jordanorelli · September 3, 2022 20:49 · Sep 3, 2022
diff --git a/iterators2.rs b/iterators2.rs
@@ -0,0 +1,63 @@
+// iterators2.rs
+// In this exercise, you'll learn some of the unique advantages that iterators
+// can offer. Follow the steps to complete the exercise.
+// Execute `rustlings hint iterators2` or use the `hint` watch subcommand for a hint.
+
+// Step 1.
+// Complete the `capitalize_first` function.
+// "hello" -> "Hello"
+pub fn capitalize_first(input: &str) -> String {
+    let mut c = input.chars();
+    match c.next() {
+        None => String::new(),
+        Some(first) => format!("{}{}", first.to_uppercase(), c.collect::<String>()),
+    }
+}
+
+// Step 2.
+// Apply the `capitalize_first` function to a slice of string slices.
+// Return a vector of strings.
+// ["hello", "world"] -> ["Hello", "World"]
+pub fn capitalize_words_vector(words: &[&str]) -> Vec<String> {
+    // Why are these two lines different? The first one does not compile but the second one does
+    // and I don't really understand the error message.
+    // words.iter().map(capitalize_first).collect()
+    words.into_iter().map(|s| capitalize_first(s)).collect()
+}
+
+// Step 3.
+// Apply the `capitalize_first` function again to a slice of string slices.
+// Return a single string.
+// ["hello", " ", "world"] -> "Hello World"
+pub fn capitalize_words_string(words: &[&str]) -> String {
+    // capitalize_words_vector(words).join("")
+    words.iter().map(|s| capitalize_first(s)).collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_success() {
+        assert_eq!(capitalize_first("h"), "H");
+        assert_eq!(capitalize_first("hello"), "Hello");
+    }
+
+    #[test]
+    fn test_empty() {
+        assert_eq!(capitalize_first(""), "");
+    }
+
+    #[test]
+    fn test_iterate_string_vec() {
+        let words = vec!["hello", "world"];
+        assert_eq!(capitalize_words_vector(&words), ["Hello", "World"]);
+    }
+
+    #[test]
+    fn test_iterate_into_string() {
+        let words = vec!["hello", " ", "world"];
+        assert_eq!(capitalize_words_string(&words), "Hello World");
+    }
+}
diff --git a/why.md b/why.md
@@ -0,0 +1,7 @@
+confused about lines 24 and 25. I'm struggling to understand the difference between this line:
+
+    words.iter().map(capitalize_first).collect()
+
+and this line:
+
+    words.iter().map(|s| capitalize_first(s)).collect()
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