Result and Option

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Exercises

Option to Result

// Fix the `fetch_last` function. Do not add any other statement.

fn fetch_last<T>(list: &mut Vec<T>) -> Option<T> {
    list.pop().ok_or()
}

fn main() {
    let mut my_nums = Vec::<i32>::new();
    match fetch_last(&mut my_nums) {
        Ok(ele) => println!("Last element: {ele}"),
        Err(error) => {
            println!("Error: {error}");
            assert_eq!(error, "Empty list".to_owned());
        }
    }
}

fn fetch_last<T>(list: &mut Vec<T>) -> Result<T, String> {
  list.pop().ok_or("Empty list".to_owned())
}

fn main() {
  let mut my_nums = Vec::<i32>::new();
  match fetch_last(&mut my_nums) {
      Ok(ele) => println!("Last element: {ele}"),
      Err(error) => {
          println!("Error: {error}");
          assert_eq!(error, "Empty list".to_owned());
      }
  }
}

Result to Option

// Use `ok` combinator to convert Result to Option.
// Do not add any statements anywhere.

fn add(num1: &str, num2: &str) -> Option<u8> {
    // TODO: only modify the 2 statements below
    let num1 = num1.parse::<u8>();
    let num2 = num2.parse::<u8>();
    num1.checked_add(num2)
}

fn main() {
    let (num1, num2) = ("4", "5");
    if let Some(sum) = add("4", "5") {
        println!("{num1} + {num2} = {sum}");
    }
}

fn add(num1: &str, num2: &str) -> Option<u8> {
  let num1 = num1.parse::<u8>().ok()?;
  let num2 = num2.parse::<u8>().ok()?;
  num1.checked_add(num2)
}

fn main() {
  let (num1, num2) = ("4", "5");
  if let Some(sum) = add("4", "5") {
      println!("{num1} + {num2} = {sum}");
  }
}