Stabilize std::borrow

This commit stabilizes `std::borrow`, making the following modifications
to catch up the API with language changes:

* It renames `BorrowFrom` to `Borrow`, as was originally intended (but
  blocked for technical reasons), and reorders the parameters
  accordingly.

* It moves the type parameter of `ToOwned` to an associated type. This
  is somewhat less flexible, in that each borrowed type must have a
  unique owned type, but leads to a significant simplification for
  `Cow`. Flexibility can be regained by using newtyped slices, which is
  advisable for other reasons anyway.

* It removes the owned type parameter from `Cow`, making the type much
  less verbose.

* Deprecates the `is_owned` and `is_borrowed` predicates in favor of
  direct matching.

The above API changes are relatively minor; the basic functionality
remains the same, and essentially the whole module is now marked
`#[stable]`.

[breaking-change]

1 files changed, 6 insertions, 6 deletions

diff --git a/src/libsyntax/util/interner.rs b/src/libsyntax/util/interner.rs
index 51144267519..5236122f585 100644
--- a/src/libsyntax/util/interner.rs
+++ b/src/libsyntax/util/interner.rs
@@ -14,7 +14,7 @@
 
 use ast::Name;
 
-use std::borrow::BorrowFrom;
+use std::borrow::Borrow;
 use std::cell::RefCell;
 use std::cmp::Ordering;
 use std::collections::HashMap;
@@ -79,7 +79,7 @@ impl<T: Eq + Hash<Hasher> + Clone + 'static> Interner<T> {
     }
 
     pub fn find<Q: ?Sized>(&self, val: &Q) -> Option<Name>
-    where Q: BorrowFrom<T> + Eq + Hash<Hasher> {
+    where T: Borrow<Q>, Q: Eq + Hash<Hasher> {
         let map = self.map.borrow();
         match (*map).get(val) {
             Some(v) => Some(*v),
@@ -128,9 +128,9 @@ impl fmt::Display for RcStr {
     }
 }
 
-impl BorrowFrom<RcStr> for str {
-    fn borrow_from(owned: &RcStr) -> &str {
-        &owned.string[]
+impl Borrow<str> for RcStr {
+    fn borrow(&self) -> &str {
+        &self.string[]
     }
 }
 
@@ -211,7 +211,7 @@ impl StrInterner {
     }
 
     pub fn find<Q: ?Sized>(&self, val: &Q) -> Option<Name>
-    where Q: BorrowFrom<RcStr> + Eq + Hash<Hasher> {
+    where RcStr: Borrow<Q>, Q: Eq + Hash<Hasher> {
         match (*self.map.borrow()).get(val) {
             Some(v) => Some(*v),
             None => None,