Hello community,

I’m trying to iterate a vector in match expression, but i don’t know what the difference if I add & at the second element of the tuple.

```
let nums = vec![100, 200, 300, 400, 500];
let mut index_hashmap = HashMap::with_capacity(nums.len());
for (idx, &n) in nums.iter().enumerate() {
```

```
let nums = vec![100, 200, 300, 400, 500];
let mut index_hashmap = HashMap::with_capacity(nums.len());
for (idx, n) in nums.iter().enumerate() {
```

I hear people said the first one will trigger the clone() method, but i can’t understand why.