String slices

Reference part of a string with &str slices.

String slices

A slice is a reference to a contiguous part of a collection; it doesn't take ownership. A string slice has the type &str and is taken with a byte range:

let s = String::from("merhaba dünya");
let ilk = &s[0..7];     // "merhaba"
let son = &s[8..];      // "dünya"
println!("{ilk} / {son}");

The range is in byte positions, not characters. "ü" takes two bytes, so "dünya" is 6 bytes.

Why are slices safe?

Because a slice borrows its source, the source can't be changed while the slice is alive:

let mut s = String::from("rust dili");
let kelime = &s[0..4];
// s.clear();          // error E0502: kelime is still going to be used
println!("{kelime}");

So the bug of an index pointing into a cleared source is caught at compile time. String literals ("merhaba") are in fact &str slices embedded in the program.

Exercise Two pieces

For let s = String::from("rust dili");, take the slices &s[0..4] and &s[5..] and print them with | between.

Show example solution

fn main() {
    let s = String::from("rust dili");
    let a = &s[0..4];
    let b = &s[5..];
    println!("{}|{}", a, b);
}

Test yourself

What happens with <code>let s = String::from("çay"); let x = &s[0..1];</code>?
- Compile error
- x = ""
- Runtime panic: 1 is not a char boundary
- x = "ç"
Show answer

Runtime panic: 1 is not a char boundary — "ç" is two bytes; byte 1 falls in the middle of a character and slicing panics.

First four bytes

let s = String::from("rust dili");
let ilk = &s[____];

Show answer

let s = String::from("rust dili");
let ilk = &s[0..4];

Expression and result

&s[0..7]

"merhaba"
&s[8..]

"dünya"
"çay"[0..1]

Panic
"dünya".len()

6

Next lesson: Slice syntax

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies