Option to Result

In the previous challenge we converted a Result<T, E> to an Option<T> by using the .ok() method, Rust provides us other mechanisms to convert an Option<T> to a Result<T, E> as well. In this challenge, you will learn how to use the .ok_or() method to convert an Option<T> to a Result<T, E>.

Your Task

Implement the function get_first_element:

  1. Takes two parameters:
    • A vector of integers (Vec<i32>).
    • A minimum allowed value (i32).
  2. Use the .first() method to retrieve the first element of the vector, this returns Option<&T>.
  3. If the value is None, convert it to a Result<T, E> using the .ok_or() method with the error message "Vector is empty".
  4. Then run a validation check to ensure the first element is greater than or equal to the minimum allowed value provided. If not, return an error with message "First element is below the minimum allowed value".
  5. If everything is ok, return a Ok(T) with the first element.

Hints

If you're stuck, here are some hints to help you solve the challenge:

Click here to reveal hints
  • You can use the .ok_or() method and propagate the error cleanly. e.g. 
    let first_element = numbers.first().ok_or("Vector is empty".to_string())?;