Merge pull request #436 from cbzehner/gigasecond

gigasecond: Update dependency to conform to usage guidelines

exercises/gigasecond/.meta/hints.md

@@ -0,0 +1 @@
+If you're unsure what operations you can perform on `DateTime<Utc>` take a look at the [chrono crate](https://docs.rs/chrono/0.4.0/chrono/) which is listed as a dependency in the `Cargo.toml` file for this exercise.

exercises/gigasecond/README.md

@@ -4,6 +4,9 @@ Calculate the moment when someone has lived for 10^9 seconds.
 
 A gigasecond is 10^9 (1,000,000,000) seconds.
 
+If you're unsure what operations you can perform on `DateTime<Utc>` take a look at the [chrono crate](https://docs.rs/chrono/0.4.0/chrono/) which is listed as a dependency in the `Cargo.toml` file for this exercise.
+
+
 ## Rust Installation
 
 Refer to the [exercism help page][help-page] for Rust installation and learning

exercises/gigasecond/example.rs

@@ -1,5 +1,5 @@
 extern crate chrono;
-use chrono::*;
+use chrono::{DateTime, Duration, Utc};
 
 pub fn after(start: DateTime<Utc>) -> DateTime<Utc> {
     start + Duration::seconds(1_000_000_000)

exercises/gigasecond/src/lib.rs

@@ -1,7 +1,7 @@
-extern crate chrono;
-use chrono::*;
-
-// Returns a Utc DateTime one billion seconds after start.
-pub fn after(start: DateTime<Utc>) -> DateTime<Utc> {
-    unimplemented!()
-}
+extern crate chrono;
+use chrono::{DateTime, Utc};
+
+// Returns a Utc DateTime one billion seconds after start.
+pub fn after(start: DateTime<Utc>) -> DateTime<Utc> {
+    unimplemented!("What time is a gigasecond later than {}", start);
+}

exercises/gigasecond/tests/gigasecond.rs

@@ -13,7 +13,7 @@ extern crate gigasecond;
  * In order to use the crate, your solution will need to start with the two following lines
 */
 extern crate chrono;
-use chrono::*;
+use chrono::{TimeZone, Utc};
 
 #[test]
 fn test_date() {