Range types

Learn the Range and RangeInclusive types.

Range types

1..4 is a Range<i32>, 1..=4 a RangeInclusive<i32> value. Besides slicing, ranges are also used in loops and as iterators:

let r = 1..=5;
println!("{}", r.contains(&5));          // true
for i in (1..4).rev() { print!("{i} "); }  // 3 2 1
let tek: Vec<i32> = (1..10).step_by(2).collect();   // [1, 3, 5, 7, 9]

Char and empty ranges

Ranges work with chars too: ('a'..='e').collect::<String>() → "abcde". If the start is equal to or greater than the end, the range is empty: (5..5).count() gives 0, and so does (5..1).count(); counting down needs rev().

let harfler: String = ('a'..='e').collect();
println!("{harfler} {}", (5..1).count());   // abcde 0

Exercise Range operations

Print, on one line, the sum of the elements of (1..=10).step_by(3) (sum::<i32>()) and the vector made from (1..5).rev() (collect::<Vec<i32>>()).

Show example solution

fn main() {
    let t: i32 = (1..=10).step_by(3).sum();
    let v: Vec<i32> = (1..5).rev().collect();
    println!("{} {:?}", t, v);
}

Test yourself

What is <code>(0..10).step_by(4).collect::<Vec<_>>()</code>?
- [0, 4, 8, 12]
- [0, 4]
- [0, 4, 8]
- [4, 8]
Show answer

[0, 4, 8] — step_by starts with the first element and skips by 4; 10 is not included.

Count down

for i in (1..=3).____() {
    print!("{i} ");   // 3 2 1
}

Show answer

for i in (1..=3).rev() {
    print!("{i} ");   // 3 2 1
}

Range and element count

1..4

3
1..=4

4
5..5

0
(0..10).step_by(4)

3 elements

Next lesson: Summary - Slices

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