use std::cmp;
let mut min = None;
- for e in v {
+ // This time, we explicitly request an iterator for the vector `v`. The method `iter` borrows the vector
+ // it works on, and provides shared borrows of the elements.
+ for e in v.iter() {
// In the loop, `e` now has type `&i32`, so we have to dereference it to obtain an `i32`.
min = Some(match min {
None => *e,
//@ As an example, consider a function which increments every element of a vector by 1.
//@ The type `&mut Vec<i32>` is the type of mutable borrows of `vec<i32>`. Because the borrow is
-//@ mutable, we can change `e` in the loop.
+//@ mutable, we can use a mutable iterator, providing a mutable borrow of the elements.
fn vec_inc(v: &mut Vec<i32>) {
- for e in v {
+ for e in v.iter_mut() {
*e += 1;
}
}
/* println!("The first element is: {}", *first); */ /* BAD! */
}
//@ `&mut` is the operator to create a mutable borrow. We have to mark `v` as mutable in order to create such a
-//@ borrow. Because the borrow passed to `vec_inc` only lasts as long as the function call, we can still call
+//@ borrow: Even though we completely own `v`, Rust tries to protect us from accidentally mutating things.
+//@ Hence owned variables that you intend to mutate, have to be annotated with `mut`.
+//@ Because the borrow passed to `vec_inc` only lasts as long as the function call, we can still call
//@ `vec_inc` on the same vector twice: The durations of the two borrows do not overlap, so we never have more
//@ than one mutable borrow. However, we can *not* create a shared borrow that spans a call to `vec_inc`. Just try
//@ enabling the commented-out lines, and watch Rust complain. This is because `vec_inc` could mutate
// As it turns out, combined with the abstraction facilities of Rust, this is a very powerful mechanism
// to tackle many problems beyond basic memory safety. You will see some examples for this soon.
-//@ [index](main.html) | [previous](part03.html) | [next](part05.html)
+//@ [index](main.html) | [previous](part03.html) | [raw source](https://www.ralfj.de/git/rust-101.git/blob_plain/HEAD:/workspace/src/part04.rs) | [next](part05.html)