feat(modules): update exercises, add modules3 (#822)

Co-authored-by: diannasoriel <mokou@fastmail.com>

exercises/README.md

@@ -9,7 +9,7 @@
 | primitive_types        | §4.3          |
 | structs                | §5.1          |
 | enums                  | §6            |
-| modules                | §7.2          |
+| modules                | §7            |
 | collections            | §8.1, §8.3    |
 | strings                | §8.2          |
 | error_handling         | §9            |

exercises/modules/README.md

@@ -4,4 +4,4 @@ In this section we'll give you an introduction to Rust's module system.
 
 ## Further information
 
-- [The Module System](https://doc.rust-lang.org/book/ch07-02-defining-modules-to-control-scope-and-privacy.html)
+- [The Module System](https://doc.rust-lang.org/book/ch07-00-managing-growing-projects-with-packages-crates-and-modules.html)

exercises/modules/modules1.rs

@@ -4,7 +4,13 @@
 // I AM NOT DONE
 
 mod sausage_factory {
+    // Don't let anybody outside of this module see this!
+    fn get_secret_recipe() -> String {
+        String::from("Ginger")
+    }
+
     fn make_sausage() {
+        get_secret_recipe();
         println!("sausage!");
     }
 }

exercises/modules/modules2.rs

@@ -1,11 +1,15 @@
 // modules2.rs
+// You can bring module paths into scopes and provide new names for them with the
+// 'use' and 'as' keywords. Fix these 'use' statments to make the code compile.
 // Make me compile! Execute `rustlings hint modules2` for hints :)
 
 // I AM NOT DONE
 
 mod delicious_snacks {
-    use self::fruits::PEAR as fruit;
+
-    use self::veggies::CUCUMBER as veggie;
+    // TODO: Fix these use statments
+    use self::fruits::PEAR as ???
+    use self::veggies::CUCUMBER as ???
 
     mod fruits {
         pub const PEAR: &'static str = "Pear";

exercises/modules/modules3.rs

@@ -0,0 +1,18 @@
+// modules3.rs
+// You can use the 'use' keyword to bring module paths from modules from anywhere
+// and especially from the Rust standard library into your scope.
+// Bring SystemTime and UNIX_EPOCH
+// from the std::time module. Bonus style points if you can do it with one line!
+// Make me compile! Execute `rustlings hint modules3` for hints :)
+
+// I AM NOT DONE
+
+// TODO: Complete this use statement
+use ???
+
+fn main() {
+    match SystemTime::now().duration_since(UNIX_EPOCH) {
+        Ok(n) => println!("1970-01-01 00:00:00 UTC was {} seconds ago!", n.as_secs()),
+        Err(_) => panic!("SystemTime before UNIX EPOCH!"),
+    }
+}

info.toml

@@ -362,11 +362,19 @@ name = "modules2"
 path = "exercises/modules/modules2.rs"
 mode = "compile"
 hint = """
-The delicious_snacks module is trying to present an external
+The delicious_snacks module is trying to present an external interface that is 
-interface (the `fruit` and `veggie` constants) that is different than
+different than its internal structure (the `fruits` and `veggies` modules and
-its internal structure (the `fruits` and `veggies` modules and
+associated constants). Complete the `use` statemants to fit the uses in main and
-associated constants). It's almost there except for one keyword missing for
+find the one keyword missing for both constants."""
-each constant."""
+
+[[exercises]]
+name = "modules3"
+path = "exercises/modules/modules3.rs"
+mode = "compile"
+hint = """
+UNIX_EPOCH and SystemTime are declared in the std::time module. Add a use statement
+for these two to bring them into scope. You can use nested paths or the glob
+operator to bring these two in using only one line."""
 
 # COLLECTIONS