Swapped longest into its declarative form.

The function was ment to use the functional programming style, however,
I forgot to uncomment and swap out the imperative style.

src/basic.rs

@@ -52,20 +52,26 @@ pub fn longest<'a>(strings: &'a [String]) -> Option<&'a str>
       return None;
    }
 
+   // Imperative programming style.
+   //
+   // ```Rust
    // This is the current longest string. (index, length)
+   // let mut longest: (usize, usize) = (0, 0);
+   // for (index, string) in strings.iter().enumerate()
+   // {
+   //    if string.len() > longest.1
+   //    {
+   //       longest = (index, string.len());
+   //    }
+   // }
+   //
+   // Some(&strings[longest.0])
+   // ```
    //
    // This can also be done with functional style:
-   // strings.iter().max_by_key(|s| s.len()).map(|s| s.as_str())
+   // When coding prefer the functional, declarative style.
-   let mut longest: (usize, usize) = (0, 0);
+   // It is just as fast or faster than the imperative style.
-   for (index, string) in strings.iter().enumerate()
+   strings.iter().max_by_key(|s| s.len()).map(|s| s.as_str())
-   {
-      if string.len() > longest.1
-      {
-         longest = (index, string.len());
-      }
-   }
-
-   Some(&strings[longest.0])
 }