A decent result after thinking about primes forever and not looking at the book

wow_neat.rs

struct Sieve<'a> {
    primes: &'a mut Vec<u32>,
}

impl<'a> Sieve<'a> {
    pub fn new(primes: &'a mut Vec<u32>) -> Self {
        Sieve { primes }
    }
}

impl Iterator for Sieve<'_> {
    type Item = u32;
    fn next(&mut self) -> Option<Self::Item> {
        let last = self.primes.last();
        if last == None {
            self.primes.push(2);
            return Some(2);
        }
        for n in last.unwrap() + 1.. {
            let mut isprime = true;
            for p in self.primes.iter() {
                if n % p == 0 {
                    isprime = false;
                    break;
                }
            }
            if isprime {
                self.primes.push(n);
                return Some(n);
            }
        }
        None
    }
}

fn main() {
    let mut primes = Vec::from([]);
    let mut x = Sieve::new(&mut primes);
    for _ in 0..5 {
        match x.next() {
            Some(n) => println!(">>>{}", n),
            None => {
                println!("WHAAAT!!");
                break;
            }
        }
    }
    println!("Hello, world!");
}