// In this exercise, you'll learn some of the unique advantages that iterators // can offer. // "hello" -> "Hello" fn capitalize_first(input: &str) -> String { let mut chars = input.chars(); match chars.next() { None => String::new(), Some(first) => first.to_uppercase().to_string() + chars.as_str(), } } // Apply the `capitalize_first` function to a slice of string slices. // Return a vector of strings. // ["hello", "world"] -> ["Hello", "World"] fn capitalize_words_vector(words: &[&str]) -> Vec<String> { words.iter().map(|word| capitalize_first(word)).collect() } // Apply the `capitalize_first` function again to a slice of string // slices. Return a single string. // ["hello", " ", "world"] -> "Hello World" fn capitalize_words_string(words: &[&str]) -> String { words.iter().map(|word| capitalize_first(word)).collect() } fn main() { // You can optionally experiment here. } #[cfg(test)] mod tests { use super::*; #[test] fn test_success() { 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"); } }