Slice syntax

Learn the [a..b] and [a..] slice syntax.

Slice syntax

The ends of the range can be omitted:

let s = "abcdef";
&s[..3]    // "abc"   (from start to 3)
&s[3..]    // "def"   (from 3 to end)
&s[..]     // "abcdef" (all of it)
&s[1..=2]  // "bc"    (2 included)

a..b excludes b, a..=b includes it. &s[..] is one way to turn a String into a &str.

Bounds checking

Going out of bounds panics: &"abc"[1..5] stops with "byte index 5 is out of bounds". It also panics if the start is greater than the end. If you don't want a panic, use get; it returns an Option:

let s = "abc";
println!("{:?}", s.get(0..2));   // Some("ab")
println!("{:?}", s.get(1..5));   // None

Exercise Three slices

For let s = "abcdef";, print the slices &s[..3], &s[3..] and &s[1..=2] on one line separated by spaces.

Show example solution

fn main() {
    let s = "abcdef";
    println!("{} {} {}", &s[..3], &s[3..], &s[1..=2]);
}

Test yourself

What is <code>&"abcdef"[2..=4]</code>?
- "bcde"
- "cde"
- "cd"
- "bcd"
Show answer

"cde" — Bytes 2, 3 and 4 are taken: c, d, e.

To the end

let s = "abcdef";
let son = &s[____];   // "def"

Show answer

let s = "abcdef";
let son = &s[3..];   // "def"

Range and result on "abcdef"

[..3]

"abc"
[3..]

"def"
[1..=2]

"bc"
[..]

"abcdef"

Next lesson: Array slices

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