.parse_expr();
-            match names.find_equiv(name) {
+            match names.get(name) {
                 None => {}
                 Some(prev) => {
                     ecx.span_err(e.span,
@@ -366,7 +366,7 @@ impl<'a, 'b> Context<'a, 'b> {
                 self.ecx.expr_path(path)
             }
             parse::CountIsName(n) => {
-                let i = match self.name_positions.find_equiv(n) {
+                let i = match self.name_positions.get(n) {
                     Some(&i) => i,
                     None => 0, // error already emitted elsewhere
                 };
@@ -410,7 +410,7 @@ impl<'a, 'b> Context<'a, 'b> {
                     // Named arguments are converted to positional arguments at
                     // the end of the list of arguments
                     parse::ArgumentNamed(n) => {
-                        let i = match self.name_positions.find_equiv(n) {
+                        let i = match self.name_positions.get(n) {
                             Some(&i) => i,
                             None => 0, // error already emitted elsewhere
                         };
diff --git a/src/libsyntax/util/interner.rs b/src/libsyntax/util/interner.rs
index 08ada3e443590..ede967bba25cd 100644
--- a/src/libsyntax/util/interner.rs
+++ b/src/libsyntax/util/interner.rs
@@ -14,9 +14,9 @@
 
 use ast::Name;
 
+use std::borrow::BorrowFrom;
 use std::collections::HashMap;
 use std::cell::RefCell;
-use std::cmp::Equiv;
 use std::fmt;
 use std::hash::Hash;
 use std::rc::Rc;
@@ -75,9 +75,10 @@ impl<T: Eq + Hash + Clone + 'static> Interner<T> {
         (*vect).len()
     }
 
-    pub fn find_equiv<Sized? Q: Hash + Equiv<T>>(&self, val: &Q) -> Option<Name> {
+    pub fn find<Sized? Q>(&self, val: &Q) -> Option<Name>
+    where Q: BorrowFrom<T> + Eq + Hash {
         let map = self.map.borrow();
-        match (*map).find_equiv(val) {
+        match (*map).get(val) {
             Some(v) => Some(*v),
             None => None,
         }
@@ -117,6 +118,12 @@ impl fmt::Show for RcStr {
     }
 }
 
+impl BorrowFrom<RcStr> for str {
+    fn borrow_from(owned: &RcStr) -> &str {
+        owned.string.as_slice()
+    }
+}
+
 impl RcStr {
     pub fn new(string: &str) -> RcStr {
         RcStr {
@@ -149,7 +156,7 @@ impl StrInterner {
 
     pub fn intern(&self, val: &str) -> Name {
         let mut map = self.map.borrow_mut();
-        match map.find_equiv(val) {
+        match map.get(val) {
             Some(&idx) => return idx,
             None => (),
         }
@@ -195,8 +202,9 @@ impl StrInterner {
         self.vect.borrow().len()
     }
 
-    pub fn find_equiv<Sized? Q:Hash + Equiv<RcStr>>(&self, val: &Q) -> Option<Name> {
-        match (*self.map.borrow()).find_equiv(val) {
+    pub fn find<Sized? Q>(&self, val: &Q) -> Option<Name>
+    where Q: BorrowFrom<RcStr> + Eq + Hash {
+        match (*self.map.borrow()).get(val) {
             Some(v) => Some(*v),
             None => None,
         }
diff --git a/src/libterm/terminfo/mod.rs b/src/libterm/terminfo/mod.rs
index 0b5092a64d0f3..c1393767c8adc 100644
--- a/src/libterm/terminfo/mod.rs
+++ b/src/libterm/terminfo/mod.rs
@@ -78,7 +78,7 @@ impl<T: Writer+Send> Terminal<T> for TerminfoTerminal<T> {
         if self.num_colors > color {
             let s = expand(self.ti
                                .strings
-                               .find_equiv("setaf")
+                               .get("setaf")
                                .unwrap()
                                .as_slice(),
                            &[Number(color as int)], &mut Variables::new());
@@ -95,7 +95,7 @@ impl<T: Writer+Send> Terminal<T> for TerminfoTerminal<T> {
         if self.num_colors > color {
             let s = expand(self.ti
                                .strings
-                               .find_equiv("setab")
+                               .get("setab")
                                .unwrap()
                                .as_slice(),
                            &[Number(color as int)], &mut Variables::new());
@@ -113,7 +113,7 @@ impl<T: Writer+Send> Terminal<T> for TerminfoTerminal<T> {
             attr::BackgroundColor(c) => self.bg(c),
             _ => {
                 let cap = cap_for_attr(attr);
-                let parm = self.ti.strings.find_equiv(cap);
+                let parm = self.ti.strings.get(cap);
                 if parm.is_some() {
                     let s = expand(parm.unwrap().as_slice(),
                                    &[],
@@ -135,19 +135,19 @@ impl<T: Writer+Send> Terminal<T> for TerminfoTerminal<T> {
             }
             _ => {
                 let cap = cap_for_attr(attr);
-                self.ti.strings.find_equiv(cap).is_some()
+                self.ti.strings.get(cap).is_some()
             }
         }
     }
 
     fn reset(&mut self) -> IoResult<()> {
-        let mut cap = self.ti.strings.find_equiv("sgr0");
+        let mut cap = self.ti.strings.get("sgr0");
         if cap.is_none() {
             // are there any terminals that have color/attrs and not sgr0?
             // Try falling back to sgr, then op
-            cap = self.ti.strings.find_equiv("sgr");
+            cap = self.ti.strings.get("sgr");
             if cap.is_none() {
-                cap = self.ti.strings.find_equiv("op");
+                cap = self.ti.strings.get("op");
             }
         }
         let s = cap.map_or(Err("can't find terminfo capability `sgr0`".to_string()), |op| {
@@ -202,9 +202,9 @@ impl<T: Writer+Send> TerminfoTerminal<T> {
         }
 
         let inf = ti.unwrap();
-        let nc = if inf.strings.find_equiv("setaf").is_some()
-                 && inf.strings.find_equiv("setab").is_some() {
-                     inf.numbers.find_equiv("colors").map_or(0, |&n| n)
+        let nc = if inf.strings.get("setaf").is_some()
+                 && inf.strings.get("setab").is_some() {
+                     inf.numbers.get("colors").map_or(0, |&n| n)
                  } else { 0 };
 
         return Some(box TerminfoTerminal {out: out,
diff --git a/src/test/bench/shootout-k-nucleotide-pipes.rs b/src/test/bench/shootout-k-nucleotide-pipes.rs
index e40c477ec66ef..e39cd743ad55a 100644
--- a/src/test/bench/shootout-k-nucleotide-pipes.rs
+++ b/src/test/bench/shootout-k-nucleotide-pipes.rs
@@ -76,7 +76,7 @@ fn sort_and_fmt(mm: &HashMap<Vec<u8> , uint>, total: uint) -> String {
 // given a map, search for the frequency of a pattern
 fn find(mm: &HashMap<Vec<u8> , uint>, key: String) -> uint {
    let key = key.into_ascii().as_slice().to_lowercase().into_string();
-   match mm.find_equiv(key.as_bytes()) {
+   match mm.get(key.as_bytes()) {
       option::None      => { return 0u; }
       option::Some(&num) => { return num; }
    }