rustlings/exercises/12_options/options2.rs

// options2.rs
//
// Execute `rustlings hint options2` or use the `hint` watch subcommand for a
// hint.


#[cfg(test)]
mod tests {
    use std::iter::Flatten;

    #[test]
    fn simple_option() {
        let target = "rustlings";
        let optional_target = Some(target);

        // TODO: Make this an if let statement whose value is "Some" type
       if let Some(word) = optional_target {
            assert_eq!(word, target);
        }
    }

    #[test]
    fn layered_option() {
        let range = 10;
        let mut optional_integers: Vec<Option<i8>> = vec![None];

        for i in 1..(range + 1) {
            optional_integers.push(Some(i));
        }

        let mut cursor = range;

        // TODO: make this a while let statement - remember that vector.pop also
        // adds another layer of Option<T>. You can stack `Option<T>`s into
        // while let and if let.

        //flatten is a method that takes a nested Option and returns an Option with the inner value
        //if the outer Option is Some and the inner Option is Some, it returns Some(inner value)
        //if the outer Option is Some and the inner Option is None, it returns None
        //if the outer Option is None, it returns None
     
       while let Some(integer) = optional_integers.pop().flatten() {
            assert_eq!(integer, cursor);
            cursor -= 1;
        }

        assert_eq!(cursor, 0);
    }
}