// Let's build a little machine in the form of a function. As input, we're going // to give a list of strings and commands. These commands determine what action // is going to be applied to the string. It can either be: // - Uppercase the string // - Trim the string // - Append "bar" to the string a specified amount of times // // The exact form of this will be: // - The input is going to be a vector of 2-length tuples, // the first element is the string, the second one is the command. // - The output element is going to be a vector of strings. enum Command { Uppercase, Trim, Append(usize), } mod my_module { use super::Command; // The solution with a loop. Check out `transformer_iter` for a version // with iterators. pub fn transformer(input: Vec<(String, Command)>) -> Vec<String> { let mut output = Vec::new(); for (string, command) in input { // Create the new string. let new_string = match command { Command::Uppercase => string.to_uppercase(), Command::Trim => string.trim().to_string(), Command::Append(n) => string + &"bar".repeat(n), }; // Push the new string to the output vector. output.push(new_string); } output } // Equivalent to `transform` but uses an iterator instead of a loop for // comparison. Don't worry, we will practice iterators later ;) pub fn transformer_iter(input: Vec<(String, Command)>) -> Vec<String> { input .into_iter() .map(|(string, command)| match command { Command::Uppercase => string.to_uppercase(), Command::Trim => string.trim().to_string(), Command::Append(n) => string + &"bar".repeat(n), }) .collect() } } fn main() { // You can optionally experiment here. } #[cfg(test)] mod tests { // Import `transformer`. use super::my_module::transformer; use super::Command; use super::my_module::transformer_iter; #[test] fn it_works() { for transformer in [transformer, transformer_iter] { let input = vec![ ("hello".to_string(), Command::Uppercase), (" all roads lead to rome! ".to_string(), Command::Trim), ("foo".to_string(), Command::Append(1)), ("bar".to_string(), Command::Append(5)), ]; let output = transformer(input); assert_eq!( output, [ "HELLO", "all roads lead to rome!", "foobar", "barbarbarbarbarbar", ] ); } } }

Quiz: options, errors, generics, traits