// Null safety in Rust
//
// ggtowell
// Oct 31. 2023

use std::cmp;

// find the min positive number from an array of 5 integers
// because it is an array, there are certainly numbers, but there is no certainty that
// there is a positive number.
// So the Option "class" is a wrapper around None ie. null ie does not exist, 
// and an actual value. 
fn arr_min(v: &[i32; 5]) -> Option<i32> {
    let mut min = None;
    for e in 0..v.len() {
        min = match min {
            None => if v[e]>0 { Some(v[e]) } else { None },
            Some(n) => if v[e]>0 {Some(cmp::min(n, v[e])) } else { Some(n) }
        };
    }
    min
}

fn main() {
    let arr = [5,4,3,2,1];
    let vmm = arr_min(&arr);
    // the thing returned is a wrapper than can either have a None or a number
    println!("{:?}", vmm);
    // doing it right to handle the possible null value
    match vmm {
        None => println!("The array has no positive numbers"),
        Some(n) => println!("The min positive number is {n}")
    }
    // doing it wrong -- or at least the quick and dirty way.
    println!("The min positive number is {}", vmm.unwrap());
}