4 files changed, 55 insertions, 64 deletions
diff --git a/exercises/09_strings/strings1.rs b/exercises/09_strings/strings1.rs
index f50e1fa..6abdbb4 100644
--- a/exercises/09_strings/strings1.rs
+++ b/exercises/09_strings/strings1.rs
@@ -1,17 +1,9 @@
-// strings1.rs
-//
-// Make me compile without changing the function signature!
-//
-// Execute `rustlings hint strings1` or use the `hint` watch subcommand for a
-// hint.
-
-// I AM NOT DONE
+// TODO: Fix the compiler error without changing the function signature.
+fn current_favorite_color() -> String {
+    "blue"
+}
 
 fn main() {
     let answer = current_favorite_color();
-    println!("My current favorite color is {}", answer);
-}
-
-fn current_favorite_color() -> String {
-    "blue"
+    println!("My current favorite color is {answer}");
 }
diff --git a/exercises/09_strings/strings2.rs b/exercises/09_strings/strings2.rs
index 4d95d16..93d9cb6 100644
--- a/exercises/09_strings/strings2.rs
+++ b/exercises/09_strings/strings2.rs
@@ -1,21 +1,14 @@
-// strings2.rs
-//
-// Make me compile without changing the function signature!
-//
-// Execute `rustlings hint strings2` or use the `hint` watch subcommand for a
-// hint.
-
-// I AM NOT DONE
+// TODO: Fix the compiler error in the `main` function without changing this function.
+fn is_a_color_word(attempt: &str) -> bool {
+    attempt == "green" || attempt == "blue" || attempt == "red"
+}
 
 fn main() {
-    let word = String::from("green"); // Try not changing this line :)
+    let word = String::from("green"); // Don't change this line.
+
     if is_a_color_word(word) {
         println!("That is a color word I know!");
     } else {
         println!("That is not a color word I know.");
     }
 }
-
-fn is_a_color_word(attempt: &str) -> bool {
-    attempt == "green" || attempt == "blue" || attempt == "red"
-}
diff --git a/exercises/09_strings/strings3.rs b/exercises/09_strings/strings3.rs
index b29f932..39fce18 100644
--- a/exercises/09_strings/strings3.rs
+++ b/exercises/09_strings/strings3.rs
@@ -1,23 +1,17 @@
-// strings3.rs
-//
-// Execute `rustlings hint strings3` or use the `hint` watch subcommand for a
-// hint.
-
-// I AM NOT DONE
-
-fn trim_me(input: &str) -> String {
-    // TODO: Remove whitespace from both ends of a string!
-    ???
+fn trim_me(input: &str) -> &str {
+    // TODO: Remove whitespace from both ends of a string.
 }
 
 fn compose_me(input: &str) -> String {
-    // TODO: Add " world!" to the string! There's multiple ways to do this!
-    ???
+    // TODO: Add " world!" to the string! There are multiple ways to do this.
 }
 
 fn replace_me(input: &str) -> String {
-    // TODO: Replace "cars" in the string with "balloons"!
-    ???
+    // TODO: Replace "cars" in the string with "balloons".
+}
+
+fn main() {
+    // You can optionally experiment here.
 }
 
 #[cfg(test)]
@@ -39,7 +33,13 @@ mod tests {
 
     #[test]
     fn replace_a_string() {
-        assert_eq!(replace_me("I think cars are cool"), "I think balloons are cool");
-        assert_eq!(replace_me("I love to look at cars"), "I love to look at balloons");
+        assert_eq!(
+            replace_me("I think cars are cool"),
+            "I think balloons are cool",
+        );
+        assert_eq!(
+            replace_me("I love to look at cars"),
+            "I love to look at balloons",
+        );
     }
 }
diff --git a/exercises/09_strings/strings4.rs b/exercises/09_strings/strings4.rs
index e8c54ac..9d9eb48 100644
--- a/exercises/09_strings/strings4.rs
+++ b/exercises/09_strings/strings4.rs
@@ -1,30 +1,36 @@
-// strings4.rs
-//
-// Ok, here are a bunch of values-- some are `String`s, some are `&str`s. Your
-// task is to call one of these two functions on each value depending on what
-// you think each value is. That is, add either `string_slice` or `string`
-// before the parentheses on each line. If you're right, it will compile!
-//
-// No hints this time!
-
-// I AM NOT DONE
+// Calls of this function should be replaced with calls of `string_slice` or `string`.
+fn placeholder() {}
 
 fn string_slice(arg: &str) {
-    println!("{}", arg);
+    println!("{arg}");
 }
 fn string(arg: String) {
-    println!("{}", arg);
+    println!("{arg}");
 }
 
+// TODO: Here are a bunch of values - some are `String`, some are `&str`.
+// Your task is to replace `placeholder(…)` with either `string_slice(…)`
+// or `string(…)` depending on what you think each value is.
 fn main() {
-    ???("blue");
-    ???("red".to_string());
-    ???(String::from("hi"));
-    ???("rust is fun!".to_owned());
-    ???("nice weather".into());
-    ???(format!("Interpolation {}", "Station"));
-    ???(&String::from("abc")[0..1]);
-    ???("  hello there ".trim());
-    ???("Happy Monday!".to_string().replace("Mon", "Tues"));
-    ???("mY sHiFt KeY iS sTiCkY".to_lowercase());
+    placeholder("blue");
+
+    placeholder("red".to_string());
+
+    placeholder(String::from("hi"));
+
+    placeholder("rust is fun!".to_owned());
+
+    placeholder("nice weather".into());
+
+    placeholder(format!("Interpolation {}", "Station"));
+
+    // WARNING: This is byte indexing, not character indexing.
+    // Character indexing can be done using `s.chars().nth(INDEX)`.
+    placeholder(&String::from("abc")[0..1]);
+
+    placeholder("  hello there ".trim());
+
+    placeholder("Happy Monday!".replace("Mon", "Tues"));
+
+    placeholder("mY sHiFt KeY iS sTiCkY".to_lowercase());
 }