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/adv_async.rs

@@ -1,3 +1,6 @@
+// SPDX-License-Identifier: Apache-2.0
+// Sealed with Magistamp.
+
 //! An example job execution framework.
 //!
 //! It includes:
@@ -8,6 +11,7 @@
 //! Jobs are run concurrently using Tokio, and results are gathered
 //! with proper error handling.
 
+use std::io::Write;
 use std::pin::Pin;
 
 use tokio::time::{sleep, Duration};
@@ -159,7 +163,16 @@ impl Job for FileJob
       where Self: Sync + 'a
    {
       Box::pin(async move {
-         Ok(String::from("Reading file"))
+         let mut write_target = std::env::temp_dir();
+         write_target.push("file_job");
+         write_target.set_extension("txt");
+
+         let mut file = std::fs::File::create(write_target)
+            .map_err(|e| Box::new(e) as Box<dyn std::error::Error + Send>)?;
+         file.write_all(b"Jason is an awesome programmer!!")
+            .map_err(|e| Box::new(e) as Box<dyn std::error::Error + Send>)?;
+
+         Ok(String::from("File written"))
       })
    }
 }
@@ -229,6 +242,7 @@ impl Job for MathJob
       where Self: Sync + 'a
    {
       Box::pin(async move {
+         let _ans = 10 * 4 + 2;
          Ok(String::from("Math stuff"))
       })
    }
@@ -251,7 +265,7 @@ mod tests
 
       let result = job.run().await;
       assert!(result.is_ok());
-      assert_eq!(result.unwrap(), "Reading file");
+      assert_eq!(result.unwrap(), "File written");
    }
 
    #[tokio::test]
@@ -299,7 +313,7 @@ mod tests
       assert_eq!(results.len(), 3);
 
       assert_eq!(results[0].0, "File Job");
-      assert_eq!(results[0].1.as_ref().unwrap(), "Reading file");
+      assert_eq!(results[0].1.as_ref().unwrap(), "File written");
 
       assert_eq!(results[1].0, "Math Job");
       assert_eq!(results[1].1.as_ref().unwrap(), "Math stuff");

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])
 }