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.
  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())?;