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Slice data type in Rust

Slice is a data type in Rust that doesn’t have ownership system.

String Slice

A string slice is a reference to part of a String.

//example of String slice
let s = String::from("hello world");
let hello = &s[0..5];
let world = &s[6..11];

We can take a specific part of String by it’s index. We use slice by using bracket [starting_index..ending_index]

If we want to start from 0, we can ignore the starting_index

let slice = &s[..2];

Or if we want to reach the end of the string, we can use the len method (length)

let len = s.len();

let slice = &s[3..len];
let slice = &s[3..];

Warning: String slice range indices must occur at valid UTF-8 character

Example program

Study case: We want to write a function that take a sentence and return only first word.

fn first_word(s: &String) -> &str {
    let bytes = s.as_bytes();

    for (i, &item) in bytes.iter().enumerate() {
        if item == b' ' {
            return &s[0..i];

    &s[..] //return whole string

fn main() {}

String literals = Slices

If we declare a string like this

let s = "Hello, world!";

The type of s is &str

Other slice

We can also implement number of array as slice, like this

fn main() {
let a = [1, 2, 3, 4, 5];

let slice = &a[1..3];

This is a post in the start learning Rust series.

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