fn main() {
    let mut t: u64 = 0;

        //  Vec is reference to memory in the heap, v is on stack
        let mut v: Vec<u64> = Vec::with_capacity(100);
        assert_eq!(0, v.len());
        for i in 0..100 {
            v.push(i)
        }
        for e in v {
            t += e
        }
        // can't say 'drop(v);' here, because the vector gets "used up" in the
        // for loop (takes each element and moves it out into e). Cant' reuse v
        // without using 'v.clone()' or 'v.iter()'


    println!("Sum was {}", t);
    // implicit free call here; or can say 'drop(t);'

}