collections: Add documentation example for as_vec

Author: Ulrik Sverdrup

src/libcollections/vec.rs

@@ -1919,6 +1919,22 @@ 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<T> from a &[T] 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 {