Array slices

Slice part of an array or vector with &[T].

Array slices

Arrays and vectors can be sliced too; the result has the type &[T]:

let a = [10, 20, 30, 40, 50];
let orta: &[i32] = &a[1..4];
println!("{:?} {}", orta, orta.len());   // [20, 30, 40] 3

let v = vec![1, 2, 3];
let hepsi: &[i32] = &v;                 // &Vec<i32> → &[i32]

A slice knows its length and has methods such as iter, contains, first and last.

Mutable slices

&mut v[a..b] gives a &mut [T]; elements can be changed through the slice but the length can't (there is no push):

let mut v = vec![1, 2, 3, 4];
let d = &mut v[1..3];
d[0] = 20;
d.reverse();
println!("{:?}", v);   // [1, 3, 20, 4]

sort, reverse, swap and fill are slice methods.

Exercise Middle part

For let v = vec![3, 1, 4, 1, 5, 9];, take the slice &v[2..5]. Print the slice and the sum of its elements (iter().sum::<i32>()).

Show example solution

fn main() {
    let v = vec![3, 1, 4, 1, 5, 9];
    let orta = &v[2..5];
    let t: i32 = orta.iter().sum();
    println!("{:?} {}", orta, t);
}

Test yourself

For <code>let v = vec![5, 6, 7]; let d = &v[1..];</code>, what is <code>d.first()</code>?
- Some(&6)
- Some(&5)
- 6
- None
Show answer

Some(&6) — The slice starts at index 1; first returns a reference to the first element inside an Option.

The middle three

let a = [10, 20, 30, 40, 50];
let orta = &a[____];   // [20, 30, 40]

Show answer

let a = [10, 20, 30, 40, 50];
let orta = &a[1..4];   // [20, 30, 40]

Method and result (on [4, 1, 5])

len()

3
first()

Some(&4)
last()

Some(&5)
contains(&1)

true

Next lesson: Slices and functions

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