Which version suits better the example?

fibonacci_iter_with_mem.rs

// This version uses mem::replace()

use std::mem;

struct Fibonacci {
    curr: uint,
    next: uint,
}

impl Iterator<uint> for Fibonacci {
    fn next(&mut self) -> Option<uint> {
        let new_next = self.curr + self.next;
        let new_curr = mem::replace(&mut self.next, new_next);
        Some(mem::replace(&mut self.curr, new_curr))
    }
}

fn fibonacci() -> Fibonacci {
    Fibonacci { curr: 1, next: 1 }
}

fn main() {
    println!("The first four terms of the Fibonacci sequence are: ");
    for i in fibonacci().take(4) {
        println!("> {}", i);
    }
    println!("The next four terms of the Fibonacci sequence are: ");
    for i in fibonacci().skip(4).take(4) {
        println!("> {}", i);
    }
}

fibonacci_iter_without_mem.rs

// This version doesn't use mem::replace()

struct Fibonacci {
    curr: uint,
    next: uint,
}

impl Iterator<uint> for Fibonacci {
    fn next(&mut self) -> Option<uint> {
        let (new_curr, new_next) = (self.next, self.curr + self.next);
        self.curr = new_curr;
        self.next = new_next;
        Some(self.curr)
    }
}

fn fibonacci() -> Fibonacci {
    Fibonacci { curr: 0, next: 1 }
}

fn main() {
    println!("The first four terms of the Fibonacci sequence are: ");
    for i in fibonacci().take(4) {
        println!("> {}", i);
    }
    println!("The next four terms of the Fibonacci sequence are: ");
    for i in fibonacci().skip(4).take(4) {
        println!("> {}", i);
    }
}

I'm referring to the iter example