Rollup merge of rust-lang#37761 - christophebiocca:borrow-stdlib-fn-refactor, r=alexcrichton

Use Borrow for binary_search and contains methods in the standard library

Fixes all standard library methods in rust-lang#32822 that can be fixed without backwards compatibility issues.

Author: alexcrichton

src/libcore/slice.rs

@@ -33,6 +33,7 @@
 // * The `raw` and `bytes` submodules.
 // * Boilerplate trait implementations.
 
+use borrow::Borrow;
 use cmp::Ordering::{self, Less, Equal, Greater};
 use cmp;
 use fmt;
@@ -100,15 +101,17 @@ pub trait SliceExt {
     #[stable(feature = "core", since = "1.6.0")]
     fn as_ptr(&self) -> *const Self::Item;
     #[stable(feature = "core", since = "1.6.0")]
-    fn binary_search(&self, x: &Self::Item) -> Result<usize, usize>
-        where Self::Item: Ord;
+    fn binary_search<Q: ?Sized>(&self, x: &Q) -> Result<usize, usize>
+        where Self::Item: Borrow<Q>,
+              Q: Ord;
     #[stable(feature = "core", since = "1.6.0")]
     fn binary_search_by<'a, F>(&'a self, f: F) -> Result<usize, usize>
         where F: FnMut(&'a Self::Item) -> Ordering;
     #[stable(feature = "slice_binary_search_by_key", since = "1.10.0")]
-    fn binary_search_by_key<'a, B, F>(&'a self, b: &B, f: F) -> Result<usize, usize>
+    fn binary_search_by_key<'a, B, F, Q: ?Sized>(&'a self, b: &Q, f: F) -> Result<usize, usize>
         where F: FnMut(&'a Self::Item) -> B,
-              B: Ord;
+              B: Borrow<Q>,
+              Q: Ord;
     #[stable(feature = "core", since = "1.6.0")]
     fn len(&self) -> usize;
     #[stable(feature = "core", since = "1.6.0")]
@@ -493,8 +496,8 @@ impl<T> SliceExt for [T] {
         m >= n && needle == &self[m-n..]
     }
 
-    fn binary_search(&self, x: &T) -> Result<usize, usize> where T: Ord {
-        self.binary_search_by(|p| p.cmp(x))
+    fn binary_search<Q: ?Sized>(&self, x: &Q) -> Result<usize, usize> where T: Borrow<Q>, Q: Ord {
+        self.binary_search_by(|p| p.borrow().cmp(x))
     }
 
     #[inline]
@@ -522,11 +525,12 @@ impl<T> SliceExt for [T] {
     }
 
     #[inline]
-    fn binary_search_by_key<'a, B, F>(&'a self, b: &B, mut f: F) -> Result<usize, usize>
+    fn binary_search_by_key<'a, B, F, Q: ?Sized>(&'a self, b: &Q, mut f: F) -> Result<usize, usize>
         where F: FnMut(&'a Self::Item) -> B,
-              B: Ord
+              B: Borrow<Q>,
+              Q: Ord
     {
-        self.binary_search_by(|k| f(k).cmp(b))
+        self.binary_search_by(|k| f(k).borrow().cmp(b))
     }
 }