Fibonacci numbers in Rust

fibs.rs

use std::iter;

fn main() {
    println!("{:?}", fibs_iter().skip(42).next().unwrap());
    println!("{}", fibs_recursive(42));
}

fn fibs_iter() -> impl Iterator<Item = u128> {
    let mut a = 0;
    let mut b = 1;
    
    let fibs = iter::from_fn(move || {
       let next = a + b;
       a = b;
       b = next;
       Some(next)
    });
    
    vec![0, 1].into_iter().chain(fibs)
}

fn fibs_recursive(n: usize) -> u64 {
    match n {
        0 => 0,
        1 => 1,
        _ => fibs_recursive(n - 2) + fibs_recursive(n - 1)
    }    
}