Rollup merge of rust-lang#24848 - bluss:deref-string, r=alexcrichton

Improve example for as_string and add example for as_vec

Provide a better example of `as_string` / `DerefString`'s unique capabilities.
Use an example where (for an unspecified reason) you need a &String, and
show how `as_string` solves the problem without needing an allocation.

Author: steveklabnik

src/libcollections/string.rs

@@ -951,12 +951,13 @@ impl<'a> Deref for DerefString<'a> {
 /// # #![feature(collections)]
 /// use std::string::as_string;
 ///
-/// fn string_consumer(s: String) {
-///     assert_eq!(s, "foo".to_string());
+/// // Let's pretend we have a function that requires `&String`
+/// fn string_consumer(s: &String) {
+///     assert_eq!(s, "foo");
 /// }
 ///
-/// let string = as_string("foo").clone();
-/// string_consumer(string);
+/// // Provide a `&String` from a `&str` without allocating
+/// string_consumer(&as_string("foo"));
 /// ```
 #[unstable(feature = "collections")]
 pub fn as_string<'a>(x: &'a str) -> DerefString<'a> {

src/libcollections/vec.rs

@@ -1915,6 +1915,22 @@ impl<'a, T> Drop for DerefVec<'a, T> {
 }
 
 /// Converts a slice to a wrapper type providing a `&Vec<T>` reference.
+///
+/// # Examples
+///
+/// ```
+/// # #![feature(collections)]
+/// use std::vec::as_vec;
+///
+/// // Let's pretend we have a function that requires `&Vec<i32>`
+/// fn vec_consumer(s: &Vec<i32>) {
+///     assert_eq!(s, &[1, 2, 3]);
+/// }
+///
+/// // Provide a `&Vec<i32>` from a `&[i32]` without allocating
+/// let values = [1, 2, 3];
+/// vec_consumer(&as_vec(&values));
+/// ```
 #[unstable(feature = "collections")]
 pub fn as_vec<'a, T>(x: &'a [T]) -> DerefVec<'a, T> {
     unsafe {