// Options

/// Baby steps
fn multiply(num: Option<usize>) -> usize {
  if num.is_some() {
    return num.unwrap() * 5;
  } else {
    return 0;
  }
}
  
/// Bit better using pattern matching
fn multiply(num: Option<usize>) -> usize {
  if let Some(x) = num {
    return x * 5;
  } else {
    return 0;
  }
}

/// Bit better using calling methods on enums (less symbols, more words, more readable)
fn multiply(num: Option<usize>) -> usize {
  return num.unwrap_or(0) * 5; // the default value must be of the same type
}
  
// if undefined is provided, return undefined, otherwise multiply by 5
fn multiply(num: Option<usize>) -> Option<usize> {
  // map allows to access the inner value if there's an inner value, if there isn't, it remains None.
  return num.map(|x| x * 5);
}
    
// if you have a function that return and Error or an Option of the same type, you can use the `?` operator
fn multiply(num: Option<usize>) -> Option<usize> {
  let num = num?; // it converts it from Option to usize.

  // '?' does under the hood
  // let num = match num {
  //  Some(x) => x * 5,
  //  None => return None, 
  // };

  return Some(num * 5);
}
  
// so basically you could
fn multiply(num: Option<usize>) -> Option<usize> {
  return Some(num? * 5);
}