}
// Now we can write `vec_min`.
-//@ However, in order to make it type-check, we have to make a full (deep) copy of e by calling `clone`.
fn vec_min(v: &Vec<BigInt>) -> Option<BigInt> {
let mut min: Option<BigInt> = None;
+ // If `v` is a shared borrowed vector, then the default for iterating over it is to call `iter`, the iterator that borrows the elements.
for e in v {
- let e = e.clone(); /*@*/
+ let e = e.clone();
min = Some(match min { /*@*/
None => e, /*@*/
Some(n) => e.min_try1(n) /*@*/
}
min
}
-//@ Now, what's happening here? Why do we have to clone `e`, and why did we not
+//@ Now, what's happening here? Why do we have to to make a full (deep) copy of `e`, and why did we not
//@ have to do that in our previous version?
//@
//@ The answer is already hidden in the type of `vec_min`: `v` is just borrowed, but
//@ underlying data is transferred from where `e` borrows from to `min`. But that's not allowed, since
//@ we just borrowed `e`, so we cannot empty it! We can, however, call `clone` on it. Then we own
//@ the copy that was created, and hence we can store it in `min`. <br/>
-//@ Of course, making such a full copy is expensive, so we'd like to avoid it. We'll some to that in the next part.
+//@ Of course, making such a full copy is expensive, so we'd like to avoid it. We'll come to that in the next part.
// ## `Copy` types
//@ But before we go there, I should answer the second question I brought up above: Why did our old `vec_min` work?